Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Aug 19 2024 16:39:03 AWUS01 KWNH 191638 FFGMPD MAZ000-NHZ000-VTZ000-CTZ000-NYZ000-NJZ000-192230- Mesoscale Precipitation Discussion 0905 NWS Weather Prediction Center College Park MD 1238 PM EDT Mon Aug 19 2024 Areas affected...eastern Upstate New York, western New England Concerning...Heavy rainfall...Flash flooding possible Valid 191637Z - 192230Z Summary...Showers and thunderstorms will increase in coverage across Upstate New York and western New England this afternoon ahead of a cold front. Short term training of 1-2+"/hr rates will create corridors of 1-3" of rain with locally higher amounts. This could produce flash flooding. Discussion...The GOES-E visible satellite imagery this afternoon shows clearing sky conditions across eastern Upstate NY into western New England. Within this clearing, SBCAPE is climbing steadily as reflected by the SPC RAP SBCAPE 3-hr change of +600 J/kg, fueling rapid growth of Cu and TCu. Some of this TCu is starting to exhibit glaciation as noted in the GOES-E day cloud phase RGB, resulting in a steady expansion of lightning cast probabilities above 25%. The 12Z U/A soundings from KALB and KOKX both measured PWs above the 90th percentile according to the SPC sounding climatology, with elevated freezing levels supporting efficient warm-rain processes. Into these impressive thermodynamics, forcing for ascent is slowly intensifying through convergence ahead of the cold front, increasing upper diffluence, and height falls downstream of the parent longwave trough and accompanying shortwave impulse. A modest impulse lifting northward from the Mid-Atlantic is accompanied by a surge of moisture noted in the 700-500mb LPW fields, and this feature will additionally enhance moisture and ascent through the afternoon. The high-res CAMs are in good agreement that convection will steadily increase in both coverage and intensity along the cold front, but may be under-forecasting cell development well in advance of it. With the environment remaining strongly forced and thermodynamically favorable, any cell that develops will have the potential to produce rainfall rates of 1-2"/hr, while the HREF neighborhood probabilities and HRRR 15-min accumulations indicate short-term rates to 3"/hr are possible, especially across New England where bulk 0-6km shear of 20-25 kts will support some modest organization. Mean 0-6km winds around 15-20 kts indicate that cells will generally remain progressive, but these winds will be broadly parallel to the front and occur in conjunction with weakening Corfidi vectors, supporting at least short-term training of cells from SW to NE. Where training occurs, rainfall totals of 1-3" are likely, with isolated amounts above 4" possible. 7-day rainfall across most of this region has been limited as reflected by AHPS departures that are just 25-50% of normal (except across southern CT and extreme southeast Upstate NY which had flooding on Sunday). This is leaving near normal soil saturation and 3-hr FFG of 1.5-2" which has a 20-30% chance of exceedance. Still, with efficient rain rates and some possible training, especially in urban areas or atop the more vulnerable soils and terrain features, instances of flash flooding could result. Weiss ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!_sPFw27F3uwuGL5yzNS6fURs_NueL8Fdt8SmIEru65NqkEhOJx2EyUOd-WgQ85hJqGkd= QVvceGKjHWv53Y8YLUggz44$ for graphic product... ATTN...WFO...ALY...BGM...BOX...BTV...GYX...OKX...PHI... ATTN...RFC...MARFC...NERFC...NWC... LAT...LON 45477304 45417219 45127172 44617150 43927158=20 43437172 42537233 41837282 41357321 41107367=20 41117418 41247452 41877480 43217459 45067412=20 =20=20=20=20=20=20=20=20=20=20=20=20 =3D =3D =3D To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM. --- SBBSecho 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .