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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207. hahaguy
3:02 PM EDT on May 23, 2008
ah i see the sst's are heating up nicely
Member Since: August 12, 2007 Posts: 2 Comments: 2838
206. moonlightcowboy
2:00 PM CDT on May 23, 2008


Member Since: July 9, 2006 Posts: 184 Comments: 29594
204. moonlightcowboy
1:55 PM CDT on May 23, 2008
Thanks, StormW. Doesn't it also help with shear?
Member Since: July 9, 2006 Posts: 184 Comments: 29594
203. moonlightcowboy
1:55 PM CDT on May 23, 2008
Photobucket
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200. moonlightcowboy
1:46 PM CDT on May 23, 2008
JP, it's centered over the coastline, now. My guess would be that it gets over into the P basin as there is a big easterly flow to its north. Again, just a guess!
Member Since: July 9, 2006 Posts: 184 Comments: 29594
199. floridastorm
6:41 PM GMT on May 23, 2008
looks like the GFS has a tropical cyclone over
florida on day 12
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198. Weather456
2:44 PM AST on May 23, 2008
193. StormW 2:34 PM AST on May 23, 2008
191. AWeatherLover 2:27 PM EDT on May 23, 2008
Hey storm, how have you been? What are you think about the new GFS runs?

Been good! You?

Have to see. I was just running over some satellite loops, and looks like the bulk of the energy and cyclonic turning is in the EPAC. The GFS may not be wrong, but I'm more apt to go with the ECMWF, as it's to my understanding, most models are 3 dimensional, and the EURO is a 4 dimensional model. I have no idea what all it looks at, but supposedly it is one of the better models. I know the past couple of seasons, it's outdone the GFS on nailing tropical systems, especially on the Pacific side.



1. Thats true

2. Thanks for that info, I didnt know that about the EURO model.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
196. moonlightcowboy
1:40 PM CDT on May 23, 2008
194. JP, first thought is that it helps to keep shear lower.

StormW, anyone?
Member Since: July 9, 2006 Posts: 184 Comments: 29594
195. moonlightcowboy
1:37 PM CDT on May 23, 2008


June cyclogenesis climatology.
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192. moonlightcowboy
1:28 PM CDT on May 23, 2008
186. Yes, JP, it is.
Member Since: July 9, 2006 Posts: 184 Comments: 29594
191. AWeatherLover
6:24 PM GMT on May 23, 2008
Hey storm, how have you been? What are you think about the new GFS runs?
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189. HurricaneSammy
6:24 PM GMT on May 23, 2008
182. NEwxguy 6:20 PM GMT on May 23, 2008
a lot storms bubbling up in Florida

Statement as of 2:20 PM EDT on May 23, 2008


The National Weather Service in Miami has issued a

* Severe Thunderstorm Warning for...
central Broward County in South Florida.

* Until 315 PM EDT

* at 219 PM EDT... National Weather Service Doppler radar indicated a
severe thunderstorm capable of producing nickel size hail... and
damaging winds in excess of 60 mph. This storm was located near
Coral Springs... and moving southwest at 6 mph.

* The storm will affect...
Coral Springs...
Tamarac...
sunrise...
and surrounding communities.

The Police Department in Coral Springs reported nickel size hail at
wiles and rock inland Road at 210 PM with this storm.

Severe thunderstorms can also produce tornadoes with little or no
advance warning. Prepare to move to a place of safety in an interior
room in the lowest floor of your house or business if a tornado is
spotted.

Report severe weather or damage to the nearest law enforcement agency
or your County emergency management. They will relay your report to
the National Weather Service forecast office in Miami. Or you can
also call the National Weather Service in Miami directly at
305.229.4528 to report severe weather.

Lat... Lon 2606 8028 2617 8047 2632 8031 2626 8014
time... Mot... loc 1820z 041deg 5kt 2624 8027





216 PM EDT Fri may 23 2008

... A Severe Thunderstorm Warning remains in effect until 245 PM EDT
for northeastern Broward County...

