Front Range reminded the unofficial start of summer also start of severe weather season

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Tornado warnings, rolling hills of hail in the roads and overflowing creeks and drainage ditches last week signaled the first big batch of severe weather this spring in the Denver metro area.



As storm cells rolled across the Front Range Wednesday, May 21, they dropped enough water and hail to cause standing or moving water in multiple parts of Commerce City, including East 96th Avenue and Tower Road, East 81st Avenue and Tower Road, East 96th Avenue and Buckley Road, East 88th Avenue and Buckley, the 13000 block of East 96th Avenue and the 9800 block of Peoria Street, according to city spokeswoman Michelle Halstead.

The influx of water prompted numerous road closures along East 96th Avenue, Tower Road and Highway 85. Fairfax Park, which was designed to act as a drainage area for stormwater runoff, was pushed to the limit of its banks for the first time since last September’s historic flooding. 

Last week’s severe weather — which included tornadoes touching down in Aurora, Watkins and other areas along the Interstate 70 corridor — was a fresh reminder of the threat twisters pose along the Front Range in the late spring and early summer months.

As we shared with you last June, the reporting team at I-News found that Adams County and Weld County had the most tornadoes in the state in the 63-year span from 1950 to 2013. Combined, they accounted for 410 tornadoes, more than one of every five.

I-News also cast a spotlight on the tornado threats posed in the area around Denver International Airport, which had more than a dozen cancelled flights and numerous more delays due to both the tornado warning and multiple aircraft being damaged by hail. 

  An I-News examination of data since 1950 kept by the National Weather Service showed that Colorado experiences frequent if not always powerful tornadoes:

— Five of the 10 counties with the most tornadoes were along the Front Range. In addition to Weld and Adams, they included El Paso, Arapahoe and Elbert counties.

Beginning in 1971, tornadoes in the United States were categorized on what was known as the Fujita Scale, a six-step ranking — from F0, the weakest, to F5, the strongest. The different categories accounted for potential for damage inflicted by a particular tornado.

In 2007, the Enhanced Fujita Scale was adopted, which updated the rating system to include a specific range of wind speed for each category of tornadoes. The new system ranked tornadoes from EF0, the weakest, to EF5, the most powerful.

Since 1950, a tornado rated either F5 or EF5 has never been recorded in Colorado. Only one twister was rated as either F4 or EF4 — a twister in 1977 in Baca County — and 21 were categorized as either F3 or EF3. 

The rest were less powerful — 111 that were F2 or EF2; 531 that were F1 or EF1; and 1,229 that were F0 or EF0, including a small but dramatic tornado that startled motorists at nearly 12,000 feet on Mount Evans road last July 28.

Another 55 of the state’s tornadoes were listed as “unknown.”

“The good news is that the vast majority of our tornadoes are weak — EF0, EF1 — so those winds go up to maybe 130 mph or so, and those tornadoes don’t cause a lot of damage,” said Bob Glancy, the warning coordination meteorologist at the National Weather Service’s Boulder office. 


This report included information originally reported by I-News, the public service journalism wing of Rocky Mountain PBS. Learn more at www.rmpbs.org/news.