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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807. CaneAddict
12:04 PM GMT on May 24, 2008
790. howarjo1943 6:02 AM GMT on May 24, 2008
The GFS is ridiculous, but I can already sense the panic in New Orleans if that scenario comes to fruition. If it forms over the SW caribbean, slowly moves north toward a weakness over the SE U.S., it could well become a hurricane when it nears Cuba. If ridging then takes place and lets the hurricane slowly move WNW over very warm southern Gulf waters, it could reach cat 3 strength over deep, warm waters and favorable conditions aloft. But, it would weaken very rapidly as it neared the coast and came ashore. The SST's are very cool in the northern Gulf right now and will still be below par for a few weeks. A lot of things would have to happen. But climotology is not on the GFS side


It would be almost impossible for this supposed disturbance to become a Category 3 hurricane, This is primarily due to conditions not being all that favorable, Yes SST's can likely support it but wind shear is to high...
IMO
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806. FloridaRick
7:16 AM EST on May 24, 2008
Here in SW Florida the onshore breeze has been keeping the storms inland. they develop about 5 miles to the east of me and keep going east. it is kind of upsetting to watch those beautiful thinder heads develop and know you are not going to get any of the rain.
Member Since: July 27, 2005 Posts: 0 Comments: 18
805. TheCaneWhisperer
12:14 PM GMT on May 24, 2008
WU has 60% chance of showers and T-Storms. Pretty good if you ask me.
804. TheCaneWhisperer
12:09 PM GMT on May 24, 2008
I guess we'll know Tuesday/Wedensday if this area is going to materialize and where.

From what I heard MF, we can expect more of the same today.
803. all4hurricanes
12:10 PM GMT on May 24, 2008
WU says you will get T-Storms I don't know how the rain was in Fl yesterday but here's your answer
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802. MasterForecaster
12:08 PM GMT on May 24, 2008
So any chance we get rain like yesterday again today in south florida?
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801. FloridaRick
6:56 AM EST on May 24, 2008
whether or not the models play out will be interesting to watch. I will be with my team of responders in Broward that week doing pre-land fall catastrophic planning, it would suck to have to travel from one end of florida to another.
Member Since: July 27, 2005 Posts: 0 Comments: 18
799. TheCaneWhisperer
11:24 AM GMT on May 24, 2008
Good Saturday to you StormW.
798. TheCaneWhisperer
11:16 AM GMT on May 24, 2008
We're getting into the almost believable time frame with the GFS. One has to start giving it credit soon. NOGAPS has a weak closed low in the caribb and a stronger storm in the EPAC.
796. Weather456
7:16 AM AST on May 24, 2008
795. TheCaneWhisperer 7:16 AM AST on May 24, 2008

Notice the cirrus streamers north of the system, they were racing at speeds faster than cloud tops associated with the wave...which was another indicator of unfavorable conditions ahead of this feature.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
795. TheCaneWhisperer
11:14 AM GMT on May 24, 2008
Very healthy wave 456. Didn't have a chance though with that TUTT axis. I looked last night and it was being ripped to shreads.
794. Weather456
6:51 AM AST on May 24, 2008
This is the tropical wave near peak organization. This channel 1 visible image was taken by METEOSAT at 1200 UTC (8am EDT) on May 23.

Member Since: July 24, 2005 Posts: 407 Comments: 19076
793. TheCaneWhisperer
10:59 AM GMT on May 24, 2008
I see the latest GFS upped the antie on our little "Ghost System". Pretty formidable, symmetrical, tropical storm running up and over the lower peninsula of Florida. Almost looks like a Cat 1 is reached just before landfall.
792. Weather456
6:21 AM AST on May 24, 2008
Posted a tropics update in the comment section of my blog.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
791. IpswichWeatherCenter
9:49 AM GMT on May 24, 2008
what happened to our florida rain then?
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790. howarjo1943
5:49 AM GMT on May 24, 2008
The GFS is ridiculous, but I can already sense the panic in New Orleans if that scenario comes to fruition. If it forms over the SW caribbean, slowly moves north toward a weakness over the SE U.S., it could well become a hurricane when it nears Cuba. If ridging then takes place and lets the hurricane slowly move WNW over very warm southern Gulf waters, it could reach cat 3 strength over deep, warm waters and favorable conditions aloft. But, it would weaken very rapidly as it neared the coast and came ashore. The SST's are very cool in the northern Gulf right now and will still be below par for a few weeks. A lot of things would have to happen. But climotology is not on the GFS side
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789. TampaSpin
1:43 AM EDT on May 24, 2008
372 hours out
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788. Michfan
12:41 AM CDT on May 24, 2008
Nvm i got the rotation of the High mixed up. :o
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787. Michfan
12:41 AM CDT on May 24, 2008
Wow i need sleep.
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786. Drakoen
5:38 AM GMT on May 24, 2008
785. Michfan 5:38 AM GMT on May 24, 2008 Hide this comment.
I always thought an anticyclone rotated in the opposite direction of a cyclone. Shows what i know!


