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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1807. weathersp
3:25 PM EDT on May 25, 2008
1804.

Sure, Here you go:
Link
Member Since: January 14, 2007 Posts: 17 Comments: 4140
1806. Drakoen
7:24 PM GMT on May 25, 2008
Nash I found the UKMET to be very conservative last year as well though it did actually pick up on the systems.
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1805. nash28
7:22 PM GMT on May 25, 2008
The NOGAPS does surprise me a little, as someone else just noted they are usually the most conservative and bullish on non-development of all of the globals.

Hell, last year the damn model failed to pick up storms that were already THERE!
Member Since: July 11, 2005 Posts: 190 Comments: 16972
1804. hurricane10
3:19 PM EDT on May 25, 2008
1784. weathersp 3:05 PM EDT on May 25, 2008
12z UKMET says the low has already started..


Can you link to that Page
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1803. Drakoen
7:22 PM GMT on May 25, 2008
I'll wait and see what the 18z NOGAPS and 18Z GFS have to say...
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1802. Drakoen
7:20 PM GMT on May 25, 2008
1799. nash28 7:19 PM GMT on May 25, 2008
Well Drak, it IS Memorial Day weekend and hey... The UKMET and ECMWF gotta get their drink on sometime, right??


I suppose so. The UKMET likes that ghost low in the EPAC too much lmfao!
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1801. weathersp
3:18 PM EDT on May 25, 2008
American Pride really high this weekend. :)
Member Since: January 14, 2007 Posts: 17 Comments: 4140
1800. Patrap
2:18 PM CDT on May 25, 2008
UNYSIS GFSx 2JUNE0Z surface Link
Member Since: July 3, 2005 Posts: 426 Comments: 128871
1799. nash28
7:19 PM GMT on May 25, 2008
Well Drak, it IS Memorial Day weekend and hey... The UKMET and ECMWF gotta get their drink on sometime, right??
Member Since: July 11, 2005 Posts: 190 Comments: 16972
1798. Drakoen
7:17 PM GMT on May 25, 2008
Looks like we will have to wait for some more model runs...

The UKMET and ECMWF are drunk...
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1796. nash28
7:15 PM GMT on May 25, 2008
Hmmmm.. Just finished yard. NOGAPS shows FL system. 12z ECMWF drops CB and puts system in EPAC. GFS still has BOC system.
Member Since: July 11, 2005 Posts: 190 Comments: 16972
1795. Drakoen
7:15 PM GMT on May 25, 2008
1793. jphurricane2006 7:13 PM GMT on May 25, 2008
but the point is while the GFS has stayed consistent, all the other models have jumped back and forth; it starts to make the GFS look sane lol


The GFS is very sane until it shoots out a 1037mb high...lol.
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1794. weathersp
3:12 PM EDT on May 25, 2008
1791..

Interesting that I deviates from the GFS and takes it northeast instead of west like the GFS.

I said earlier today that the GFS was off kilter once in reached the GOM and it would take a northerlyish track because of the Enormous Steering High over the North Atlantic.
Member Since: January 14, 2007 Posts: 17 Comments: 4140
1792. Drakoen
7:11 PM GMT on May 25, 2008
1790. jphurricane2006 7:11 PM GMT on May 25, 2008
lol you are right Drak, wow that run had too much Guiness in it I guess lol


yea lmfao!
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1791. FLWeatherFreak91
3:11 PM EDT on May 25, 2008
nogaps vort long range

Strong system central fl west coast
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1789. Patrap
2:10 PM CDT on May 25, 2008
<
Member Since: July 3, 2005 Posts: 426 Comments: 128871
1788. WX12B
7:09 PM GMT on May 25, 2008
Good afternoon all,
Anyone from the Keys on here? It looks like an interesting start for us here on Cudjoe Key! If..(if) the models "pan" out,It appears we could finally get some rain..and...a little bit more. Have a safe holiday all happy Memorial day...Thank you!
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1787. weathersp
3:09 PM EDT on May 25, 2008
Not to often that the EMCWF is the odd man out..
Member Since: January 14, 2007 Posts: 17 Comments: 4140
1786. Drakoen
7:07 PM GMT on May 25, 2008
1785. jphurricane2006 7:05 PM GMT on May 25, 2008
ok the 12Z ECMWF is back with an EPAC system, but I see a fairly intesnse one at 192 hours and then 24 hours later it poofs, so im not too sure about that


lol if you notice that is the same low. The run starts out with an area low pressure moving into the Caribbean from the EPAC. The low moves into the BOC then back into the EPAC lol. Its makes a 360.
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1784. weathersp
3:02 PM EDT on May 25, 2008
12z UKMET says the low has already started..



10.2 N 100.1 W
Member Since: January 14, 2007 Posts: 17 Comments: 4140
1783. Drakoen
7:03 PM GMT on May 25, 2008
Nothing really from the ECMWF 12z run.
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1782. Drakoen
7:01 PM GMT on May 25, 2008
1780. moonlightcowboy 7:01 PM GMT on May 25, 2008
1763. Drakoen 1:31 PM CDT on May 25, 2008
Very decent system on the NOGAPS 12z:

G'afternoon, Drak, all! I see their still churning something out for us! Ugh.

Most interesting in that post, too, is the large Atl high and its bridging far west.


Afternoon MLC. Interesting stuff from the NOGAPS not only the High but the low pressure system over the Northern Central Plains region. NOGAPS think it will be strong enough to creating a weakness in the GOM.
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1781. IKE
2:02 PM CDT on May 25, 2008
12Z ECMWF...Link
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1780. moonlightcowboy
1:58 PM CDT on May 25, 2008
1763. Drakoen 1:31 PM CDT on May 25, 2008
Very decent system on the NOGAPS 12z:


G'afternoon, Drak, all! I see their still churning something out for us! Ugh.

