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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1456. stormdude77
10:11 PM AST on May 24, 2008
These are the lastest reports from Exuma and Freeport, in the Bahamas.

George Town, Exuma, Bahamas
At 9:01 PM GMT-5 SAT MAY 24 2008

Lightning Observed
Temp: 25°C
Humidity: 78%
Wind Speed: CALM
Barometer: 1012 mb
Dewpoint: 21°C
Heat Index: 26°C
Wind Chill: 25°C


Freeport, Grand Bahama, Bahamas
At 7:36 PM GMT-5 SAT MAY 24 2008

Light Rain
Temp: 22°C
Humidity: 94%
Wind Speed: S 5 MPH
Barometer: 1012 mb
Dewpoint: 21°C
Heat Index: 22°C
Wind Chill: 22°C

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1455. BahaHurican
10:07 PM EDT on May 24, 2008
Yup, it's raining out - a nice downpour which should go a long way in relieving the dust problem . . .
Member Since: October 25, 2005 Posts: 19 Comments: 22583
1454. lopaka001
10:13 PM EDT on May 24, 2008
Hey Hey what storm?
I must have miss the post..
First possible storm for us Floridians?
Sorry been dealing with these Strong T-Storms all day after a lonngg drought!
I need to go back and read the board I think.
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1453. hurricane23
10:12 PM EDT on May 24, 2008
18z Nogaps also has development down in the region.
Member Since: May 14, 2006 Posts: 8 Comments: 13839
1452. hahaguy
10:11 PM EDT on May 24, 2008
i'm still getting rain lol. been 4 hrs of constant rain.
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1451. stormdude77
10:08 PM AST on May 24, 2008
Hey, Baha...the wind was pretty ''gusty'' over your area, earlier today... (this info below is from the NHC)

DOPPLER RADAR INDICATES SHOWERS
AND TSTMS MOVING SE ALONG THE EAST COAST OF FLORIDA. A SEVERE
THUNDERSTORM WATCH REMAINS IN EFFECT FOR ALL OF MAINLAND SOUTH
FLORIDA UNTIL 9 PM EDT THIS EVENING. DAMAGING WINDS AND LARGE
HAIL ARE STILL POSSIBLE WITH THE STRONGEST TSTMS. FREEPORT IN
THE BAHAMAS REPORTED A GUST WIND OF 43 KT WITH A TSTM OVERHEAD.

THE SFC LOW IS FORECAST TO JOIN THE FRONTAL BOUNDARY THAT WILL
MOVE FROM THE SE CONUS ACROSS THE NE GULF AND THE STATE OF
FLORIDA TONIGHT/EARLY SUN.
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1450. TheCaneWhisperer
2:06 AM GMT on May 25, 2008
This should be the last round Lop, loosing steam as I type. Looks like things are beginning to wrap up for the night.

Looked like a long period of T-Storms there for a bit.
1449. bystander
2:07 AM GMT on May 25, 2008
Drak,
This may be a dumb question..........What is QPF?
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1448. ClearH2OFla
10:07 PM EDT on May 24, 2008
Hey Storm W. any truth to a storm heading our way.
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1447. BahaHurican
10:06 PM EDT on May 24, 2008
Gone back outside with my digital .. .
Member Since: October 25, 2005 Posts: 19 Comments: 22583
1446. BahaHurican
9:56 PM EDT on May 24, 2008
1417. stormpetrol 9:22 PM EDT on May 24, 2008
Notice a nasty flare up over Central America mainly Guatemala/Belize region , don't know what would happen if got offshore near the Gulf of Honduras.Might have some potential.


Hey, storm, hard to miss that on the IR loop. Looks like it might be headed west, though. Yet another sign that the tropical weather season is upon us. . . .

