DenverMark's WunderBlog

Front Range Tornado Climatology

By: DenverMark, 10:51 PM GMT on May 22, 2008

TORNADO CLIMATOLOGY FOR THE FRONT RANGE AREA

I did some research on tornadoes along the Colorado Front Range in the last 100 years. The area I studied is the I-25 corridor from Colorado Springs up through Douglas County, the entire Denver metro area, and the northern Front Range (generally west of US 85) including the Boulder, Greeley, Loveland and Fort Collins areas. Finally, I included the Cheyenne, WY area.

First, here are some tornado statistics for counties along and near the Front Range:

County/Total tornadoes 1950 through 2007
Weld...227
Adams...148
Laramie Co, WY...90
Elbert...79
El Paso...79
Arapahoe...76
Douglas...52
Larimer...30
Jefferson...13
Denver...12
Boulder...10

County/F2 or stronger tornadoes 1950 through 2007
Weld...16
Adams...11
El Paso...9
Laramie Co, WY...5
Denver...4
Elbert...4
Larimer...3
Boulder...2
Douglas...2
Arapahoe...1
Jefferson...1
(Source: NCDC Storm Database)

Weld and Adams Counties in particular have had large numbers of tornadoes, but the vast majority are weak. Also, most of the tornadoes occur in the eastern parts of these counties (east of US 85), which are out on the plains and thinly populated. Other counties which extend out into the plains (Laramie County in Wyoming, and Arapahoe, Elbert and El Paso Counties) also record more tornadoes than the remaining counties which are in and close to the foothills. Some surprises include the relatively high tornado frequency in Douglas County close to the foothills, and also the fact that only one F2 or stronger tornado has occurred in Arapahoe County since 1950, despite the fact that Arapahoe extends well out into the plains.

However, the western part of Weld County between US 85 and I-25 has been struck by a number of strong tornadoes over the years and does seem to be somewhat more vulnerable than other areas of the Front Range urban corridor. There has even been one violent (F4) tornado here, near Johnstown in 1928. The reason for this is that a convergence zone can set up in this area when southeast winds pump up moist air toward the foothills. When conditions are right, as occurred last Thursday, this can trigger explosive growth of supercell thunderstorms which produce tornadoes. This area has also seen a large increase in population during the last 10 years, so there is now a higher risk of a strong tornado doing major damage and causing injuries and deaths than in years past.


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SOME NOTABLE TORNADOES ALONG THE FRONT RANGE IN THE LAST 100 YEARS

May 5, 1920 (Weld County)
An F3 touched down 4 miles west of Severance (not far from Windsor), destroying some farm houses. Fortunately, no one was injured or killed. Other tornadoes caused damage all the way up to the Wyoming state line.

June 29, 1928 (Weld County)
This was a bad one! A violent F4 touched down 10 miles SSW of Johnstown and moved north, passing 1 mile west of town. The tornado was 1/2 mile wide and was on the ground for 15 miles. Many farm houses were destroyed, 2 people were killed and 50 injured. Again, this tornado struck not far from where last Thursday's tornado did.

June 10, 1932 (El Paso County)
An F2 damaged 40 homes in Colorado Springs. 5 people were injured.

April 10, 1943 (Weld County)
An F2 touched down 2 miles N of Platteville and moved north 8 miles to a point between Milliken and Greeley.

May 15, 1952 (Weld County)
An F2 was on the ground for 5 miles and passed 3 miles SE of Kersey. 5 people were injured.

May 30, 1957 (Larimer/Weld County)
An F2 touched down near the Larimer/Weld County line and moved east for 8 miles, passing very near to Windsor.

May 18, 1975 (Adams County)
An F3 touched down in Adams County northeast of Denver and was on the ground for 4 miles. The tornado was 1/4 mile wide and was visible from much of the Denver metro area. If a similar tornado occurred in this location today, there would be major damage to Denver International Airport!!

June 24, 1979 (El Paso County)
An F2 struck Manitou Springs. 1 person was injured.

July 16, 1979 (Laramie County, Wyoming)
An F4 struck the north part of Cheyenne, including the airport area. Several National Guard C-130 aircraft were damaged and 140 homes were destroyed. One person was killed and 40 injured.

