FLASH FLOODS: DEFINING AND FORECASTING. Matt Kelsch 28 & 30 June 2000 [email protected] For more detailed flash flood presentations: www.comet.ucar.edu/class/index.html for more information on the Fort Collins flash flood and a detailed case summary with links:
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28 & 30 June 2000
For more detailed flash flood presentations:
for more information on the Fort Collins flash flood and a detailed case summary with links:
for a link to our Venezuela flash flood and landslide page:
What Are They?
What is the correlation with precipitation amount?
What is the correlation with precipitation rate?
How important is the hydrology?
Flash Flood forecasting requires more than accurate forecasts of excessive accumulation
A flash flood is a situation where the causative precipitation and the subsequent runoff are occurring on the same scales.
Flash Floods lack objective definition and verification
There isn’t a reliable correlation between rainfall amount and flash flood severity.
Severe weather occurs first, if both occur in the same storm.
Improvements to the Flash Flood Watch stage have occurred since the 70’s
What about Warnings?
1) In an attempt to make sure everyone in the threat area is warned, long-duration warnings are issued for large areas
2) In a conscientious attempt to provide specific detail in space and time, there is little or no lead time
0500 UTC 7 Aug 1999
0700 UTC 7 Aug 1999
KLOT (Chicago) Radar Storm Total Accumulation as of 1400 UTC 18 July 1996
Enhanced Precipitation Efficiency
Ponds Overflowing, rapid water rescues begin
Most intense rain commences
Storm begins to dissipate and move northeast
Trailer Park Flooding, Fires, Train Derailment
Declared City Disaster
Tropical Maritime Connection
Deep above-freezing cloud layer (4 km)
** beware of storm-specific enhancement
Thin, impermeable soil or; deep, saturated soils
Altered Basin Hydrology
IT DOESN’T HAVE TO ROTATE TO KILL YA!