Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Aug 06 2024 18:42:06 AWUS01 KWNH 061841 FFGMPD RIZ000-CTZ000-NYZ000-NJZ000-PAZ000-DEZ000-MDZ000-070030- Mesoscale Precipitation Discussion 0820 NWS Weather Prediction Center College Park MD 241 PM EDT Tue Aug 06 2024 Areas affected...Mid-Atlantic States from central MD through southern CT including the I-95 corridor Concerning...Heavy rainfall...Flash flooding likely Valid 061840Z - 070030Z Summary...Showers and thunderstorms will expand across the Mid-Atlantic states this afternoon and evening. Rainfall rates will steadily increase to 2+"/hr, which through training could produce 2-4" of rain with locally higher amounts above 5". Instances of flash flooding are likely. Discussion...The GOES-E day-cloud phase distinction RGB this afternoon shows expanding Cu/TCu with increasing glaciation indiciating of strengthening updrafts and thunderstorms. Within this area, the Lightningcast probabilities have increased to more widespread 50-70%, further indicative of the strengthening environment, and likely the precursor to widespread thunderstorms through the aftn. This convection is blossoming within an extremely robust thermodynamic environment characterized by PWs measured by GPS around 2 inches, colocated with MLCAPE that has climbed steadily to 1500-2000 J/kg. A complicated surface pattern is enhancing the convective risk as well, with a wave of low pressure analyzed along a stationary front draped from PA into southern CT, and multiple surface troughs (sea breeze boundary north of the Chesapeake Bay, outflow boundary over Long Island) causing enhanced convergence for ascent. Recent radar-estimated rain rates within this fresh convection has locally already exceeded 1.5"/hr. The recent HRRR runs have really under-initialized the ongoing convective coverage, and while the 17Z run is a bit better, the ARW/ARW2 appear to be a much better indicator of the future. These models suggest convection will become widsepread and focused along the front, which is where convergence of the best moisture transport vectors occurs within the gradient of highest instability. This will be in addition to development along the residual surface troughs, and this should result in activity rapidly blossoming to become widespread during the next few hours. Rainfall rates within the intense thermodynamics have a high probability (>70%) on both the HREF and REFS to exceed 2"/hr, with brief more intense rates to 3"/hr possible, especially where any organization into clusters can occur through 0-6km bulk shear of 25-35 kts. Individual cells will remain progressive to the east as propagation vectors suggest storm motions of 15-25 kts, however, these are aligned to the mean 0-6km winds and the front, indicating a high potential for training cells. Additionally, there is potential for some backbuilding cells along the surface troughs where they interact with locally higher PWs/instability. This may be most likely near the northern Chesapeake Bay, or in the vicinity of the Tri-State area of NY/CT/NJ. Confidence is modest in this evolution, but mesoscale ingredients support this, and is reflected by locally higher HREF and REFS neighborhood probabilities for 3"/6hr and 5"/6hr reaching 70-80% (10-20%). This indicates that many areas could receive 2-4" of rain with locally higher amounts above 5" possible. The flash flood potential will be most significant over urban areas, especially where any backbuilding can occur to lengthen the duration of heavy rain. However, AHPS 7-day rainfall in much of the region has exceeded 150% of normal which is reflected by 3-hr FFG as low as 1.5"/3hrs in some areas. Flash flooding is possible trough training anywhere this evening, but is most likely along the I-95 corridor where isolated significant flash flooding is possible. Weiss ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!6QpBpbNJbIaf1AJhIvV2gg2xhUkECAiHmfNbh7t6O9LAM-RUfn6N3qtUGSGmhXF15c9J= Rxn-pqZ15lfx6_TrZe691eQ$ for graphic product... ATTN...WFO...ALY...BGM...BOX...CTP...LWX...OKX...PHI... ATTN...RFC...MARFC...NERFC...NWC... LAT...LON 41507233 41207136 40857160 40537224 40047351=20 39917366 39307560 39197679 39437738 39947769=20 40507763 40987695 41367564 41497416=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) .