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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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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656. Weather456
10:01 PM AST on May 23, 2008
Notice the tropical wave is entering an area filled with stratocumulus clouds, not a conducive enviroment for tropical cyclone formation.

Member Since: July 24, 2005 Posts: 407 Comments: 19076
655. howarjo1943
2:00 AM GMT on May 24, 2008
Whew, thank goodness it missed Gburg. Sorry about the typo, my keys don't work well w/ my laptop on my stomach. Yeah another tornado is about to go through Ellis, and it has been confirmed by spotters as being large and damaging.
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654. StormJunkie
2:02 AM GMT on May 24, 2008
lmao :~)

I think we could probably make them look like what ever we want since they don't exist yet!
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653. pottery
10:00 PM AST on May 23, 2008
OK, 77. Some proper rain next week would be very good if that happens. Expecting a shower tonight myself.
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652. TerraNova
10:01 PM EDT on May 23, 2008
Yea, as C2 said, That would be dangerous

Sorry...spelling error. Wonder what badeballs (not baseballs) would look like, though. LOL.
Member Since: July 30, 2007 Posts: 76 Comments: 4063
651. StormJunkie
1:59 AM GMT on May 24, 2008
You too TN

badeballs?

Yea, as C2 said, That would be dangerous
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650. TerraNova
9:58 PM EDT on May 23, 2008
hojo, you got to watch those typos. 18lbs, I think not! Maybe 1.8 :~)

I wouldn't want that one falling on my head...and we thought baseballs were deadly :) Great to see you, SJ.
Member Since: July 30, 2007 Posts: 76 Comments: 4063
648. stormdude77
9:55 PM AST on May 23, 2008
Hi Pottery

It looks good now (in term's of structure)...however, there is some dry air in front of the wave, along with stronger wind shear. So, I expect no development, but it may some rainfall around us by mid next week.
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647. StormJunkie
1:55 AM GMT on May 24, 2008
Largest hailstone in US history

hojo, you got to watch those typos. 18lbs, I think not! Maybe 1.8 :~)
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646. TerraNova
9:52 PM EDT on May 23, 2008
The National Weather Service is reporting slight damage about 3 miles west of Greensburg, but no damage within the town itself. Spotter Network and NWS is reporting that the power is still on in Greensburg.

Moderate to major damage, however, is being reported in Ellis. I'm hearing from KSN that one building has been destroyed and another has suffered severe roof damage. Ellis is about to get hit by the storm's tornado warned tail end, which also seems to be harboring a strong circulation.
Member Since: July 30, 2007 Posts: 76 Comments: 4063
645. pottery
9:53 PM AST on May 23, 2008
Hi there 77.
Your take on the wave in the East Atl. ??
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643. pottery
9:49 PM AST on May 23, 2008
DDR. If a wave just passed us, then I hope its one of a set. Look out for the big one outside ! LOL
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641. howarjo1943
1:46 AM GMT on May 24, 2008
sorry, I meant baseball. I think the biggest stone ever weighed 18lbs so it probably possible, especially w/ 73,000 ft tops. Probably the tornado missed Greensburg, Greensburg is only a mile wide. What are the chances of getting hit two years in a row by monster twisters almost to the date? Probably has happened before but who knows.
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640. stormdude77
9:46 PM AST on May 23, 2008
Evening all
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639. StormJunkie
1:49 AM GMT on May 24, 2008
633

Evening nash, and I concur!

Basketball is like armageddon type ....
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638. Ivansrvivr
1:43 AM GMT on May 24, 2008
625, in 04, the Bermuda high was in near constant flux all summer. The Cape Verde storms generally developed far south and got recurved into Florida. In 07 the Bermuda high was parked over Nashville and was extremely large and strong. It blocked tropical moisture from moving northward and drove dry continental air around it's backside deep into tropics. Anything that did develop was generally small and was pushed rapidly westward, totally blocked from moving towards the U.S. This looks more like 04 than 07 but every season is different.
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637. DDR
1:47 AM GMT on May 24, 2008
LOL! same here
That wave most likely just passed us
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636. pottery
9:44 PM AST on May 23, 2008
Yo, DDR.
A Different little breeze tonight for sure. And I just had 6 drops of Rain.
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635. StormJunkie
1:44 AM GMT on May 24, 2008
Nasty
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634. StormJunkie
1:43 AM GMT on May 24, 2008
That seems dangerous

Ya think C2 ¿~)
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633. nash28
1:43 AM GMT on May 24, 2008
Basketball? I don't think so. Baseball? Probably.
Member Since: July 11, 2005 Posts: 190 Comments: 16972
632. HIEXPRESS
9:34 PM EDT on May 23, 2008
609/13/20
jp I just made it home ahead of it. Trail running in the woods, no data - just watching the sky, couldn't see the anvil, but I knew it was there. Wasn't there when I checked the radar b4 heading out. Cut short the run. Unusual 2nd round for us today. The humidity was wicked. I measure it in seconds/mile.
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631. DDR
1:37 AM GMT on May 24, 2008
good night all.
Pottery how are you? Seems like our weather is changing tonight
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630. C2News
1:42 AM GMT on May 24, 2008
Jeez, more tornadoes.

