QPE-to-FFG Ratio - Warning Decision Training Division (WDTD)

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QPE-to-FFG Ratio

Short Description

Analogous to the ratio provided in FFMP, this is the ratio of the current MRMS Radar-Only QPE value at each grid point to the current nationally-mosaicked FFG value for the same grid point.

Subproducts

Available for rainfall durations of 1-, 3-, and 6-hours. A maximum product exists which finds the maximum ratio across all accumulation durations.

Primary Users

NWS: WFO, RFC

Input Sources

MRMS Radar-Only QPE, and Nationally-Mosaicked FFG

Resolution

Spatial: ~1 km x 1 km

Temporal: 2 minutes (Keep in mind FFG only updated every 6 hours)

Product Creation

The FLASH system takes the MRMS Radar-Only QPE value for the defined accumulation periods (1-, 3-, and 6-hours) and compares those gridded values to the corresponding nationally-mosaicked FFG gridded values.

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 the comparisons are done at each grid, the spatial resolution is much greater than the basin-averaged QPE-to-FFG ratio done in FFMP

MRMS Radar-Only QPE for 3-, and 6-hour durations are only updated once an hour, but the ratio product for these durations is still updated every 2 minutes using intermediate rainfall adjustments.

Limitations

All limitations associated with MRMS Radar-Only QPE and FFG apply

Nationally-mosaicked FFG grids are only updated once every 6 hours

Updated FFG grids during event may cause ratios to become unrealistically high

Local changes to FFG will not be incorporated

No way of telling if the maximum ratio product came from 1-, 3-, or 6-hour duration

Quality Control

This product is subject to the MRMS 3D Reflectivity Cube quality control (QC) process.

Applications

Monitor whether rainfall amounts have exceeded FFG values in order to begin thinking about flash flooding possibilities

Example Images

Figure 1. The MRMS QPE for this event was producing rainfall estimates well above the FFG values for 1-hr, 3-hr, and 6-hr durations, as shown by the predominance of yellow and orange pixels. And, if you had confidence in the MRMS radar-only QPE values, then this would trigger you to consider a flash flood warning for these areas.