It does lol. Cyclones are counter-clockwise and anticyclones are clockwise.
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785. Michfan
12:34 AM CDT on May 24, 2008
I always thought an anticyclone rotated in the opposite direction of a cyclone. Shows what i know!
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784. StormJunkie
5:37 AM GMT on May 24, 2008
Thanks Drak, see ya tomorrow.

Morning TS

I am out as well.

Night y'all
Member Since: August 17, 2005 Posts: 26 Comments: 16874
783. Drakoen
5:34 AM GMT on May 24, 2008
781. StormJunkie 5:33 AM GMT on May 24, 2008
That is what is messing me up. The back of the barb points in to the wind, correct?

Yep!

I'm gonna go now its 1:35am. I need some sleep. I'll be up early though if you need anymore help.
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782. TampaSpin
1:33 AM EDT on May 24, 2008
Hello storm and drak
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781. StormJunkie
5:30 AM GMT on May 24, 2008
That is what is messing me up. The back of the barb points in to the wind, correct?
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780. TampaSpin
1:30 AM EDT on May 24, 2008
check out this 7 day loop..Link you can see the wave i think that the GFS model is picking up.
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779. StormJunkie
5:27 AM GMT on May 24, 2008
Westerly the wind blows to the W no? And the barb tip points in to the wind?

I always get this messed up. I need a lefty lucy for wind barbs and directions!
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778. Drakoen
5:29 AM GMT on May 24, 2008
776. Michfan 5:21 AM GMT on May 24, 2008
High = counterclockwise. Anticyclone = clockwise.


both are clockwise and are the same thing.
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777. Drakoen
5:25 AM GMT on May 24, 2008
Actually you have the flow mixed up SJ. The flow over the U.S. is westerly and in the Caribbean is easterly.
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776. Michfan
12:19 AM CDT on May 24, 2008
High = counterclockwise. Anticyclone = clockwise.
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775. Drakoen
5:19 AM GMT on May 24, 2008
That looks like an upper level High SJ!
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774. StormJunkie
5:07 AM GMT on May 24, 2008
00z GFS 360hr 200mb wind, ht


First the HT is height, right?

Then, I see E to W flow across the Conus, and the W to E flow across the W Carib. In between, I see the relaxed winds, and something similar to anticyclonic flow to some extent, but nothing well defined?

Is there a better time frame for me to post so I may be able to see the light through the Draks eyes :~)
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773. howarjo1943
5:05 AM GMT on May 24, 2008
Its not hurricane season until the GFS landfalls a significant hurricane 16 days out on the northern Gulf Coast with another tropical storm lurking in the Bahamas, all in the first week of JUNE!!! They should ban that 16 day out crap. With Dean last year, even 3-7 days out, the GFS had major problems handling steering currents. Not to mention, the GFS didn't even "see" Felix until it was a cat 5 because of its small size. Sometimes it can be right on, but mostly it is what it is, guidance.
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772. StormJunkie
5:06 AM GMT on May 24, 2008
Evening Michfan :~)

Alright, stick with me Drak....Be right back
Member Since: August 17, 2005 Posts: 26 Comments: 16874
771. Michfan
12:01 AM CDT on May 24, 2008
Yeah that track is kinda of scary. Im somewhat suprised that the GFS has been so consistent with this system. It does love to spin up storms but its a hell of alot more accurate than the CMC which spits out anything it pleases.
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770. Drakoen
5:03 AM GMT on May 24, 2008
769. StormJunkie 5:01 AM GMT on May 24, 2008
I did not want to have to wait for the pretty pictures! Was hoping to learn to understand a little more about the NCEP page :~)


