April 27 - 30 Severe Weather Outbreak: 39 Dead, $1 Billion+ in Damage

By: Dr. Jeff Masters , 5:24 PM GMT on May 01, 2014

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The deadly and devastating U.S. severe weather outbreak of April 27 - 30, 2014, has finally drawn to a close. The death toll from nature’s 4-day rampage of deadly tornadoes, extreme flooding, and damaging severe thunderstorms has killed at least 39 people, and will end up costing more than $1 billion, according to disaster expert Steve Bowen of Aon Benfield. NOAA’s Storm Prediction Center (SPC) lists 133 preliminary tornadoes over the four days in 14 states; damage surveys are on-going, and 38 of these tornadoes had been confirmed as of noon on May 1.


Figure 1. Rainfall derived from the TRMM' satellite’s Microwave Imager (TMI) and Precipitation Radar (PR) data is shown overlaid on GOES-EAST infrared satellite images captured on April 29, 2014 at 0402 UTC and 0532 UTC. Red symbols show the locations where numerous tornadoes were reported from Monday afternoon through Tuesday morning. Image credit: NASA.

Extreme rainfall and flooding in Pensacola and Mobile
Torrential rains on Tuesday night in Pensacola, Florida brought an all-time calendar-day record of 15.55” of rain to the city. The old calendar day record of 15.29" in October 1934 was due to a tropical storm that made landfall just to the west of the city. Mobile, Alabama saw 11.24" during the calendar day on Tuesday, their 3rd greatest calendar day total on record. The Pensacola Airport recorded a remarkable 5.68 inches of rain in just one hour ending at 10 pm Tuesday night, and numerous high-water rescues had to be performed Tuesday night and Wednesday morning. One drowning occurred, in a vehicle that tried to cross flooded Highway 29. According to a nice flood event summary from the Mobile/Pensacola NWS, the 5.68" that fell in 1 hour was between a 1 to 200 and 1 to 500 year event, and the two day estimated total for Pensacola of 20.47" lies between a 1 in 100 to 1 in 200 year event. As discussed by Andrea Thompson at Climate Central, these type of extreme precipitation events have increased in the U.S. in recent decades, are are expected to continue to increase as a warming climate puts more moisture into the atmosphere. A comparison for perspective: Wichita, Kansas is having it's second driest start to the year since 1936, with 2.01” since January 1, 2014; Pensacola received 2 1/2 times as much rain in one hour than Wichita has seen all year. Pensacola finished April with 29.53” of rain, breaking the all-time record for any month (not just April) of 24.46” set in April 2005. This also makes it the wettest year-to-date on record in Pensacola.


Figure 2. Natural gas leaks spray into the sky on Piedmont Street in the Cordova Park neighborhood in Pensacola, Florida, after the road washed out due to heavy rains on April 30, 2014. (Photo by Marianna Massey/Getty Images)


Video 1. Aerial drone footage of the Scenic Highway near Pensacola, Florida, after being washed out by extreme flooding on April 30, 2014. Another YouTube drone video here of the Pensacola flooding also shows the impressive scale of the event.

Heavy rains and flooding in the Mid-Atlantic and Northeast
The storm also brought heavy rains and damaging flooding to much of the Mid-Atlantic and Northeast on Wednesday. The 4.97" that fell in New York City at Central Park was the Big Apple’s 2nd wettest April day on record, behind the 7.57" that fell on April 15, 2007. In Pennsylvania, during a nine-hour period that ended early Thursday, Chester County got 6.6 “ of rain, Delaware and Montgomery counties got 5.5”, and Philadelphia nearly 5 inches. At least 62 people were rescued overnight in Chester County from their vehicles, most after driving past closed road signs and barriers. Heavy rains in Baltimore caused a washout of a retaining wall, causing multiple cars to plunge down into a flooded railway line.


Figure 3. View of the Charles Village, Baltimore retaining wall collapse near 26th St on April 30, 2014. There were no injuries, but at least six cars plunged down onto the CSX railroad tracks below. According to meteorologist Justin Berk, who took the photo, local residents said they have had concerns about this wall for a long time.

Two EF-4 tornadoes from the outbreak
At least two EF-4 tornadoes have been surveyed so far from the outbreak, and there may be others once damage surveys are complete:

Vilonia, Arkansas: A violent high-end EF-4 tornado with winds of 180 - 190 mph tore through Vilonia and Mayflower, Arkansas on April 27, killing 15 people. This tornado was also the widest (3/4 mile) and longest lived (60 minutes) twister of the outbreak. There is a report that the tornado picked up a truck in Mayflower and deposited it in a field northeast of Vilonia, 27 miles away. Update: When contacted about this again by a reporter, the man who's car was transported admitted some confusion about where his car had been parked at the time of the tornado, so this remarkable story is dubious.

Louisville, Mississippi: An EF-4 with 185 mph winds hit Louisville, Mississippi on April 28. The tornado killed nine people, carved a path 35 miles long and up to 3/4 mile wide, and stayed on the ground for 56 minutes. The tornado carried a door 30 miles from Louisville and deposited it on the Mississippi State University campus.

The longest path tornado of the event was an EF-1 twister with a path length of 46 miles that stayed on the ground 46 minutes, and killed two people near Martinsburg and Kinross, Iowa on April 27.


Figure 4. Volunteers help clean up debris where homes once stood after the area was hit by a tornado April 29, 2014 in Vilonia, Arkansas. (Photo by Mark Wilson/Getty Images)


Video 2. Aerial drone footage of tornado damage from April 28, 2014 in Bessemer, Alabama just west of Birmingham. The EF-2 tornado with maximum winds of 120 mph stayed on the ground 4.9 miles and hit a golf course and an apartment complex, with a near miss of the Bessemer Hospital. It’s remarkable to see the huge number of trees pulled out by their roots. According to an article in Forbes, “The FAA claims the broad authority to prohibit the ‘commercial’ use of drones, and has included the use of drones for journalism or search and rescue under that ban. The FAA’s determination comes despite having lost an enforcement action at the administrative judge level….Despite the clear value of drones in disaster response and search and rescue operations, one search and rescue group based out of Texas has been forbidden from flying their drones in search and rescue operations, prompting them to sue the federal government. That case has sent a message to all would be search and rescue groups, letting them know they should keep their drones grounded, lest they face fines for trying to help find lost persons.”

