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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757. StormJunkie
4:34 AM GMT on May 24, 2008
Yea Drak, showing a lot of vorticity and L's on the pac side as well though. Not sure how to take that, but at 108hrs we really are starting to get in to a little more believable time frame. Granted 108 is still a long way out when one is talking intensity or genesis.
Member Since: August 17, 2005 Posts: 26 Comments: 16828
756. Drakoen
4:35 AM GMT on May 24, 2008
I have never been one to go against the GFS when its penchant like this but it needs some model support.
Member Since: October 28, 2006 Posts: 57 Comments: 30559
755. StormJunkie
4:30 AM GMT on May 24, 2008
00z GFS 72hrs out with the stalled front.




00z GFS 108hrs out




00z GFS 138hrs out

Member Since: August 17, 2005 Posts: 26 Comments: 16828
754. Drakoen
4:26 AM GMT on May 24, 2008
Well the 00z run on the GFS still wants that Caribbean storm showing a good amount of convection associated with the system. Will see if the other 00z runs agree with this or continue with the EPAC system. GFS vs. 3 reliable computer forecast models.
Member Since: October 28, 2006 Posts: 57 Comments: 30559
753. hahaguy
12:22 AM EDT on May 24, 2008
i'm still standing by by prediction 17,9,4. But no matter what this is going be a interesting season.
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752. Drakoen
4:13 AM GMT on May 24, 2008
748. hahaguy 4:04 AM GMT on May 24, 2008
yep rained up here in st lucie for a good hr. my grass was happy lol


Well its only model simulations but this year could very well end up like 2004 with the amount of hits toward the U.S. east coast as well as the eastern coast states. Time will tell but I have been contemplating upping my numbers from 15,9,5 to 16,9,5.
Member Since: October 28, 2006 Posts: 57 Comments: 30559
750. Drakoen
4:11 AM GMT on May 24, 2008
.
Member Since: October 28, 2006 Posts: 57 Comments: 30559
749. Drakoen
4:08 AM GMT on May 24, 2008
748. hahaguy 4:04 AM GMT on May 24, 2008
yep rained up here in st lucie for a good hr. my grass was happy lol


Got some nice rain here too in Palm beach county about an hour too!
Member Since: October 28, 2006 Posts: 57 Comments: 30559
748. hahaguy
12:04 AM EDT on May 24, 2008
yep rained up here in st lucie for a good hr. my grass was happy lol
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747. Drakoen
4:03 AM GMT on May 24, 2008
745. hahaguy 4:01 AM GMT on May 24, 2008
well thats good for us drak


Yep. We need the rain!
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746. JRRP
3:55 AM GMT on Mayo 24, 2008
i mean in the caribbean the shear will increase
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745. hahaguy
12:00 AM EDT on May 24, 2008
well thats good for us drak
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744. Drakoen
4:00 AM GMT on May 24, 2008
Tomorrow could be a yet again another wet day in Florida. A stationary front lies draped across the northern portion of the Southeast along with a shortwave trough. A surface low will cut-off from the frontal boundary and develop off the east coast. The frontal boundary associated with the low and a negative lift index will provide for rain chances starting in northern Florida and working its way down the state in the afternoon hours. Chance for rain throughout most of the state, with the highest totals in central Florida during the 24 hr period.
Member Since: October 28, 2006 Posts: 57 Comments: 30559
743. pottery
11:49 PM AST on May 23, 2008
An earthquake, a typhoon, a tsunami, a volcano, a hurricane. Any one of these things, and "blink", one hundred thousand souls lost.
Kind of frightening you know........
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742. StormJunkie
3:52 AM GMT on May 24, 2008
715 & 708

:~) I second and third those remarks!
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741. stormdude77
11:47 PM AST on May 23, 2008
Anyway, I'm out of here...good night all
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740. JRRP
3:36 AM GMT on Mayo 24, 2008

the shear will increase
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739. pottery
11:48 PM AST on May 23, 2008
...makes us realise how fragile life is sometimes.
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738. pottery
11:37 PM AST on May 23, 2008
When you see what storm surge can do there, and you know those people in the Irawwady had houses made of sticks.........
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737. Patrap
10:36 PM CDT on May 23, 2008
Thats Port Fouchoun Se. La Aug 30th 2005
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736. pottery
11:33 PM AST on May 23, 2008
You sure that was not a case of bad navigation, Pat ?
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735. Michfan
10:36 PM CDT on May 23, 2008
It will be interesting to see what the 00Z run says.
Member Since: September 7, 2007 Posts: 0 Comments: 1733
734. stormdude77
11:30 PM AST on May 23, 2008
Well Pottery...I guess that from the ''low level patches'' drfting in and out of the region (keeping moisture levels high)...
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733. Patrap
10:33 PM CDT on May 23, 2008
The Power of Hurricane Storm Surge

