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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1557. FLWeatherFreak91
9:12 AM EDT on May 25, 2008
DELETED
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1556. Weather456
8:20 AM AST on May 25, 2008
.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
1555. moonlightcowboy
7:35 AM CDT on May 25, 2008
Well, I hope everyone "remembers" why they get to blog, and those that sacrifice everything for so many! God bless our soldiers whose shoulders, whose patriotism and courage is always steadfast and defends FREEDOM!

...Amen!

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1554. TerraNova
8:21 AM EDT on May 25, 2008
Houston/Galveston, Texas WFO

MODELS CONTINUE TO SHOW
DEVELOPMENT OF A TROPICAL SYSTEM NEAR THE YUCATAN THAT EVENTUALLY
MOVES WEST INTO THE BAY CAMPHECHE...EARLIER RUNS SHOWED IT MAY
STALL OVER THE YUCATAN THEN HEADOFF TH THE EAST BUT BOTH GFS/ECMWF
NOW HAVE LESS OF A WEAKNESS ACROSS THE WESTERN GULF...BUT ENOUGH
RIDGING ACROSS THE NORTHERN GULF AND TEXAS TO STEER IT WEST
KEEPING IT WELL SOUTH. MAY MAKE FOR A WET SUNDAY IN SETX THE
FIRST SUNDAY AND MONDAY OF JUNE IF IT DEVELOPS AND TRACKS WEST
TAPING INTO THE ASSOCIATED MOISTURE.

Brownsville, Texas WFO

ALTHOUGH THE 2008 HURRICANE SEASON DOES NOT START FOR
ANOTHER 7 DAYS...THE TROPICAL ACTIVITY APPEARS TO BE INCREASING
ALREADY AS A TROPICAL WAVE WITH ASSOCIATED CONV IS NOW MOVING INTO
THE BAY OF CAMPECHE. ALSO...BOTH THE ECMWF AND THE GFS TRY TO
DEVELOP A SURFACE LOW IN THE WESTERN CARIB SEA AROUND 5/31-6/1
EVENTUALLY MOVING THIS SURFACE TROUGH/LOW INTO THE SOUTHWESTERN GULF
OF MEX DURING THE FIRST WEEK OF JUNE. PLEASE REFER TO THE LATEST
STATEMENTS AND OUTLOOKS FROM NHC/HPC CONCERNING THIS POTENTIAL
FEATURE.
Member Since: July 30, 2007 Posts: 76 Comments: 4063
1553. moonlightcowboy
7:17 AM CDT on May 25, 2008
...you ask me why I love her? Why our soldiers love her! There's weather and whether all across this country, by some, many! Remember our Vets...those gone and those serving!

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1552. TheCaneWhisperer
12:11 PM GMT on May 25, 2008
I think the models will get a better handle on this situation when and if something develops. There are many undetermined things to answer that we're not able to now because there is nothing to look at (Size, Strength, Location of Development). All those play a major role in determining where it will go.
1551. TerraNova
7:59 AM EDT on May 25, 2008
1548. FLWeatherFreak91 7:53 AM EDT on May 25, 2008

Thanks FLWeatherFreak.
Member Since: July 30, 2007 Posts: 76 Comments: 4063
1549. stoormfury
11:42 AM GMT on May 25, 2008
well we are back at it this morning with the unpredictabilitity of the models' runs. there might be something trying to evolve in either the Epac or the SW carib. the matter is nothing is imminient and all i can say i that cimatology has it going for the epac. a few days aco it was on the 22nd for the sw carib now it is the 29th . right now the models are hatching on to something after all the runs are based on what information is fed into the computers. according to 456 the best bet is to see what is available in the form of what is present to make a forecast eg sat pics instict and other met information. the old tool of tropical met. after all the models were disappoiting last year dean was a typical example when it was a few hunderd miies east of the windward islands. we are a few days away from the start of the season and the focus should be on preparation in stead of looking for a system which the models showing confusion
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1548. FLWeatherFreak91
11:51 AM GMT on May 25, 2008
From the Galveston forecast discussion:
MODELS CONTINUE TO SHOW
DEVELOPMENT OF A TROPICAL SYSTEM NEAR THE YUCATAN THAT EVENTUALLY
MOVES WEST INTO THE BAY CAMPHECHE...EARLIER RUNS SHOWED IT MAY
STALL OVER THE YUCATAN THEN HEADOFF TH THE EAST BUT BOTH GFS/ECMWF
NOW HAVE LESS OF A WEAKNESS ACROSS THE WESTERN GULF...BUT ENOUGH
RIDGING ACROSS THE NORTHERN GULF AND TEXAS TO STEER IT WEST
KEEPING IT WELL SOUTH. MAY MAKE FOR A WET SUNDAY IN SETX THE
FIRST SUNDAY AND MONDAY OF JUNE IF IT DEVELOPS AND TRACKS WEST
TAPING INTO THE ASSOCIATED MOISTURE.

