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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1007. Stormchaser2007
12:30 PM EDT on May 24, 2008
GFS showing it over Nicaragua now...this might inhibit strengthening in the next forecast hours...

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1006. atmoaggie
4:23 PM GMT on May 24, 2008
Does anyone know where I can sign up for free severe weather alerts to be received on my cell phone??

I just googled "cell phone severe weather alerts" and got many. TWC is one.

This looked cool: Link, but might involve too much in the way of ads or junk mail.

If you have unlimited text messages, you can put an email address in that will deliver text messages to your phone. For example:
verizon: [number]@vtext.com
sprint: [number]@messaging.pcs.com
att: i dunno

I get messages from work systems this way every time NDBC, NCEP, NRL, etc. has modeling or network problems.
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1005. SouthDadeFish
4:27 PM GMT on May 24, 2008
The GFS really forecasts the W Caribbean to moisten up around the 96 hour time frame, which just so happens to be right around the time it forecasts the low to develop.
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1004. 0741
4:29 PM GMT on May 24, 2008
has always been doing that lol. 850mb vorticity advection and moisture advection.

The latest run has it a bit more organized a stronger than the 06z run but forming in the same location and taking the same track so far. The other models should be avaliable soon. ECMWF should be avaliable later this afternoon. The GFS now develops the low in 102 hours.
keep us updated to new run TY
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1003. TerraNova
12:23 PM EDT on May 24, 2008
It has always been doing that lol. 850mb vorticity advection and moisture advection.

The latest run has it a bit more organized a stronger than the 06z run but forming in the same location and taking the same track so far. The other models should be avaliable soon. ECMWF should be avaliable later this afternoon. The GFS now develops the low in 102 hours.

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1002. 0741
4:13 PM GMT on May 24, 2008
here near miami airport it getting dark it look like trip see marlins play going to be cancel at 7:10pm
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1001. stoormfury
4:14 PM GMT on May 24, 2008
WHAT a lot excitement and intrigue. models are hinting devlopment in the Epac and others in the western carib. what separates the two probabilities is the isthmus of Panama. according to climatology both areas are favourable. what pans out could be anyone's guess. what i do know we are approaching the official start of the season, and yet conditions are not too conducive for cyclogenesis at this moment.
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1000. Drakoen
4:22 PM GMT on May 24, 2008
Well its doing the same thing on the 12Z run as it did on the 06z. Hugging the coast Nicaragua.
Member Since: October 28, 2006 Posts: 57 Comments: 29942
999. Ivansrvivr
4:18 PM GMT on May 24, 2008
StormW, your nasa sattelite loop is showing generally westerly surface winds in E-Pac. That is not what I would call "normal". There should be light easterlies in E-Pac now. That does make Caribbean more likely spot for development at the moment.
998. StormJunkie
4:20 PM GMT on May 24, 2008
Morning Gams :~)

Yep, they are going to be of the pop up on you type.
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997. atmoaggie
4:19 PM GMT on May 24, 2008
Hmmm, thanks BaHa.

Wonder if it will propagate to our GFS's genesis area by Thursday. Better chances for development N of 10 lat.
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996. Drakoen
4:20 PM GMT on May 24, 2008
994. StormJunkie 4:19 PM GMT on May 24, 2008
988.

And it looks like it is transitioning it from the E Pac on this run as well.


It has always been doing that lol. 850mb vorticity advection and moisture advection.
Member Since: October 28, 2006 Posts: 57 Comments: 29942
995. seflagamma
12:17 PM EDT on May 24, 2008
I just looked at our radar and it is clean; nothing on the radar for SE Florida at all!

I guess they are predicted to "develope" these storms we are under the watch for! LOL

See:

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994. StormJunkie
4:18 PM GMT on May 24, 2008
988.

And it looks like it is transitioning it from the E Pac on this run as well.
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993. atmoaggie
4:16 PM GMT on May 24, 2008
Alerts...I dunno.

Phone web browser access to NWS radar, severe statements, watches, and warnings...I use it all the time.

HTTP enabled wireless devices: mobile.weather.gov

WAP enabled wireless devices: cell.weather.gov
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992. hahaguy
12:18 PM EDT on May 24, 2008
that's interesting Baha
Member Since: August 12, 2007 Posts: 2 Comments: 2838
991. BahaHurican
12:13 PM EDT on May 24, 2008
Hmmm. Look how much higher the right-hand Twave is forecast to be.

