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:

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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1157. BoynSea
7:24 PM GMT on May 24, 2008
1152. hurricane23 7:21 PM GMT on May 24, 2008

Thank you.
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1156. Drakoen
7:25 PM GMT on May 24, 2008
Interesting stuff from the HPC adrian...
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1155. hurricane23
3:22 PM EDT on May 24, 2008
Hey SW!

Getting some scattered heavy rainfall here in dade county but nothing severe yet and hopefully it will stay under severe limits with all this cloud cover hanging around.
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1154. WhereIsTheStorm
7:22 PM GMT on May 24, 2008
gamma - 1144 - Don't say that. The last time the ACOE thought we were going to have a lot of rain they lowered the lake to save the levee and we still haven't recovered.
If they lower it again we will have to start taking showers once a week.


Member Since: August 14, 2006 Posts: 0 Comments: 458
1152. hurricane23
3:19 PM EDT on May 24, 2008
1149. BoynSea 3:19 PM EDT on May 24, 2008
Storm Junkie: Excuse me, but where are you getting those images? Good coverage of my area (North Abaco, Bahamas)

GHCC GOES 12 Interactive Viewer
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1151. Drakoen
7:18 PM GMT on May 24, 2008
1147. TerraNova 7:04 PM GMT on May 24, 2008
The new ECMWF develops the Caribbean low and takes it across the Yucatan, into the Bay of Campeche.

Yea. Its creating this unusual ridge over Gulf of Mexico i doubt any storm this time of year would be able to make it that far west without getting picked up by a trough.
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1150. KrazyKaneLove
7:17 PM GMT on May 24, 2008
the sunsport weather station in Loxahatchee is daying the temp here is 99.7F and press. is falling and at 17.71 in.? any1 else in fl. experiencing this heat?
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1149. BoynSea
7:18 PM GMT on May 24, 2008
Storm Junkie: Excuse me, but where are you getting those images? Good coverage of my area (North Abaco, Bahamas)
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1148. hurricane23
3:17 PM EDT on May 24, 2008
Here's what HPC had to say in todays Tropical discussion....


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1147. TerraNova
3:03 PM EDT on May 24, 2008
1146. StormJunkie
7:01 PM GMT on May 24, 2008
Not really Gamma

It seems to be the most interesting blob right now. That does not make it that interesting though :~)

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1145. KrazyKaneLove
6:57 PM GMT on May 24, 2008
It seems as though we always have these systems right off the e.c. of fl. this time of year that sneak up on us but don't ever amount to much..
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1144. seflagamma
2:53 PM EDT on May 24, 2008
OK, I peek back in and see so much going on.
StormW, I clicked that link by the Yukan and saw that swirl; it is really a rotation there... and SJ, of course you are teasing about that blog right off my coast! LOL

and all this talk about something next week???? at least we should get some rain..

just spoke with my Dad (today's his 74th birthday) and they are finally out of their 3 years drought. of course they got all their rain too fast and too much at once, but he said it will help the fishing, but not the farming. But their drought is now over.

That is the way it is feast or famine! I have a feeling Florida's 2 year drought will end in about a month from now and Lake O will probably need some draining again by September! LOL
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1143. Drakoen
6:48 PM GMT on May 24, 2008
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1142. Drakoen
6:47 PM GMT on May 24, 2008
The area of low pressure should migrate into the Caribbean with that westerly flow. I noticed that the UKMET and the CMC are showing development in the EPAC in different areas and different tracks. I'm inclined to go with the GFS, NOGAPS, and ECMWF solutions now.
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1141. CaneAddict
6:41 PM GMT on May 24, 2008
Good Afternoon Folks!
I am only posting once and getting off, Have to run! I don't have much time to explain but mark my words, I believe something is going to surprise us in terms of a Sub-tropical system off the East Coast of Florida.....

Be back tomorrow.
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1140. Weather456
2:22 PM AST on May 24, 2008
The only thing the models can agree on is that development will intially start in the EPAC

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1139. Drakoen
6:43 PM GMT on May 24, 2008
The NOGAPS is showing the same moistening of the Caribbean that the GFS is showing by Wednesday.
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1138. TerraNova
2:41 PM EDT on May 24, 2008
Wind shear in the SW Caribbean is currently at 5-10 knots. Link to Shear analysis.
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1137. 0741
6:39 PM GMT on May 24, 2008
shear in area????
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1136. TerraNova
2:38 PM EDT on May 24, 2008
Thanks Drakoen.
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1135. Drakoen
6:36 PM GMT on May 24, 2008
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1134. TerraNova
2:34 PM EDT on May 24, 2008
1132. Drakoen 2:32 PM EDT on May 24, 2008

Could you post a link to where you got those pics?
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1133. 0741
6:33 PM GMT on May 24, 2008
what we need the rain not thing else how shear in area????
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1132. Drakoen
6:31 PM GMT on May 24, 2008
12z GFS:

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1131. stormlvr
6:19 PM GMT on May 24, 2008
1106. TerraNova 5:45 PM GMT on May 24, 2008
As of now iam leaning towards some development in the pacific which is were thunderstorm activity apparently is trying to organize.The GFS may have the right idea but wrong basin wise.