U.S. billion-dollar weather-related disasters of 2014
1) The January 5 - 8 "Polar Vortex" winter weather outbreak, which Aon Benfield estimated caused $3 billion in damage.
2) The California drought, with $3.6 billion in agricultural damages so far, as estimated by the California Farm Water Coalition.
3) Severe weather outbreak of April 27 - 30, which Aon Benfield estimated caused $1+ billion in damage.

Disaster Relief Donations Needed
The devastation from this week’s tornadoes have brought a need for donations for disaster relief. The Portlight.org disaster relief charity, founded by members of the wunderground community, is supporting the efforts of a group of local volunteers in Arkansas doing search and rescue, and needs donations. Portlight volunteers are working in tornado-hit towns to clear debris and help with other clean-up efforts. This team will also be visiting shelters and reaching out to survivors with disabilities to determine their immediate needs, whether for replacement of durable medical equipment and ramps, or for assistance with shelter and transportation issues. The Red Cross is also a great place to send your donation dollars.

This will likely be my last post until Tuesday afternoon, as I plan on taking a few days off.

Jeff Masters

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from the 2003 ibc

R802.10.5 Truss to wall connection.

Trusses shall be connected to wall plates by the use of approved connectors having a resistance to uplift of not less than 175 pounds (79.45 kg.) and shall be installed in accordance with the manufacturer's specifications. For roof assemblies subject to wind uplift pressures of 20 pounds per square foot (0.958 kN/m2) or greater, as established in Table R301.2(2), adjusted for height and exposure per Table R301.2(3), see section R802.11.
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Rescuers in Afghanistan have given up hope of finding any more survivors in a double landslide that is feared to have killed more than 2,500 people.

They have stopped digging through the earth and mud that swamped a whole village in the remote north-east province of Badakhshan on Friday.

Officials now say the site has become a mass grave for the village of Ab Barik.

At the bottom of the valley, there is little evidence left of where the village was because the mud is so deep.

Officials here say it is very unlikely any of the bodies will be found. People have now given up the search because they realise it is hopeless.

It may be that we never have a final figure for the number of dead.

The BBC's David Loyn, who has arrived at the scene, described it as desolate and distraught as the surviving villagers try to settle in to their temporary new homes on the hillside.

He said heavy rain is believed to have triggered Friday's two landslides, the first of which buried hundreds of homes and the second then killed rescuers who had arrived at the scene to help reach survivors.
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Quoting ACSeattle:
Sar: just a few years ago, in Harrison County. MS (post Katrina) I was using cut nails in sill plates to hold them on the snaped lines. This was in addition to the anchor bolts, nuts, and washers

Really? All my experience was in California, so things must be different here. What kind of cut nails were you using? Were they square cut masonry type nails or what?
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798. Skyepony (Mod)
Heat Wave in India on Saturday, 03 May, 2014 at 05:13 (05:13 AM) UTC.
Description
Khammam sizzled at an unbearable 47 degrees Celsius on Friday even as Hyderabad experienced its hottest day of this summer with the maximum temperature touching a sweltering 40.7 degrees. Heatwave conditions are prevailing in several districts and the Met department predicted that the trend is likely to continue with May being the peak summer month. "The day temperature in the state capital is likely to rise further and touch 43 degrees Celsius during the second or third week of May," an official said. Some city streets wore a deserted look in the afternoon as residents preferred to stay indoors to beat the heat, while those who ventured out had to cover their faces to dodge hot winds. "I decided not to venture out in the afternoon to avoid the blazing sun. My neighbour has already suffered a sunstroke and I don't want to be the next victim," said Srinivas Kanaparthy, a resident of Secunderabad. The traffic flow on the city roads came down considerably in the afternoon because of the heat. Elsewhere in the Telangana region, several districts recorded high temperatures with Rentachintala in coastal AP recording 44 degrees, Adilabad 43.5 degrees and Nizamabad experiencing a scorching 42.4 degrees.

Normal life was also disrupted in several districts in the state with residents confining themselves indoors between 10 am to 6 pm in Khammam, Nizamabad, Adilabad, Karimnagar, Hanamkonda and Kurnool. A severe heatwave also disrupted normal life in coal belt areas such as Bellampalli, Mandamarri, Mancherial, Goliwada, and Srirampur of Adilabad district. Many villagers took shelter under trees to get some respite and were drinking coconut water, butter milk and other cool drinks to beat the heat. "The scorching heat is unbearable and the long load sheddings have made our life miserable this summer. We are eagerly waiting for the monsoon to commence," said T Nagaiah, a resident of Nizamabad. While the temperatures are likely to go up further, weathermen said the abundant heating over the land and the moisture feed from Bay of Bengal because of the formation of an anti-cyclone might bring in pre-monsoon showers during the next week in the evenings or nights. Rayalaseema and coastal Andhra, however, were slightly better off with the mercury hovering around 40 degrees Celsius at many places.
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797. Skyepony (Mod)
Sorry Gearst~ Had 0.58" in the last 24hrs here in ECFL. Not alot of lightning.

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Quoting ricderr:
It is however, secured by two 8 inch square cut clinching nails every 18 inches, with each nail doubled over itself. The engineer said he'd never seen an installation like this but, when he did the calcs, it came out to about twice as strong as a traditional anchor bolt. Some of those old timers apparently knew what they were doing, long before any building codes. :-)


i don't know about uplift though sar....next time you get a rolling earthquake there in bama......you might be in trouble...LOL