June 3, 1981 (Adams County)
The Thornton Tornado. I witnessed this one! The F2 tornado touched down near 88th and Washington St and did major damage to two shopping centers, then damaged about 600 homes in Thornton. 197 homes either had major damage or were destroyed. 42 persons were injured. Damage was $10 million in 1981 dollars ($25 million inflation-adjusted). This was Colorado's costliest tornado at that time. About 2:30 that afternoon, I had finished mowing and trimming a park in Northglenn. The sky turned pitch black and the street lights came on. As I drove back to our shop, large hail began falling. At 104th and Washington, I stopped at the red light and saw the tornado and debris flying around about 1 1/2 miles away. I was ready to abandon my vehicle and take cover if the tornado came toward me, but fortunately it turned more east and then lifted. I arrived back at the shop in torrential rain and golfball size hail.
This began a very active period for severe weather in the Denver metro area during the 1980s.

May 18, 1984 (Weld County)
An F2 was on the ground for 5 miles near Hudson.

July 19, 1985 (Douglas County)
An F2 struck the Surrey Ridge area. The tornado crossed I-25 and threw two vehicles off the highway. 3 persons were injured.

June 8, 1986 (Denver/Arapahoe County)
An F2 hit an apartment complex and a shopping mall. 6 people were injured.

July 7, 1987 (Weld County)
An F2 was on the ground for 5 miles, from Kersey to 3 miles east of Gill.

June 5, 1988 (Adams/Weld County)
An F2 hit a campground near I-25 and Colorado Hwy 7. An RV was destroyed and other vehicles were damaged, but there were no injuries.

June 15, 1988 (Denver)
The most destructive tornado to strike within the City and County of Denver. This F3 was on the ground for 2 1/2 miles in the southern part of the city, doing major damage near Broadway and Evans Ave. 7 people were injured. Inflation-adjusted damage total is $25 million. Another F2 tornado struck in northeast Denver, causing additional damage.

July 31, 1996 (Weld County)
An F2 was on the ground near Gill.

May 22, 2008 (Weld County)
The Windsor Tornado.

(sources: Significant Tornadoes 1680-1991 by Tom Grazulis, and NCDC Storm Database)


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WINDSOR TORNADO...THURSDAY, MAY 22, 2008

Late Thursday morning, the atmosphere became extremely unstable along the Colorado Front Range, and supercell thunderstorms developed rapidly north of the Denver area in Weld County. About 11:30, a tornado touched down near Platteville, overturning some tractor-trailers on US 85. The tornado then moved north-northwest, killing one person at a campground 8 miles west of Greeley, then devastating parts of Windsor, a town of 16,000. At Windsor, the tornado was up to one mile wide, and has been assigned a preliminary rating of EF3. The tornado continued moving north-northwest and finally lifted northeast of Fort Collins. Path length was 35 miles, one of the longest tracks ever recorded for a tornado anywhere in Colorado. In all respects, this was a remarkable storm for the Front Range. This was only one of two killer tornadoes to ever occur along the Front Range (within 30 miles of the foothills).

I was working outdoors (on a tractor mowing) and noticed by mid-morning that the atmosphere was already becoming unstable with towering cumulus rapidly forming. It didn't look good, and I suspected we were at least under a Tornado Watch by lunch time. Sure enough, we were...and when I hit the Denver NWS site, there was the Tornado Warning for Weld County. When I came in for lunch, a huge supercell thunderstorm blew up just north of our area (Northglenn, CO). I got a picture of it. This cell dropped a tornado west of Dacono, about 12 miles north of us, prompting a second Tornado Warning. There were no tornadoes or damage in the Denver metro area, including Northglenn and Thornton.

For many years, from 1960 until last year, there were no tornado deaths anywhere in Colorado. Then an EF3 tornado struck Holly in southeast Colorado on March 28, 2007, killing 2 persons. Now, just over a year later, there has been another death. While strong or violent tornadoes are not nearly as common along the Front Range as they are farther east on the Plains, they do occur occasionally. As the population has grown rapidly here, there is now much more exposure to the tornadoes than there was in years past.


