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

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

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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
Tornado1
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

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1057. Weather456
12:57 PM AST on May 24, 2008
Notice how the southwesterlies south of the system freshens....thats an indicator of a northward push in the monsoon trough probably induced by the MJO.



Total Cloud Cover

Member Since: July 24, 2005 Posts: 407 Comments: 19076
1056. Ivansrvivr
4:56 PM GMT on May 24, 2008
456, I agree. I usually would bet on development in the E-Pac when it is likely for both Caribbean and W-Pac early. Westerlies in E-Pac is much more like late season pattern as is front passing totally thru Florida by tomorrow.

Westerlies in E-Pac in late May-SOI likely dropping further. If that continues, becomes pattern it would indicate possible emerging El Nino.
1054. BahaHurican
1:01 PM EDT on May 24, 2008
Nah, Drak, we were singing along . ..
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1053. Patrap
12:00 PM CDT on May 24, 2008

This weekend is a Hurricane Tax Holiday for Louisiana Residents Statewide..Link







Evacuation Considerations for the Elderly, Disabled and Special Medical Care Issues Link

Your Evacuation Plan Link


Disaster Supplies Kit
Link

NOAA Alert Weather Radio's: Link
Member Since: July 3, 2005 Posts: 428 Comments: 129903
1052. stormhank
4:59 PM GMT on May 24, 2008
thanks 456...well, GFS has been consistent, so I guess it cant totally be ignored.
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1051. Drakoen
5:01 PM GMT on May 24, 2008
My jokes are getting too dry...
Member Since: October 28, 2006 Posts: 57 Comments: 30833
1050. hahaguy
12:57 PM EDT on May 24, 2008
It really pissed me off that our wonderful Governer Charlie Crist cut our tax free on hurricane supplies.
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1049. Patrap
11:57 AM CDT on May 24, 2008
Tomorrow is Hurricane History day ..Link
Member Since: July 3, 2005 Posts: 428 Comments: 129903
1048. Drakoen
4:57 PM GMT on May 24, 2008
1044. Patrap 4:56 PM GMT on May 24, 2008
Tis the season...Link


To be jolly fa-la-la-la-lah la-la-la-la.
Member Since: October 28, 2006 Posts: 57 Comments: 30833
1047. Weather456
12:54 PM AST on May 24, 2008
RE: Post 1040,

What the GFS has been predicting is the development of a low pressure area in the monsoon trough just south of Panama. This normally causes development in the EPAC, but occasionally the monsoon trough shifts northward into the SW Caribbean normally in the early part of the season (May/June) and the late part of the season (October/November) which causes development to occur there rather than in the EPAC. Any passing tropical waves normally enhances development. Now if one was to look at an infrared image...one would see the monsoon trough lies in the EPAC indicated by the amount of shower activity, but any northward shift could make a difference between the whether the CMC/UKMET or GFS/ECMWF is correct.

Past examples were Beta in 2005 and Mitch in 1998.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
1046. Patrap
11:56 AM CDT on May 24, 2008
National Hurricane Preparedness Week Link

History teaches that a lack of hurricane awareness and preparation are common threads among all major hurricane disasters. By knowing your vulnerability and what actions you should take, you can reduce the effects of a hurricane disaster. Hurricane Preparedness Week during 2008 will be held May 25th through May 31st.

The goal of this Hurricane Preparedness Web site is to inform the public about the hurricane hazards and provide knowledge which can be used to take ACTION. This information can be used to save lives at work, home, while on the road, or on the water.
Member Since: July 3, 2005 Posts: 428 Comments: 129903
1045. hahaguy
12:55 PM EDT on May 24, 2008
And they only know about that one from their barometer on the Mayan-Kuwaiti oil tanker.

lol
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1044. Patrap
11:55 AM CDT on May 24, 2008
Tis the season...Link

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1042. atmoaggie
4:53 PM GMT on May 24, 2008
know 1 was a fish storm though.

And they only know about that one from their barometer on the Mayan-Kuwaiti oil tanker.
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1041. Weather456
12:52 PM AST on May 24, 2008
999. Ivansrvivr 12:23 PM AST on May 24, 2008
StormW, your nasa sattelite loop is showing generally westerly surface winds in E-Pac. That is not what I would call "normal". There should be light easterlies in E-Pac now. That does make Caribbean more likely spot for development at the moment.


I also wondering why the flow is westerly rather than southeasterly. That further supports a monsoon trough that could move north into the Sw Caribbean...perhaps the reasoning behind the GFS.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
1040. stormhank
4:50 PM GMT on May 24, 2008
right now the sw carribean is cloud free..but Ive noticed the GFS continues to want to develop a system sown there..My question is what supposedly?? triggers this formation? of course things can develop 7-10days out right?
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1039. Patrap
11:53 AM CDT on May 24, 2008
Things are vary interesting...
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1038. Ivansrvivr
4:50 PM GMT on May 24, 2008
It was major El Nino in 110b.c. There were only 3 named storms that season. I can't read enough Mayan to understand them. I know 1 was a fish storm though.
1037. GBlet
11:49 AM CDT on May 24, 2008
Good morning everyone! Just finished reading over posts from last nite. Thank you everyone for your concern. We spent several hours duckin and dodgin nados. To our surprise damage is not so bad for everything we were facing.
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1036. SouthDadeFish
4:47 PM GMT on May 24, 2008
Drak I completely agree. What is imortant from that run is that the GFS continues to focus development around the same time frame and moves it in generally the same direction for the first few days after. Any landfall location after 200 hours out is completely rediculous and we still don't even know if this potential system will develop. However, it is still fun that the GFS forecasts an early beginning to the season. :~) I'll take any sheared rainmaking system the GFS forecasts to hit Florida.
Member Since: August 12, 2007 Posts: 11 Comments: 2448
1035. StormJunkie
4:48 PM GMT on May 24, 2008
1029.