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990. flsky
12:14 PM EDT on May 24, 2008
Does anyone know where I can sign up for free severe weather alerts to be received on my cell phone??
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989. atmoaggie
4:11 PM GMT on May 24, 2008
severe thunderstorm watch is being issued with nothing on the miami radar

Maybe should have had one here (SE LA) yesterday, too. Storms with a good wind, lightning, and a hard rain popped up very quick. All of the above while we still had bright sun light from the west. Sunny all the way through...neat.
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988. Drakoen
4:13 PM GMT on May 24, 2008
The GFS still wants its Caribbean system on the 12z run...
Member Since: October 28, 2006 Posts: 57 Comments: 29942
987. hahaguy
12:12 PM EDT on May 24, 2008
yes gamma we should be getting storms later today
Member Since: August 12, 2007 Posts: 2 Comments: 2838
986. seflagamma
12:09 PM EDT on May 24, 2008
good morning again, just catching up.
so us in S Fla should get some rain today an storms? sure hope the storms wait until I get off work at 7pm... LOL I doubt that; will probably be over with by then.

thanks for all the info.. will check back in later.
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985. CaneAddict17
4:02 PM GMT on May 24, 2008
You know its summer in south florida when a severe thunderstorm watch is being issued with nothing on the miami radar. Those storms are going to come quick.
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984. WhereIsTheStorm
4:06 PM GMT on May 24, 2008
962 CCHSweatherman
972 hurricane23

The local news channel just popped up a severe weather alert on the bottom of the TV. Case and point, I got the info here first.
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983. atmoaggie
4:05 PM GMT on May 24, 2008
Hmmmm.... Maybe I'll wash both cars instead..

I washed one car last weekend. Rained every day since, but one. It really works...too well.

Thanks WITS.

Later all. Putting hurricane straps on studs to rafters in my workshop (which my 3-yr-old calls my playhouse). Also leveling ground for above-ground pool.
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982. WhereIsTheStorm
4:00 PM GMT on May 24, 2008
969/967
You're welcome.
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980. nash28
4:04 PM GMT on May 24, 2008
Ok... Time for me to get crackin' outside. Be back later guys.
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979. Stormchaser2007
12:03 PM EDT on May 24, 2008
Hmmmm.... Maybe I'll wash both cars instead... That usually brings rain:-)O

LOL!
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978. Stormchaser2007
12:02 PM EDT on May 24, 2008
Little guy here has some possible not so little hail....

Link
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977. nash28
4:01 PM GMT on May 24, 2008
Not for me and StormW it appears...

So I can do my yard work in this ridiculous soupy air.

Hmmmm.... Maybe I'll wash both cars instead... That usually brings rain:-)O
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976. atmoaggie
3:57 PM GMT on May 24, 2008
I noticed that when I switched from Cable to DirectTV I no longer get the Local on the 8s

On Dish when I go to TWC, I get an interactive local forecast, current conditions, radar, etc. if I choose to invoke it. A little icon in the corner shows up and hit select to do so.

I can glean more real info out of that than I can from the on-air marketing professionals.
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974. Stormchaser2007
11:58 AM EDT on May 24, 2008
Well I better hold off my yard work today. The WRF is showing large area of showers and thunderstorms coming through the WPB area....
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973. StormJunkie
3:56 PM GMT on May 24, 2008
72hr 12z GFS still shows some left over 850mb vorticity in the area of the front moving off the E coast. Does not look like much, but still looks like a blob to watch at very least!
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972. hurricane23
11:57 AM EDT on May 24, 2008
000
FXUS62 KMFL 241551 CCA
AFDMFL

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MIAMI FL
1151 AM EDT SAT MAY 24 2008

...SEVERE THUNDERSTORM WATCH IN EFFECT FOR ALL OF MAINLAND SOUTH FL
UNTIL 9 PM EDT THIS EVENING...
...DAMAGING WINDS AND LARGE HAIL POSSIBLE...