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732. Drakoen
3:31 AM GMT on May 24, 2008
00Z GFS run is coming out. Should get around the 144hr mark in an hour.
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731. TampaSpin
11:30 PM EDT on May 23, 2008
81 deg amd 78% humid. in Tampa now at 11:30pm really muggy
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730. pottery
11:22 PM AST on May 23, 2008
77, I'm surprised to see your humidity is at 83 % now. From the image you posted, I thought more in the 50's.
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729. pottery
11:14 PM AST on May 23, 2008
Thanks for the link there 77
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728. pottery
11:06 PM AST on May 23, 2008
Yeah, 77. There is not a lot of moisture there in the GoM or indeed across the islands and eastward too.
The hope is, for me, that the ITCZ can creep up 2 or 3 degrees in a day or two. You will have to wait a little longer !
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727. KEEPEROFTHEGATE (Mod)
11:07 PM EDT on May 23, 2008
i know 77 but things change real fast it will be interesting to see if anything is really there or if it will just disappear the next few runs.
Member Since: July 15, 2006 Posts: 173 Comments: 54283
726. stormdude77
11:07 PM AST on May 23, 2008
Good 77.
Do you know if we will be able to access the info. ?


Not sure...I'll monitor the CDERA main page though, for any updates...
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725. JLPR
11:08 PM AST on Mayo 23, 2008
yeah stormdude77 like I said before its dry, I have allergies thanks to that dry air, arrg lol but at least im not in the very dense dry air =)
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724. Patrap
10:09 PM CDT on May 23, 2008
NEXRAD Radar
Dodge City Base Reflectivity 0.50 Degree Elevation Range 124 NMI Link

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723. Thundercloud01221991
3:08 AM GMT on May 24, 2008
greensburg is under a tornado warning
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722. stormdude77
11:03 PM AST on May 23, 2008
Wow, look how dry the caribbean is, there would have to be a significant increase in moisture in the W caribbean, for any system to form there...

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721. pottery
11:04 PM AST on May 23, 2008
Good 77.
Do you know if we will be able to access the info. ?
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720. KEEPEROFTHEGATE (Mod)
11:02 PM EDT on May 23, 2008
gems global model showing rain rates of 75 to 100 mm per 12 hr period in a system to dev off s cost ric/n pan east coasts in sw carb for thur 12 z may 29 2008
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719. Patrap
10:03 PM CDT on May 23, 2008
Nitey Ivan & Mo
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718. stormdude77
11:01 PM AST on May 23, 2008
Pottery...one will also be in Belize...
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717. Ivansrvivr
3:01 AM GMT on May 24, 2008
gotta go run the cat so i can sleep later. Have a good nite.
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716. DDR
2:59 AM GMT on May 24, 2008
Great,its about time they got some mordern technology.
Goodnight all
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715. Ivansrvivr
2:53 AM GMT on May 24, 2008
Think about this; you know how good our VETS really are because most people rarely think about them. Never in history has a nation had such servicemen and women as we have. Thanks to all who have served or are serving our country.
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714. TheCaneWhisperer
2:53 AM GMT on May 24, 2008
It's very hard to question so many days of consistency in the GFS Patrap. Kinda like a roach picking off a shrimp tail from 40 meters.
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713. pottery
10:51 PM AST on May 23, 2008
Apparently they are installing one in Guyana as well, 77 and DDR.
So, Guyana, Trinidad, Barbados. Good coverage there.
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712. Ivansrvivr
2:48 AM GMT on May 24, 2008
705 &707 That is interesting, question is does it form in W.Caribbean and go north or E-Pac and go west? The total lack of anything resembling a bermuda high in both those models is just as interesting as possible development. Usually the Bermuda high will have pinched off the Azores high by June.
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711. stormdude77
10:47 PM AST on May 23, 2008
I can't wait for the Doppler Radar here in Barbados to be completed and ready for use...forecasting will be much easier
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710. HIEXPRESS
10:45 PM EDT on May 23, 2008
Thanks for the WV links - I'm just not sure if there is more WV than normal mid-level. Hard to just look at years of that kind of data & figure that out. Even if one had the data.
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709. Patrap
9:50 PM CDT on May 23, 2008
Thanx p&a,..have a Safe Weekend
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708. pearlandaggie
2:46 AM GMT on May 24, 2008
alright, folks...i'll stop poking the bear for now.

ya'll have a great Memorial Weekend and remember to thank Vet if you see one!

THANK YOU FOR YOUR SERVICE, PATRAP!
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707. Patrap
9:46 PM CDT on May 23, 2008
850mb same day Link
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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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