Using MRMS rainfall estimates at ILM

A minor flooding event this morning (Nov 3, 2015) in the Wilmington, NC forecast area was the first time I utilized MRMS (Multi-Radar Multi-Sensor) data operationally.

Sustained isentropic lift across a stalled front over eastern Georgia led to widespread moderate rain during the night of November 2 into the morning of November 3.  Widespread 2 to 4 inch rainfall amounts were reported by gauges across Brunswick and Horry counties.  A CoCoRaHS observer from station SC-HR-75 seven miles north of Myrtle Beach reported 6.50 inches of rain, the highest total in the region.

This was a warm rain/coalescence-dominated event, and legacy Storm-Total Precipitation from the KLTX radar underestimated by 50% versus gauge data.  That error plus beam blockage made the product virtually unusable.  ILM forecasters have been dealing with radar beam blockage over the past several years due to a large and growing pine plantation near our NEXRAD radar site in Shallotte, NC.  Dual-Pol precipitation estimates were closer to gauge totals but still suffered from beam blockage over the highly populated regions of coastal Brunswick, Horry and Georgetown counties.

MRMS precipitation estimates with gauge-bias correction was outstanding, particularly when verified against some of the higher CoCoRaHS totals we had in Brunswick and Horry counties.  MRMS is already proving itself to be an excellent new tool both in terms of data accuracy and removing beam blockage artifacts.



MRMS rainfall estimates

Location        Gauge    MRMS    Difference
Wilmington       2.19    2.03      -7%
N. Myrtle Beach  2.30    2.70     +17%
Lumberton        1.09    1.28     +17%
Florence         0.46    0.49      +7%

Southport 5.9W   1.98    1.84      -7%
Varnamtown 1.3SW 2.23    2.24       0%
Calabash 1.2NW   3.86    3.59      +7%
Conway 5 SSE     3.10    3.28      +6%
Conway 6.2 E     4.08    3.83      -6%

Tim Armstrong       NWS Wilmington, NC

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4 Responses to Using MRMS rainfall estimates at ILM

  1. hurricanebob says:

    Can’t speak for how it did overall down here in NWS Charleston’s area but we did notice for a few sites at least that MRMS did much better than even the dual pol estimates.

  2. Thanks for the post Tim. I forwarded your blog to Greg Stumpf at NSSL. The folks who work with MRMS appreciate the feedback and posts like these.

  3. Grant Wise says:

    Hey, I was wondering if there is a place the public can access high-res MRMS data. There is this: but it is obviously not nearly as good resolution as the MRMS data you all use.

  4. nwstimarmstrong says:

    I believe only the NWS and FAA have high-res data available at this time. It’s 1km x 1km horizontal resolution updated every 2 minutes. All of the meteorologists at the ILM office recently went through MRMS training, but I don’t remember reading anything specifically about timelines for releasing additional data.

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