LOL. One of the reasons I'm here is that seismic risk, while not zero, is about a zillion times less than when you can see a fault that's the third most likely to break...out your front window. I spent a fair bit of money making my home more earthquake resistant, including adding washer to anchor bolts I could access without tearing the walls apart, adding additional plates to the connections from the main beam of the roof to the sidewalls, and bolting and strapping everything I could to the walls inside the home. I lived there for 30 years. Total earthquake damage - some cracks in the exterior stucco from the Loma Prieta earthquake. The home is still standing, almost 10 years after I moved out. In retrospect, all of that was a waste of money. Maybe, some time in the five minutes, it won't be a waste of money. Fifty years from now, it might still have been a waste of money. One just never knows, and it's the kind of thing that makes tougher building codes so difficult to put in place.
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795. Skyepony (Mod)
Landslide in Canada on Saturday, 03 May, 2014 at 05:20 (05:20 AM) UTC.
Description
A landslide has sent mud and vegetation down Cooke Creek into the Shuswap River, 25 kilometres east of Enderby in B.C.'s North Okanagan, leaving about 200 residents stranded. The slide washed out Mabel Lake Road and a bridge spanning the creek, isolating residents on the other side. B.C. Hydro reports nearly 700 people are without power but the utility can't get into the area until the road is opened. Crews with the Ministry of Transportation are working to clear the road, but it's estimated the road will be closed until Monday. Vernon, B.C., Search and Rescue has been called to the scene. Emergency officials say no one was injured in the slide but they are keeping watch as a large amount of logs and debris flows toward Enderby. Dairy farmer Michael Haak lives five kilometres from the slide site and says he's never seen the waterway so clogged with debris and logs. "It was moving pretty good. It was getting hung up a little bit on the irrigation intakes, and it kinda ripped them out," he said. The town of Enderby has activated the regional emergency operations centre. "We are taking every step we can to be well prepared in case there is any threat to infrastructure," said Tate Bengtson, Enderby's chief administrative officer.
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Not even a drop for me, so dry and hot.
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793. Skyepony (Mod)
ESPI is 1.48! El Nino conditions are coming, should go moderate somewhat quickly, within a few months.

90W just got tagged in the West Pacific. 11.6 141.1 15kts

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This is a pretty cool map.
It's a rotational velocity map from the May 20, 2013 outbreak. You can easily pick out the Moore Tornado streak across the center of the map.
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Quoting 788. TylerStanfield:


I need a link to this! ;) (Hint hint)


Wind

thats the program....
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Quoting TropicalAnalystwx13:


Now that's a hook echo....
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Quoting ricderr:
Cut nails? They haven't been used since the early 20th century. What's in use now are steel wire nails, or common nails. I can't imagine an engineer using the term "cut nails" for modern construction. Be that as it may, nailing a wall to a sill is a sure way to have a structure fail in wind or earthquake. Toenailing roof joists to the wall structure is a sure way to have a roof fail in wind or earthquake. Both, however, are the minimum standards required by the International Building Code in areas away from the coast

cut nails are still a common term sar.....although now it refers to a concrete nail because their shape resembles the cut nails of old....as far as trusses...since the 2003 IRC straps have been required...of course you're right though as there are still municipalities that don't utilize any uniform building code

They weren't a common term used by any of the construction companies I worked with, and certainly not for any type of nail used in ordinary wood frame construction. Our specs always called for wire nails, (steel, copper...whatever was the appropriate metal for the purpose). If the plans called for cut nails, which we had in a few cases with historic structures, it meant forged, square cut nails.

Hurricane ties or clips are not required by the IBC. Local jurisdictions can require them, and builders in an area where wind loads on a roof are 200 pounds per square foot or higher are required by the IBC to construct a roof tie system capable of resisting those wind loads. There are several ways to do this without using hurricane ties or straps, but it's up to an inspector to determine if it was done, and done correctly. If you don't live on a coast subject to hurricanes, or a seismic risk zone, it's pretty much up to you to determine if the structure is built in such a way that you think it's reasonably safe. I'm not saying this is a good thing, but it's the way things are when it comes to private home construction.
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Quoting 746. KEEPEROFTHEGATE:

gfs RH layer for tus may 6 shows a second system weak but it may be something to watch as well



models are for guidance only and do not depict final solution

I need a link to this! ;) (Hint hint)
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Quoting 773. Ameister12:

Today is the 15th anniversary of the May 3, 1999 tornado outbreak, one of the worse to affect Oklahoma. 73 tornadoes, including 3 F4's and an F5 (the infamous Bridge Creek-South OKC tornado) left 43 dead, hundreds injured, and thousands of structures destroyed.



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i have "how do they do it" on the office tv today...this episode now playing...has a segment on how they're building homes to make them safer in tornadoes and hurricanes
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It is however, secured by two 8 inch square cut clinching nails every 18 inches, with each nail doubled over itself. The engineer said he'd never seen an installation like this but, when he did the calcs, it came out to about twice as strong as a traditional anchor bolt. Some of those old timers apparently knew what they were doing, long before any building codes. :-)


i don't know about uplift though sar....next time you get a rolling earthquake there in bama......you might be in trouble...LOL
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Quoting Ameister12:
Today is the 15th anniversary of the May 3, 1999 tornado outbreak, one of the worse to affect Oklahoma. 73 tornadoes, including 3 F4's and an F5 (the infamous Bridge Creek-South OKC tornado) left 43 dead, hundreds injured, and thousands of structures destroyed.



I feel very fortunate to have moved away from that region. We used to live in the neighborhood on the other side of S.W. 134th street just off May Av. We didn't have a basement and none of my friends homes had basements.
Both of the Moore Tornadoes went just barely south of that location.
I graduated from Moore High School and I still have a lot of friends in that area.


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Sar: just a few years ago, in Harrison County. MS (post Katrina) I was using cut nails in sill plates to hold them on the snaped lines. This was in addition to the anchor bolts, nuts, and washers
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Quoting pottery:


Surely the Insurance people will see the wisdom in this, and offer a reduced rate for houses that are less liable to blow away ?? This will serve to mitigate the $500 additional cost.

Having said that, if I were buying a house that had a roof that was built of cardboard and guaranteed to leak, and there was an option (for $500) to have a roof that would keep the rain out, I know which I would choose…...

That's a good point, Pott, and it's something that's not done on an ordinary basis. Insurance companies don't send an inspector to verify how well your home is built. They insure based on the age of the house and the risk presented by the area and the history of risk. I did get a discount on my homeowner's insurance by showing the results of a home inspection done by an engineer. However, that was another $300, and it was done mostly for my own piece of mind, and secondarily for insurance. If your home was built in a way that made it likely to fail in a tornado and there was a 100% chance it would be hit by a tornado, then the building code would mandate better construction, albeit at a high cost. Given that the probability of any square mile of land will be hit by any kind of tornado, let alone a particular house, is only about once every thousand years, we roll the dice and hope we don't win the tornado lottery. I imagine you've seen the same kind of thing in Trinidad. There are poor people's houses and then other people's houses. Its' not much different here.
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Getting a lot of heavy rain in Fort Lauderdale.