Ok. You have to make sure that the anticyclonic flow is closed around a certain area. Remember the flow is clockwise. You have to know how to read the barbs.
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769. StormJunkie
5:01 AM GMT on May 24, 2008
I did not want to have to wait for the pretty pictures! Was hoping to learn to understand a little more about the NCEP page :~)

Does look like a very similar Ivan landfall location. Again though, this should be a "get out of jail free card" for this area.

Almost annoying to be able to watch 384 hours out since we are not very good at it yet.
Member Since: August 17, 2005 Posts: 26 Comments: 16874
768. Drakoen
4:57 AM GMT on May 24, 2008
766. StormJunkie 4:55 AM GMT on May 24, 2008
Hopefully that 384hr time frame will be what it usually is, a guaranteed free pass for a miss to the area shown....


LOL. The looks like an Ivan type track.
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767. Drakoen
4:54 AM GMT on May 24, 2008
765. StormJunkie 4:53 AM GMT on May 24, 2008
200hr time frame your anticyclone would be centered around the Honduras/Nicaragua boarder, or is it the much broader area?

This just for my learning, not suggesting any qualifications of the gfs at 200hrs!


Nope. Maybe it would be better for you to go here: http://tc.met.psu.edu/ and wait around a bit for the 00z run to fully load. The wind shear imagery goes all the way out to 384hrs and the flow is much easier to see.
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766. StormJunkie
4:53 AM GMT on May 24, 2008
Hopefully that 384hr time frame will be what it usually is, a guaranteed free pass for a miss to the area shown....
Member Since: August 17, 2005 Posts: 26 Comments: 16874
765. StormJunkie
4:47 AM GMT on May 24, 2008
200hr time frame your anticyclone would be centered around the Honduras/Nicaragua boarder, or is it the much broader area?

This just for my learning, not suggesting any qualifications of the gfs at 200hrs!
Member Since: August 17, 2005 Posts: 26 Comments: 16874
764. Drakoen
4:46 AM GMT on May 24, 2008
762. StormJunkie 4:45 AM GMT on May 24, 2008
Could not agree more Drak. Still interesting to see each run continue to show it. Few runs here and there that did not, but the GFS has been on this for the most part. Persistence is not always key with the models, just ask the CMC :~)


LOL no point in asking the cyclogenesis machine if you already know the answer its gonna give you!
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763. Drakoen
4:44 AM GMT on May 24, 2008
761. StormJunkie 4:44 AM GMT on May 24, 2008
How are you identifying an anticyclone Drak? Which maps?

Also, are you saying that with a anticyclone over much of the carib that the E Pac areas might not interfere with the Carib area?


Go to the 200mb graphics and look at the wind barbs. Its a bit far out to tell but an upper anticyclone would favor development.
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762. StormJunkie
4:44 AM GMT on May 24, 2008
Could not agree more Drak. Still interesting to see each run continue to show it. Few runs here and there that did not, but the GFS has been on this for the most part. Persistence is not always key with the models, just ask the CMC :~)

Model support though, that is a different story.
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761. StormJunkie
4:42 AM GMT on May 24, 2008
How are you identifying an anticyclone Drak? Which maps?

Also, are you saying that with a anticyclone over much of the carib that the E Pac areas might not interfere with the Carib area?

TIA
Member Since: August 17, 2005 Posts: 26 Comments: 16874
760. Drakoen
4:41 AM GMT on May 24, 2008
SJ I think we need to wait until Sunday or even Monday to get a better grasp with the models.
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758. Drakoen
4:38 AM GMT on May 24, 2008
I noticed on the upper air graphic that for the most part a large upper air anticyclone will be over the Caribbean.
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757. StormJunkie
4:34 AM GMT on May 24, 2008
Yea Drak, showing a lot of vorticity and L's on the pac side as well though. Not sure how to take that, but at 108hrs we really are starting to get in to a little more believable time frame. Granted 108 is still a long way out when one is talking intensity or genesis.
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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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