Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Jul 10 2025 00:48:42 AWUS01 KWNH 100048 FFGMPD NJZ000-PAZ000-DEZ000-MDZ000-VAZ000-NCZ000-DCZ000-100630- Mesoscale Precipitation Discussion 0632 NWS Weather Prediction Center College Park MD 848 PM EDT Wed Jul 09 2025 Areas affected...Mid-Atlantic States Concerning...Heavy rainfall...Flash flooding likely Valid 100047Z - 100630Z Summary...A line of thunderstorms along a pre-frontal trough will continue to move E/NE through the evening. Rainfall rates of 1-3"/hr are likely within these storms, leaning to stripes of 2-4" of rain and additional instances of flash flooding. Discussion...The regional radar mosaic this evening shows an impressive squall line with continuous thunderstorms aligned from near Philadelphia, PA southwest to Charlotte, NC. This line has been slowly but steadily moving east, while cells along the line track northeast. As this line has moved east, it has left a swath of MRMS measured rainfall of 1-3" with locally as much as 4" in the past 6 hours, and radar-estimated rain rates from radars along the line continue to be 1.5-2.0"/hr. There is good agreement that the squall line will continue to pivot slowly eastward, although some faster progression has been noted recently across NC/VA. Thermodynamics downstream of the line remain impressive and favorable for the continuation of heavy rain. MLCAPE is above 2000 J/kg in a narrow corridor generally along and east of I-95, with collocated PWs of 1.9 to 2.2 inches, or +1.5 standard deviations according to the SREF. 850mb inflow is measured out of the S/SW at around 20 kts according to regional VWPs downstream of the line, which when combined with the highly anomalous PWs will continue to push anomalous 850-700mb moisture flux into the region. This will support the persistence of heavy rain rates above 2"/hr as progged by HREF 2"/hr neighborhood probabilities of 30-40%, with brief rain rates above 3"/hr possible as reflected by HRRR 15-min rainfall reaching 0.75" or more. Bulk shear along and ahead of the line will remain 20-30 kts through the evening, suggesting multi-cell clusters (and isolated supercells) will continue, and this organization may briefly intensify and temporally extend the heavy rain rates. This will be in addition to training of cells that is expected from SW to NE due to parallel 0-6km mean winds and Corfidi vectors from VA northeast. Farther south into NC, Corfidi vectors pivot to become aligned anti-paralle to the mean wind, indicating that regenerating and backbuilding cells into the greater instability is also expected. Either way, this suggests a high potential for training the next several hours, leading to rainfall that could reach 2-4", or locally higher, according to HREF 6-hr neighborhood probabilities. 0-10cm soil moisture percentiles over this area are generally well above normal, and above the 98th percentile in parts of NC and from Washington, D.C northeast through coastal NJ. This is reflected by extremely compromised 1-hr FFG that is 1.5" or less, suggesting even outside of the urban areas the soils have limited infiltration capacity and are vulnerable to rapid runoff/flash flooding. With these intense rain rates expected to continue for several more hours as the line translates eastward, any training would likely overwhelm these soils quickly, leading to additional flash flooding across the region. Weiss ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!9r5T94Fa3iGEQvrUHdg6ZTRmV78a9FieTHz6yf2eHYvZnUTkGy_DAKcqVohbS6qCxLJ-= oOAT5kPkw13QSM4pIc-jC10$ for graphic product... ATTN...WFO...AKQ...CTP...GSP...LWX...MHX...PHI...RAH...RNK... ATTN...RFC...ALR...RHA...NWC... LAT...LON 40527440 40277397 39617407 39097437 37317565=20 36307665 35677769 35257893 35397955 35668005=20 35948038 36388017 36757932 37297844 38157752=20 39327662 40167588 40467534=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) .