Looking at the NASA loop, it seems like my hopes for rain may come to fruition. Nothing has actually fallen here as yet, but it looks like Freeport / Grand Bahama got hammered.
Member Since: October 25, 2005 Posts: 19 Comments: 22583
1445. hahaguy
10:06 PM EDT on May 24, 2008
good idea lol
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1444. bystander
2:03 AM GMT on May 25, 2008
3rd period is usually good for us.......Enough about hockey, back to weather
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1443. hahaguy
10:02 PM EDT on May 24, 2008
we better bystander lol
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1442. WhereIsTheStorm
2:00 AM GMT on May 25, 2008
Well goodnight everyone have a great evening.
It's been an interesting weather day.
I'll be checking in tomorrow when I can.
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1441. bystander
2:00 AM GMT on May 25, 2008
HaHa,
Pens need to pick it up!!
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1440. lopaka001
10:01 PM EDT on May 24, 2008
Holy Toledo Sgnalla!
Round 4 is coming geez..
Link
I would have thought the cooler temps at night would have settle down these storms like they normally do this time of the year but what is driving these cells towards us?
I see dry air is trying to push in but maybe something off the coast is spawning these cells?
At least the Lake is getting lots of water..
This one is going to be windy I see it is moving fast!
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1439. TheCaneWhisperer
2:01 AM GMT on May 25, 2008
Thank You for the input SW, always appreciated.
1438. BahaHurican
9:53 PM EDT on May 24, 2008
Back at the board . . .

Well, as I was stepping inside the house just now the wind was gusting to about 25 mph and there was a light mist blowing sideways. I hope it actually moves from there into a downpour . . .
Member Since: October 25, 2005 Posts: 19 Comments: 22583
1437. Patrap
8:54 PM CDT on May 24, 2008
It depends whos loading the images at ESL.
I believe.
I dont think they self update till the season.
Member Since: July 3, 2005 Posts: 426 Comments: 129093
1435. lopaka001
9:40 PM EDT on May 24, 2008
Patrap I look at those images a hour ago and it said updated every 10-15 mins.Do they change the update frequently or is every 30mins the norm?
Thanks for the links btw very nice flare down south.

..ahh never mind I see the Gulf of Mexico is updated more!
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1434. WhereIsTheStorm
1:40 AM GMT on May 25, 2008
1419. StormW 1:28 AM GMT on May 25, 2008
Take a look over the Yucatan Peninsula and where stormpetrol mentioned

IR AVN LOOP

Patrep mentioned it earlier too; but I didn't expect it to get that big. There is some serious potential for mud slides as well as flooding from this storm.
Do you think this is going to slide off to the east or the west?
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1433. TerraNova
9:47 PM EDT on May 24, 2008
I threw out the GFS 18z run. That EPAC low looks heavily QPF bomb induced.

Ya, exactly what I was thinking. Too much convection all of a sudden to be possible under the conditions expected to be in that area. Plus, it shows a fujiwara interaction taking place over land with the weaker low winning. The GFS is notorious for the QPF bombs...I think it's something in the algorithm that the programmers can't seem to fix. The 12z model runs from the GFS and ECMWF are more reasonable. Also the NAM is starting to catch on to a potential development in the SW Caribbean.

Good night everyone.
Member Since: July 30, 2007 Posts: 76 Comments: 4063
1431. Drakoen
1:41 AM GMT on May 25, 2008
Hey StormW!

I threw out the GFS 18z run. That EPAC low looks heavily QPF bomb induced.
Member Since: October 28, 2006 Posts: 57 Comments: 30615
1430. Drakoen
1:39 AM GMT on May 25, 2008
The area of convection is an in area of convergence east of an upper level high creating upper level diffluence and upper level divergence enhancing the activity.
Member Since: October 28, 2006 Posts: 57 Comments: 30615
1429. extreme236
1:39 AM GMT on May 25, 2008
NHC is going to add yet another tropical wave to the 0Z sfc map...looks like a pretty steady stream of tropical waves have been emerging off Africa.
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1428. lopaka001
9:39 PM EDT on May 24, 2008
Lol like I said before my buddy is in Cancun for the weekend
and that storm is growing..
What a flare up!
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1426. Patrap
8:36 PM CDT on May 24, 2008
Gulf and Tropics (Updated every~1/2 hour) Link

Member Since: July 3, 2005 Posts: 426 Comments: 129093
1425. TheCaneWhisperer
1:29 AM GMT on May 25, 2008
What would you attribute that flare up to over the Yucatan StormW? By the time these models figure this thing out it will be the 2nd Caribb prime time.

Looks like we're in for a stormy night here in Palm Beach County. Surface trough developed off the low training storms in it's path.
1423. TerraNova
9:30 PM EDT on May 24, 2008
Take a look over the Yucatan Peninsula

Oh wow...huge flare!
Member Since: July 30, 2007 Posts: 76 Comments: 4063
1422. hahaguy
9:30 PM EDT on May 24, 2008
rain has been constant here since around 6pm
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1421. moonlightcowboy
8:20 PM CDT on May 24, 2008
Tornadoes rake parts of Kan., Okla.; 2 found dead - full story.

KANSAS CITY, Mo. - Authorities checking on a car stranded in a field Saturday morning found two people killed by a powerful storm that raked the state a day earlier with at least 17 tornadoes.

The Friday storm destroyed several buildings and injured at least six people, including one hospitalized in serious condition in Wichita, authorities said. Several tornadoes touched down Saturday in northwestern Oklahoma.
The car the man and woman found dead Saturday were in was blown 150 yards off the highway they were on into a field about 13 miles east of Pratt, the Pratt County Sheriff's Office said. Gary S. Whitlow, 33, and Kimberly S. Whitlow, 29, were pronounced dead at the scene.

....Their car, barely visible from the road, was destroyed by a twister that also swept a semi-truck off the highway and knocked down power poles and lines across the road.
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1418. Patrap
8:26 PM CDT on May 24, 2008
UNYSIS Day 10 GFSx Surface 3JUNE 0Z Link
Member Since: July 3, 2005 Posts: 426 Comments: 129093
1417. stormpetrol
1:18 AM GMT on May 25, 2008
Notice a nasty flare up over Central America mainly Guatemala/Belize region , don't know what would happen if got offshore near the Gulf of Honduras.Might have some potential.
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1416. all4hurricanes
1:09 AM GMT on May 25, 2008
We need more rain, all the tadpoles that put there homes in puddles are going to die. It should rain Tuesday
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1415. sngalla
9:07 PM EDT on May 24, 2008
Looks like it is starting to fall apart as it gets close to me. Just a little rain now.
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1414. Skyepony (Mod)
12:58 AM GMT on May 25, 2008
JFV~ I gotta agree with the Miami NWS on that.

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.

interesting the models are gettin edgy. Each season we've had different better preformers & certainly there has been some tweeking over the winter..
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1413. lopaka001
9:03 PM EDT on May 24, 2008
I am getting hit now but cooper city might get the worst of it me thinks!
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1411. sngalla
8:59 PM EDT on May 24, 2008
Lots of lightning. Looks like the rain is just minutes away. You getting it yet?
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1410. lopaka001
8:56 PM EDT on May 24, 2008
Geez the lightning is worst in this 3rd cell!
Sgnalla you getting slam yet?
The FLL airport is getting pounded!
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1409. pearlandaggie
12:53 AM GMT on May 25, 2008
1408. where the HAIL is cooper city?
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1408. cchsweatherman
8:48 PM EDT on May 24, 2008
Just finished checking the computer models and I'm in total agreement that the 18UTC GFS needs to be thrown out. Looks completely discombobulated.

Still intrigued by a possible tropical storm/hurricane in South Florida in the first week of June, but I still remain skeptical. Need to see some low forming down in the Southwest Caribbean to get my full attention.

Got some very nasty weather here in Cooper City and are about to get slammed again, possibly with some hail in this next wave. Looks like we still got some more weather coming our way before midnight.
Member Since: April 14, 2007 Posts: 8 Comments: 5169

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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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