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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1357. Drakoen
11:41 PM GMT on May 24, 2008
1356. moonlightcowboy 11:40 PM GMT on May 24, 2008
Drak, I very much respect and follow your weather knowledge, but I don't "trust" any model. And, Dean was hardly 100 percent congruent. There was much talk about a Houston landfall, etc, with Dean.



I meant with initial development of the coast of Africa not track.
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1356. moonlightcowboy
6:38 PM CDT on May 24, 2008
Drak, I very much respect and follow your weather knowledge, but I don't "trust" any model. And, Dean was hardly 100 percent congruent. There was much talk about a Houston landfall, etc, with Dean.


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1355. Ivansrvivr
11:35 PM GMT on May 24, 2008
Vort, this is a tropical weather blog. I dont think that last comment was appropriate for folks like Drakoen and Nash or 456 who are all very knowledgeable in the meteorology dept.
oh and by the way, a cat 3 cane is as real a cyclone as they get.
1354. Patrap
6:39 PM CDT on May 24, 2008
Classic Cheyenne Twister roping out.

Member Since: July 3, 2005 Posts: 421 Comments: 127702
1352. Drakoen
11:37 PM GMT on May 24, 2008
You try to have a decent conversation in here and theres always one in the bunch...
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1349. Ivansrvivr
11:26 PM GMT on May 24, 2008
1340, tornados don't keep my interest. I understand why others are fascinated by them and Vort, you do an excellent job of tracking that kind of weather for us here. the thing is when you are studying tropics, everything works totally opposite of mid latitude systems so for some of us(like me) it is simply too much to process at the same time. I have all the respect in the world for those folks here that focus on both mid latitude systems and tropics at the same time. For me it is one or the other.
1347. Drakoen
11:32 PM GMT on May 24, 2008
Vortfix please if you wish to address me do so with some manners.
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1346. Patrap
6:30 PM CDT on May 24, 2008
Cyclone Bob here.

I got this sucka...




Member Since: July 3, 2005 Posts: 421 Comments: 127702
1344. MasterForecaster
11:27 PM GMT on May 24, 2008
Wow...rain is horizontal in North Miami near the Dade-Broward border. It's pretty crazy right now.
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1343. Drakoen
11:24 PM GMT on May 24, 2008
1339. moonlightcowboy 11:23 PM GMT on May 24, 2008
Drakoen, that's cool, but models don't agree 75 percent of the time even after initializing a real storm, at least not until after it gets up and going good. Hey, they're tools just like loops, sfc maps, etc. They all have their place, but following models two weeks out, etc, really is nothing more than a WAG, lol.



Trust me I know that and i'll use Dean as my example for 100% model consensus. The models have the ability to see ahead its just a matter of how the handle the atmosphere and whether they can agree or not.
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1342. Weather456
7:24 PM AST on May 24, 2008
1339. moonlightcowboy 7:23 PM AST on May 24, 2008
Drakoen, that's cool, but models don't agree 75 percent of the time even after initializing a real stormm, at least not until after it gets up and going. Hey, they're tools just like loops, sfc maps, etc. They all have their place, but following models two weeks out, etc, really is nothing more than a WAG, lol.


Exactly
Member Since: July 24, 2005 Posts: 407 Comments: 19076
1341. Ivansrvivr
11:21 PM GMT on May 24, 2008
1337. I have found that forecasting models are good for watching trends. Trends within the various models seem to be more accurate tool than just the models themselves.(for me at least)
1339. moonlightcowboy
6:22 PM CDT on May 24, 2008
Drakoen, that's cool, but models don't agree 75 percent of the time even after initializing a real storm, at least not until after it gets up and going good. Hey, they're tools just like loops, sfc maps, etc. They all have their place, but following models two weeks out, etc, really is nothing more than a WAG, lol.
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1338. Ivansrvivr
11:20 PM GMT on May 24, 2008
1334. what models do we believe...drunk rich ones.
1337. Drakoen
11:20 PM GMT on May 24, 2008
I'm a big fan of the models when 75% of them can agree on something at a reasonable time frame under reasonable conditions.
Member Since: October 28, 2006 Posts: 57 Comments: 29942
1336. Ivansrvivr
11:18 PM GMT on May 24, 2008
MLC, I prefer climatology over models which favors E-Pac.
1335. Weather456
7:15 PM AST on May 24, 2008
1332. moonlightcowboy 7:14 PM AST on May 24, 2008
456, now that sounds like wise weather! lol, I'm just not a big fan of the models.


Neither am I...I had plan to implement them much more in 2008 than in any other year since I began tracking storms, but I'm just better off the old fashion way....looking at the current realtime conditions and determine a forecast for myself based on climatlogy, knowledge and instinct.
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1333. Ivansrvivr
11:12 PM GMT on May 24, 2008
Adrian, that is actually a good Idea with it being so early in the season, many people haven't done their prep yet. If something does develop there it could sneak up on us fairly quickly. the NWS is trying to make sure folks are prepped this year. I really doubt we will see development there but the NWS mentioned the possible activity in the proper context.
1332. moonlightcowboy
6:13 PM CDT on May 24, 2008
456, now that sounds like wise weather! lol, I'm just not a big fan of the models.
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1331. Drakoen
11:13 PM GMT on May 24, 2008
Interesting stuff Adrian. Didn't look at the Miami discussion. I agree with the NWS though. We really need to wait till early next weeks model runs to get a grasp of whats going on.
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1330. Weather456
7:07 PM AST on May 24, 2008
At this point...I am better off watching the satellite loops rather than look at these models with much interest. I dont think some are handling the siuation logically so therefore, its time use my head. I would throw out the 18Z GFS run also.
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1329. hurricane23
7:11 PM EDT on May 24, 2008
NWS in Miami makes note of possible Tropical Storm!