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NWS DOES STORM SURVEY...WINDSOR TORNADO LIKELY AN EF3

On Friday, May 23, National Weather Service personnel did a storm survey of the damage in Windsor. Preliminary findings indicate EF2 and EF3 intensity through Windsor.

Updated: 5:39 AM GMT on May 29, 2008

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86 Sunday/Garden Planted!

By: DenverMark, 12:09 PM GMT on May 13, 2008

Sunday afternoon brought the warmest temperatures so far this year in Denver. The high at the airport reached 86, with 88 in our neighborhood in Thornton. However, we didn't challenge the May 18 record (93 in 1996).

We got our vegetable garden planted...this year we will have tomatoes, zucchini, jalapenos and lettuce. Our strawberry plants are blooming and will produce their first crop of the year shortly.

Temperatures will be in the mid 80s Monday, then upper 70s to low 80s through Wednesday. Later in the week, highs will cool to the low 70s. Lows at night will be in the 50s, then cooling into the 40s later in the week. There will be slight chances of showers and thunderstorms. The warm weather should help the garden get off to a good start!


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RAIN IN TOWN/SNOW IN THE FOOTHILLS...Tuesday, May 13

Upslope conditions developed along the Front Range Monday night, with light rain overnight and Tuesday morning. Denver International Airport picked up .36" storm total, while we had .49" at our house. In the foothills, up to 12" of snow fell near Evergreen.


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NEBRASKA SAND HILLS TRIP...May 10-11

Needing to get away from the hustle, bustle and traffic congestion of metro Denver, we decided to do a weekend up in the Nebraska Sand Hills. While some people find the Great Plains boring to travel through, I have always been fascinated with some of the topography and geological features...and of course enjoy the wide open spaces and country roads. We've visited rock arches in Kansas, the Sand Hills and Niobrara River valley in Nebraska, and the Badlands in both South and North Dakota. Farther north, we loved the old grain elevators (Saskatchewan Pool) in the Canadian prairies, which unfortunately are mostly gone now.

The weekend provided some interesting scenery and weather. Saturday was a cold and very windy day with occasional showers, but we had the promise of much nicer weather for Sunday. We drove up to Sidney to shop at Cabela's and wrapped up the day with a great dinner at a steakhouse in Ogallala, where we spent the night. While it was still windy, skies cleared by sunset.

Sunday morning was sunny but quite cold. The low in Ogallala was 28 and there was heavy frost on our car. Lows were in the mid to upper 20s across most of western Nebraska. We took Hwy 61 up past Lake McConaughy. The water level is still well below full pool due to the long-term drought of the 2000s, but is perhaps not as low as it was a couple of years ago. Continuing farther north, we went through the small community of Arthur. It was so quiet and peaceful on a Sunday morning. We headed east on Hwy 92 to Tryon, passing countless cattle and lots of windmills, along with a pond which had beautiful white swans swimming on it. This is prime cattle raising country. We then took Hwy 97 up to Mullen. Along the way, we crossed the Dismal River. We didn't think it looked dismal, as wild plums were in bloom in this scenic little valley. Some people now take canoeing trips on this river, which is spring-fed. The Sand Hills sit atop the Ogallala Aquifer which is one of the world's biggest groundwater reservoirs. Thousands of farmers in Nebraska and other Plains states irrigate their crops with water pumped from the Ogallala Aquifer. Unfortunately, the water table is dropping as recharge from precipitation can't keep up with the amount of water being pumped out.

At Mullen, we turned west on Hwy 2 to Alliance. The Burlington Northern/Santa Fe Railroad parallels the highway. Much of the coal burned in power plants in the Midwest travels this way from where it is mined in the Powder River Basin in Wyoming. While generating power from coal isn't the best option, it will be with us for a long time yet. The railroad provides many jobs for people living in these small towns. At Alliance, we went up to Carhenge where classic cars are planted in the ground to look like Stonehenge in England! There are also other sculptures...all made out of auto parts. Then it was time to head home. By mid-afternoon Sunday, the chilly weather was just a memory as temperatures had rebounded into the mid to upper 70s.


Updated: 3:11 AM GMT on May 19, 2008

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I've been fascinated by the weather all my life and also enjoy my job working outdoors. It's great to be able to share my weather and photos here!

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