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Mile-wide tornado smashes Windsor, Colorado; plus, hurricane season commentary

By: Dr. Jeff Masters , 1:23 PM GMT on May 23, 2008

A mile-wide tornado swept through Colorado between 11am and noon yesterday, ripping the roofs off buildings, tossing cars into the air, and killing at least one person in Weld County, northeast of Denver. Hail up to 2.75" in diameter accompanied the storm, which took an unusual north-northwesterly track , parallel to the Rocky Mountains north of Denver. Hardest hit was the town of Windsor, between Fort Collins and Greely, where damage appeared to be at least EF3. A local TV station took some impressive live video of the tornado, and a wunderground web cam video in Windsor, Colorado (Figure 1) caught the funnel as it passed east of the camera.

Figure 1.Webcam view looking east at 11:45am MDT in Windsor, Colorado as the tornado passed by. Note the golf ball-sized hail covering the ground. Image credit: windsorweather.com.

The Weather Underground's tornado expert, Rob Carver, had this explanation of yesterday's tornadoes:

Two low pressure systems over the Western U.S. were the cause of the severe weather outbreak of May 22. A strong upper-level low over the Great Basin formed a surface low in the lee of the Rockies, and brought a strong southerly mid-level jet over the Plains of Colorado and Kansas. As the surface low formed, it brought warm moist air northwards, forming a warm front. This warm air moved westward, rising with the terrain, causing thunderstorms to form. Once these storms formed, the juxtaposition of easterly flow at the surface with southerly flow aloft (i.e., wind shear) produced significant spin in the horizontal direction, which was tilted by the storms to vertical spin, which triggered the formation of tornadic thunderstorms. This movement of the warm front up the slope of the Rockies to help trigger tornadic thunderstorms is a rare occurrence.

Figure 2. Radar reflectivity image (top) of the Windsor, Colorado tornado at 11:45am MDT May 22, 2008. Note the classic hook-shaped echo associated with the tornado. Bottom: Doppler velocity image of the tornado, showing a small core of red and blue colors right next to each other, denoting strong winds towards and away from the radar, the classic signature of a tornado vortex. For those interested, we've saved an animation of the reflectivity and Doppler velocity.

Severe weather forecast
Severe weather is expected today over Kansas, Nebraska, and surrounding states. NOAA's Storm Prediction Center has placed portions of this area under its "Moderate Risk" category for severe weather, one step below its highest level of concern, "High Risk". Yesterday was also a "Moderate Risk" day, which SPC later upgraded to "High Risk" once the tornadoes started pounding Colorado. More severe weather is expected Saturday and Sunday over the Midwest as the upper-level low pressure system responsible moves slowly eastward. The Weather Underground Severe Weather page and Tornado page and WebCam page are good places to go to follow the severe weather. Also, tune in to the chase accounts and awesome storm photos from Wunderblogger Mike Theiss, who was in Kansas yesterday, and has posted many spectacular photos of yesterday's storms. According to Mike's blog:

Today Cloud 9 Tours saw 4 tornadoes and ONE developing almost overhead. We experienced winds over 100mph from the circulation of the meso that passed overhead as a cone tornado developed. Stay Tuned....

Possible development in the Eastern Pacific late next week
The past four days, the ECMWF model has been predicting the formation of a tropical storm in the the Eastern Pacific, just off the coast of Guatemala, around May 29. The GFS model has also been predicting something might develop, but in the Western Caribbean near Mexico's Yucatan Peninsula. The GFS has been rather inconsistent with its handling of this potential storm, and I am inclined to discount its forecast--especially since last night's long range runs of the NOGAPS, Canadian, and UKMET models all show development in the Eastern Pacific, not the Caribbean. All five models predict a northward shift in the jet stream and substantial relaxation in wind shear over the Eastern Pacific and Western Caribbean next week. It is common to see May tropical storms in the Eastern Pacific, and it would not be a surprise to see something develop there. I'd put the odds of something popping up in the Western Caribbean or Gulf of Mexico at less than 10%, though.