THE FCST CONTINUES RATHER UNCERTAIN FOR LATE NEXT WEEK INTO NEXT
WEEKEND. GFS SHOWS ANOTHER SHORTWAVE DIVING SE INTO THE AREA...BUT
THE BULK OF IT STAYS TO OUR NORTHEAST. ECMWF DOES NOT SHOW THIS.
STILL...BOTH MODELS DO SHOW A SLOW INCREASE IN MOISTURE
BEGINNING THURSDAY AND CONTINUING INTO NEXT WEEKEND. GFS/ECMWF HAVE
BEEN CONSISTENT IN DEVELOPING A TROPICAL SYSTEM OVER THE WESTERN
CARIB...BUT HOW STRONG AND WHERE IT WOULD GO...IF EVEN ANYTHING
DEVELOPS...IS JUST WAY TOO FAR OUT TO TELL AT THIS TIME.
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1328. Drakoen
11:09 PM GMT on May 24, 2008
1326. SouthDadeFish 11:09 PM GMT on May 24, 2008
So Drak if i understand QPF correctly it means Quantitative Precipitation Forecast. If I'm right, what would cause the GFS to think the E Pac system would bomb like that?


Sudden increase in in 500mb vorticity maxima they are usually small but very strong and can help generate large amounts of Precipitation.
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1326. SouthDadeFish
11:07 PM GMT on May 24, 2008
So Drak if i understand QPF correctly it means Quantitative Precipitation Forecast. If I'm right, what would cause the GFS to think the E Pac system would bomb like that?
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1325. Drakoen
11:01 PM GMT on May 24, 2008
I took this from the 180hr. Big increase in 500mb vorticity maxima and sudden increase in a convection from 3.5in -5.5inches between 174hr and 180hr. Signs of the QPF bomb.

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1324. Ivansrvivr
10:56 PM GMT on May 24, 2008
1306. Hello JFV. There is a slight possibility of a W.Caribbean storm. That is assuming storm doesn't develop in the E-Pac and rob it of it's moisture and several factors come together at the perfect time and then we would most likely end up with a typical lopsided sub-tropical system that would bring some good rain to Florida and that is about all.
1323. FLWeatherFreak91
6:57 PM EDT on May 24, 2008
um yeah new GFS is weird
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1322. nash28
10:58 PM GMT on May 24, 2008
Ok gang... Time for me to grab the 12 pack, chips and dip and get ready for Game 1 of the Stanley Cup Finals!!!!

GO WINGS!!!!
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1321. SouthDadeFish
10:54 PM GMT on May 24, 2008
No problem. :~) I would keep monitoring the situation though... That is quite a violent storm and things could change rapidly.
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1320. FEEDERBAND
10:52 PM GMT on May 24, 2008
thanks southdadefish... much appreciated...worried about family only gives me more gray hair...
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1319. SouthDadeFish
10:51 PM GMT on May 24, 2008
1311, Drak can you explain what that means please? :~)
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1318. stormhank
10:49 PM GMT on May 24, 2008
Hey Drak n all. Saw the GFS 18Z run . still seems to try to develop something in carribean and carry it up toward gulf coast?? of course that far out, has got to be taken with grain of salt, unless other models start developing something also.. time will tell i guess
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1317. WPBHurricane05
6:49 PM EDT on May 24, 2008
Oklahoma tornado coverage Link


another tornado on the ground....
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1316. SouthDadeFish
10:49 PM GMT on May 24, 2008
Oh the storm in Oklahoma.... Here's a loop of the current radar. I believe it should stay south of ponca city. Link
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1315. IKE
5:49 PM CDT on May 24, 2008
1304. SouthDadeFish 5:44 PM CDT on May 24, 2008
Well apparently the GFS believes a low pressure is going to stay in the BoC until the 2009 hurricane season... lol


LOL.
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1314. Patrap
5:49 PM CDT on May 24, 2008
Severe Weather Warnings Page Link
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1313. nash28
10:48 PM GMT on May 24, 2008
Agreed Drak. Dump the 18z run.
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1312. FEEDERBAND
10:47 PM GMT on May 24, 2008
was reading the comments on previous page and someone mentioned a storm possibly spawning a tornado near ponca city.... was asking if there might be more news on that?
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1311. Drakoen
10:47 PM GMT on May 24, 2008
That EPAC storm is so QPF bomb induced its not even funny....
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1310. nash28
10:46 PM GMT on May 24, 2008
18z GFS is either out to lunch, or out to lunch..

:-)

Let's wait for the 00z
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1309. Patrap
5:46 PM CDT on May 24, 2008
Be Prepared for June 1

This weekend is a Hurricane Tax Holiday for Louisiana Residents Statewide..Link







Evacuation Considerations for the Elderly, Disabled and Special Medical Care Issues Link

Your Evacuation Plan Link


Disaster Supplies Kit
Link

NOAA Alert Weather Radio's: Link
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1308. SouthDadeFish
10:45 PM GMT on May 24, 2008
1305, where is that?
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1307. Drakoen
10:45 PM GMT on May 24, 2008
I'm going to throw out that GFS 18z run. Its really bullish...
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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.