At 215 PM EDT... National Weather Service Doppler radar continued to
indicate a severe thunderstorm capable of producing damaging winds in
excess of 60 mph. This storm was located between Margate and Coral
Springs. This storm was nearly stationary.

The severe thunderstorm will be near...
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188. atmoaggie
6:24 PM GMT on May 23, 2008
Probably not a direct response, but this is a little strong.
Buoy 42056...well NW of 456's W. Caribbean low:
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187. Ivansrvivr
6:10 PM GMT on May 23, 2008
456, that surface low is likely being enhanced by or caused by topography. The coastline shaped the way it is in that area supports counterclockwise turning of the winds due to sea/land interaction. Similar to the seabreeze/landbreeze effect in Florida. That is part of what makes that area so favorable for development early and late in the season. When the E-Pac is active, such systems usually migrate westward and or get absorbed by E-Pac systems. If that is an actual developing low, watch to see if it lasts through the night. If the spin disappears at night, it was simply caused by topography. If it lasts through the night, then the topography will actually help it to develop if it doesn't move westward.
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185. Weather456
2:12 PM AST on May 23, 2008
173. AWeatherLover 2:11 PM AST on May 23, 2008
164- weather456: is that the low the GFS was developing or is it something else completely?


Frankly, that current low is a suprise to me...didnt expected one to be down there. But that current low does not fit the location and time frame of the latest GFS model. The model begins developing the SW caribbean system around the 28th. Development of this wave may occur in the EPAC tho according to the 12 CMC run.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
184. TerraNova
2:21 PM EDT on May 23, 2008
Concerning the possible cyclone next week...

EPAC
CMC 12z
UKMET 12z (Although it shows a very weak low pressure area in the SW Caribbean)
NOGAPS 00z
NAM 12z
ECMWF 00z (Although it shows a weak low pressure center in the SW Caribbean)

SW Caribbean/Atlantic
GFS 12z
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182. NEwxguy
6:18 PM GMT on May 23, 2008
a lot storms bubbling up in Florida
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181. moonlightcowboy
1:15 PM CDT on May 23, 2008


Latest Available 850mb Vorticity

The lows are clearly showing up.
Member Since: July 9, 2006 Posts: 184 Comments: 29594
179. HurricaneSammy
6:16 PM GMT on May 23, 2008
174. StormW 6:14 PM GMT on May 23, 2008
Hey Alicia!


Your Back !
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178. atmoaggie
6:16 PM GMT on May 23, 2008
Bayou-welcome

Bonjour, cher.
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177. HurricaneSammy
6:13 PM GMT on May 23, 2008
FLA RAINS !

http://www.wunderground.com/radar/mixedcomposite.asp?region=d5&size=2x&ID=AMX19
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176. TheCaneWhisperer
6:12 PM GMT on May 23, 2008
Just the presence of a low in the W Caribbean has to lend the GFS "SOME" credit. It might not be so far fetched after all.
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173. AWeatherLover
6:06 PM GMT on May 23, 2008
164- weather456: is that the low the GFS was developing or is it something else completely?
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172. Weather456
2:08 PM AST on May 23, 2008
169. atmoaggie 2:06 PM AST on May 23, 2008
Another Low
\
That is remarkibly close to the developments in the GFS runs of late. If it deepens through the weekend and drifts NNW, the GFS becomes somebody's girlfriend around here.

Who said that?


LOL....I did...cane said it would be his wife.
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171. hahaguy
2:06 PM EDT on May 23, 2008
ok thanks alot ivan
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170. groundswell
6:04 PM GMT on May 23, 2008
Bayou-welcome....One always hopes they don't get hit, LA sure doesn't need another. But of course, someday it will happen again, just don't know when.
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169. atmoaggie
6:04 PM GMT on May 23, 2008
Another Low
\
That is remarkibly close to the developments in the GFS runs of late. If it deepens through the weekend and drifts NNW, the GFS becomes somebody's girlfriend around here.

