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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1857. CaneAddict
8:12 PM GMT on May 25, 2008
1830. Drakoen 8:03 PM GMT on May 25, 2008
Wonder what Arthur will be like...


LOL, the day Arthur forms you can bet this blog to go through 30 pages of comments like never before....The first storm tends to always be the most exciting...after a good 6-8 month spree of no tropical activity the first storm hypes everyone up..just to see a track drawn by the NHC for the system or the satellite presentation of a nice circulation....that's when the season really starts :-)!
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1856. Patrap
3:15 PM CDT on May 25, 2008
There is NO storm.

Only some Models that show possible genesis.

One cant compare a model run to a Historical Storm.

Even if I could say a Storm was to strike Pensacola in a Week,..One couldnt say at what Hour,what angle,Size, nor Strength.

Member Since: July 3, 2005 Posts: 415 Comments: 125628
1855. presslord
4:16 PM EDT on May 25, 2008
Hey SJ...got in late last nite...let's chat soon....went out to Folly Beach this AM....way too many day trippers.....
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1854. StormJunkie
8:14 PM GMT on May 25, 2008
Afternoon all :~)

press, you back in town? I just got back from walking the docks of the City Marina and Patriots. Talked with a lot of folks. Was a nice day to be out though.
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1853. nash28
8:13 PM GMT on May 25, 2008
LOL!!! You're welcome Presslord. Gotta have the upper hand on the youngins:-)
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1852. presslord
4:12 PM EDT on May 25, 2008
Nash....Thanks...that's what I was after...now my teenagers will be dazzled to see that I know something they don't....
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1851. nash28
8:12 PM GMT on May 25, 2008
It's also a bad season if you come out unscathed, but one or more of your WU family gets whacked.
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1850. cdo
8:12 PM GMT on May 25, 2008
Other than Andrew, the "A" storms here lately seem to be hybrid/sheared out systems, which is to be expected early in the season.
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1849. CaneAddict
8:10 PM GMT on May 25, 2008
1841. FLWeatherFreak91 8:08 PM GMT on May 25, 2008
Could this Storm be Alma's twin?


Looks very possible right now in terms of track, I however in my opinion dont think it would be possible for it to reach cat. 3 strength due to high levels of wind shear.....The track though is something to watch for...
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1848. weathersp
4:08 PM EDT on May 25, 2008
I hope its not Alma's twin
Member Since: January 14, 2007 Posts: 17 Comments: 4140
1847. presslord
4:11 PM EDT on May 25, 2008
yup...it ain't really a bad season 'til your house gets blown off it's stilts...
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1845. nash28
8:06 PM GMT on May 25, 2008
Hey Presslord! Well, as in every year, everyone who lives in hurricane prone areas needs to be prepared as if it is their year to get whacked, but I digress...

The Eastern Seaboard is at more of a risk than last year because of the projected position and weakness of the Bermuda High. Last year we saw a very strong (1038-1042mb) Bermuda High that was positioned much further west and also bridged up with a bullish SE ridge (High) which made it impossible for the storms that formed to gain much latitude or recurve.

This year appears to be the opposite. Still too early to say for sure, but it appears the High will be much weaker, further east and that will allow systems to gain latitude and possibly ride the western edge of the High into the CONUS.
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1844. Patrap
3:09 PM CDT on May 25, 2008
I personally believe all the seasonal forecast BS takes away from Folks attention to Preparation.
Member Since: July 3, 2005 Posts: 415 Comments: 125628
1843. CaneAddict
8:07 PM GMT on May 25, 2008
1824. Weather456 7:58 PM GMT on May 25, 2008
Well as long as the models have consensus, I'll be watching that area closely dis week. Interesting times ahead.


Indeed....I am really interested in what pans out and what doesn't....As you stated earlier...It appears the low-pressure area is already forming in the East Pacific...based on visible imagery.
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1842. presslord
4:07 PM EDT on May 25, 2008
Pat....exactly...I tend to view it as a zero sum game...that's why I'm curious....
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1841. FLWeatherFreak91
4:05 PM EDT on May 25, 2008
Could this Storm be Alma's twin?
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1840. cdo
8:07 PM GMT on May 25, 2008
Hey everyone, the start of Hurricane Season right around the corner!

