Mile-wide tornado smashes Windsor, Colorado; plus, hurricane season commentary

By: Dr. Jeff Masters , 1:23 PM GMT on May 23, 2008

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:

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
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

The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

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2207. nash28
1:43 AM GMT on May 26, 2008
What has my eye is the NOGAPS for now. Usually fairly conservative. Two straight runs spinning up a system in the CB, not the EPAC. For now anyways, the EPAC solution is fading.
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2206. kmanislander
1:42 AM GMT on May 26, 2008

Hi there

I only start to pay attention to models 48 hrs out.
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2205. Weather456
9:41 PM AST on May 25, 2008
2191. Patrap 9:37 PM AST on May 25, 2008
Why in the hell didn't Gilbert turn north and hit florida. It went through the Hebert box. So did Lily, and Ivan, and bunch of other damn hurricanes

Because they dont read the Blog..of course

LOL...this is too funny
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2204. Michfan
8:42 PM CDT on May 25, 2008
Michael needs to chill out a bit. Those who take this blog too seriously need to be on meds.
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2202. nash28
1:41 AM GMT on May 26, 2008
Michael. You seem to be a bit on edge.

Maybe you oughta take a cue from some on here...
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2200. kmanislander
1:37 AM GMT on May 26, 2008

May is supposed to be a wet month in the Caribbean but so far this year nothing.

Would I be surprised if precip showed up soon, absolutely not. Having said that, I do know from years of watching the Caribbean that tropical systems do not ramp up quickly in June or October and November.

The MJO pulse will not change history.
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2199. Stormchaser2007
9:39 PM EDT on May 25, 2008
Sorry MLC....I was just thinking of that graphic soon after I read your post....
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2197. Stormchaser2007
9:38 PM EDT on May 25, 2008
Sorry didnt see your post...
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2195. moonlightcowboy
8:38 PM CDT on May 25, 2008
Thanks, Chaser, I was just about to post that.
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2194. nash28
1:38 AM GMT on May 26, 2008
Hell, even Lixion got shown up last year a bit! It happens.
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2193. Stormchaser2007
9:36 PM EDT on May 25, 2008
Speaking of MJO....

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2192. nash28
1:36 AM GMT on May 26, 2008
The boxes are there. But Mother Nature dictates where they go. The upper level synoptics change so rapidly it's difficult to call. How many times have seasoned Mets had their ass handed to them on the forecast?

Momma Nature has the last say.
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2191. Patrap
8:36 PM CDT on May 25, 2008
Why in the hell didn't Gilbert turn north and hit florida. It went through the Hebert box. So did Lily, and Ivan, and bunch of other damn hurricanes

Because they dont read the Blog..of course
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2190. SouthDadeFish
1:35 AM GMT on May 26, 2008
Chaser no need to be sorry :~) I'm not even sure if I'm right lol just making a guess from what I read. But yeah I also think the boxes are just coincidence. Well I mean its to do with climatology and that this area usally favors a Floria landfall but by no means says that it is guaranteed.
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2188. moonlightcowboy
8:33 PM CDT on May 25, 2008
K'man, I posted the MJO comment to see what your thoughts were with it maybe bringing some precip. Do you think the models are calculating this?

btw-I'm in agreement with your take on the models.
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2187. Michfan
8:32 PM CDT on May 25, 2008
The boxes are nothing but a straight up statistical analysis of historical tracks.
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2186. nash28
1:33 AM GMT on May 26, 2008
Pretty favorbale JRRP.
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2185. Stormchaser2007
9:32 PM EDT on May 25, 2008
2180. Oh sorry about that I didnt see that part of his post....
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2184. moonlightcowboy
8:32 PM CDT on May 25, 2008
I like Pat's HBox opinion - I've never followed that, but some people may! And, there may be some truth to it, I've just never paid it much mind.
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2183. Stormchaser2007
9:31 PM EDT on May 25, 2008
imho the hebert boxes are bs.

Yeah there just pure luck.....
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2182. kmanislander
1:28 AM GMT on May 26, 2008
If there is rain where the models are forecasting a storm later this week I will be impressed.

