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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1707. davidw221
5:33 PM GMT on May 25, 2008
The more I read this blog, the more educated I have become, thank you all for your work
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1706. Patrap
12:31 PM CDT on May 25, 2008


Scu

Member Since: July 3, 2005 Posts: 415 Comments: 125628
1705. nash28
5:30 PM GMT on May 25, 2008
Timing, timing, timing....

Trough digs, periphery of ridge weakens... How long? Who knows?
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1704. HurricaneKing
1:29 PM EDT on May 25, 2008
I think the GFS has the high to strong and a track (if anything even forms) farther east is likely.
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1703. cchsweatherman
1:19 PM EDT on May 25, 2008
Just took a very close look at satellite imagery from off the Costa Rican coast and must agree that this could possibly be the beginnings of the forecasted Eastern Pacific system. The circulation continues to become better defined with each passing image and convections has been slowly building with this possible low-level circulation. I will begin watching this now for possible tropical development.

By the way, this is not 10 days away. Based upon all the models, we should see the Eastern Pacific storm having crossed over into the Northwest Caribbean within a week. By Tuesday into Wednesday, we will have to watch that region very closely and to see how much an impact the MJO will have.

About the GFS model, I find the run very reasonable, if not believable, until the point it reaches the Yucatan Peninsula. If anything with the trough swinging across the Northern US and the developing weakness, the storm should go more easterly and northerly and the ridge should not be able to rebound that quickly. Drak is correct; the forecasted 1037mb high is quite overdone and unbelievable, especially after a trough weakens it.
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1702. HurricaneKing
1:26 PM EDT on May 25, 2008
I like the other definition of grits.
Girls Raised In The South.
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1701. hahaguy
1:22 PM EDT on May 25, 2008
dam guesscasters lol
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1700. nash28
5:21 PM GMT on May 25, 2008
LOL Guesscasting!

Add that one to the lexicon:-)
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1699. Patrap
12:18 PM CDT on May 25, 2008
Mama fed us lotsa grits and butter. Link



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1698. scottsvb
5:20 PM GMT on May 25, 2008
Its way too early to speculate on development if any... by weds we will have a idea. Anything now is a guess or guesscasting!
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1697. Orcasystems
5:18 PM GMT on May 25, 2008
1659. catastropheadjuster 4:35 PM GMT on May 25, 2008 Hide this comment.
You Welcome Nash. Go eat your bacon sound really good. We had eggs,grits,link sausage,homemade biscuits for breadfast.
oops sorry back to weather. So you all think this thing is gonna be a rain maker for Fla?
Sheri


Stupid Question of the Day, and off topic.

What is "grits" I have heard the term often, but I never knew what it was. I looked it up on the internet... and it basically appears to be porridge? that may or may not be made out of corn?
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1696. IKE
12:06 PM CDT on May 25, 2008
1694. weathersp 12:04 PM CDT on May 25, 2008
1691. IKE

Its still 10 days away alot of things are going to change between now and then. GFS might be on a wild goose chase for all we know.


Yup.
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1695. IKE
12:04 PM CDT on May 25, 2008
......
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1694. weathersp
1:02 PM EDT on May 25, 2008
1691. IKE

Its still 10 days away alot of things are going to change between now and then. GFS might be on a wild goose chase for all we know.
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1693. Weather456
12:58 PM AST on May 25, 2008
Well I continue to see an evident spin just west of Costa Rica. Also notice the slight increase in 850 vort in exactly the same area.
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1692. Patrap
12:01 PM CDT on May 25, 2008
I heading to Jax Thursday Evening.So Im not gonna comment..LOL
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1691. IKE
11:58 AM CDT on May 25, 2008
1689. weathersp 11:55 AM CDT on May 25, 2008
Yeah.. I don't know why GFS puts a big ridge in the plains and stalls the system dead center of the GOM. It would seem to me that if that 1037mb High were that controlling to pull it up out of the EPAC it wouldn't change course and ride the clockwise flow around the high. Of course that would mean having it make US landfall around the Florida Panhandle.


Which is where I live....they usually go north in June according to the NHC, but.."These figures only depict average conditions."..from the NHC.
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1690. IKE
11:56 AM CDT on May 25, 2008
So maybe the GFS was right all along when this first started showing up...time will tell.
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1689. weathersp
12:51 PM EDT on May 25, 2008
Yeah.. I don't know why GFS puts a big ridge in the plains and stalls the system dead center of the GOM. It would seem to me that if that 1037mb High were that controlling to pull it up out of the EPAC it wouldn't change course and ride the clockwise flow around the high. Of course that would mean having it make US landfall around the Florida Panhandle.
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1686. TheCaneWhisperer
4:52 PM GMT on May 25, 2008
Is the ghost starting to show it's face?
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1685. Patrap
11:52 AM CDT on May 25, 2008
GOM 60 Hour WAVE Forecast Model Link
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1684. KEEPEROFTHEGATE (Mod)
12:49 PM EDT on May 25, 2008
from what i see we may have an invest by thur of this week 29 of may i figure if models continue showing a system
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1683. nash28
4:50 PM GMT on May 25, 2008
Depends on the strength of the trough. That part of the upper synoptics is always the hardest for the models to work out.
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1682. Patrap
11:47 AM CDT on May 25, 2008
GOM 120 Hour Water Surface Temperature Forecast Model Link
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1681. IKE
11:50 AM CDT on May 25, 2008
They usually go north in June.
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1680. Weather456
12:46 PM AST on May 25, 2008
Also notice the 12Z GFS is predicting development off the Coast of Africa. It was also seen on the 00Z and 06Z runs.

