Dr. Jeff Masters' WunderBlog

Mile-wide tornado smashes Windsor, Colorado; plus, hurricane season commentary
Posted by: Dr. Jeff Masters, 13:23 GMT le 23 mai 2008 +2
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
Categories: Tornado
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2101. StormJunkie 00:09 GMT le 26 mai 2008    
lol mlc!
Member Since: 17 août 2005 Posts: 26 Comments: 15240
2102. Drakoen 00:10 GMT le 26 mai 2008    
I'll be here for the first picture and the 00z GFS run LOL...
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2103. StormJunkie 00:10 GMT le 26 mai 2008    
Sure you are listening mlc, but just in case, 90 minutes until first pictures :~)
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2104. nash28 00:11 GMT le 26 mai 2008    
Just fantastic! I myself am speechless.
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2105. aspectre 00:11 GMT le 26 mai 2008    
First pictures from the Phoenix due in about an hour and a half.
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2106. surfmom 00:12 GMT le 26 mai 2008    
hopefully this is the start of a future job for my young buck - his eyes are sparkling with excitement watching the control crew etc. (thanks for the great links patrap) This is what gives our kids hope, direction and purpose - what a terrific "UP" for all of us. It's all been rather dismal news lately --this is just GREAT! Watching my kid view this, I see he recognizes his dreams can be a reality! It makes all his geometry, algebra, science, chem, etc. have a purpose!
Member Since: 18 juillet 2007 Posts: 30 Comments: 26538
2107. StormJunkie 00:12 GMT le 26 mai 2008    
Ditto nash, can not wait until we get to put a foot down over there. Can only hope I get to live long enough to see it.
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2108. surfmom 00:13 GMT le 26 mai 2008    
a rare moment Nash! ...hee hee
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2109. Cavin Rawlins 00:14 GMT le 26 mai 2008    
A possible tropical wave across West Africa



This is no doubt an african easterly wave across Central Africa



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2110. moonlightcowboy 00:14 GMT le 26 mai 2008    
2103. Yeah, SJ, listening! What a happy crew...still hearing lots of laughter. UofA now takes on the mission - .25 degree tilt? That's like perfect! WTG, NASA!

Yeah, those pictures should be awesome!!!
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2112. StormJunkie 00:16 GMT le 26 mai 2008    
Dude said pucker factor....lmao :c)
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2113. Drakoen 00:17 GMT le 26 mai 2008    
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2114. moonlightcowboy 00:18 GMT le 26 mai 2008    
456, sure seems CV is shooting pretty hard, fairly early - like a sling shot pulling back ready to fire all that potential energy. Does this seem normal to you, timeliness and frequency, now, at which they're rolling off? Or is it just me noticing them more?
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2115. Drakoen 00:18 GMT le 26 mai 2008    
Yea W456, I was just looking at the EUMETSAT animations on that.
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2116. surfmom 00:20 GMT le 26 mai 2008    
older son graduates as a commercial diver/diver EMT & underwaterwelding --graduates this Friday...looks like a job in the gomex or Malta. If it's the gulf - should be interesting.

younger son dreams of doing some kind of engineering for the space program - this kind of an event really stokes the fires in a kid.

So I'll have one working the heavens, the other under the sea.
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2117. Cavin Rawlins 00:20 GMT le 26 mai 2008    
2093. moonlightcowboy 8:03 PM AST on May 25, 2008
2078. Gotcha 456, but weeks ago we came to consensus in here that most dust rides at the mid-levels. The cATL shows really nothing in the upper levels and only a spot in the mids. Water vapor looks plentiful and Navy's TPW product pretty much reflects that, too.


Ur correct, and I just check TRMM measurements...near-above normal moisture out there.
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2118. Patrap 00:21 GMT le 26 mai 2008    
Join Barometer Bob for The 2008 Hurricane Preparedness Week will be held May 25th through May 31st.


Bob will be hosting "Hurricane Hollow's Hurricane Awareness Week" Internet Broadcasts each evening beginning at 8PM/ET on WRBN.Net with your host Barometer Bob Brookens and special guests.