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Cut nails? They haven't been used since the early 20th century. What's in use now are steel wire nails, or common nails. I can't imagine an engineer using the term "cut nails" for modern construction. Be that as it may, nailing a wall to a sill is a sure way to have a structure fail in wind or earthquake. Toenailing roof joists to the wall structure is a sure way to have a roof fail in wind or earthquake. Both, however, are the minimum standards required by the International Building Code in areas away from the coast

cut nails are still a common term sar.....although now it refers to a concrete nail because their shape resembles the cut nails of old....as far as trusses...since the 2003 IRC straps have been required...of course you're right though as there are still municipalities that don't utilize any uniform building code
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Quoting ricderr:
"Bottom-line - we either build them (our houses) stronger or communities must accept that certain number of homes randomly selected by nature's wrath, will be blown away and kill people in every moderately strong tornado for the foreseeable future."

it's been part of the ubc (universal building code)....since 1949....i believe that all states now have a minimum standards...but that's been more of a recent issue in the last two decades before that in some places the requirements between county by county were amzingly different

The UBC has been gone since 1997. The International Building Code replaced it. In the Southeast, we had our own code (Standard Building Code) that was used rather than the UBC, which is one reason structures in the Southeast are generally not as well built in other sections of the country. We now use the IBC...sort of. At least in many counties in Alabama, there is still no building code outside cities. Home builders generally adhere to the IBC, at least in terms of plans, because they don't want to get sued in the event of a failure. Without building inspectors, however, many of the details of the IBC aren't followed to cut corners. Most cities now use the IBC, but all homes built before about 1998 used the SBC which, for homes, was about as minimum as you could get. It's basically up to homebuyers to determine how built a home is before they buy it. I paid several hundred dollars for a detailed inspection of my home before I bought it, since it was built in 1895. My home is not secured to the foundation by anchor bolts. It is however, secured by two 8 inch square cut clinching nails every 18 inches, with each nail doubled over itself. The engineer said he'd never seen an installation like this but, when he did the calcs, it came out to about twice as strong as a traditional anchor bolt. Some of those old timers apparently knew what they were doing, long before any building codes. :-)
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Quoting sar2401:

Cut nails? They haven't been used since the early 20th century. What's in use now are steel wire nails, or common nails. I can't imagine an engineer using the term "cut nails" for modern construction. Be that as it may, nailing a wall to a sill is a sure way to have a structure fail in wind or earthquake. Toenailing roof joists to the wall structure is a sure way to have a roof fail in wind or earthquake. Both, however, are the minimum standards required by the International Building Code in areas away from the coast and not in a seismic risk area. The IBC tries to strike a balance between risk mitigation and probability of risk, since building a wood frame home to a higher risk mitigation standard inevitably increases the cost of the structure. Even in the Mayflower/Vilonia area, the vast majority of structures suffered little to no damage. It's really up to people who live in the Southeast, as one example, to petition lawmakers to upgrade the IBC for their state, if they believe the additional cost, plus the probability of damage, warrants such a change. Using anchor bolts in a 2000 square foot structure, for example, adds about $400-$500 to the cost of the structure. That may not seem like much but, for some people, it's the difference between getting and not getting a mortgage. Would we rather have people in structures that may fail in a tornado, or in structures that will fail, like mobile or manufactured homes? It's a difficult balance to strike.


Surely the Insurance people will see the wisdom in this, and offer a reduced rate for houses that are less liable to blow away ?? This will serve to mitigate the $500 additional cost.

Having said that, if I were buying a house that had a roof that was built of cardboard and guaranteed to leak, and there was an option (for $500) to have a roof that would keep the rain out, I know which I would choose…...
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Indian Hills, Riverside, California (PWS)
Updated: 12:03 PM PDT on May 03, 2014
Clear
87.1 °F
Clear
Humidity: 15%
Dew Point: 34 °F

Wind: 5.0 mph Variable
Wind Gust: 5.0 mph
Pressure: 29.88 in (Falling)
Heat Index: 84 °F
Visibility: 10.0 miles
UV: 11 out of 16
Pollen: 5.40 out of 12
Pollen Forecast new!
Clouds:
Clear -
(Above Ground Level)
Elevation: 1070 ft

Airport is 89F
Forecast is 94F
87.1 here as of 12:06PDT
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Quoting Stormlover16:

Not trying to stir up a fight, but if you watch the "Storm Stories" episode about the tornado, you can see that some of those killed were in fact in the main part of the school.

I haven't watched that episode. Was it a reconstruction of what happened, or did it show where the students were actually located in the structure? I'll have see if I can find the diagram of where the students were again. It showed them being in a hallway that was built essentially as a weather protection shelter against rain or snow leading from the front of the school to the gym, not a part of the main school building.
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Quoting TropicalAnalystwx13:
Up on Little Rock's survey page this morning:

"During damage surveys, it was noted that numerous homes were removed from their foundations, with only slabs remaining. Years ago, that might be justification for an F5 rating on the original Fujita scale. These days, the quality of the construction is examined before a rating is assigned. One of the factors determining the rating is the use of anchor bolts.

Back in 2004, the Wind Science and Engineering Center at Texas Tech University submitted A Recommendation for an Enhanced Fujita Scale (EF-Scale) to the National Weather Service. The document went into great detail about wind speeds and resulting damage based on building standards and no "glaring weak links" in the construction. According to the document:

"A weak link is a discontinuity in the load path, which runs from the building surface through the structural system to the foundation. Inadequate nailing of wood roof decking, marginal anchoring of roof structure to top of wall, discontinuity in the connection between first and second floor, and use of cut nails instead of anchor bolts to attach sill plate to foundation are examples of load path discontinuities."

In Vilonia (Faulkner County), for example, there was little indication of anchor bolts where homes used to stand. At a subdivision to the southwest of town, the official survey results read as follows: "Houses completely destroyed; only slabs remaining at several places. No anchor bolts used in foundations."

Using cut nails to secure homes to the foundation is widely practiced and the minimum standard in most of the building codes. This is according to Dr. David Prevatt, Associate Professor of Civil and Coastal Engineering at the University of Florida. According to Dr. Prevatt:

"It is my opinion that cut nails can only be considered a temporary connection while installing a wall. They are in no way, shape or form have the capacity to resist the sliding loads or the uplift loads reduced by high winds that impact the walls of a building."

