Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Jul 09 2023 13:30:43 AWUS01 KWNH 091330 FFGMPD NYZ000-NJZ000-PAZ000-DEZ000-MDZ000-VAZ000-DCZ000-WVZ000-091840- Mesoscale Precipitation Discussion 0673 NWS Weather Prediction Center College Park MD 929 AM EDT Sun Jul 09 2023 Areas affected...Northern Mid-Atlantic Concerning...Heavy rainfall...Flash flooding likely Valid 091330Z - 091840Z SUMMARY...An unusually strong upper trough for mid-July coinciding with copious amounts of moisture and sufficient instability will result in areas of flash flooding this today. Some cases of flash flooding could be significant with areas sporting more saturated soils most at-risk. DISCUSSION...An impressive synoptic-scale setup for mid-July is unfolding at the same time as a moisture-loaded and increasingly unstable atmosphere takes shape. Excellent upper level divergence aloft, aided by a sharp 500-250mb trough tracking into the central Appalachians, will foster exceptional vertical motion in the atmospheric column today. Meanwhile, a stationary front has already acted as a trigger for morning thunderstorms in central PA. The 12Z IAD sounding is already primed with around 1,000 MLCAPE, PWATs of 1.71", low level RH values >80%, an a warm cloud layer a little over 11,000ft deep. The 12Z WAL sounding, sampling an airmass that will be advected north later today, sported 2.10 PWATs and a warm cloud layer over 13,000ft deep. As daytime heating increases and southerly 850mb moisture transport picks up, MLCAPE will range between 1,000-2,000 J/kg with the higher values farther south. PWATs will also rise to 1.8-2.0", the highest of which will reside from the Delaware Valley on south to the northern DelMarVa. RAP forecasts also suggests warm cloud layers will grow to as much as 12,000-13,000ft deep by mid-afternoon. The complex interactions of the wind flow and available moisture/instability will determine where the heaviest rainfall sets up. One area of concern is northeast MD, northern DE, and the Lower Susquehanna Valley where southerly 850mb flow off the Chesapeake Bay can give rise to a convergence axis in these areas. Speaking of the southerly 850mb flow, it is also ideal for upslope enhancement as far north as the Poconos, northern NJ, and Lehigh Valley. The aforementioned front in central PA and into NY is oriented quasi-parallel to the mean 850-500mb streamlines, supporting not just training convection but backbuilding cells as well. Lastly, there's a large area of heavily urbanized cities at risk, and these areas not only have a greater concentration of hydrophobic surfaces, but many have also seen 300-400% of normal rainfall over the last 7-14 days. These ingredients mixed together lay the groundwork for flash flooding on a larger scale. The 06Z HREF depicted >50% probabilities for 6-hr FFG exceedance between 18-00Z, culminating with 60-80% probabilities in northwest NJ and to the east of Binghamton. These probabilities are similar to the HREF's odds of 6-hr QPF > 10-yr ARI, and there are even some 20-40% probabilities for 6-hr QPF > 100-yr ARI in northern NJ and into south-central NY. In the hardest hit areas, water rises in poor drainage areas, along roadways, and along creeks and streams can occur very quickly and pose a larger threat to life and property. Mullinax ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!5jJHthF0fCUnd99-21k-pxmtZGwc60SXAbIYLVR3hK8gnxyCk_en8ybuwTWWaLhP89Aq= mg6VrgQRTIA4k_gjti8q980$ for graphic product... ATTN...WFO...ALY...BGM...CTP...LWX...OKX...PHI... ATTN...RFC...MARFC...NERFC...NWC... LAT...LON 42897479 42467383 41047391 38957591 38687768=20 39237820 40477786 41697711 42497615=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 3.14-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .