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.
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