Most interesting in that post, too, is the large Atl high and its bridging far west.
Member Since: July 9, 2006 Posts: 184 Comments: 29610
1779. InTheCone
2:54 PM EDT on May 25, 2008
Mets, schmets,

This blog provides an excellent forum for the discussion of the tropics. If you read along over a period of time you get a very detailed and comprehensive pic. of what's going on. The people that read all this are intrigued by the possibilities or why would they bother??

I certainly wouldn't be hearing of potetial development on TWC!!!
Member Since: September 1, 2007 Posts: 0 Comments: 1990
1778. Drakoen
6:53 PM GMT on May 25, 2008
On another note, SST anomalies are showing 1-2 degree Celsius above average temperatures in the eastern Gulf of Mexico and especially in the Bahamas.
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1777. Weather456
2:46 PM AST on May 25, 2008
1776. Drakoen 2:44 PM AST on May 25, 2008
W456 I think the surface reflection is very weak. The wind barbs are showing light winds.


Yes...that is true...not saying it was established...saying it is forming.
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1776. Drakoen
6:42 PM GMT on May 25, 2008
W456 I think the surface reflection is very weak. The wind barbs are showing light winds.
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1775. hahaguy
2:43 PM EDT on May 25, 2008
no problem glad to help.
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1774. Bamatracker
6:40 PM GMT on May 25, 2008
sweet...thans Hahaguy....i am stepping up to either two or three computers this year during hurricane season so I'm trying to get all my links straight.
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1773. hahaguy
2:41 PM EDT on May 25, 2008
does anyone really believe in the Herbert box?
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1771. hahaguy
2:39 PM EDT on May 25, 2008
Link

FSU link
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1770. Drakoen
6:38 PM GMT on May 25, 2008
1767. Bamatracker 6:37 PM GMT on May 25, 2008
the models seem excited about the beginning of hurricane season


apparently lol. They need a system within the first week.
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1769. Weather456
2:28 PM AST on May 25, 2008
1755. Drakoen 2:23 PM AST on May 25, 2008
...TROPICAL WAVES...
TROPICAL WAVE IS ANALYZED OVER LAND N OF 13N ALONG 89W/90W AND
REMAINS NEARLY STATIONARY. THE WAVE IS EMBEDDED IN A VERY BROAD
AREA OF CYCLONIC TURNING...WITH WESTERLY WINDS NOTED TO THE
SOUTH AND WEST OF THE WAVE. THESE WESTERLY WINDS CONTINUE TO
MAKE THE WAVE DIFFICULT TO DETECT AS A DISTINCT FEATURE AT THIS
TIME. MOST OF THE STRONG CONVECTION THAT WAS ASSOCIATED WITH THE
WAVE IS NOW WELL WEST OF THE WAVE...GENERALLY WITHIN 180 NM OF
THE ITCZ BETWEEN 93W AND 102W. GLOBAL MODELS ARE FORECASTING A
BROAD AREA OF LOW PRESSURE TO DEVELOP IN THE AREA OF THE WAVE
OVER THE NEXT SEVERAL DAYS.


One is already forming based on surface observations, satellite derived winds, QUIKSCAT/ASCAT (which caught the oceanic part of it) and visible imagery.

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1768. Bamatracker
6:37 PM GMT on May 25, 2008
can somebody post that link to the FSU model site add Penn state site please?
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1767. Bamatracker
6:37 PM GMT on May 25, 2008
the models seem excited about the beginning of hurricane season
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1766. weathersp
2:34 PM EDT on May 25, 2008
Very Interesting Drak... Usually the NOGAPS is conservative.
Member Since: January 14, 2007 Posts: 17 Comments: 4140
1765. Drakoen
6:33 PM GMT on May 25, 2008
1764. IKE 6:32 PM GMT on May 25, 2008
That NOGAPS is impressive....


Yea. Haven't seen the NOGAPS get like that in a while lol.
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1764. IKE
1:31 PM CDT on May 25, 2008
That NOGAPS is impressive....
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1763. Drakoen
6:29 PM GMT on May 25, 2008
Very decent system on the NOGAPS 12z:

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1762. CaneAddict
6:28 PM GMT on May 25, 2008
1761. IKE 6:27 PM GMT on May 25, 2008
Well said CaneAddict.......not sure of his purpose other than to stir the kettle....like he's pissed at us for following the tropics.....


Lol, true....oh well i'm not going lose sleep over some unintelligent untrue speculation he made, anyways im off for a bit BBL!
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1761. IKE
1:23 PM CDT on May 25, 2008
Well said CaneAddict.......not sure of his purpose other than to stir the kettle....like he's pissed at us for following the tropics.....
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1760. Bamatracker
6:26 PM GMT on May 25, 2008
where is the blob currently that the global models are predicting genesis from?
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1759. charliesurvivor
6:20 PM GMT on May 25, 2008
Hi eveybody,I just looked at the models and am totally surprised at the predicted strength of the possible nw carribe. developement.I love reading the input on this blog and I think we are all the better for it.
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1758. FLWeatherFreak91
2:23 PM EDT on May 25, 2008
1755

They have now acknowledged what we've been talking about for a long time... It looks like we'll have ourselves an invest here soon
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1757. weathersp
2:19 PM EDT on May 25, 2008
Why can't we be friends? Oh why Can't we be friend's.. :D
Member Since: January 14, 2007 Posts: 17 Comments: 4140

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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.

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