BTW, great post about the models TerraNova

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1547. Weather456
7:48 AM AST on May 25, 2008
1545. hurricane10 7:48 AM AST on May 25, 2008

That is a likely, and reasonable scenario. What ever happens intial genesis is most likely to occur in the EPAC. Yes it may cross central america, where? and how?....time will answer all.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
1546. Weather456
7:38 AM AST on May 25, 2008
Today's theme of the Hurricane Prepardness week is history...he's a little quote you can carry on this day, it was modified from actual quote by Dutch philospher:

The tropics move forward but we only understand it by looking backwards.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
1545. hurricane10
11:45 AM GMT on May 25, 2008
does anybody think that the EPAC storm will develope and then hit Nicaragua and then cross in the CAR. and develope again.
Just throwin it out there.
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1544. TerraNova
7:42 AM EDT on May 25, 2008
Climatology would favor the EPAC right now. However the ECMWF and NOGAPS forecasts of an all-Atlantic cyclone are mostly based on the possibility of the monsoon trough lifting northward. This would happen due to the upward MJO pulse. Wind shear is favorable for development; however, whether anything develops or not depends on how much moisture the trough pumps into the SW Caribbean, which is beyond bone dry at the moment.
Member Since: July 30, 2007 Posts: 76 Comments: 4063
1543. TerraNova
7:42 AM EDT on May 25, 2008
Morning everyone. Interesting models this morning...

The GFS has been behaving very strangely for the past three models runs or so...it has the Caribbean system going through a whole series of energy transfers before finally developing. Initially (84 hours out) it has the Caribbean low as the stronger low, but then has it making landfall in Nicaragua shortly after and transfers all of its energy to the EPAC low. Then it has the EPAC low making landfall in Honduras, then transferring its energy to a developing low near the Yucatan. Then that becomes our Caribbean cyclone. This would all actually be very interesting to see happen...only time will tell!

The ECMWF still shows development in the Atlantic rather than the Pacific. The ECMWF seems to have the better edge on this as far as the Atlantic portion of this system goes. It predicts the low to begin developing at around 92 hours.

The CMC, although it still develops the EPAC, has a potential development near the Yucatan similar to how the GFS has the eastern pacific cyclone surviving the cross.

The NOGAPS has a system developing in the West Caribbean and following a northwest track, initially hugging the coast of Nicaragua. The NOGAPS predicts system initiation in about 96 hours.

The UKMET and NAM both have the EPAC low dominating over the Caribbean low and do not show it crossing into the Atlantic.
Member Since: July 30, 2007 Posts: 76 Comments: 4063
1542. IKE
6:38 AM CDT on May 25, 2008
I remember seeing it yesterday afternoon.
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1541. moonlightcowboy
6:35 AM CDT on May 25, 2008
Does anyone remember seeing pearlandaggie's post of lightning hitting the Twin Towers? I can't find it. Has it been pulled, or he banned/removed?
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1540. IKE
6:30 AM CDT on May 25, 2008
I see the turning in the east PAC on satellite....
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1539. all4hurricanes
11:31 AM GMT on May 25, 2008

Tornadoes from 2008 we've had a lot but I don,t think we've had an F5 yet
Member Since: March 29, 2008 Posts: 0 Comments: 2373
1538. Weather456
7:25 AM AST on May 25, 2008
Also, I think we are being unfair to the tropics by focusing only on the computer models. Today is the 25th of May, only four more days until the predicted 29th day and much of the genesis potential remains in the EPAC. Its not to say that the CARIB wont get development, its not impossible, U and I know that, becuz we are still expecting the upward pulse in the MJO, but until we start seeing signs of that occuring in the SW caribbean, it all comes down to what is actually there based on all tools available - in favor of the EPAC.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
1537. BahaHurican
7:24 AM EDT on May 25, 2008
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1536. extreme236
11:26 AM GMT on May 25, 2008
Well the CPC is saying that convection should become more active in the SW Caribbean so by the time anything starts developing it could happen in either area.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
1535. BahaHurican
7:20 AM EDT on May 25, 2008
Anyway, ya'll, I'm out for a good part of the day. I'll stick my nose in when I get back to see what's going on with the potential first storm of the season . . .
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1534. Weather456
7:18 AM AST on May 25, 2008
1530. IKE 7:16 AM AST on May 25, 2008
456...ECMWF and NOGAPS have development in the Atlantic basin...... + the GFS.


