Precipitation Return Periods - Warning Decision Training Division (WDTD)

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Precipitation Return Periods

Short Description

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

Subproducts

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.

Primary Users

NWS: WFO, RFC

Input Sources

MRMS Radar-Only QPE, NOAA Atlas 14 Precipitation Frequency Estimates

Resolution

Spatial: ~1 km x 1 km

Temporal: 2 minutes

Product Creation

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)

Technical Details

Latest Update: MRMS Version 12

NOTE: In version 12, all FLASH products now use the instantaneous rainfall rates from the Dual-pol radar synthetic QPE product.

Accessible on:

Operational AWIPS
1. V11.5 -- MRMS menu
2. V12 -- via LDM, if set-up
MRMS Development site

References

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.

Strengths

Because NOAA Atlas 14 data is not available everywhere in the CONUS, the FLASH project uses statistical modeling to fit the NOAA Atlas 14 data into the areas of the CONUS where data do not exist.

Limitations

All limitations associated with MRMS Radar-Only QPE apply

NOAA Atlas 14 data are extrapolated using a statistical model

Precip frequency estimates are determined using gauge data fit to a grid

Higher return periods are associated with higher uncertainty

Quality Control

This product is subject to the MRMS 3D Reflectivity Cube quality control (QC) process as well as any Atlas-14 QC processes.

Applications

Determine the rarity of a rainfall amount over a given time period for a given location

Example Images

Figure 1. This maximum return period is approaching 10-20 years. In other words, it is a 5-10% chance of this rainfall event occurring during a given year.