Scheduled Guests

Sunday May 25 - Lew Fincher, from HurricaneConsulting.Net. You have seen him on the History Channel special about "Isaac's Storm" the 1900 Galveston Hurricane.
Monday May 26 - Jamie Rhome, Hurricane Specialist at the National Hurricane Center.
Tuesday May 27 - Bob Breck, Chief Meteorologist from WVUE-TV - Fox 8 in New Orleans, LA.
Wednesday May 28 - Laura Algeo, FEMA Region IV, National Flood Insurance Program.
Thursday May 29 - Eric Blake, Hurricane Specialist at the National Hurricane Center. We will also have Butch Loper "AKA sandcrab", Emergency Operations/Civil Defense Director for Jackson County, MS.
Friday May 30 - Leslie Chapman-Henderson, Director of FLASH.Org.
Saturday May 31 - Michelle Jantz Manager, Program Management and Support Preparedness and Health and Safety Services from the American Red Cross.

Hurricane Hollow's Eye on the Storm June 1st Broadcast

I will have special guests, callers and you can join us in Storm Chat!
My guests include:
Spokeperson from 511 the Traffic Information Portal.
Gary Padgett, from the Tropical Cyclone Summeries.
And more! Stay tuned for more information on the 8 nights of broadcasts from www.WRBN.Net!


Come join in chat for a full week of Hurricane Prepardness.

Show Link Link

StormChat Link
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2119. surfmom 00:24 GMT le 26 mai 2008    
have a good evening all, thanks for those phoenix links, and keep an eye on what's cooking in the BOC ---I like seeing those channel swell waves visit my beach from there.
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2120. Cavin Rawlins 00:27 GMT le 26 mai 2008    
2114. moonlightcowboy 8:18 PM AST on May 25, 2008
456, sure seems CV is shooting pretty hard, fairly early - like a sling shot pulling back ready to fire all that potential energy. Does this seem normal to you, timeliness and frequency, now, at which they're rolling off? Or is it just me noticing them more?


The frequency is matched with 2005 and to some extent 2004. We have a little more than 2004. But thats not really what suprises me, its the organization of these waves in May. They are not normal. I have spotted several waves this month that had the organization of June, July and August waves. The only difference between these waves and the ones found during those months is the latitude. What is also extraordinary is that one of these waves aquired a close circulation. If another waves attempt that even late next month or July at 10-15N with more moisture, less shear....1 plus 1 equals 2.
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2121. Drakoen 00:29 GMT le 26 mai 2008    
I think in July we could see a CV storm or 2 form easily especially judging from the anomalously high precip values that area forecast by the CFS and ECMWF..
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2122. moonlightcowboy 00:30 GMT le 26 mai 2008    
2120. Thought so, thanks. 1 + 1 = T R O U B L E, ugh!
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2123. FLWeatherFreak91 00:34 GMT le 26 mai 2008    
This season will have all different types of storms like many of them do but I can almost totally assure you it will be known as mainly a bad CV season. 456 is correct about the overly high organization of these early waves. In years past i can't recall talking about an atlantic wave until mid or late july
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2124. hahaguy 00:34 GMT le 26 mai 2008    
Does anyone believe the hebert box box? truthfully i dont.
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2125. keywestdingding 00:37 GMT le 26 mai 2008    


i wonder if they will ever fix the sst's on here. most of the GOMex is already at 80.
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2126. moonlightcowboy 00:38 GMT le 26 mai 2008    
I know if "ifs and butts" were candy and nuts, we'd all have a merry Christmas; BUT, that last wave with the closed low would have probably developed absent the TUTT - prolly a fish storm, but could have real easily been our first invest, first storm. Granted a right turn would have found cooler waters though. Still, very interesting so early in the season (May), lol!
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2127. Cavin Rawlins 00:39 GMT le 26 mai 2008    
090. aspectre 7:02 PM CDT on May 25, 2008
....Welcome to the North Pole of Mars."


I am a big fan of mars....I want them to confirm frozen water and find some sort of present or signs of past life. It would be awesome of that rover could melt a sample of the ice.
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2128. Cavin Rawlins 00:44 GMT le 26 mai 2008    
Speaking of the TUTT....remember the TUTT is maintained by subsidence in the subtropical ridges. If those ridges are forecasted to be weaker than normal, then that is an idicator of the strength and nature of the TUTT. An example would be to look at two years on different ends of the spectrum:

2007 and 2004
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2130. moonlightcowboy 00:48 GMT le 26 mai 2008    
2128. 456, ok, expand, plz, on that comment. TIA
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2131. hahaguy 00:51 GMT le 26 mai 2008    
does anyone actually believe the theory about the Hebert boxes?
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2132. Cavin Rawlins 00:52 GMT le 26 mai 2008    
2130. moonlightcowboy 8:48 PM AST on May 25, 2008
2128. 456, ok, expand, plz, on that comment. TIA


Remember when I posted the graphic ealrier in the yr.