Without anchor bolts, it took less wind to sweep houses away in Vilonia (Faulkner County). This explains the EF4 (instead of EF5) rating that was ultimately decided upon. The non-use of anchor bolts did not sit well with Dr. Prevatt:

"Bottom-line - we either build them (our houses) stronger or communities must accept that certain number of homes randomly selected by nature's wrath, will be blown away and kill people in every moderately strong tornado for the foreseeable future."

Cut nails? They haven't been used since the early 20th century. What's in use now are steel wire nails, or common nails. I can't imagine an engineer using the term "cut nails" for modern construction. Be that as it may, nailing a wall to a sill is a sure way to have a structure fail in wind or earthquake. Toenailing roof joists to the wall structure is a sure way to have a roof fail in wind or earthquake. Both, however, are the minimum standards required by the International Building Code in areas away from the coast and not in a seismic risk area. The IBC tries to strike a balance between risk mitigation and probability of risk, since building a wood frame home to a higher risk mitigation standard inevitably increases the cost of the structure. Even in the Mayflower/Vilonia area, the vast majority of structures suffered little to no damage. It's really up to people who live in the Southeast, as one example, to petition lawmakers to upgrade the IBC for their state, if they believe the additional cost, plus the probability of damage, warrants such a change. Using anchor bolts in a 2000 square foot structure, for example, adds about $400-$500 to the cost of the structure. That may not seem like much but, for some people, it's the difference between getting and not getting a mortgage. Would we rather have people in structures that may fail in a tornado, or in structures that will fail, like mobile or manufactured homes? It's a difficult balance to strike.
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Building on the rock isn't worth much if the home isnt firmly attached to it.

EF-4 it is.
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Today is the 15th anniversary of the May 3, 1999 tornado outbreak, one of the worse to affect Oklahoma. 73 tornadoes, including 3 F4's and an F5 (the infamous Bridge Creek-South OKC tornado) left 43 dead, hundreds injured, and thousands of structures destroyed.

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Quoting 750. sar2401:


Schools in Alabama built since 2002 have at least one tornado resistant area as part of the construction plan. The construction plans I've seen are generally in line with what FEMA recommends, although there's no effort to get a FEMA certification, since it increases the cost about 15% for no benefit. Any school constructed with masonry material (brick, concrete block) since about 1960 would offer some level of protection in interior halls, away from windows. Compared to what many people live in in Alabama - old or poorly constructed homes, or mobile/manufactured homes - any school would offer more protection. It's one of the reasons I wish they'd stop releasing students early when there's a severe weather threat.


Even then it doesn't always work out. The Enterprise tornado painted that school between a rock and a hard place. That day sucked.
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Quoting 768. sar2401:


So you're proposing that building an underground shelter for 1,000 students and staff is both cheap and practical? Adding things like climate control systems, toilet facilities, electricity, water supply, phone lines, and backup power to a minimum size underground shelter that would require at least 7,000 square feet of floor space and about 8500 square feet over all is cheap and practical? Moving 1,000 students and staff into such a facility within the average 13 minute warning period is practical? I don't think many people in the construction industry or school administrators would agree.

The goal with construction of public facilities like schools and hospitals is to have the structures survive intact in the case of a direct hit from an EF-3 tornado, and to provide the maximum protection from flying debris in a larger tornado. There have been a total of 19 students killed in schools due to tornadoes since 1967. Of that number, 8 were killed in Enterprise AL because they left the tornado resistant section of the high school and were waiting for school busses, due to early dismissal, in an non-resistant hallway leading to the gym, when the tornado hit. No other students in the school were killed. During the same period of time, about 700 children were killed in homes of various types. There's no practical or cheap way to offer 100% protection from any tornado, but increasingly better construction of schools over the past 50 years has shown that such structures still offer better protection than the average private home.

Not trying to stir up a fight, but if you watch the "Storm Stories" episode about the tornado, you can see that some of those killed were in fact in the main part of the school.
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nrt,up to 50% at 12z.



Link

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"Bottom-line - we either build them (our houses) stronger or communities must accept that certain number of homes randomly selected by nature's wrath, will be blown away and kill people in every moderately strong tornado for the foreseeable future."

it's been part of the ubc (universal building code)....since 1949....i believe that all states now have a minimum standards...but that's been more of a recent issue in the last two decades before that in some places the requirements between county by county were amzingly different
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Quoting Jedkins01:


What to me seems like a smarter solution is to just build underground shelters where possible at all schools and build above ground saferooms at all schools where its not possible for below ground saferooms.

To make schools resistant to strong tornadoes is extremely expensive, but even then, unless you want a dome school without windows, as soon as those windows go, that building will receive massive damage and will be gutted from the inside out.

I think its smarter to not focus on spending money on making schools stronger, but rather underground shelters and safe rooms, which offer safer protection for much cheaper. Obviously they should still be built strong, but such disasters are rare to hit any given area, so its not like students will have to routinely need to cram into safe rooms and shelters. They are cheaper and safer than just hiding a school itself with no shelter, and will only have to be used on rare occasions.

I really don't see why everyone is focusing on making tornado resistant schools which isn't practical rather than focusing on building safe rooms and shelters which is safe and practical.

It should be standard for all schools, and it baffles me with all the billions upon billions the government wastes on nonsense yet things like this aren't law. It seems like government budgets are small for all the important things (tiny NWS budget anyone?) and overinflated for unimportant things or money is simply poured into things that should never see funding to the light of day.

if schools become standard to have such, it will make so much sense for kids to be kept at schools under the emergency of an impending tornado. Parents could feel safe knowing their children are being kept at a school with a shelter that is highly likely to survive the impact even if the school building is damaged worse than expected, which I see repeatedly happen to stronger structures during the most violent tornadoes.

So you're proposing that building an underground shelter for 1,000 students and staff is both cheap and practical? Adding things like climate control systems, toilet facilities, electricity, water supply, phone lines, and backup power to a minimum size underground shelter that would require at least 7,000 square feet of floor space and about 8500 square feet over all is cheap and practical? Moving 1,000 students and staff into such a facility within the average 13 minute warning period is practical? I don't think many people in the construction industry or school administrators would agree.