I wish people would comment on things they just cut and paste from another site
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1839. catastropheadjuster
8:02 PM GMT on May 25, 2008
Nash Thank you. I appreciate the explanation. gone back lurking.
sheri
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1838. Drakoen
8:04 PM GMT on May 25, 2008
HPC discussion:

AFTN 12Z GFS IS MUCH WEAKER AND CONSIDERABLY FARTHER OFFSHORE WITH
THE CLOSED LOW OFF THE PAC COAST FROM DAY 4 ONWARD AND RESULTS IN
A SLOWER EJECTION OF A SHORTWAVE COMING ACROSS THE NRN PLAINS INTO
THE GREAT LAKES REGION BY THE END OF THE PERIOD. THIS SOLUTION IS
CLOSER TO AND WWD OF THE 00Z GFS ENS MEANS. NEW 12Z CMC REMAINS
CONTINUITY WITH ITS OLDER RUN AS DOES UKMET.

CMC/ECMWF/GFS ALL CONT THEIR PERSISTENT TREND TOWARDS TROPICAL
CYCLOGENESIS NEAR YUCATAN MID PERIOD AS MODELS BUILD UPPER LEVEL
RIDGING WITH LOW WIND SHEAR OVER CENTRAL AMERICA/WEST CARRIBEAN.
HPC POSITIONING IS A MODEL/ENSEMBLE MEAN LOCATIONAL AND PRESSURE
AVERAGE.
Member Since: October 28, 2006 Posts: 57 Comments: 29714
1837. Patrap
3:06 PM CDT on May 25, 2008
Every year Brings the Same risk.This one is no Different.
Preparation is the Key.
Never the forecast for the season.
They are useless as to when and where in my view.
Member Since: July 3, 2005 Posts: 415 Comments: 125628
1836. catastropheadjuster
8:02 PM GMT on May 25, 2008
Nash Thank you. I appreciate the explanation. gone back lurking.
sheri
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1835. presslord
4:01 PM EDT on May 25, 2008
I'm beginning to see some of you refer to the notion that North and South Carolina might be at some particular risk this year...Can anyone give me a first grade level thumbnail of why this is being speculated upon? Thanks in advance....
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1834. catastropheadjuster
8:02 PM GMT on May 25, 2008
Nash Thank you. I appreciate the explanation. gone back lurking.
sheri
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1832. Patrap
3:02 PM CDT on May 25, 2008
And 1992 showed that a Late Start can Bring Calamity fast.

Andrew.Link
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1831. weathersp
4:03 PM EDT on May 25, 2008
Only 1 can ruin your season..
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1830. Drakoen
8:03 PM GMT on May 25, 2008
Wonder what Arthur will be like...
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1829. nash28
8:01 PM GMT on May 25, 2008
Pat is right. We don't need 25 named systems for the year to be bad. You could have a freakish early cane in June hit, or like 1992 have a slow year, and the first named storm wrecks many lives.
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1828. Patrap
2:46 PM CDT on May 25, 2008
1965 Link..shows again.It dont have to be active, To be Bad.
Betsy was the first Billion Dollar Damage Storm , and started my interest in Canes.at 5.5 yrs of age.
Betsy flooded New Orleans ,but not nearly as Bad as 2005 Did.
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1827. nash28
7:59 PM GMT on May 25, 2008
I would imagine Dr. Masters will be posting about the expected development come Tuesday.
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1826. cchsweatherman
3:49 PM EDT on May 25, 2008
Just got done working on my nightmare-ish looking pool for about three hours. Sucks.

Well anyways, back to the topic at hand. Just finished analyzing the latest models and must say that this is thus far the highest model consensus that we have had. Considering (like a few had mentioned) the NOGAPS conservative style, it looks like there may be a very impressive system in the Northwest Caribbean this week. Thus far, the NOGAPS model seems the most reasonable with the CMC following behind. The GFS seems the most reasonable, but gets real screwy (haven't used that word in years) once it gets to around the Yucatan Peninsula. The latest UKMET and ECMWF models should be thrown out as the UKMET already has the storm developed and the ECMWF just goes in a circle. Quite rare to say that regarding those models.
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1825. nash28
7:57 PM GMT on May 25, 2008
Not a dumb question at all Sheri. Whether the blob can become something significant depends on SST's, whether there is an Upper Level High in the right place to help aid in outflow, and more importantly, if the shear is relaxed enough for a good period of time to allow the system to deepen.
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1824. Weather456
3:50 PM AST on May 25, 2008
Well as long as the models have consensus, I'll be watching that area closely dis week. Interesting times ahead.
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1823. catastropheadjuster
7:53 PM GMT on May 25, 2008
Since there's not many folks on i am gonna ask a question. This little blob can't really become nothing since it's so early in the season. Right. I mean the steering and all that other stuff really isn't set up yet. And when will the BH set in it's place for the summer? I know these maybe dumb questions but just wondering.
Sheri
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1822. Drakoen
7:54 PM GMT on May 25, 2008
1821. nash28 7:53 PM GMT on May 25, 2008
Drak beat me:-)


