FFMP Receives High Praise From WFO Salt Lake City

I wanted to let you know how very useful the FFMP capability has been for WFO SLC this summer and in particular last week. We had a good monsoon episode at the end of the week with considerable flash flooding. On Saturday Aug. 23rd flash flooding on the Freemont River (river is generous since its a dry wash all summer) resulted in flows of over 11,000 cfs and many miles of road closures near Capitol Reef National Park. This was the highest flow in over 25 years. At least one person was stranded in the rapidly rising water and was rescued just before being washed away. The Paria River (another dry wash) also flash flooded on this day and did about $500k damage to the town of Tropic near Bryce Canyon National Park.

There has been uniform high praise for FFMP by the forecasters at SLC. We run it every day when there are convective storms anywhere in our CWA. It helps us pinpoint the appropriate basin and gives us a much better handle on instantaneous rainfall rates, basin accumulations, whether there have been repeat storms, and other trends. Our warnings have become much smaller and more specific, and our lead time is much better than it would have been without FFMP. On the 23rd, we got verification of flooding in 8/9 warnings and lead times on the warnings that were not extensions to existing warnings averaged 48 minutes. And there were no reports of flooding outside of the warned areas!

Although we are using a blanket 1"/hour flash flood guidance for all basins at this time, we have started to use a GIS-based flash flood potential index developed by Greg Smith of CBRFC. It graphically shows us static flash flood potential based on land use, vegetation, slope, and basin characteristics.

Lawrence B. Dunn, Ph.D.
email: larry.dunn@noaa.gov
Meteorologist in Charge
National Weather Service Forecast Office
Salt Lake City, UT 84116