Also,

2007 - Positive NAO ridge, potent TUTT
2004 - Negative NAO, weak TUTT
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2133. moonlightcowboy 00:54 GMT le 26 mai 2008    
Ok, then we can expect less and weaker TUTTS; again, trouble. hhhhhmmmm!
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2134. JLPR 00:55 GMT le 26 mai 2008    
I hope this season gets 30 storms with 28 being fish storms =)
if not then can I have only 12 storms =)
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2135. moonlightcowboy 00:59 GMT le 26 mai 2008    
456, do you still have that graphic close? If not, no big deal. Thanks.
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2136. JLPR 01:00 GMT le 26 mai 2008    
Hey Weather456 considering the fact that 08 may have an active cape Verde season and with the amount and the organization of the tropical waves in May do you think the islands are in for a bad season?
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2137. moonlightcowboy 01:01 GMT le 26 mai 2008    
- haha, I've heard several talk about the HBox before, but I've not gotten a great deal out of it's theory. Baha could probably give some good info on that!
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2138. Cavin Rawlins 01:06 GMT le 26 mai 2008    
MLC I will try to find it and post it


2136. JLPR 9:00 PM AST on May 25, 2008
Hey Weather456 considering the fact that 08 may have an active cape Verde season and with the amount and the organization of the tropical waves in May do you think the islands are in for a bad season?


I am afraid to answer lol, but in my forecast and other forecasts put out by Caribbean mets...it appears the Caribbean is at a higher risk especially the northern part. But that does not mean anything....Every year we get affected by hurricanes, that is one thing I can guarantee.
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2139. kmanislander 01:08 GMT le 26 mai 2008    
I have been watching the discussions on the blog about the various models forecasting a NW Caribbean system at the end of this week.

Climatology has shown year after year that if tropical systems do develop in either the early or late part of the season they tend to do so in the Southern Caribbean. In addition, such development tends to be very slow, often taking 4 to 5 days to produce a closed low.

Given the extremely dry conditions seen so far and still prevailing in the Caribbean I would be surprised if the models verify with a tropical cyclone in 5 to 7 days. Looking at the basin now there is not even a rain shower around.

To go from this to a well organised system by the end of this week is, in my opinion, more than a stretch
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2140. hahaguy 01:09 GMT le 26 mai 2008    
hey kmanislander how are you doing tonight.
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2141. pottery 01:10 GMT le 26 mai 2008    
All Americans should feel justifiably proud, of that incredible piece of precision engineering.
Amazing performance by all concerned.
Congratulations..........
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2142. Stormchaser2007 01:10 GMT le 26 mai 2008    
Hello all, hows everyone tonight!!
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2143. moonlightcowboy 01:10 GMT le 26 mai 2008    
K'man, hey! Makes plenty of sense to me, lots of dry air hangin' round those parts.
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2144. Michfan 01:10 GMT le 26 mai 2008    
Looks like the GFS is aiming for the Panhandle of Florida. I still see that it has a 1034 mb high forecast that far out but with a trough weakening its western side as the low pressure moves north through the gulf. Can't wait to see the 00Z run says. Looks like the season is going to start at the very least with a bang. They have us model watching already.
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2145. kmanislander 01:11 GMT le 26 mai 2008    
Hi there haha

Just throwing in my 2 cents worth

I think that too much reliance is being placed on computer generated storms.

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2146. kmanislander 01:12 GMT le 26 mai 2008    
Hi MLC

If the Caribbean can go from bone dry with major subsidence to tropical storm in 6 days that would be a first !
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2147. Stormchaser2007 01:12 GMT le 26 mai 2008    
Jeez dont all answer at once......
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2148. JLPR 01:13 GMT le 26 mai 2008    
ahh lol Weather456
I have been 10years hurricane free I am afraid something ends that time of peace =(

But I guess that comes with living on an island in the ocean =P
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2149. Michfan 01:13 GMT le 26 mai 2008    
The most interesting thing about the models is seeing if they are actually right in the long run. I think most of us like to see if they do in fact predict cyclogenesis fairly well.
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2150. hahaguy 01:13 GMT le 26 mai 2008    
i'm pretty good how bout you chaser.
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2151. StormJunkie 01:13 GMT le 26 mai 2008    
2141 :~))

2145...
So now the government is using computers to generate a storm that will hit Pensacola next week ¿~)
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About JeffMasters
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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