EVENT SUMMARY: Severe Thunderstorm May 18th, 2012

On Friday, May 18th, 2012 a strong trough of low pressure and associated cold front moved across the Cowboy State, bringing scattered thunderstorms to the region. Shortly after 2 PM a line of thunderstorms developed along the eastern slopes of the Wind River Mountains and began to move northeast. As this line moved through Lander it dropped moderate rain, small hail, and copious lightning (see video from County10 below).

As the line of storms moved towards Riverton it began to accelerate and developed a bit of a bow shape which indicates the potential for very strong winds. By the time it arrived at the Riverton Regional Airport it had winds gusting to 77 MPH. This was the highest wind gust recorded at the Riverton Regional Airport since the Automated Surface Observing System was commissioned in 1995 (the previous record was 74 MPH in May of 2008, more info here). As the storm moved through the city of Riverton, it had winds gusting to around 70 MPH with BB to pea-sized hail, heavy rain, and lightning (see storm reports here). Two meteorologists from the NWS office in Riverton were participating in the annual Spring Fling Outdoor Expo at the local Walmart retail store. They were able to capture some video clips after then initial gust front (see video below). They were also able to provide enough advance warning to the event organizers so other participants could properly prepare for the wind, rain, and hail.

Radar Imagery - 5/18/2012 from 2:38 - 3:53 PM MDT  (Note: loops may not synchronize)

0.5 Degree Reflectivity (click to enlarge)

This loop shows the line of thunderstorms forming on the eastern slopes of the Wind River Mountains and moving northeast across the Wind River Basin.

0.5 Degree Radial Velocity (click to enlarge)

This loop shows the same period of time as the other but viewing the wind speeds associated with this storm. The brightest colors indicate winds of 60-70 MPH.

Video Courtesy County10.com
Video Courtesy Reid Wolcott, NWS


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