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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1257. Stormchaser2007
5:38 PM EDT on May 24, 2008
Would not be surprised to see an EF3/4 on the ground if they were still up there and also if the doggoned tornado wasn't so embedded in rain.
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1256. Blizzard92
5:39 PM EDT on May 24, 2008
Yes the cell is beginning to become not as organized on the reflectivity radar, the hook echo is not as easy to detect.
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1255. nash28
9:39 PM GMT on May 24, 2008
Live stream over...
Member Since: July 11, 2005 Posts: 190 Comments: 16972
1254. nash28
9:37 PM GMT on May 24, 2008
Starting to weaken.... Went from around 50,000ft now down to 40,000ft.
Member Since: July 11, 2005 Posts: 190 Comments: 16972
1253. Weather456
5:31 PM AST on May 24, 2008
The 12Z ECMWF is predicting development in the EPAC similar to the CMC, but the system crosses central America and ends somehwere just offshore the Yucatan Peninsula.

Member Since: July 24, 2005 Posts: 407 Comments: 19076
1252. zoomiami
9:37 PM GMT on May 24, 2008
This is some of the most amazing weather footage I have seen - to see the tornado actually generating in real time is unbelievable
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1251. Stormchaser2007
5:35 PM EDT on May 24, 2008
This thing dose not cease to impress.

Link
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1250. nash28
9:36 PM GMT on May 24, 2008
I love it!!! Now he's having to justify getting fuel!
Member Since: July 11, 2005 Posts: 190 Comments: 16972
1249. Midweststorm
9:33 PM GMT on May 24, 2008
Quite strong supercell. reminds me of one a couple of years ago that went from southeastern Kansas and moved across Missouri into Illinois overnite. That was a long sleepness night as I watched it.
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1248. nash28
9:35 PM GMT on May 24, 2008
This is indeed impressive. This one cell has been parked there forever it seems. Has not died out yet.
Member Since: July 11, 2005 Posts: 190 Comments: 16972
1247. nash28
9:34 PM GMT on May 24, 2008
LOL guys! Are we wrapped into this or what??

Tops are lowering a bit on this cell...
Member Since: July 11, 2005 Posts: 190 Comments: 16972
1246. Blizzard92
5:33 PM EDT on May 24, 2008
nash28- I guess that it is good that is moving so slow so it stays over rural land.
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1245. weathersp
5:32 PM EDT on May 24, 2008
Dang Fuel... just when it gets good.
Member Since: January 14, 2007 Posts: 17 Comments: 4140
1244. Stormchaser2007
5:33 PM EDT on May 24, 2008
Ow damn they gotta go and get fuel now.....
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1243. nash28
9:31 PM GMT on May 24, 2008
This thing is only moving at around 2kts. SLOW.
Member Since: July 11, 2005 Posts: 190 Comments: 16972
1242. Blizzard92
5:31 PM EDT on May 24, 2008
I cannot see my local NEWS in a helicopter in a supercell thunderstorm, lol.

Huge wall cloud!
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1241. weathersp
5:29 PM EDT on May 24, 2008
That thing is soo rain wraped..
Member Since: January 14, 2007 Posts: 17 Comments: 4140
1240. Stormchaser2007
5:29 PM EDT on May 24, 2008
WEDGE TORNADO was ON THE GROUND!!
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1239. Stormchaser2007
5:28 PM EDT on May 24, 2008
Last time I saw something romeotley close to this was back in June 05 with my brother in Oklahoma.
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1238. Stormchaser2007
5:25 PM EDT on May 24, 2008
This is one of the best super-cell thunderstorms Ive seen so far as tornadic potential goes.
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1237. weathersp
5:25 PM EDT on May 24, 2008
Oh my gosh thats a HUGE base to the wall cloud.
Member Since: January 14, 2007 Posts: 17 Comments: 4140
1236. weathersp
5:23 PM EDT on May 24, 2008
yay audio's back..

This Storm is out of control!

Link
Member Since: January 14, 2007 Posts: 17 Comments: 4140
1235. Blizzard92
5:24 PM EDT on May 24, 2008
Wow that live video is impressive. I have never seen anything like that here in Pennsylvania.
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1234. Stormchaser2007
5:23 PM EDT on May 24, 2008
Oh lord... some real rotation now.
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1233. weathersp
5:22 PM EDT on May 24, 2008
Vorticies doin their dance... wish it wasn't rapped in rain.
Member Since: January 14, 2007 Posts: 17 Comments: 4140
1232. Stormchaser2007
5:22 PM EDT on May 24, 2008
Never mind it lated :34 seconds on the ground. (yeah I counted)
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1231. Stormchaser2007
5:21 PM EDT on May 24, 2008
Large tornado on the ground!! Also its wrapped in hail and rain....so its pretty had to see.
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1230. weathersp
5:20 PM EDT on May 24, 2008
Is that on the ground I can't tell
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1229. weathersp
5:17 PM EDT on May 24, 2008
massive Rotation in the Funnel
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1228. TerraNova
5:17 PM EDT on May 24, 2008
Was that a tornado?

