Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Aug 18 2024 17:12:02 AWUS01 KWNH 181711 FFGMPD NYZ000-NJZ000-PAZ000-DEZ000-MDZ000-VAZ000-DCZ000-WVZ000-182300- Mesoscale Precipitation Discussion 0898 NWS Weather Prediction Center College Park MD 111 PM EDT Sun Aug 18 2024 Areas affected...Mid-Atlantic States from southern Upstate NY through central MD Concerning...Heavy rainfall...Flash flooding possible Valid 181710Z - 182300Z Summary...Showers and thunderstorms will expand ahead of a cold front through this evening. These thunderstorms will train to the northeast with rain rates of 1-2"/hr or more. This will produce 2-4" of rain and possible flash flooding. Discussion...The regional radar mosaic this afternoon shows a rapid expansion of reflectivity along a pre-frontal trough ahead of a cold front. This cold front will move out of the Ohio Valley and into the Mid-Atlantic the next few hours, to combine with increasing upper diffluence in the LFQ of a poleward arcing jet streak, robust height falls as a longwave trough axis pivots eastward, and subtle embedded shortwaves to produce impressive deep layer ascent. This lift will impinge into intensifying thermodynamics characterized by PWs of 1.5 to 1.7 inches, and MLCAPE above 1000 J/kg to support the expanding and intensifying convection. Recent radar-estimated rainfall rates have exceeded 1"/hr in the stronger updrafts, and these will likely continue to intensify through the afternoon. The high-res CAMs are in good agreement that showers and thunderstorms will become widespread across PA and also extend into MD and and NJ by this evening. While the exact placement of storms varies, there will likely be multiple clusters moving SW to NE on 0-6km mean winds of 15-20kts. This will keep storms generally progressive, but Corfidi vectors aligned to the mean wind and becoming increasingly parallel to the front/pre-frontal trough suggests an enhanced training potential. Additionally, a bubble of locally enhanced bulk shear reaching 20-25 kts across the eastern Mid-Atlantic states could help organize cells as well. Together, this provides support for the HREF neighborhood probabilities which reach 20-40% for 2"/hr rates by this evening, which through training could produce 2-4" of rain with locally higher amounts. The CAMs generally focus the heaviest rain between I-95 and I-81, where the HREF PMM in the next 6 hours shows locally as much as 5 inches of rain is possible. Training of these intense rain rates have the potential to produce flash flooding, especially across urban areas. However, some of this region has also been quite wet as reflected by AHPS 7-day rainfall as much as 600% of normal. This has lead to extremely compromised FFG of 1-1.5"/3hrs for which the HREF exceedance probabilities reach as high as 60%. Anywhere these rates train could cause instances of flash flooding, but it will be most likely across urban areas or atop these more vulnerable and pre-conditioned soils. Weiss ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!5yRNtkciBGw0Zu01mYdJ9BUqWKFPTF8bMxLwysoNx7mMCXnxAFW57RuUAWi4-NR3llO2= UMEbmofKcyYLj2kVe9ednYE$ for graphic product... ATTN...WFO...ALY...BGM...BUF...CTP...LWX...OKX...PHI... ATTN...RFC...MARFC...NERFC...OHRFC...NWC... LAT...LON 42487606 42337496 42017447 41347434 40777443=20 40247470 39757529 39277595 38907676 38917706=20 38967750 39067787 39257823 39537850 39977867=20 40307876 41357857 42157758=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) .