Thunderstorms moving through southern Utah and northern Arizona caused deadly flooding Monday September 14 through Tuesday September 15th, 2015. These thunderstorms were associated with a shortwave trough moving through the Southwest. This trough initiated the movement of warm, moist air from the Gulf of California northward, providing the moisture and instability necessary for thunderstorms to develop.
Topography was a major factor in this flooding event. Heavy precipitation fell in a short period of time over steep and somewhat impermeable terrain, causing the storm water to flow into the valley and overwhelm Short Creek.
In a two day span along the boarder of Utah and Arizona the National Weather Service (NWS) in Salt Lake City issued seven flash flood warnings, the NWS in Flagstaff issued two flash flood warnings and a severe thunderstorm warning, and the NWS in Las Vegas issued two flash flood warnings. All of these warnings explained the dangers of flash floods and urged the public to take action by retreating to higher ground.
MetStorm™ was used to analyse this storm and determine how rare of an event it was from a precipitation stand point. Below are the total storm map, showing the maximum estimated precipitation to be 4.5″ in the 48-hour period, and the Average Recurrence Interval (ARI) map which depicts the rarity of this event.
The ARI, or “return period” for this storm at a one-hour time period, for the location north-northeast of Hildale and Colorado City, was 258.36 years, or a 0.39% chance of occurring in any given year. This represents the likelihood of 2.47″ falling in a one-hour period at this location.
Please note that the maps presented here are preliminary and will be updated when new data become available. If you are interested in this product, or any other product from our MetStorm™ Precipitation Analysis tool, please contact us at firstname.lastname@example.org or through our contacts page at http://metstat.com/contact-us/
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(edited: 9/25/2015 )