Yes; it lifted just a few seconds ago after becoming rainwrapped. New funnel now.
Member Since: July 30, 2007 Posts: 76 Comments: 4063
1227. weathersp
5:16 PM EDT on May 24, 2008
Was that a tornado?
Member Since: January 14, 2007 Posts: 17 Comments: 4140
1226. WhereIsTheStorm
9:14 PM GMT on May 24, 2008
Current conditions South Broward
Heavy rail, thunder and according the radar we should have hail shortly.
The storm is moving quickly and should be out of here within 10 min.
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1225. TerraNova
5:15 PM EDT on May 24, 2008
5th tornado just touched down.
Member Since: July 30, 2007 Posts: 76 Comments: 4063
1224. surfmom
9:13 PM GMT on May 24, 2008
thanks weathersp - got to relate to the kitchen now --bbL
Member Since: July 18, 2007 Posts: 30 Comments: 26536
1223. juniormeteorologist
9:10 PM GMT on May 24, 2008
Hey everyone! Im glad to be back in the blog! anywho, is there any tropical activity going on right now?
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1222. weathersp
5:07 PM EDT on May 24, 2008
Glad you had fun!
Member Since: January 14, 2007 Posts: 17 Comments: 4140
1221. TerraNova
5:05 PM EDT on May 24, 2008
Fortunately this storm hasnt hit any populated areas yet, and the 'nados are short lived. great viewing though

The first tornado it produced hit a pig farm on live TV. Injuries (none life threatening, luckily) are being reported from there.

Holy cow, 3.25 inch hail!
Member Since: July 30, 2007 Posts: 76 Comments: 4063
1220. surfmom
9:03 PM GMT on May 24, 2008
5PM - chest high swell at best south facing beaches GOMEX/SRQ/TAMPA - water 82 at my break - EXTREME RIP TIDE in SRQ! But the waves were wonderful, a real swell from the Yucatan!! Lovely rids once I could get past the breakers through the rip. Water visibility was perfect! Just a grand day!
Member Since: July 18, 2007 Posts: 30 Comments: 26536
1219. Stormchaser2007
5:03 PM EDT on May 24, 2008
Holy.... this things got huge hail in it!!!

Link
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1218. Midweststorm
9:02 PM GMT on May 24, 2008
Fortunately this storm hasnt hit any populated areas yet, and the 'nados are short lived. great viewing though
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1217. weathersp
5:01 PM EDT on May 24, 2008
What the heck is this storm doing.. It cant make up its mind to drop one or not..
Member Since: January 14, 2007 Posts: 17 Comments: 4140
1216. nash28
9:00 PM GMT on May 24, 2008
It's trying... Impressive rotation nontheless.

I don't come CLOSE to seeing this in Tampa!!!

I miss Dallas!
Member Since: July 11, 2005 Posts: 190 Comments: 16972
1215. Stormchaser2007
4:59 PM EDT on May 24, 2008
Potential for a monster!!
Link
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1214. Midweststorm
8:57 PM GMT on May 24, 2008
Looks like from the radar, as soon as a hook dissipates another one pops up. good chance this will go on for another hour or 2.
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1213. weathersp
4:57 PM EDT on May 24, 2008
Dang... drop one or dont make up your mind..
Member Since: January 14, 2007 Posts: 17 Comments: 4140
1212. weathersp
4:54 PM EDT on May 24, 2008
Its goona drop another one..
Member Since: January 14, 2007 Posts: 17 Comments: 4140
1211. nash28
8:54 PM GMT on May 24, 2008
That storm for the moment lost its TVS. It is back building again, and this will gain it momentarily. Hook echo is returning.
Member Since: July 11, 2005 Posts: 190 Comments: 16972
1210. weathersp
4:53 PM EDT on May 24, 2008
Sooner or later one of those mini wall cluds in gonna reach all the way to the ground..
Member Since: January 14, 2007 Posts: 17 Comments: 4140
1209. Midweststorm
8:54 PM GMT on May 24, 2008
Here is a link to the radarLink
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1208. nash28
8:53 PM GMT on May 24, 2008
Kudos to CNN and the local chopper folks!!!

Very educational for everyone!
Member Since: July 11, 2005 Posts: 190 Comments: 16972
1207. Midweststorm
8:51 PM GMT on May 24, 2008
Ive been watching since the 2nd 'nado dropped. this storm continually creates new hook echos and they build fast and strong
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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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