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1678. nash28
4:48 PM GMT on May 25, 2008
We shouldn't be zeroing in on track right now. That will bounce around from run to run. What we should zero in on is the formation, which appears to be highly likely.
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1677. Drakoen
4:47 PM GMT on May 25, 2008
That high at 1037mb is crazy and to think a ridge could build back in that quickly after that trough moved through.
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1676. IKE
11:46 AM CDT on May 25, 2008
It's too far out in time to put a lot of stock in it turning west...this run has it going further north before turning west.
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1675. nash28
4:42 PM GMT on May 25, 2008
Ok, before mowing.... GFS is thinking a strong blocking ridge will force the system back to the W after getting into the central GOMEX.
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1674. weathersp
12:44 PM EDT on May 25, 2008
12z GFS has it making landfall near Brownsville,TX after meandering in the GOM for a day and a half.
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1673. IKE
11:43 AM CDT on May 25, 2008
1000 mb's at 240 hours.
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1672. Weather456
12:43 PM AST on May 25, 2008
1666. weathersp 12:41 PM AST on May 25, 2008
Highest wind barb I see is 35kts..


Which is pretty strong in realtime.
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1671. Drakoen
4:43 PM GMT on May 25, 2008
1669. Weather456 4:43 PM GMT on May 25, 2008
So Drak, that is the same short-wave trough that you was looking at over the plains?


Yes. Looks like it will create a weakness but not enough to make it go north into the Gulf coast states.
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1670. IKE
11:42 AM CDT on May 25, 2008
This is becoming more interesting...doesn't seem sheared on this run...
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1669. Weather456
12:41 PM AST on May 25, 2008
So Drak, that is the same short-wave trough that you was looking at over the plains?
Member Since: July 24, 2005 Posts: 407 Comments: 19076
1668. 882MB
4:40 PM GMT on May 25, 2008
Hey everybody, I just seen the NOGAPS model and it has the same track as the GFS 12z.Also seen the ECMWF model also showing something coming up from the carribean.
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1667. IKE
11:41 AM CDT on May 25, 2008
Is that a strong trough Drak?
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1666. weathersp
12:40 PM EDT on May 25, 2008
Highest wind barb I see is 35kts..
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1665. TerraNova
12:38 PM EDT on May 25, 2008
Current 12z GFS out 138 hours (current intiation time is 84 hours). The current GFS argument seems reasonable enough...the energy needed for the cyclone flows into the SW Caribbean from the EPAC through Costa Rica or Nicaragua and then develops soon after.

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1664. Drakoen
4:39 PM GMT on May 25, 2008
1662. IKE 4:38 PM GMT on May 25, 2008
Interesting model run on the 12Z GFS...that trough to the north is key to where it may go...assuming it forms. This model run has a stronger system!


500mb trough.
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1663. weathersp
12:36 PM EDT on May 25, 2008
At 216 Hrs GFS Shows it right smack in the center of the GOM at around 1000mb
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1662. IKE
11:36 AM CDT on May 25, 2008
Interesting model run on the 12Z GFS...that trough to the north is key to where it may go...assuming it forms. This model run has a stronger system!
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1661. Stormchaser2007
12:37 PM EDT on May 25, 2008
Dunno about Florida.....

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1660. cchsweatherman
12:34 PM EDT on May 25, 2008
By the way, the 12UTC GFS develops a large weakness in the ridge right when the possible Western Caribbean storm starts strengthening near the Yucatan Peninsula at the 162 hour time frame. This could be quite intriguing.
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1659. catastropheadjuster
4:29 PM GMT on May 25, 2008
You Welcome Nash. Go eat your bacon sound really good. We had eggs,grits,link sausage,homemade biscuits for breadfast.
oops sorry back to weather. So you all think this thing is gonna be a rain maker for Fla?
Sheri
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1658. IKE
11:31 AM CDT on May 25, 2008
Strengthens it at 162 hours over the NE Yucatan.
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1657. Weather456
12:33 PM AST on May 25, 2008
oh I guess u guys saw it already
Member Since: July 24, 2005 Posts: 407 Comments: 19076

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About JeffMasters

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.