.UPDATE...SENT PRODUCT UPDATES TO INCLUDE NEW SEVERE THUNDERSTORM
WATCH ISSUED BY THE STORM PREDICTION CENTER EFFECTIVE UNTIL
9 PM EDT THIS EVENING. THE WATCH ENCOMPASSES ALL OF MAINLAND
SOUTH FL AS SEVERE JUST CANNOT BE RULED OUT ANYWHERE.
HOWEVER...ORIGINAL EARLIER MORNING THOUGHTS ON THE FOCUS BEING FROM
LAKE OKEECHOBEE TO ALONG THE EAST COAST FROM PALM BEACH COUNTY
SOUTH TO MIAMI-DADE STILL LOOKS ON TARGET. DAMAGING WINDS AND
LARGE HAIL ARE THE MAIN THREATS WITH THE STORMS. AS IS ALWAYS THE
CASE THOUGH...WILL HAVE TO CLOSELY MONITOR STORMS ALONG
BOUNDARIES...ESPECIALLY THE ATLANTIC SEA BREEZE FOR A QUICK
TORNADO SPIN UP...BUT OVERALL THREAT IS FOR WIND/HAIL...WHICH
COULD EXTEND INTO THE EVENING HOURS DUE TO THE SHORTWAVE
ENERGY/PVA COMING IN FROM THE NORTH. /GREGORIA


Member Since: May 14, 2006 Posts: 8 Comments: 13640
970. Stormchaser2007
11:55 AM EDT on May 24, 2008
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967. StormJunkie
3:52 PM GMT on May 24, 2008
Good to see ya WITS and thanks :~)
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966. FLWeatherFreak91
11:52 AM EDT on May 24, 2008
omg the entire peninsula is under a sever t-storm watch EXCEPT TAMPA BAY!
Member Since: December 1, 2006 Posts: 2 Comments: 3619
965. nash28
3:52 PM GMT on May 24, 2008
That's exactly right JP. It's tough to pin the seabreeze to the coast to fire off the storms here. Usually, it collides N and E of the I-4 I-75 corridor.
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964. TerraNova
11:51 AM EDT on May 24, 2008
962. cchsweatherman
11:51 AM EDT on May 24, 2008
Severe Thunderstorm Watch
SEVERE THUNDERSTORM WATCH OUTLINE UPDATE FOR WS 346
NWS STORM PREDICTION CENTER NORMAN OK
1105 AM EDT SAT MAY 24 2008

SEVERE THUNDERSTORM WATCH 346 IS IN EFFECT UNTIL 900 PM EDT
FOR THE FOLLOWING LOCATIONS

FLC009-011-015-021-027-043-049-051-055-061-069-071-085-086-087-
093-095-097-099-105-111-117-119-127-250100-
/O.NEW.KWNS.SV.A.0346.080524T1505Z-080525T0100Z/

FL
. FLORIDA COUNTIES INCLUDED ARE

BREVARD BROWARD CHARLOTTE
COLLIER DESOTO GLADES
HARDEE HENDRY HIGHLANDS
INDIAN RIVER LAKE LEE
MARTIN MIAMI-DADE MONROE
OKEECHOBEE ORANGE OSCEOLA
PALM BEACH POLK SEMINOLE
ST. LUCIE SUMTER VOLUSIA
$$



--------------------------------------------------------------------------------
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961. WhereIsTheStorm
3:51 PM GMT on May 24, 2008
Good Morning Everyone,
I thought this might be something of interest to the group.
I noticed that when I switched from Cable to DirectTV I no longer get the Local on the 8s.
Of course, I still get all the latest info from the internet anyway, especially from this blog.
It also took the cable company 5 weeks to restore their service to this area after Wilma.

I would like to take this time to thank all the blogger for posting here; it is invaluable to many of us that don't normally post.
Thanks, StormW, Drakeon, SJ, 456, Patrap, CCHSweatherman, StormJunkie, atmoaggie, and all the rest. Sorry I couldn't list everyone.
Wanted to get this in before a blob showed up..LOL
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960. StormJunkie
3:48 PM GMT on May 24, 2008
Morning SW :~)

Something is up with your link. If you are trying to link to the GHCC site, it does not work that way.

Have to go in here, or actually post a still image in the blog.

That site is also one of the many great imagery sites on this page. Also find model, wind data, and preparedness pages from there.
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959. nash28
3:49 PM GMT on May 24, 2008
Yeah well.... It comes with living on the coast instead of inland.
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957. nash28
3:48 PM GMT on May 24, 2008
12z is at 48hrs now...
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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.