Comparison of the MRMS Radar-Only QPE value at each grid point with the NOAA Atlas 14 precipitation frequency estimate for the same grid point to determine how rare a precipitation estimate is for that grid point for the given duration
Available for rainfall durations of 30-min, 1-, 3-, 6-, 12-, and 24-hours. A maximum product exists which finds the maximum return period across all accumulation durations.
NWS: WFO, RFC
MRMS Radar-Only QPE, NOAA Atlas 14 Precipitation Frequency Estimates
Spatial: ~1 km x 1 km
Temporal: 2 minutes (Keep in mind FFG only updated every 6 hours)
The FLASH system takes the MRMS Radar-Only QPE value for the defined accumulation periods (1-, 3-, 6-, 12-, and 24-hours) and compares those gridded values to the corresponding NOAA Atlas 14 precipitation frequency estimate to determine how frequently that rainfall amount for that duration has occurred in the past. It is reported in years, but it is better to take 1 divided by the yearly value to think of it as the percentage chance a rainfall amount of that value will occur in a given year (e.g. a 25-year return period means the current rainfall amount for that duration and location had a 4% chance of occurring…in other words it is a fairly rare event you are observing)
Gourley, J., Z. Flamig, H. Vergara, P. Kirstetter, R. Clark III, E. Argyle, A. Arthur, S. Martinaitis, G. Terti, J. Erlingis, Y. Hong, and K. Howard, 2016: The Flooded Locations And Simulated Hydrographs (FLASH) project: improving the tools for flash flood monitoring and prediction across the United States. Bull. Amer. Meteor. Soc. doi:10.1175/BAMS-D-15-00247.1, in press.