Flash Flood Guidance
Issued by NWS
Issued by NWS
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014 AWUS01 KWNH 211613 FFGMPD MAZ000-NHZ000-RIZ000-VTZ000-CTZ000-NYZ000-NJZ000-PAZ000-WVZ000-OHZ000-212211- Mesoscale Precipitation Discussion 0480 NWS Weather Prediction Center College Park MD 1212 PM EDT Fri Jun 21 2024 Areas affected...Portions of the Upper Ohio Valey...Northern Mid-Atlantic...New York...Southern New England Concerning...Heavy rainfall...Flash flooding possible Valid 211611Z - 212211Z SUMMARY...Scattered to broken areas of showers and thunderstorms are expected this afternoon across areas of the Upper Ohio Valley, northern Mid-Atlantic, New York and New England. Heavy rainfall rates and potentially some localized instances of cell-training may support some instances of flash flooding. DISCUSSION...GOES-E visible satellite imagery is showing rapidly expanding areas of CU/TCU across large areas of northwest PA through NY state. The airmass is already moderately unstable with a belt of MLCAPE values of 1500+ J/kg across much of northwest to north-central PA through southern NY, and with this nose of instability also becoming increasingly focused across southern New England to the south of a west/east oriented frontal zone. Differential heating boundaries in close proximity this front along with some terrain-induced circulations/forcing involving areas of higher terrain will support increasing coverage of showers and thunderstorms this afternoon as additional strong solar insolation/boundary layer destabilization occurs. The low-level wind fields are also generally rather convergent and especially across south-central NY through southern New England, and there will be some modest effective bulk shear traversing this corridor for some locally organization swaths of multi-cell convection. More separately farther to the west, areas away from Lake Erie involving northeast OH and northwest PA may have focus for convection from not only close proximity of the front, but some lake-breeze convergence/interactions. The 12Z HREF guidance favors some of the heaviest rainfall potential across areas of southern New England where some of the higher PWs and better overall forcing will be in place. PWs across these areas are already locally over 1.75 inches which is a solid 2+ standard deviations above normal. Also, there are considerations of a separate lee-side trough axis noted over southern New England down near CT/RI which should tend to provide additional small-scale forcing. Rainfall rates of 1 to 2 inches/hour are expected with the stronger storms, and with some localized potential for repeating/training convective cells, there may be some pockets of 2 to 4 inch rainfall totals. Some instances of flash flooding will be possible as a result of this. Orrison ...Please see www.wpc.ncep.noaa.gov for graphic product... ATTN...WFO...ALY...BGM...BOX...BUF...CLE...CTP...GYX...OKX... PBZ...PHI... ATTN...RFC...MARFC...NERFC...OHRFC...NWC... LAT...LON 43737405 43377368 42927322 42957238 42737170 42367126 41957101 41517132 41307274 40877385 40717462 40887673 40797911 40228136 40398251 41018276 41398239 41798151 42218011 42567925 42837823 42997731 43007645 43237554 43697478