Who said that?
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168. Ivansrvivr
5:53 PM GMT on May 23, 2008
159, it depends on where the storms form and or which way they move early. A few miles early in the track will make a huge difference in landfall location later. The pattern that steered all the storms into FL in 04 would have steered them into Carolinas if they had developed or moved slightly north of the way they did(except for Jeanne). Had Francis moved north of the Islands, it would have easily been a Carolina storm. Charley and Ivan hit FL out of the Caribbean. It was the southerly location of where those storms formed that had a major influence on Florida getting hit 4 times. If CV storms stay weak, or continue rolling off Africa between 5 and 10N and dont develop early and recurve it may not be Carolina year. If the favored storm track trends north of Puerto Rico, those will most likely head up the Eastern seaboard.
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167. moonlightcowboy
12:59 PM CDT on May 23, 2008
163. Good point, too. Really not much shear, comparatively, unless it's about there in the eATL where the TUTT is.

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166. Weather456
2:00 PM AST on May 23, 2008
- 456, has thing been out there 24 hours yet? When was the low added to the wave? It may be so far out, and little chance of making it that an invest won't be considered.

The low became notable around 07Z this morning...it was added to the TPC maps at 12Z this morning. The wave has been out there since Tuesday. It first display mid-level turning on Wednesday and Thursday, then this morning I discovered it had reached the surface.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
165. Bayoucanetracker
12:46 PM CDT on May 23, 2008
First time posting all, i had to jump off the fence...been watching in the background, after working in the gulf for 9yrs. Hoping we have a season of misses like last year...missing the LA coast that is...
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164. Weather456
1:47 PM AST on May 23, 2008
Another Low

Source QuikSCAT

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163. franck
5:58 PM GMT on May 23, 2008
Shear dropping significantly in the Gulf of Mexico.
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162. TexasGulf
5:50 PM GMT on May 23, 2008
I know. Been to Covington a few times. There are a few areas that flood, but mostly that area drains well INTO Lake Ponchartrain. There are a few areas of Covington where I wouldn't write a policy, but I'd be more worried about the tree falling risk (esp. around Sanctuary) than flooding.

If MY house gets flooded, Houston and the entire nation are in trouble. Lake Houston would have to rise by 18 feet... 10 feet above the spillway for my house to get an inch of water. If that happens, the whole San Jacinto river valley all the way to the coast will be completely under water. The entire Downtown Houston area would have nearly 40-feet of sea water if my house has an inch.

Still... we are a flooding risk, especially if a large asteroid slams into the gulf. Hah.
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161. Ivansrvivr
5:44 PM GMT on May 23, 2008
456, climatology and SSTs favor the E-Pac now. The warmer than normal SSTs in the E-Pac compared to the average SSTs in the Caribbean make the E-Pac look like the most favorable area early in the season. I expect the E-Pac to be quite active early based on SSTs, which makes early W.Caribbean activity look unlikely. This could easily be season that starts with CV activity or with development along stalled front in GOM or near Bahamas.
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160. Patrap
11:15 AM CDT on May 23, 2008
wdsu.com interactive radar. Nola Link
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159. hahaguy
1:49 PM EDT on May 23, 2008
so now its looking like a carolina yearr?
Member Since: August 12, 2007 Posts: 2 Comments: 2838
158. moonlightcowboy
12:47 PM CDT on May 23, 2008
Nice ob, Ivan. And, of all of that is just nauseating.

Photobucket

- 456, has thing been out there 24 hours yet? When was the low added to the wave? It may be so far out, and little chance of making it that an invest won't be considered.
Member Since: July 9, 2006 Posts: 184 Comments: 29594
157. NEwxguy
5:42 PM GMT on May 23, 2008
severe th strm warning around boca raton

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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.