The goal with construction of public facilities like schools and hospitals is to have the structures survive intact in the case of a direct hit from an EF-3 tornado, and to provide the maximum protection from flying debris in a larger tornado. There have been a total of 19 students killed in schools due to tornadoes since 1967. Of that number, 8 were killed in Enterprise AL because they left the tornado resistant section of the high school and were waiting for school busses, due to early dismissal, in an non-resistant hallway leading to the gym, when the tornado hit. No other students in the school were killed. During the same period of time, about 700 children were killed in homes of various types. There's no practical or cheap way to offer 100% protection from any tornado, but increasingly better construction of schools over the past 50 years has shown that such structures still offer better protection than the average private home.
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Quoting 755. Skyepony:

CaribBoy~ GEOS-5 is hinting at a blob or system around then too. Maybe a little slower to form than those others are hinting.


Excellent news because some islands have big rain deficits. 
Here in St Barts, the deficit isn't significant, but the island is kind of dry so rain is always welcome!
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Interesting read on the correlation of the Arctic Oscillation on the West Coast Ridge and El Nino.

Searching for correlations

Two of the usual suspects for weather variability on the West Coast are the El Niño Southern Oscillation and the Pacific Decadal Oscillation. This winter, however, both were pretty much neutral. To look for links between the jet stream and other events, Utah State University’s Simon Wang and his collaborators created an index measuring the difference in the latitude of the jet stream over the West Coast and the Eastern US. The only oscillation that showed any hint of correlation with this index was the Arctic Oscillation—a see-saw of atmospheric pressure that periodically allows Arctic air to spill southward—but that didn’t explain much.

They did, however, find a decent correlation with something else interesting. Winters just before an El Niño (in which warm water pools at the surface in the eastern equatorial Pacific) tended to produce this year’s pattern. As it happens, forecast models have been converging on the development of an El Niño later this year.

Unless El Niños can travel through time, something else must have set up that jet stream ridge off the West Coast. The researchers identified conditions in the vicinity of the Philippine Sea in the late summer and fall that appear to have been responsible. Those same conditions in the western side of the North Pacific have previously been suggested to help trigger the development of an El Niño. That strengthens the case that the correlation between West Coast ridges and winters and upcoming El Niños is meaningful.

Finding larger trends

But does climate change have anything to do with it? The researchers’ index of jet stream detours over North America showed that this winter pattern has become more variable over time—although a calmer period occurred in the 1970s.

Many studies testing the contribution of climate change to an extreme event run large numbers of simulations with and without anthropogenic greenhouse gas emissions, comparing the probability of that same extreme event in each. If it’s considerably more common in the anthropogenic simulations, you can conclude that climate change made the extreme event more likely, much as steroid use in baseball made home runs more likely.

In this case, however, the researchers were looking at trends in variability to see whether they would give us a reason to think climate change contributed to the extreme nature of last winter’s drought. They compared two climate model simulations to this data: one that only took natural climate forcings (like solar activity and volcanic eruptions) into account and one that took only changing greenhouse gas forcings into account.

The “greenhouse gas only” simulation produced behavior remarkably similar to the observed trend—with variability increasing in recent years. The variability in the “natural forcings only” simulation, on the other hand, decreased from 1970 to the present.

Now, that still means this potential “El Niño precursor” gave rise to the ridge and added to the cold invasion of the Eastern US, which probably also got a boost from the Arctic Oscillation. But climate change may have amplified that behavior. The researchers write, “The inference from this study is that the abnormal intensity of the winter ridge is traceable to human-induced warming but, more importantly, its development is potentially predictable.” That is, the western North Pacific could tell us when the US is in for this type of winter weather pattern, which is projected to generally become more intense in the future.

While interesting, this study is a first-pass look at something that will undoubtedly be explored in more detail. Researchers will want to investigate how it is, for example, that climate change could cause this increase in variability. That will feed into the ongoing focus on the subtle ways that climate change might be affecting the jet stream, and thus mid-latitude weather extremes.

Geophysical Research Letters, 2014. DOI: 10.1002/2014GL059748 (About DOIs).
http://arstechnica.com/science/2014/04/climate-ch ange-el-nino-cold-winters-and-californias-drought/
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Looks like some heavy rain is headed for the Palm Beach area.
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Quoting 651. jeffs713:


Of note: while the concrete barriers are moved and/or toppled, the pavement on the roadway is intact. In a clear-cut EF5, the pavement would be partially removed (see: Jarrell, TX tornado of 1997).

That said... the Vilonia tornado likely had spots with EF5 damage, but nothing consistent, so those spots could have been just gusts, a lack of luck, or interesting wind dynamics.
Let's face it, the Enhanced Fujita scale is subjective and not all that scientific. For example, the ultimate "peeling of pavement" and "asphalt scouring" - does anyone believe that is a constant for all roads? No. It will be much more difficult to remove pavement from well-paved city roads with brick base than peeling back asphalt laid on former country gravel roads. Use the EF scale as a good rule of thumb for damage comparison but do not take it on par with the laws of physics, it is not.
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763. flsky
One thing I've thought about for schools - reinforce all ground floor restrooms as emergency safe rooms.
Removing windows and reinforcing doors and walls would not be cost prohibitive.

Quoting 756. Jedkins01:



What to me seems like a smarter solution is to just build underground shelters where possible at all schools and build above ground saferooms at all schools where its not possible for below ground saferooms.

To make schools resistant to strong tornadoes is extremely expensive, but even then, unless you want a dome school without windows, as soon as those windows go, that building will receive massive damage and will be gutted from the inside out.

I think its smarter to not focus on spending money on making schools stronger, but rather underground shelters and safe rooms, which offer safer protection for much cheaper. Obviously they should still be built strong, but such disasters are rare to hit any given area, so its not like students will have to routinely need to cram into safe rooms and shelters. They are cheaper and safer than just hiding a school itself with no shelter, and will only have to be used on rare occasions.

I really don't see why everyone is focusing on making tornado resistant schools which isn't practical rather than focusing on building safe rooms and shelters which is safe and practical.