That is true....but the models are only one tool. Other tools indicate much of the low level turning and activity remains in the EPAC along with the backing of climalolgy and model consensus, it is more likely an EPAC event but SW Carib should still be watch incase anything changes.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
1533. BahaHurican
7:17 AM EDT on May 25, 2008
What do u guys think of the IWIC forecast? It's a bit lower than some of the others I've seen.

Also, I'm very interested now in seeing Gray et al's new forecast. Should be interesting to see if they back off on their DEC numbers or expand on them.
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1532. Weather456
7:15 AM AST on May 25, 2008
Also, Hurricane Prepardness week begins today, May 25.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
1531. BahaHurican
7:14 AM EDT on May 25, 2008
1523. moonlightcowboy 6:53 AM EDT on May 25, 2008
Baha, that is the publisher's lament! Edit is a quite familiar term in my realm, but sometimes one has to acquiesce - the nature of the beast, as is it is.


LOL I know what u mean. My spelling is not the world's best, and everyone can make mistakes, but IMO when it's for publication it should be as perfect as you can get it. . .
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1530. IKE
6:15 AM CDT on May 25, 2008
456...ECMWF and NOGAPS have development in the Atlantic basin...... + the GFS.
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1529. IKE
6:12 AM CDT on May 25, 2008
Somethings gonna form somewhere in that area...eastern PAC...SW Caribbean...just a question of where...
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1528. Weather456
3:45 AM AST on May 25, 2008
Look at the models consensus, infrared image, quiskact seas winds.....EPAC development likely but SW CARIB not out of the question...updating my blog.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
1527. extreme236
11:02 AM GMT on May 25, 2008
The 06Z GFS seems to have the system move around very awkwardly. It has it start developing in the EPAC (although it looks like the system splits and is fighting with the Caribbean system in the beginning) and then it moves into the Gulf of Honduras then it dances around the Yucatan.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
1526. IKE
5:56 AM CDT on May 25, 2008
UKMET 0Z has a system in the east PAC heading north.....

Link
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1525. IKE
5:55 AM CDT on May 25, 2008
0Z NOGAPS has a western Caribbean system.......

Link
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1524. IKE
5:53 AM CDT on May 25, 2008
0Z CMC model.....

Link
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1523. moonlightcowboy
5:48 AM CDT on May 25, 2008
Baha, that is the publisher's lament! Edit is a quite familiar term in my realm, but sometimes one has to acquiesce - the nature of the beast, as is it is.
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1522. IKE
5:51 AM CDT on May 25, 2008
The 6Z GFS has one dancing around in the GOM and Yucatan for days....

Link
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1521. IKE
5:46 AM CDT on May 25, 2008
0Z ECMWF has a GOM system......

Link
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1520. BahaHurican
6:18 AM EDT on May 25, 2008
Morning, everyone.

re.1500.

I know I'm being petty and pedantic, but I find it a bit harder to accept a scientific forecast, in writing, from someone who can't spell basic words right. In the IWIC forecast, the word "bare" (meaning uncovered, naked) is used instead of "bear"(meaning carry, keep) in the phrase "Bear in mind".

Around here, where people are dashing off a new message every few seconds, it seems, a few minor spelling errors are only to be expected. That forecast page is going to hang around for a long time; it shouldn't have such simple mistakes on it.
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1519. TheCaneWhisperer
5:13 AM GMT on May 25, 2008
Is it Wednesday yet? It's going to be November before the models have this mess sorted out.
1518. SouthDadeFish
5:05 AM GMT on May 25, 2008
Well that run just adds to the confusion of the 18Z run. I shall now go to sleep in a highly confused state. :~)
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1515. Drakoen
4:44 AM GMT on May 25, 2008
Can't really tell whats gonna happen. I wait for next weeks model runs to get a better idea.
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1514. TampaSpin
12:40 AM EDT on May 25, 2008
The GFS model im looking at still has a storm moving in on Florida so, im not sure what model your referring.
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1512. Drakoen
4:24 AM GMT on May 25, 2008
LOL I just noticed that when the other models want to move in the Caribbean system the GFS wants to move in on the EPAC system.
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1511. Patrap
11:23 PM CDT on May 24, 2008
Scu
Member Since: July 3, 2005 Posts: 424 Comments: 128344
1510. Drakoen
4:18 AM GMT on May 25, 2008
As far as I can tell the GFS 00z might drop the Caribbean system.

The IWIC is forecasting for a near normal season.
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1509. Stormchaser2007
12:14 AM EDT on May 25, 2008
Looks like the GFS finally dropped the storm....for now.
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1508. pottery
12:12 AM AST on May 25, 2008
Well. That all looks pretty well thought-out, concise and plausible.
Time will tell no doubt.
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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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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.