So far, the early season does not appear to me to be getting ready to produce a tropical system. There is nothing out there, other than computer models, to suggest that there is a transition in the works for the Caribbean
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2181. JRRP
1:29 AM GMT on Mayo 26, 2008
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2180. SouthDadeFish
1:28 AM GMT on May 26, 2008
2169, it did but the information MLC posted says usually they hit Florida when storms go through there late in the year so I'm guessing Dean was earlier than this "later" time period.
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2179. Stormchaser2007
9:29 PM EDT on May 25, 2008
Hey what are you guys using for monitoring the Tropical waves since RAMMB has shut down that area to civilians? I know there was some other nice links that i had but I recently had my computer wiped and I lost all my links...
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2178. StormJunkie
1:30 AM GMT on May 26, 2008
Post landing commentary and first images starting now.
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2177. moonlightcowboy
8:26 PM CDT on May 25, 2008

The phase diagram shows the last 40 days of the phase and amplitude of the MJO. Counter-clockwise movement around the diagram indicates an eastward propagating signal across eight phases from the Indian Ocean to the Pacific and later the western hemisphere. Color of lines distinguish different months and dates are marked. The farther away from the center of the circle the stronger the MJO signal.

So, the MJO appears to be in Phase 8, or in the western hemisphere showing a considerably stronger pulse as it moves eastwards.
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2176. juniormeteorologist
1:29 AM GMT on May 26, 2008
i just took another look at the gfs models, and it is still showing that disturbance hitting southern florida on Monday-Tuesday. I believe that this week will be interesting..Maybe it will be a named storm be June 1! But I will try to make a prediction of this system in a few.
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2175. Patrap
8:29 PM CDT on May 25, 2008
Voodoo tropical Economics

Hebert Boxes.
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2174. nash28
1:29 AM GMT on May 26, 2008
It's called blob withdrawl!!!!

Sorry, winter storms are about as exciting as a sock drawer!
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2172. JRRP
1:25 AM GMT on Mayo 26, 2008
2165: good information
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2171. hahaguy
9:28 PM EDT on May 25, 2008
imho the hebert boxes are bs.
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2170. Stormchaser2007
9:28 PM EDT on May 25, 2008
hey guys! I am back..are you guys still talking about those disturbances in the atlantic?

Nothing out there yet....
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2169. Stormchaser2007
9:26 PM EDT on May 25, 2008
Didn't Dean this year pass through Herbert box No.2? I know that there was the large high blocking Dean but still it puts a little nick in the theory....IMO
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2168. juniormeteorologist
1:25 AM GMT on May 26, 2008
hey guys! I am back..are you guys still talking about those disturbances in the atlantic?
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2167. Stormchaser2007
9:18 PM EDT on May 25, 2008
If theres a storm or anything close to a storm near where the GFS is forecasting the potential systsem to be then I would be very impressed due to the fact that it was forecasting the possible system about a week out and that the other models (CMC and NOGAPS) models have come on board just recently. Also the GFS is forecasting a very low shear scenario across the MDR region and most of the Caribbean with the exception of the Florida region. Im very interested in what will play out next week.
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2166. hahaguy
9:23 PM EDT on May 25, 2008
actually i already knew about the hboxes lol . i was just asking if anyone believed in it
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2165. moonlightcowboy
8:21 PM CDT on May 25, 2008
-- HaHa, here you go and any others that might be interested.

Many people visiting hurricanecity have asked "what is this hebert box I keep hearing about"?. The HebertBox was "discovered" in the late 1970s by Paul Hebert. This former nws & nhc forecaster found many major hurricanes that hit South Florida had to first pass through these boxes.

This image shows the two Hebert boxes.

The first box is located east of Puerto Rico and the second box is located over the Cayman Islands.

Every Major Hurricane that passed through Box 2 late in the year, hit the Florida peninsula prior to 1950. Hebert says that a Hurricane does not have to pass through these boxes to hit, but if they do "you better pay attention". The 1935 Labor day Hurricane that devastated the Florida Keys developed west of this box and Hurricane Andrew passed NE of this box, so there are exceptions to the rule.

If Floridians want an indication of a possible hit they need to keep an eye on any hurricane that passes through these boxes. Nearly every major Hurricane that hit S Florida since 1900 passed through these boxes. When major Hurricanes miss these boxes,they virtually always miss South Florida. If a major Hurricane moves into these boxes South Florida really needs to watch out. These boxes approx 335 miles x 335 miles includes the Virgin Islands but not Puerto Rico. The pattern has proven accurate for 9 out of 10 storms storms that developed & hit Dade,Broward & Palm Bch Counties. The following is a list showing Hurricanes that passed through these Boxes,starting with Box #1.