NOAA's seasonal hurricane forecast
NOAA issued its annual seasonal hurricane forecast yesterday, which I discussed in detail in yesterday's blog entry. Yesterday's forecast came out with a little more uncertainty attached to it than previous forecasts, which is a good thing. The media attention and fanfare that accompanies these forecasts is rather excessive, given the low skill they have. In fact, we don't even know if the NOAA forecasts have ANY mathematical skill, because they've never released a verification study of their forecasts. I doubt that the skill is very high--as Eric Berger of the Houston Chronicle pointed out in a blog yesterday, NOAA has blown its forecast of Accumulated Cyclone Energy (ACE) each of the last six years. NOAA held its usual press conference to announce the forecast; this year, it was held at the home of the NOAA Hurricane Hunter aircraft, MacDill AFB in Tampa. The NOAA dignitaries present said all the right things, preaching the need for preparedness regardless of the forecast for the upcoming hurricane season. Still, I wonder if NOAA might be hurting themselves by making such a public spectacle over the release of a forecast that no one knows the accuracy of, and has performed poorly by some measures in recent years. I do like the fact they are issuing public hurricane forecasts, as I expect their accuracy and value will improve in coming years, but they're definitely not worth the attention they're getting at present.

Jeff Masters

Tornado1 (kd7tda)
One of several tornados. This one was near Grainfield, KS
Tornado Damage 3 (jlg)
Damage from today's Tornado in Windsor, Colorado
Tornado Damage 3
Mean Looking Meso with Cone Tornado (MikeTheiss)
Photo os a wallcloud with a developing tornado passing just to the north of our location on May 22nd, 2008. Photo copyright Mike Theiss
Mean Looking Meso with Cone Tornado

The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

Reader Comments

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557. weathersp
7:41 PM EDT on May 23, 2008
555. How'd you know :0
Member Since: December 31, 1969 Posts: Comments:
556. weathersp
7:39 PM EDT on May 23, 2008
552. Not as much.. but it does take a turn NE through 228 hrs.
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554. charley11
11:37 PM GMT on May 23, 2008
also, there's a decent chance the models' predicted storm in the pacific will come to fruition.
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553. weathersp
7:37 PM EDT on May 23, 2008
550. jphurricane2006 7:37 PM EDT on May 23, 2008
sp and jp?

hey are we related? we have the same last um letter LOL

Freaky Dude..
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552. hurricane23
7:37 PM EDT on May 23, 2008
Might want to and the 18z nogaps to that pack JP.
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551. charley11
11:17 PM GMT on May 23, 2008
the gfs dropped the storm?

ah, thought so. but you know, it might pick back up on it in the next couple runs.

Regardless, this episode should serve as a wake-up call that the Tropical Atlantic has now PASSED the point where cyclonic formation is no longer unlikely.

On that note, I've got a bad feeling about that little spin lurking out in the distance by Africa. The implications of the presence of a tropical LOW in MAY scare me more than anything I've seen lately.
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546. weathersp
7:31 PM EDT on May 23, 2008

Storm gosh dont scare me like that JP asks somthing about your opinion and you pop up behind our backs!

stalker... Just Kidding StormW
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543. weathersp
7:27 PM EDT on May 23, 2008
Hey LoCal thanks for showing that.. That is really neat that there arent any high mountains there to cut a storm apart.

Interesting. Learn somthing new every day.
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542. weathersp
7:26 PM EDT on May 23, 2008
I take things way to seriously.. I have personal problem even in real life with that.
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541. moonlightcowboy
6:24 PM CDT on May 23, 2008
Hey, LoCal! Good to see you in here! Nice post!

...could be some funky creature down there stirring thing up! ;P
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539. weathersp
7:20 PM EDT on May 23, 2008
I do not mean in any way mean to insult people. Thank you for telling me. If I did insult anyone I am sorry.
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537. emguy
11:21 PM GMT on May 23, 2008
CCHS...On close look at the GFS model...the philosphy continues to be a complex one, where competing lows are in the neighborhood. One in the Caribbean, the other in the Pacific. The second low moving into SW Florida is the Pacific System, the first area moving over the south Florida and the Florida Straits is the Caribbean System.

Time will tell what...if anything may occur and the model timeframe is still in the "crystal Ball" period beyond 5 days.

If something is there in another few days, it is not impossible that it may be a disturbance that forms in the "mean location" of these two areas (Over Central America). After that, maybe Florida gets benificial rain and not much else. Who knows, but it unique that the Pacific Low is also pointed toward Florida on the GFS and as such, this may be a reasonable explanation if something pops up in the coming days.
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536. LowerCal
4:23 PM PDT on May 23, 2008
500. TerraNova 3:38 PM PDT on May 23, 2008

I havn't seen the ECMWF do this so far. I don't think a low could survive the trek across mexico. Does the ECMWF factor in elevation?

The highest point of the Isthmus of Tehuantepec is 735 ft. In the 1923 hurricane season a tropical storm came from the Pacific, crossed the Isthmus of Tehuantepec, and became a hurricane to hit Louisiana.