I think the ECWMF and GFS are depending on the monsoon trough to lift northward due to the upward MJO pulse, which is possible

Yes, the timing of the pulse is key along with the amplification to the north.
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1130. nash28
6:17 PM GMT on May 24, 2008
Every model past one week is unreliable. The atmosphere and synoptics change so rapidly that there is not one model that can fully grasp anything beyond a certain point.
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1129. Drakoen
6:17 PM GMT on May 24, 2008
From the NOGAPS 12z it looks like it wants to develop the Caribbean system though not as robust as the GFS.
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1128. weathersp
2:15 PM EDT on May 24, 2008
Thats why I only trust GFS through 180 hrs.
Member Since: January 14, 2007 Posts: 17 Comments: 4140
1127. Drakoen
6:12 PM GMT on May 24, 2008
This should give you an idea of how unreliable the GFS in the long range. This is the 228hr mark where the system will be by the Yucatan Peninsula. You can see the big dip in the flow with represents the trough however you can see the ensemble means differ on the position of the trough.
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1126. Drakoen
6:03 PM GMT on May 24, 2008
The GEFS plots are for the most part in agreement with the upper air synopsis with jet stream become more zonal and a bit further to the north allowing a ridge in Atlantic basin. The troughs won't be able to invade as far south since the lows associated with them travel along the jet stream flow. That should allow for some relief with the upper level winds. Two highs center over the northern Central Plains and out in the Atlantic will allow for lowering pressures in the EPAC and Caribbean. The high east enough to allow the southerly steering stream in the Caribbean.
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1125. weathersp
1:59 PM EDT on May 24, 2008
I don't think the east coast blob is that much to be concerned with. Its a small area of low pressure located along a front. In 36 hrs it will be riding off into the sunrise.
Member Since: January 14, 2007 Posts: 17 Comments: 4140
1:52 PM EDT on May 24, 2008
7 days out
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1123. weathersp
1:55 PM EDT on May 24, 2008
I am really interested to see what the 12z Euro says about the EPAC Storm. If it goes with what the NAVY/CMC or if it goes with the GFS.
Member Since: January 14, 2007 Posts: 17 Comments: 4140
1122. StormJunkie
5:56 PM GMT on May 24, 2008
Have fun surfmom.

Think I am off for a little while myself. Give the E coast blob a little time to fester and me some time to get some yard work and grilling done!
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1121. 0741
5:54 PM GMT on May 24, 2008
we getting good shower here by miami airport now
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1120. surfmom
5:54 PM GMT on May 24, 2008
1-2 clean Yucatan swell this AM, very clean, very uncrowded on the Gomex SRQ/Tampa/St. Pete. S. facing might be over by now,just finished work, maybe I can get some leftovers BBL

Gulf temp 81
Member Since: July 18, 2007 Posts: 30 Comments: 26536
1119. nash28
5:54 PM GMT on May 24, 2008
Correct Ivan. It was so bad here last summer that I PRAYED for a TS or even CAT 1 hurricane because I knew that was our only chance for substantial rain! That massive heat ridge bridging with the 1042mb High just made it unbearable.
Member Since: July 11, 2005 Posts: 190 Comments: 16972
1118. Ivansrvivr
5:54 PM GMT on May 24, 2008
Be back later. time to eat.
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1117. Ivansrvivr
5:48 PM GMT on May 24, 2008
1111. We've had some good ones over here last few days. As we move into summer pattern will shift to S.E. eventually. It always starts and ends as SW flow and is usually SE in the middle. there has been good rains over interior areas which will contribute to the daily rains through evaporation. That never happened last summer and the interior and w.coast went dry.
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1116. Drakoen
5:50 PM GMT on May 24, 2008
1108. nash28 5:46 PM GMT on May 24, 2008
12z GFS doesn't bring the low into the picture until basically a week from now...

The GFS bring the closed low about on Thursday.
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1115. StormJunkie
5:52 PM GMT on May 24, 2008
Yep nash.

Looks like at the vary least we will have a blob to watch in the Carib, right about time this E coast blob is finished off.
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1114. nash28
5:50 PM GMT on May 24, 2008
'Tis the season SJ!!!!!
Member Since: July 11, 2005 Posts: 190 Comments: 16972
1113. StormJunkie
5:46 PM GMT on May 24, 2008
Wind shift still there as well as falling pressure.

Station 41010 - CANAVERAL EAST 120NM East of Cape Canaveral

Again, please don't anyone mistake me as taking this for anything much. Just good ol' fashion, physician monitored, blob watching :~)
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1112. Ivansrvivr
5:45 PM GMT on May 24, 2008
23, westerly surface winds over whole E-Pac make that development alot less likely. Watch the front over FL (and the low to our east) make it's move southward which could draw the W.Pac moisture northward.
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1111. nash28
5:46 PM GMT on May 24, 2008
Yep. The WLY flow is the only thing gumming up the works. Otherwise, we'd also be in for a rocking afternoon. CAPE is certainly supportive of it as well as lift.
Member Since: July 11, 2005 Posts: 190 Comments: 16972
1110. weathersp
1:45 PM EDT on May 24, 2008

CMC has it going N then east GFS takes it south then east into the Caribbean then North.
Member Since: January 14, 2007 Posts: 17 Comments: 4140
1:39 PM EDT on May 24, 2008
Another option, just as likely says the M8B model:
We got enough rain to put a damper on the fires here in FL, so I think we should cancel the TS we had on order (which was backordered anyway due to shear and/or not being able to get a big enough cluster of storms together to keep out the dry mid-level air. See all the arcs?

Broad low can rain out some of the energy starting to build up down South, & the rest can transport North efficiently enough without all the dramatic cyclonic turning.
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1108. nash28
5:45 PM GMT on May 24, 2008
12z GFS doesn't bring the low into the picture until basically a week from now...

I can easily see both EPAC and CB systems verifying.
Member Since: July 11, 2005 Posts: 190 Comments: 16972
1107. StormJunkie
5:45 PM GMT on May 24, 2008
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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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