BOX #1 (since 1950)
1950 Baker--Alabama....1950 Dog--out to sea....1951 Charlie--Yucatan/Mexico....1952 Baker-- out to sea....1953 Carol--Nova scotia....1954 ALice--Leeward isl out to sea....1955 Connie--N Carolina....1955 Ione--N Carolina....1956 Betsy--N Antilles, PR,Bahamas....1958 Fifi--out to sea....1958 Ilsa--out to sea....1960 DonnaN Antilles,Bahamas,Fla,east seaboard....1963 Edith--windward isl,PR,Hispaniola....1964 Cleo--N Antilles,Hispaniola,Haiti,Cuba,Fla....1966 Faith--N Antilles....1966 Inez--N Antilles,Hispaniola,Haiti,Cuba,Bahamas,Fla,Yucatan,Mex....1967Beulah--Hispaniola,Yucata,S Texas....1975 Eloise--Hispaniola,Fla panhandle....1979 David--Antilles,Hispaniola,Haiti,Fla,Ga,Sc....1984 Klaus--out to sea....1985 Gloria--NE U.S....1989 dean--Bermuda,Newfoundland....1989 Hugo--N Antilles,PR,SC....1990 Klaus-- out to sea....1995 Luis--N Antilles,New foundland....1995 Marilyn--N antilles,VI.PR....1996 Bertha--N antilles,VI,PR,N carolina....1996 Fran--N Carolina....1996 Hortense--PR,Nova scotia....1997 Erika--out to sea....1998 Georges--N antilles,VI,PR,Hispaniola,Haiti,Cuba,Keys,mississippi....1999 Jose--N antilles,VI....1999 Lenny--N antilles....2000 Debby--n antilles,VI,Hispaniola....2004 FrancesBahamas,Treasure coast,Fla....

BOX #2 (since 1950)
1951 Item Cayman isl,Cuba....1952 FoxCaymans,Cuba,Bahamas....1961 HattieBelize....1981 KatrinaCuba,Bahamas....1988 GilbertYucatan,mexico....1995 RoxanneYucatan....1998 MitchHonduras....2001 irisBelize....2001 MichelleCuba,Bahamas....2004 Charley W cuba,Fla....2005 EmilyYucatan,Mexico....2005 WilmaYucatan,S Fla....

So what does all this mean when a hurricane passes or develops in the Hebert Box east of Puerto Rico since 1950?

1) N Carolina has as much of a chance to get hit as Florida.
2) 20.58% or most go out to sea without hitting land.
3) Only 8.82% make it into the Gulf of Mexico when they pass through the box as a hurricane.
4) Puerto Rico will get hit 20.58% of the time (the highest outside of n Antilles).

What about Box #2, hurricanes developing or moving through after Oct 1st since 1950?

Cuba & the Bahamas are at highest risk late in the season.

To wrap things up, two significant Hurricanes that hit South Fla did not pass through this box, Andrew 1992, and Betsy 1965!. Data may be slightly off because these boxes were based on data going back to 1900. We chose named storms since 1950 for recognition purposes.

(all above info from hurricanecity)
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2164. HadesGodWyvern (Mod)
1:20 AM GMT on May 26, 2008
2154. Stormchaser2007 1:16 AM GMT on May 26, 2008
Hades whats the next name that will be used if this thing develops??

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2163. Michfan
8:21 PM CDT on May 25, 2008
God forbid if a Cat 5 anarchy
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2162. JLPR
9:19 PM AST on Mayo 25, 2008
yep weather Puerto Rico =)
Im amazed that no hurricane has passed since Georges they all or go North of us, or go south of us =P
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2161. hahaguy
9:19 PM EDT on May 25, 2008
serinity now lol
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2160. pottery
9:16 PM AST on May 25, 2008
WHOA...2150 posts, in 2 days, in May. And there aint a cloud anywhere to be seen anywhere.
Someone said there is going to be a cloud next week, and ZING.......

LOL man.
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2159. Weather456
9:16 PM AST on May 25, 2008
2148. JLPR 9:13 PM AST on May 25, 2008

Neither do I...10-9 years free. Btw, ur from PR right? 10 yr anniversary of Hurricane Georges this yr.
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2158. StormJunkie
1:17 AM GMT on May 26, 2008
the serinity prayer.

lol, it will be used much this season, for many, by many, and for many reasons!
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2157. Michfan
8:16 PM CDT on May 25, 2008
Also noticing on the 18z GFS that its predicting that same anticyclone to setup 10 days out above the low pressure system.
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Cat 6 lead authors: WU cofounder Dr. Jeff Masters (right), who flew w/NOAA Hurricane Hunters 1986-1990, & WU meteorologist Bob Henson, @bhensonweather

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