lol of course ;P
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1821. nash28
7:52 PM GMT on May 25, 2008
Drak beat me:-)
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1820. hydrus
7:48 PM GMT on May 25, 2008
PATRAP-I have been looking at these models and I noticed this year looks a little bit like the 1966 hurricane season.
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1819. nash28
7:51 PM GMT on May 25, 2008
Next runs are 18z. Those runs initialize at 2pm. We see them around 8pm.
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1818. catastropheadjuster
7:50 PM GMT on May 25, 2008
I am still lurking. Hubbies watching tv and i'm lurking. LOL
Sheri
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1817. Drakoen
7:51 PM GMT on May 25, 2008
1816. JFV 7:50 PM GMT on May 25, 2008
When do the next set of brand new and fresh model runs are suppose to come out gang?


The next set of runs are the 18z GFS and NOGAPS. The GFS comes out at 5:30pm EDT. I think the NOGAPS comes out a little later than that.
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1815. Patrap
2:48 PM CDT on May 25, 2008
It's a Family Day,Holiday weekend.
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1814. Weather456
3:43 PM AST on May 25, 2008
.
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1813. Drakoen
7:46 PM GMT on May 25, 2008
I'm still here. No one is posting though lol.
Member Since: October 28, 2006 Posts: 57 Comments: 29714
1812. catastropheadjuster
7:44 PM GMT on May 25, 2008
Gosh I think just about everyone has left. I was really enjoying and learning with everyones post. I like coming in here reading what you all have to say. And I learn alot. Thank You all so much. Some pretty smart folks in here.
Sheri
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1811. nash28
7:42 PM GMT on May 25, 2008
Agreed Drak.
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1810. Drakoen
7:33 PM GMT on May 25, 2008
Well whatever develops and where it goes will largely be dependent on the strength of the high and the timing and strength of the low pressure/shortwave system.
Member Since: October 28, 2006 Posts: 57 Comments: 29714
1809. Patrap
2:41 PM CDT on May 25, 2008
Join Barometer Bob for The 2008 Hurricane Preparedness Week will be held May 25th through May 31st.


Bob will be hosting "Hurricane Hollow's Hurricane Awareness Week" Internet Broadcasts each evening beginning at 8PM/ET on WRBN.Net with your host Barometer Bob Brookens and special guests.


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Sunday May 25 - Lew Fincher, from HurricaneConsulting.Net. You have seen him on the History Channel special about "Isaac's Storm" the 1900 Galveston Hurricane.
Monday May 26 - Jamie Rhome, Hurricane Specialist at the National Hurricane Center.
Tuesday May 27 - Bob Breck, Chief Meteorologist from WVUE-TV - Fox 8 in New Orleans, LA.
Wednesday May 28 - Laura Algeo, FEMA Region IV, National Flood Insurance Program.
Thursday May 29 - Eric Blake, Hurricane Specialist at the National Hurricane Center. We will also have Butch Loper "AKA sandcrab", Emergency Operations/Civil Defense Director for Jackson County, MS.
Friday May 30 - Leslie Chapman-Henderson, Director of FLASH.Org.
Saturday May 31 - Michelle Jantz Manager, Program Management and Support Preparedness and Health and Safety Services from the American Red Cross.

Hurricane Hollow's Eye on the Storm June 1st Broadcast

I will have special guests, callers and you can join us in Storm Chat!
My guests include:
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And more! Stay tuned for more information on the 8 nights of broadcasts from www.WRBN.Net!


Come join in chat for a full week of Hurricane Prepardness.

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StormChat Link
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1808. nash28
7:26 PM GMT on May 25, 2008
True Drak. Those two were the most conservative, while the CMC without fail was like a 10 year old with a crayon and a pound of sugar in his system:-)
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1807. weathersp
3:25 PM EDT on May 25, 2008
1804.

Sure, Here you go:
Link
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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.