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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: 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
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

The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

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1507. Tazmanian
9:13 PM PDT on May 24, 2008
so looks like they are forcasting 12 name storms 7 huricanes and 3 cat 3 or higher
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1506. SouthDadeFish
4:13 AM GMT on May 25, 2008
No low so far from the GFS....
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1505. Tazmanian
9:12 PM PDT on May 24, 2008
As summer fades into fall before the peak of the season, this feature will become increasingly dominant over the subtropical ridge by pulling any nearby hurricane northwestward, generally towards the Carolinas.

bad news
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1504. Tazmanian
9:08 PM PDT on May 24, 2008
While several tropical cyclones are forecast to impact this area, there is a bright side. As stated in the Gulf of Mexico sub-section, there is not enough evidence that would support a forecast of major hurricane formation in the Gulf of Mexico or northwest Caribbean Sea. Thus, three to four named storms and one to two hurricanes, perhaps as strong as moderate intensity, are expected to strike the central Gulf coast.

i dont like the way they put that talk about $6 gas????
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1503. Tazmanian
9:07 PM PDT on May 24, 2008
this is from Tropicaldiscussion blog

This morning's Tropical Weather Analysis consists of plenty of dry air stretching from the Gulf of Mexico east and southeastward through the entire Caribbean. In addition, wind shear values range from 30 to 50 knots across the Gulf of Mexico and western Atlantic to less than 10 knots over the central Caribbean southeast of Jamaica. In the grand scheme of things, tropical cyclone formation is not expected through at least Monday or Tuesday. With that said, the latest runs of the GFS, European model, and Canadian model are all forecasting either a tropical system forming in the southwestern Caribbean or a tropical system forming in the eastern Pacific and tracking across Mexico and emerging into the Bay of Campeche late next weekend.

Gfs Model

First, let's look at the GFS model: The GFS model continues to forecast some sort of tropical low pressure to form in the southwest Caribbean near the coast of Panama on Wednesday. It then forecasts this system to track slowly north-northwest so that by next Saturday it is forecast to be located just east of Belize.

European model

The latest run of the European model is forecasting a tropical low to form in the western and southwestern Caribbean around Wednesday or Thursday and the European model forecasts this system to be located near the Yucatan Peninsula by next Saturday. The Canadian model shows a slightly different scenario, it forecasts a tropical system to form in the eastern Pacific on Wednesday and forecasts this system to track northward and make landfall along the Mexican coast on Friday. After that, the Canadian model forecasts this system to track northward and be located near the coast of the Yucatan Peninsula in 10 days.

Tropical development forecast guidance
Okay, now let's take a step back and look at this with the current tropical weather analysis: Right now, the tropical Atlantic is unfavorable for development and the latest tropical development forecast guidance indicates that the area we are looking at in the western and southwestern Caribbean should remain unfavorable for development through at least Wednesday, although the eastern Pacific will be favorable for development next week which would lend credence to the Canadian model's forecast. At this point, I have a wait and see attitude about this entire scenario. The consistency of the GFS model continues to be very interesting and the fact that both the Canadian and European model have jumped on board with some sort of development adds to the interest
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1502. Tazmanian
9:05 PM PDT on May 24, 2008
so its going to be the Carolinas this year
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1501. Drakoen
4:06 AM GMT on May 25, 2008
1500. hurricane23 4:03 AM GMT on May 25, 2008
Just out...

IWIC 2008 Atlantic Basin Hurricane Season Forecast

Long read.
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1500. hurricane23
12:00 AM EDT on May 25, 2008
Just out...

IWIC 2008 Atlantic Basin Hurricane Season Forecast

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1499. Tazmanian
8:53 PM PDT on May 24, 2008
take a look at this blog this is a vary good blog this is a most read/see blog

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1498. weatherblog
3:47 AM GMT on May 25, 2008
1496- It's true. It should be starting around this time I think. Well, I think everybody's waiting for it...hence, the quiteness.
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1497. Drakoen
3:47 AM GMT on May 25, 2008
The 00z GFS is coming out.
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1495. BahaHurican
11:36 PM EDT on May 24, 2008
Good night, ya'll.
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1494. JRRP
3:31 AM GMT on Mayo 25, 2008
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1493. lopaka001
11:34 PM EDT on May 24, 2008
Thanks H23 for that footage..
Did you see the video where it destroys some barns?
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1492. TheCaneWhisperer
3:20 AM GMT on May 25, 2008
From the NHC 8TWD



Is it Wedensday Yet?
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1491. stormdude77
11:13 PM AST on May 24, 2008
This may be obvious...but tropical waves are now coming off further north (off the African West coast), great news for us here in the Eastern Caribbean...
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1490. pottery
11:04 PM AST on May 24, 2008
5.7 earthquake in Columbia, kills 6.
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1489. JRRP
3:04 AM GMT on Mayo 25, 2008

new tropical wave
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1488. HurrikanEB
3:09 AM GMT on May 25, 2008
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1487. jholmestyle
2:50 AM GMT on May 25, 2008
Thanks H23, I've been at work all day and hadn't seen that. Incredible footage. I live in Johns Island South Carolina, and we had a tornado come thru just under 1 mile from my house. Crazy weather patterns, usually the seabreaze interaction here weakens them to an extent.
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1486. pottery
11:03 PM AST on May 24, 2008
OK Hurrican. I figured as much.
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1485. TheCaneWhisperer
3:00 AM GMT on May 25, 2008
Adrian, in reference to the like you provided to the 08 Forecast. Wasn't a similar trough in place over the midwest in 04 that pulled the big 4 over our state? Their saying only if the present trough is gone will it pose a larger threat to the SE US coast, I'm confused.
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1484. HurrikanEB
3:01 AM GMT on May 25, 2008
1477. pottery 2:41 AM GMT on May 25, 2008
is that minus 54 degrees, Hurrican ?

whoops ment 54*F. above not minus
im in new york
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1483. pottery
10:56 PM AST on May 24, 2008
WOW 23, that was / is totally incredible man...........
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1482. MississippiBoy
9:44 PM CDT on May 24, 2008
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1481. HadesGodWyvern (Mod)
2:43 AM GMT on May 25, 2008
yup use YouTube if you can upload a video from your computer.
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1480. hurricane23
10:37 PM EDT on May 24, 2008
This is insane! MUST SEE

Great quality!