I've seen that before. Almost like the atmospheric conditions are set on the map, then the base map shifts; or like you said, the frames shows, but not updated yet. Something fishy happens during release.

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1034. Drakoen
4:49 PM GMT on May 24, 2008
1032. hahaguy 4:48 PM GMT on May 24, 2008
no i think its like 110 b.c. lol


LOL.
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1033. Stormchaser2007
12:47 PM EDT on May 24, 2008
I think this hurricane season will be like the one of 1478 who disagrees with me

LOL
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1032. hahaguy
12:48 PM EDT on May 24, 2008
no i think its like 110 b.c. lol
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1031. StormJunkie
4:46 PM GMT on May 24, 2008
If course, let's not put too much faith in track right now.

I concur! Just for the record, anytime you hear me talk about a landfall spot out more then 144hrs, please assume that I put very little stock in it.

What is interesting is that we have yet another GFS run that wants to head a somewhat developed system towards the Gulf.
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1029. Drakoen
4:46 PM GMT on May 24, 2008
1025. StormJunkie 4:46 PM GMT on May 24, 2008
Tampa?

Looks more like W Fla panhandle? Did I miss something?


It looks like the frame changed. Originally it was Tampa. I guess that was the wrong frame.
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1028. all4hurricanes
4:45 PM GMT on May 24, 2008
I think this hurricane season will be like the one of 1478 who disagrees with me
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1027. Drakoen
4:45 PM GMT on May 24, 2008
The only thing I was interested about in that run is development in the Caribbean. Now to see what the other 12z runs say. The ECMWF should be out around 3:30pm EDT. The rest of the model should be out before that time.
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1025. StormJunkie
4:44 PM GMT on May 24, 2008
Tampa?

Looks more like W Fla panhandle? Did I miss something?
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1024. TerraNova
12:44 PM EDT on May 24, 2008
LOL Drak.
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1023. Stormchaser2007
12:43 PM EDT on May 24, 2008
.
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1022. TerraNova
12:42 PM EDT on May 24, 2008
It has it making landfall in Nicaragua but emerges of the coast within 12 hours AFTER THAT DO IT DO?

The new GFS has it heading towards the west coast of Florida, but then loops it back west and aims it towards Mississippi. Of course, let's not put too much faith in track right now.
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1021. Drakoen
4:40 PM GMT on May 24, 2008
LOL now the GFS wants to claim Tampa!!!
Member Since: October 28, 2006 Posts: 57 Comments: 30833
1020. Stormchaser2007
12:41 PM EDT on May 24, 2008
For anyone who dose not already have it heres the link to the 12z GFS.
Link
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1019. 0741
4:34 PM GMT on May 24, 2008
It has it making landfall in Nicaragua but emerges of the coast within 12 hours AFTER THAT DO IT DO?
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1018. Stormchaser2007
12:38 PM EDT on May 24, 2008
Sorry about that Drak...
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1017. Patrap
11:36 AM CDT on May 24, 2008
LSU ESL site for imagery and more, Link
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1016. Stormchaser2007
12:35 PM EDT on May 24, 2008
If you look at my image that I just posted there a weak WPAC storm to its west.
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1015. Drakoen
4:35 PM GMT on May 24, 2008
Lets not continually post the GFS run frame by frame please...
Member Since: October 28, 2006 Posts: 57 Comments: 30833
1014. miami22
4:27 PM GMT on May 24, 2008
Hi all - im new here and love to read and learn form all of you. 0742 - Should I not make the trip out to the stadium tonight? I was going to tailgate for hours before but I'm scared to make the trip out there today...
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1013. Drakoen
4:34 PM GMT on May 24, 2008
lol Pat. I'm actually hoping to see a little action in the Caribbean. I want to win Bob's contest lmfao!
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1012. Stormchaser2007
12:34 PM EDT on May 24, 2008
Yeah now its at 1004mbs right under the Yucatan.

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1011. SouthDadeFish
4:33 PM GMT on May 24, 2008
1007,

Its pretty much the same spot as it was in the previous GFS run. The last run had it moving north after that and had it resuming its strengthening so lets see what this run has it doing.
Member Since: August 12, 2007 Posts: 11 Comments: 2448
1010. TerraNova
12:31 PM EDT on May 24, 2008
keep us updated to new run TY

Sure... You're welcome.
The CMC, NOGAPS, and UKMET are accessible from this site.
ECMWF is released on this page.
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1009. Drakoen
4:31 PM GMT on May 24, 2008
It has it making landfall in Nicaragua but emerges of the coast within 12 hours.
Member Since: October 28, 2006 Posts: 57 Comments: 30833
1008. Patrap
11:32 AM CDT on May 24, 2008
UNYSIS GFSx Day 10 3JUNE 0Z

500mb hght pres (mb)Link

Surface pres Link



I dont like that run,..
Member Since: July 3, 2005 Posts: 428 Comments: 129903
1007. Stormchaser2007
12:30 PM EDT on May 24, 2008
GFS showing it over Nicaragua now...this might inhibit strengthening in the next forecast hours...

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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.

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