It should be standard for all schools, and it baffles me with all the billions upon billions the government wastes on nonsense yet things like this aren't law. It seems like government budgets are small for all the important things (tiny NWS budget anyone?) and overinflated for unimportant things or money is simply poured into things that should never see funding to the light of day.

if schools become standard to have such, it will make so much sense for kids to be kept at schools under the emergency of an impending tornado. Parents could feel safe knowing their children are being kept at a school with a shelter that is highly likely to survive the impact even if the school building is damaged worse than expected, which I see repeatedly happen to stronger structures during the most violent tornadoes.
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What to me seems like a smarter solution is to just build underground shelters where possible at all schools and build above ground saferooms at all schools where its not possible for below ground saferooms.

To make schools resistant to strong tornadoes is extremely expensive, but even then, unless you want a dome school without windows, as soon as those windows go, that building will receive massive damage and will be gutted from the inside out.



i would have to disagree as although the upfront cost is expensive....rebuilding a lesser built school could very well be more expensive...and it also must be coupled with the cost of transferring students to other schools during construction that would add to the cost.....
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Quoting 754. TropicalAnalystwx13:

Up on Little Rock's survey page this morning:

"During damage surveys, it was noted that numerous homes were removed from their foundations, with only slabs remaining. Years ago, that might be justification for an F5 rating on the original Fujita scale. These days, the quality of the construction is examined before a rating is assigned. One of the factors determining the rating is the use of anchor bolts.

Back in 2004, the Wind Science and Engineering Center at Texas Tech University submitted A Recommendation for an Enhanced Fujita Scale (EF-Scale) to the National Weather Service. The document went into great detail about wind speeds and resulting damage based on building standards and no "glaring weak links" in the construction. According to the document:

"A weak link is a discontinuity in the load path, which runs from the building surface through the structural system to the foundation. Inadequate nailing of wood roof decking, marginal anchoring of roof structure to top of wall, discontinuity in the connection between first and second floor, and use of cut nails instead of anchor bolts to attach sill plate to foundation are examples of load path discontinuities."

In Vilonia (Faulkner County), for example, there was little indication of anchor bolts where homes used to stand. At a subdivision to the southwest of town, the official survey results read as follows: "Houses completely destroyed; only slabs remaining at several places. No anchor bolts used in foundations."

Using cut nails to secure homes to the foundation is widely practiced and the minimum standard in most of the building codes. This is according to Dr. David Prevatt, Associate Professor of Civil and Coastal Engineering at the University of Florida. According to Dr. Prevatt:

"It is my opinion that cut nails can only be considered a temporary connection while installing a wall. They are in no way, shape or form have the capacity to resist the sliding loads or the uplift loads reduced by high winds that impact the walls of a building."

Without anchor bolts, it took less wind to sweep houses away in Vilonia (Faulkner County). This explains the EF4 (instead of EF5) rating that was ultimately decided upon. The non-use of anchor bolts did not sit well with Dr. Prevatt:

"Bottom-line - we either build them (our houses) stronger or communities must accept that certain number of homes randomly selected by nature's wrath, will be blown away and kill people in every moderately strong tornado for the foreseeable future."


Interesting, makes sense.

And, this is the case where practical design change will make a difference. Building extremely expensive fortified superstructures is not practical, but taking measures like that is.

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Quoting ScottLincoln:

I seem to recall seeing highway barriers after crashes on numerous occasions and seeing them displaced.
Homes of typical construction - that is, not notably below average construction and without above average construction - have an expected wind speed of 200 mph for the highest degree of damage. That is high-end EF4. It takes better-than-average construction of a residential single-family home to reach EF5 winds (>200mph).
Debarking of trees is the highest degree of damage available on the EF-scale. Although it's the highest DOD, it only has expected winds of 131mph (softwood) and 143mph (hardwood)... high-end EF2 to low-end EF3. The debarking of trees is thus not a good indicator of EF5 winds.

It's rather an exercise of counting how many angels can dance on the head of a pin, in any case. As shown by McCarthy's paper on the subject, surveys on done on damage, and the damage seen, is back fit to arrive at the likely winds speeds that caused the damage. Each survey conducted by different teams will arrive at somewhat different results, since no team has the time or resources to even see all the damage, let alone minutely examine each damage site, especially with a damage path around 40 miles long. A "high end" EF-4, in this case, was rated at about 10 mph less than an EF-5, so the real life damage isn't enough less for the average person to be concerned with. The team that did this survey arrived at their rating by seeing a lot more than any of us, looking at some pictures that made it to the net. A different team might have arrived at different results, but it only matters for the record books. It was still a really bad tornado.
Member Since: October 2, 2004 Posts: 0 Comments: 21140
759. flsky
Have you tried the FEMA website. You might also contact your local emergency manager.

Quoting 698. Dakster:



I wish you luck in your research. I don't even know where I would begin to get that information, much less have the patience to aggregate it.
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Looks like we will have Amanda in 5 days.



Another band of rain offshore ready to push in. Having flooding problems in parts of Tampa, yesterday one of the parking lots at USF was completely underwater.



Forecast shows relief in site as the next 6 days shows dry conditions with temperatures warming up to near 90 at the end of the week. Pretty much can say summer is here.

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I finally got my rain. First a nice gust front came through with winds in the 30-40 mph range followed by about 20 minutes of real hard rain. It's still raining, but not too hard.

Next, S.E. Florida and the Keys
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Quoting 750. sar2401:


Schools in Alabama built since 2002 have at least one tornado resistant area as part of the construction plan. The construction plans I've seen are generally in line with what FEMA recommends, although there's no effort to get a FEMA certification, since it increases the cost about 15% for no benefit. Any school constructed with masonry material (brick, concrete block) since about 1960 would offer some level of protection in interior halls, away from windows. Compared to what many people live in in Alabama - old or poorly constructed homes, or mobile/manufactured homes - any school would offer more protection. It's one of the reasons I wish they'd stop releasing students early when there's a severe weather threat.


What to me seems like a smarter solution is to just build underground shelters where possible at all schools and build above ground saferooms at all schools where its not possible for below ground saferooms.

To make schools resistant to strong tornadoes is extremely expensive, but even then, unless you want a dome school without windows, as soon as those windows go, that building will receive massive damage and will be gutted from the inside out.

I think its smarter to not focus on spending money on making schools stronger, but rather underground shelters and safe rooms, which offer safer protection for much cheaper. Obviously they should still be built strong, but such disasters are rare to hit any given area, so its not like students will have to routinely need to cram into safe rooms and shelters. They are cheaper and safer than just hiding a school itself with no shelter, and will only have to be used on rare occasions.