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1479. HadesGodWyvern (Mod)
2:42 AM GMT on May 25, 2008
Arabian Sea Tropical Weather Outlook

Joint Typhoon Warning Center

Tropical Disturbance Summary (0200z 25May)

An area of convection (97A) located near 12.9N 64.8E or 790 NM east of Cape Guardafui, Somolia. Recent animated infrared satellite imagery shows fairly new convection building near an area of increasingly pronounced low to mid level cyclonic turning. The low level circulation center is partially exposed to the east of the central convection due to low to moderate easterly vertical wind shear. A 2140z AMSRE Microwave Image also indicates formative banding building to the south of the low level circulation center. The system lies to the south of the subtropical ridge axis with marginal upper level diffluence. Sea surface temperatures and ocean heat content are optimal.

Maximum sustained winds near the center is 15-20 knots with a minimum sea level pressure of 1006 mb. Because the convection has yet to fully build and organize around the newly-defined low level circulation center, the potential for this disturbance to form into a significant tropical cyclone within the next 24 hours is POOR.
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1478. stormdude77
10:36 PM AST on May 24, 2008
Any clues on how I can upload a small video to the site?

I'm not really sure...but how about youtube?
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1477. pottery
10:39 PM AST on May 24, 2008
is that minus 54 degrees, Hurrican ?
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1476. atmoaggie
2:37 AM GMT on May 25, 2008
Hey everyone,
Gee, storms in the midwest, bahamas, yucatan, florids- everyone's getting something-54 degrees and starry out at my place

Nothing in SE LA, but the usual. 80something and very humid.

Where is 54? Minnesota?

G'nite storm.
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1475. HurricaneGeek
10:36 PM EDT on May 24, 2008
good evening everybody! If you wish, you still may join my contest, the 25 is the last day, (until midnight the 26). Please see my blog and I'll be happy to add you.
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1473. HurrikanEB
2:33 AM GMT on May 25, 2008
Hey everyone,
Gee, storms in the midwest, bahamas, yucatan, florids- everyone's getting something. 54 degrees and starry out at my place
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1472. BahaHurican
10:34 PM EDT on May 24, 2008
I can't believe I'm this excited about a little cold-core induced rain . . .LOL
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1471. pottery
10:34 PM AST on May 24, 2008
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1470. pottery
10:23 PM AST on May 24, 2008
Post £ 1465. Nice one, 23.
That will boost some folks anxiety levels for sure.
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1469. BahaHurican
10:30 PM EDT on May 24, 2008
Any clues on how I can upload a small video to the site? I got a bit of lightning flashing.

Geez, it really coming down now . .. :o) I have a big grin on my face right now . . . Only worry is potential power outage due to high winds . . .
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1468. lopaka001
10:29 PM EDT on May 24, 2008
The rain is coming down hard again!
Looks like some of stations are reporting winds at 57.3mph in the last cell.
Where did all the Broward peeps go?
Just lost the my Tivo again..
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1467. BahaHurican
10:28 PM EDT on May 24, 2008
Rain in Nassau, still ongoing. We've even had a few lightning flashes and some thunder - first in months . . .

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1466. BahaHurican
10:14 PM EDT on May 24, 2008
1451. stormdude77 10:11 PM EDT on May 24, 2008
Hey, Baha...the wind was pretty ''gusty'' over your area, earlier today

The only way I'd know is by reading the posts and looking at the satloops LOL. We had very still conditions by comparison all day in Nassau. . . however right about now I'm thinking we may end up with a few high gusts before the night is over . . .
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1465. hurricane23
10:23 PM EDT on May 24, 2008
Not sure if this was posted but here is wxrisk.com 2008 atlantic hurricane season forcast.Scroll down towards the bottom.Pretty interesting.
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1464. bystander
2:22 AM GMT on May 25, 2008
No worries Drak.
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1463. pottery
10:20 PM AST on May 24, 2008
Although, strickly speaking, dry and hot constitutes weather, as well.
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1462. Drakoen
2:21 AM GMT on May 25, 2008
1461. bystander 2:21 AM GMT on May 25, 2008
Thanks Drak. Just googled it.

Sry for the late answer I was busy.
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1461. bystander
2:18 AM GMT on May 25, 2008
Thanks Drak. Just googled it.
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1460. Drakoen
2:18 AM GMT on May 25, 2008
1449. bystander 2:09 AM GMT on May 25, 2008
This may be a dumb question..........What is QPF?

QPF= Quantitative Precipitation forecast.
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1459. pottery
10:11 PM AST on May 24, 2008
Well, seems like everyone has weather overhead, except me !
Still dry and hot. Oh well........
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1458. lopaka001
10:13 PM EDT on May 24, 2008
Where you at canewhisperer?
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