Flash Flood Guidance
Issued by NWS
Issued by NWS
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411 AWUS01 KWNH 201731 FFGMPD MEZ000-MAZ000-NHZ000-VTZ000-CTZ000-NYZ000-PAZ000-202330- Mesoscale Precipitation Discussion 0472 NWS Weather Prediction Center College Park MD 130 PM EDT Thu Jun 20 2024 Areas affected...Portions of Far Northern PA...Much of NY...New England Concerning...Heavy rainfall...Flash flooding possible Valid 201730Z - 202330Z SUMMARY...Scattered showers and thunderstorms will be developing this afternoon across portions of northern PA, much of NY, and across New England. High rainfall rates with the stronger storms may result in a few instances of flash flooding. DISCUSSION...The midday GOES-E visible satellite imagery shows a well-defined MCV exiting Lake Ontario and starting to cross northern NY. This energy coupled more broadly with a very moist and unstable airmass pooling ahead of a cold front approaching from southeast Canada will set the stage for scattered showers and thunderstorms this afternoon. MLCAPE values are currently already on the order of 1500 to 2500 J/kg across eastern NY, NH, VT and southern ME, and with aid from strong solar insolation and surface dewpoints in the low 70s. Some additional uptick in instability is expected over the next couple of hours, and this coupled with modest effective bulk shear of 20 to 25 kts, and the arriving MCV energy along with areal orographics involving the northern Appalachians should favor pulse and multicell convective development. Convective initiation is well underway right now near Lake Champlain and also farther south over south-central NY where highly agitated CU/TCU fields are expanding in coverage. Additional areas of far southern Quebec and approaching the higher terrain of western ME show notable areas of CU development/expansion. The PWs are rather high with magnitudes locally over 1.75 inches, and these are also as much as 2 to 3 standard deviations above normal. This moisture coupled with the strong instability parameters should yield thunderstorms with enhanced rainfall rates with some rainfall rates that may reach 1.0 to 1.5 inches in as little as 30 minutes. Some of the 12Z HREF guidance suggests some localized 2 to 4 inch rainfall totals, with the heaviest rains likely to focused near the Champlain Valley and portions of the Green and White Mountains. However, locally heavy showers and thunderstorms should extend as far southwest as southern NY and far northern PA, and locally heavy totals can be expected across these areas as well. A few instances of flash flooding will be possible. Orrison ...Please see www.wpc.ncep.noaa.gov for graphic product... ATTN...WFO...ALY...BGM...BOX...BTV...BUF...CAR...CTP...GYX... ATTN...RFC...MARFC...NERFC...OHRFC...NWC... LAT...LON 45317066 45166980 44886922 44406909 43836946 43047091 42357215 41947365 41747525 41677645 41637832 41767910 42167929 42557797 42927665 43397584 44107524 44737471 44927394 45037296 45167169