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:

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

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706. Ivansrvivr
2:45 AM GMT on May 24, 2008
701. that is a week away. The GFS will have 3 cat5s hitting Florida between now and then.
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10:42 PM EDT on May 23, 2008
Somebody asked about TUTT(s) earlier - a link I had to a NOAA tutorial that included some TUTT info
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703. pearlandaggie
2:43 AM GMT on May 24, 2008
701. you know, we already had a discussion about how unreliable that mud wrestling model is! LOL
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701. stormhank
2:43 AM GMT on May 24, 2008
Link european model has a low in bay of campeche out 240 hrs
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700. Ivansrvivr
2:41 AM GMT on May 24, 2008
696. LOL twice.
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699. pottery
10:38 PM AST on May 23, 2008
DDR. Im not sure. The man I spoke to said that the info about the radar is available on the Caribbean Meteorological Society website. But I have not gone there yet.
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697. Ivansrvivr
2:38 AM GMT on May 24, 2008
685, all the sahara dust got used up last year. Now the Africans need to import some more sand. They can afford it as much as they are charging for oil!!!
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695. hahaguy
10:40 PM EDT on May 23, 2008
now its a party the geek is here lol
Member Since: August 12, 2007 Posts: 2 Comments: 2838
693. JLPR
10:39 PM AST on Mayo 23, 2008
Hey Geek =)
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692. stormdude77
10:39 PM AST on May 23, 2008
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691. JLPR
10:38 PM AST on Mayo 23, 2008
wow lol Mo has a big appetite =)
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690. HurricaneGeek
10:38 PM EDT on May 23, 2008
Hi everybody. I've been lurking but now I'm posting =)
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689. Ivansrvivr
2:37 AM GMT on May 24, 2008
P.A.,The not so funny thing is my cat would eat that cat along with the cheese.
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688. hahaguy
10:37 PM EDT on May 23, 2008
it seems like mother nature will have some tricks up her sleeves this yr :o
Member Since: August 12, 2007 Posts: 2 Comments: 2838
686. Ivansrvivr
2:34 AM GMT on May 24, 2008
Patrap, there is already more moisture over the Atlantic now than at the peak of the season last year.
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685. JLPR
10:33 PM AST on Mayo 23, 2008
Hey Patrap
seeing that graphic it shows the persistent dry air in the Caribbean, argg lol when is it finally going away, I have allergies =(
Also Sal is missing lol I saw a graphic at CIMSS and Sal off the coast of Africa is missing =P
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684. pearlandaggie
2:34 AM GMT on May 24, 2008
that's not my fat cat either! LOL
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683. Ivansrvivr
2:32 AM GMT on May 24, 2008
That is a funny pic, but your cat isn't a 6 lb eating machine like mine is.
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680. DDR
2:29 AM GMT on May 24, 2008
Pottery i saw you post something about a local weather radar system,do you know if they are going online with images and stuff?
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679. pearlandaggie
2:31 AM GMT on May 24, 2008
i figured you folks might get a kick out of that one...cracks me up everytime i see it! :)
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10:24 PM EDT on May 23, 2008
Was thinking the robust waves indicated anomalously favorable conditions in the mid levels out there. Any one know of a graphic digesting info to show anom RH over Africa & or E Atl?
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677. Ivansrvivr
2:29 AM GMT on May 24, 2008
Mo would eat that cheese in two bites then beg for more.
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676. JLPR
10:29 PM AST on Mayo 23, 2008
674. pearlandaggie
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675. stormdude77
10:28 PM AST on May 23, 2008
Hey DRR...good to see ya, I had a few sprinkles of rain last night
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674. pearlandaggie
2:24 AM GMT on May 24, 2008
seems like our wave is destined for an epic fail...
something like this...

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673. Ivansrvivr
2:23 AM GMT on May 24, 2008
656, that is sign of cooler SSTs and stable air but the fact that that low survived this long in May is very unusual. I am a little worried that those conditions will tend to keep tropical development a little farther south in the central Atlantic which would be bad for caribbean and Fl.
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672. pottery
10:22 PM AST on May 23, 2008
Trinidad weather now

79f mostly cloudy
78 % humidity
dew pt. 72 f
pressure 1014 rising.
Time 10:28 pm

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671. JLPR
10:24 PM AST on Mayo 23, 2008
yep weather456 it scares me to think about August - September
It going to be a very ugly Cape Verde season, right now it depends on the High Pressure and where does it decides to sit.
I just hope that all the Cape Verde systems go to the west, then north west , then north and then north east =P
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670. DDR
2:22 AM GMT on May 24, 2008
Hey! stormdude77 whats up?
yea lets hope we get some rain next week
after all its almost june 1st our rainy season.
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669. Weather456
10:19 PM AST on May 23, 2008
661. JLPR 10:16 PM AST on May 23, 2008
yeah weather456
But I guess this one was never meant to develop but it may give us an idea of whats to come. If a wave like this one would have exited Africa with very favorable conditions for Tropical cyclone formation we would be talking of a storm already =P.

As I said earlier today, its a taste of what 08 has in store for us.....this is rather impressive for May and a lat of 6N. Imagine the waves in June & July at 10N, and August and September at 10-15N.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
668. Ivansrvivr
2:21 AM GMT on May 24, 2008
666, either a tropical wave or the arrival of the ITCZ?
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667. hahaguy
10:20 PM EDT on May 23, 2008
hey jfv how you doing tonight ?
Member Since: August 12, 2007 Posts: 2 Comments: 2838
666. stormdude77
10:17 PM AST on May 23, 2008
Also, I get the feeling we (the southern windward islands) might get some rain by mid next week. The WU forecast gives my island (Barbados) a 40% chance of rain on Tuesday night. Trinidad has a 50% chance of rain for next Wednesday...
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665. Ivansrvivr
2:18 AM GMT on May 24, 2008
663. Most likely development will occur in the E-Pac, but anything is possible.
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661. JLPR
10:13 PM AST on Mayo 23, 2008
yeah weather456
But I guess this one was never meant to develop but it may give us an idea of whats to come. If a wave like this one would have exited Africa with very favorable conditions for Tropical cyclone formation we would be talking of a storm already =P.
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660. stormdude77
10:13 PM AST on May 23, 2008
The EATL wave has a good spin to it though...very impressive for May
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659. pottery
10:11 PM AST on May 23, 2008
Thanks, 456.
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10:09 PM EDT on May 23, 2008
the highest is
softball size hail after that dosent much matter
Member Since: July 15, 2006 Posts: 187 Comments: 57781
657. atmoaggie
2:10 AM GMT on May 24, 2008
2.25 # hailstone, largest weighed
largest diameter = 7 inches Link

Hi y'all...Bye y'all. Cannot stay.

BTW, it is Friday night, so...

Git up offa that thing, and shake it 'till you feel better.

g'nite ;-)
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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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