Storm Prediction Center Forecasts Heavy Rain Today

The Storm Prediction Center in College Park, Maryland has issued a Mesoscale Precipitation Discussion regarding the potential for heavy rain today. They are forecasting 1 to 2 inches of rain per hour later today (probably in the afternoon) with the possibility of some locations seeing rates as high as 2 to 4 inches an hour this afternoon. A complete copy of the discussion is posted below for those interested.

If you live in an area that is prone to flash flooding or are anticipating driving through areas with poor drainage, please be careful and drive a little slower than normal when it is raining and shortly afterward. Today’s daily weather briefing can be found at this link.

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Mesoscale Precipitation Discussion 0404
NWS Weather Prediction Center College Park MD
746 AM EDT Mon Jun 10 2019

Areas affected…Southern Appalachians

Concerning…Heavy rainfall…Flash flooding possible

Valid 101146Z – 101746Z

Summary…Showers with heavy rain are increasing in coverage across northeast GA and northwest SC. Hourly totals up to 1-2″ with local amounts of 4″ are expected over areas with saturated soils.

Discussion…Radar trends since 0930z show a slow increase in shower activity across northeast GA and northwest SC, with radar indicating hourly amounts to 1″ as of late. This is occurring within a moist environment with precipitable water values around 1.8″ in lower elevations and 1.4″ in terrain. Inflow at 850 hPa is light per VAD wind profiles — 15 knots. However, the mean 850-400 hPa wind in the region is closer to 10 knots, which would lend itself to rainfall efficiency. MU CAPE values of 250-500 J/kg lie here, which has trended slightly upward during the past couple hours ahead of a linear, elongated shortwave approaching the region from central TN and to the north of an upper level low over the FL panhandle.

The mesoscale guidance is struggling in this area. Trends in the 06z HREF probabilities of 1″+ an hour have been downward since 08z, which is in direct opposition to trends on radar and satellite imagery. The Galvez-Davison index, useful in regimes with high moisture, matches radar trends in showing increasing instability over the next several hours which implies increasing convective coverage. The 00z NMMB, 06z 4 km NAM, and 10z HRRR have a limited/highly localized signal for local amounts of 3-4″.
Considering increasing coverage on radar, feel their signal is too small in scale. Hourly rain totals up to 1-2″ with local amounts to 4″ are expected through 1745z. Rainfall anomalies over the past 14 days (mostly during the past few days) are 300-600% of normal, which has likely saturated area soils. Stream flow in the area within the National Water Model output is at or above average. This degree of rainfall would be problematic, especially considering some of the nearby topography.

Published at 9:33am on MOnday, June 10, 2019