And basketball sized hail? That seems dangerous. That could probably punch through the roof of a house.
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629. pottery
9:35 PM AST on May 23, 2008
Basket ball size hail ? Really ?
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628. StormJunkie
1:38 AM GMT on May 24, 2008
Evening all :~)

Basketball size hail.

Is that even possible?
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627. nash28
1:40 AM GMT on May 24, 2008
Large tornado in Greensburg. Dear God.
Member Since: July 11, 2005 Posts: 190 Comments: 16972
626. C2News
1:39 AM GMT on May 24, 2008
Hi all, what's going on this evening?
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625. jba1a
1:35 AM GMT on May 24, 2008
Has the Burmuda high set up as of yet and if so, is it more like it was in 2004 or 2007?
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624. howarjo1943
1:31 AM GMT on May 24, 2008
The couplet on the Greensburg cell reintensified as it passed near Gburg. Max echo tops 73,000 feet. Basketball size hail. Greensburg might be the new Pensacola. Hopefully it just missed em.
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623. Ivansrvivr
1:27 AM GMT on May 24, 2008
JP, those storms are forming in the drier upper level air in Central FL. The sun was probably out much of the day there. When storms shift southward, that often indicates severe wx.
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622. howarjo1943
1:24 AM GMT on May 24, 2008
The motion of that storm has gone back a little to the left again, I guess because the rotation has weakened somewhat. Check out that Freakin HUGE cell to the north, currently crossing I-70. They,ve confirmed a large wedge on the ground with that one.
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621. pottery
9:26 PM AST on May 23, 2008
Ivans post 619.
OK. Thanks.
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619. Ivansrvivr
1:20 AM GMT on May 24, 2008
it would end up in the hurricane graveyard to the north. SSTs are cooler, atmosphere is more hostile. However, the jog to the north is a temporary sign of impressive strength given this is still May. Usually shear/cold ssts destroy everything coming off of Africa this time of year.

Remember, this is May. We usually dont see much CV action till August! The fact that that low is there is very impressive for this time of year.
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618. howarjo1943
1:18 AM GMT on May 24, 2008
I think ur right Terranova, looking at the last few images the main rotation has weakened and the hook is not quite as pronounced, and that new protrution to the south may be a new dominant rotation trying to form. Still would not want to be in Gburg right now. Its like russian roulette in the Plains States when these town size monster twisters head your way.
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617. pottery
9:04 PM AST on May 23, 2008
Ivans. Hi. If the low jogs north it will dissipate ?? Why ?
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616. TerraNova
9:12 PM EDT on May 23, 2008
If you really zoom in on doppler, it looks like there are two other areas of rotation around the most intense rotation, possibly satellite tornadoes or multiple vortices. I'm still amazed at how that storm right moved as if it was homing in on Greensburg.

The main vortex has weakened, but a new circulation is developing to it's south. Luckily this new circulation will likely miss Greensburg to the east.
Member Since: July 30, 2007 Posts: 76 Comments: 4063
615. howarjo1943
1:07 AM GMT on May 24, 2008
If you really zoom in on doppler, it looks like there are two other areas of rotation around the most intense rotation, possibly satellite tornadoes or multiple vortices. I'm still amazed at how that storm right moved as if it was homing in on Greensburg.
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614. Ivansrvivr
1:08 AM GMT on May 24, 2008
We had small hail very briefly in eastern PBC today.
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612. Ivansrvivr
1:06 AM GMT on May 24, 2008
It is still very impressive to see action like that in E-Atl before June. If the atmosphere settles down a bit more we may be seeing CVs by the end of June.
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611. Patrap
8:06 PM CDT on May 23, 2008
GOES-12 WV False Color Atlantic Link
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610. howarjo1943
1:02 AM GMT on May 24, 2008
I,ve been tracking that huge cell approaching Greensburg the past couple of hours when it developed over Oklahoma. it looked for most of the time like it would go well to the west of Gburg, but when it entered into Kansas it began to turn right, and thats when the doppler couplet really became pronounced. I am worried this is another large, powerful tornado that may hit them 2 years in a row.
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608. Ivansrvivr
1:03 AM GMT on May 24, 2008
MLC, it looks (to me )like the E-Atl low has jogged northward somewhat which is sign of current strengthening but would spell it's end shortly.
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607. moonlightcowboy
8:03 PM CDT on May 23, 2008
First spin of the season, and impressive, too, I might add and especially for so early in the season.
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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.