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532. cchsweatherman
7:06 PM EDT on May 23, 2008
There has been a very interesting development with the 18UTC GFS. It now agrees with the ECMWF and brings the Eastern Pacific Storm over Mexico and into the Bay of Campeche where it lingers for about a day or two before developing into a tropical storm and hitting the SW Florida coast in 360 hours. This brings about a whole new ball game. Even thought it would be very unlikely to happen, but imagine if the Western Cairbbean system developed into a tropical storm and moved over Florida then the new storm the GFS projects hits Florida just a week later. That could end the drought and give a huge jolt to Lake Okeechobee.
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531. weathersp
7:05 PM EDT on May 23, 2008
529. JP

Yeah I noticed that after most of the convection around the COC faded there was a burst of convection right at dead center of the system... Quite the curveball.
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528. weathersp
7:03 PM EDT on May 23, 2008


A general good rule of thumb is not take everything past 180hrs with a grain (or two) of salt.
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527. weathersp
6:57 PM EDT on May 23, 2008

I realise that... I know its supposed to lose some of its convection right now because it is the durnal minimum. I was pointing out that it only looked good because it had convection which was provided by the Durnal Max
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526. pearlandaggie
10:58 PM GMT on May 23, 2008
GFS equals.........fail??

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525. Stormchaser2007
6:54 PM EDT on May 23, 2008
look off of Africa.....

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524. cchsweatherman
6:49 PM EDT on May 23, 2008
For the first time in the past several days, the GFS has dropped the potential Western Caribbean system as it has only a weak tropical depression in the Western Caribbean late next weekend, then weakens it completely. The GFS continues to maintain forecasting some significant tropical rainfall for South Florida by late next week and lasting for quite some time.
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523. atmoaggie
10:50 PM GMT on May 23, 2008
Example Miami. I have only been once, but it seemed to me that when you got 30 yards off the beach you were already up off water level 10 to 20 feet. Where as along a shelf 30 yards in may only gain you a few feet, hence the same size surge in both areas would actually be perceived as larger where there is a more gradual slope because the water would be allowed to travel further inland at a higher level?

Of course topography matters. Miami would have a decent surge in downtown and up the river. I think you are giving the area more elevation in your mind that it really has, though.

Next I was wondering what the typical tides are like in the Gulf, and how they vary from the typical tides along the E coast?

Regular tides in the GoM have about a meter in amplitude at the most. Atlantic can have a couple.

Under the right circumstances (esp storm motion direction), JAX could have a catastrophe. The shelf, the river there, the coastal building boom, etc.
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522. pearlandaggie
10:53 PM GMT on May 23, 2008
LOL, patrap.
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518. Patrap
5:50 PM CDT on May 23, 2008
If yall keep chasing dem models...someone may drive right off a cliff.
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517. atmoaggie
10:44 PM GMT on May 23, 2008
Maybe I'll meet Bill Read there?!

If he is around, would not surprise me a bit. Seemed a friendly enough, down-to-Earth guy. Probably got that in H-town.
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515. cchsweatherman
6:47 PM EDT on May 23, 2008
Seems like the GFS drops the low in the Western Caribbean at 216 hours.
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514. HurricaneGeek
6:45 PM EDT on May 23, 2008

I think Ivan of 2004. I think. Although if memory serves I think it was closer to 8-9N
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513. hurricane23
6:47 PM EDT on May 23, 2008
At 192hrs its already tracking north on the 18z GFS.weak 1009mb low pressure area.
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512. Drakoen
10:45 PM GMT on May 23, 2008
I'm still not putting much faith into the system developing in the Caribbean. The CMC, ECMWF, NOGAPS, and UKMET all want this EPAC system and I'll go with the model consensus.
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510. all4hurricanes
9:43 PM GMT on May 23, 2008
surf mom i already brought the tadpoles in and I live in Fairfax VA I feed them boiled lettuce I never tried fish food. I'm pretty sure they're gray tree frogs we've raised this type of tadpole before and they become small light green frogs the eventually get grayer It is good to show children the metamorphosis of the frogs, its interesting to
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509. mississippiwx23
10:43 PM GMT on May 23, 2008
Forget it, I will stop making stupid comments. Lots of storms have formed down there, but most were weak and made landfall into central america and were late in the season, not this early.
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507. weathersp
6:42 PM EDT on May 23, 2008
The Atlantic Wave looks like it was riding the Durnal Max phase... it really looks striped of convection now.

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Cat 6 lead authors: WU cofounder Dr. Jeff Masters (right), who flew w/NOAA Hurricane Hunters 1986-1990, & WU meteorologist Bob Henson, @bhensonweather

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