I really don't see why everyone is focusing on making tornado resistant schools which isn't practical rather than focusing on building safe rooms and shelters which is safe and practical.

It should be standard for all schools, and it baffles me with all the billions upon billions the government wastes on nonsense yet things like this aren't law. It seems like government budgets are small for all the important things (tiny NWS budget anyone?) and overinflated for unimportant things or money is simply poured into things that should never see funding to the light of day.

if schools become standard to have such, it will make so much sense for kids to be kept at schools under the emergency of an impending tornado. Parents could feel safe knowing their children are being kept at a school with a shelter that is highly likely to survive the impact even if the school building is damaged worse than expected, which I see repeatedly happen to stronger structures during the most violent tornadoes.
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755. Skyepony (Mod)
CaribBoy~ GEOS-5 is hinting at a blob or system around then too. Maybe a little slower to form than those others are hinting.

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Up on Little Rock's survey page this morning:

"During damage surveys, it was noted that numerous homes were removed from their foundations, with only slabs remaining. Years ago, that might be justification for an F5 rating on the original Fujita scale. These days, the quality of the construction is examined before a rating is assigned. One of the factors determining the rating is the use of anchor bolts.

Back in 2004, the Wind Science and Engineering Center at Texas Tech University submitted A Recommendation for an Enhanced Fujita Scale (EF-Scale) to the National Weather Service. The document went into great detail about wind speeds and resulting damage based on building standards and no "glaring weak links" in the construction. According to the document:

"A weak link is a discontinuity in the load path, which runs from the building surface through the structural system to the foundation. Inadequate nailing of wood roof decking, marginal anchoring of roof structure to top of wall, discontinuity in the connection between first and second floor, and use of cut nails instead of anchor bolts to attach sill plate to foundation are examples of load path discontinuities."

In Vilonia (Faulkner County), for example, there was little indication of anchor bolts where homes used to stand. At a subdivision to the southwest of town, the official survey results read as follows: "Houses completely destroyed; only slabs remaining at several places. No anchor bolts used in foundations."

Using cut nails to secure homes to the foundation is widely practiced and the minimum standard in most of the building codes. This is according to Dr. David Prevatt, Associate Professor of Civil and Coastal Engineering at the University of Florida. According to Dr. Prevatt:

"It is my opinion that cut nails can only be considered a temporary connection while installing a wall. They are in no way, shape or form have the capacity to resist the sliding loads or the uplift loads reduced by high winds that impact the walls of a building."

Without anchor bolts, it took less wind to sweep houses away in Vilonia (Faulkner County). This explains the EF4 (instead of EF5) rating that was ultimately decided upon. The non-use of anchor bolts did not sit well with Dr. Prevatt:

"Bottom-line - we either build them (our houses) stronger or communities must accept that certain number of homes randomly selected by nature's wrath, will be blown away and kill people in every moderately strong tornado for the foreseeable future."
Member Since: July 6, 2010 Posts: 113 Comments: 34090
Quoting 751. Jedkins01:



Hmmm, well I certainly won't argue if you've seen it, but I haven't myself, so that's why I said it. Tornado damage to such heavy and low lying objects though in tornadoes is an example of why tornadoes are so destructive. I'm not entirely sure why tornado winds are so excessively destructive. I think it may be due to the rapid change in wind velocity over a short period of time (direction and speed) along with the vertical normal component of wind present in tornadoes that is responsible for the tornado winds being worse.


Well it's more of a recollection. I certainly have not spent the time yet digging around for videos of crashes against said barriers or looked for engineering specs. I've just seen some in construction zones where they've looked toppled or bowed out from wrecks.

The understanding is that tornadic winds tend to be more destructive than straight-line winds of the same magnitude due to the turning component. I've seen some of the results of modeling studies done by graduate students in my department while in school and, from a model output sense, the load on structures is higher with the turning component.
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Quoting 744. Sfloridacat5:

Not too impressive but a 40mph gust was just recently measure out on Captiva Island.

NWUS52 KTBW 031653
LSRTBW

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE TAMPA BAY AREA - RUSKIN FL
1253 PM EDT SAT MAY 03 2014

..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..

1235 PM MARINE TSTM WIND 1 S CAPTIVA 26.51N 82.19W
05/03/2014 M40 MPH LEE FL MESONET

WEATHER STATION AT TWEEN WATERS INN MEASURED 40 MPH WIND
GUST.


Nice place...Especially 35 years ago.
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Quoting 745. ScottLincoln:


I seem to recall seeing highway barriers after crashes on numerous occasions and seeing them displaced.
Homes of typical construction - that is, not notably below average construction and without above average construction - have an expected wind speed of 200 mph for the highest degree of damage. That is high-end EF4. It takes better-than-average construction of a residential single-family home to reach EF5 winds (>200mph).
Debarking of trees is the highest degree of damage available on the EF-scale. Although it's the highest DOD, it only has expected winds of 131mph (softwood) and 143mph (hardwood)... high-end EF2 to low-end EF3. The debarking of trees is thus not a good indicator of EF5 winds.


Hmmm, well I certainly won't argue if you've seen it, but I haven't myself, so that's why I said it. Tornado damage to such heavy and low lying objects though in tornadoes is an example of why tornadoes are so destructive. I'm not entirely sure why tornado winds are so excessively destructive. I think it may be due to the rapid change in wind velocity over a short period of time (direction and speed) along with the vertical normal component of wind present in tornadoes that is responsible for the tornado winds being worse. I don't really know though so I don't want to speak with authority at all, just my speculation.

Also, yes debarking of trees definitely isn't a good a indicator of ef5 winds. Trees were debarked well inland along the pathway of hurricane Charley, as far inland as Desoto county. Obviously Charley had very intense winds, but it wasn't wasn't an EF5 tornado, and certainly would have weakened at least some by the time it reached Desoto County.

Obviously comparing tornadoes in hurricanes is futile, but the point is yes, debarking trees does require winds, but as you noted, it has been proven to begin occurring a bit below 150 mph.
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Dr. Masters co-founded wunderground in 1995. He flew with the NOAA Hurricane Hunters from 1986-1990. Co-blogging with him: Bob Henson, @bhensonweather

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