Flash Flood Guidance
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Issued by NWS
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937 AWUS01 KWNH 300414 FFGMPD VAZ000-NCZ000-WVZ000-301010- Mesoscale Precipitation Discussion 1083 NWS Weather Prediction Center College Park MD 1213 AM EDT Mon Sep 30 2024 Areas affected...east-central VA/NC border into central VA and far eastern WV Concerning...Heavy rainfall...Flash flooding likely Valid 300412Z - 301010Z Summary...Heavy rain showers are expected to maintain a flash flood threat for portions of VA into WV over at least the next 3-6 hours. Rainfall rates of 1 to 2+ in/hr are expected, overlapping with wet antecedent grounds. Discussion...Regional radar imagery at 0345Z showed an axis of showers extending from the foothills of the Blue Ridge Mountains in central VA, southeastward to the east-central VA/NC border between I-85 and I-95. These showers were warm-topped, only -5 to -15C on "clean channel" infrared imagery with collision and coalescence processes dominating and have been rather efficient despite the fact that the bulk of the available instability is weak and limited to the 0-6 km AGL layer (via 00Z RNK/IAD and RAP analysis soundings). MLCAPE was only a few hundred J/kg but precipitable water values were estimated via 03Z SPC mesoanalysis data to be 1.6 to 1.9 inches. It appears low level convergence (925-850 mb) was playing a role in the location of these showers with some degree of isentropic/orographic ascent aiding in lift. Short term forecasts of instability from the RAP indicate only gradual weakening and low level convergence of southeasterly winds to slowly shift north over the next 3-6 hours. Rainfall rates have been observed locally over 2 in/hr and similar potential will exist overnight with slow moving and repeating showers likely to continue, though some weakening should be expected where instability is lower or decreases with time. Much of the area still contains lower flash flood guidance due to wet antecedent conditions due to rainfall over the past week. Therefore, while perhaps not widespread in coverage, at least a localized flash flood threat will be likely to continue into the night with rainfall rates of 1 to 2+ in/hr at times. Additional storm totals may exceed 3 inches on an isolated basis. Otto ...Please see www.wpc.ncep.noaa.gov for graphic product... ATTN...WFO...AKQ...LWX...RAH...RLX...RNK... ATTN...RFC...MARFC...OHRFC...SERFC...NWC... LAT...LON 38757826 38247779 37147703 36477710 36337764 36437820 37157878 37297994 37728022 38337988 38737935