Subj : HVYRAIN: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Jul 09 2023 07:36:06 FOUS30 KWBC 090736 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 335 AM EDT Sun Jul 09 2023 Day 1 Valid 01Z Sun Jul 09 2023 - 12Z Sun Jul 09 2023 ....THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE MID-ATLANTIC INTO WESTERN NEW ENGLAND... ....Mid-Atlantic to New England... Signals for heightened risk for flash flooding with isolated significant localized impacts possible across the Mid-Atlantic into Northwestern New England are coming into focus. A potent shortwave is starting to round the base of the larger scale trough across the Ohio Valley, resulting in some increased negative tilt by late afternoon. Strengthening broad southerly flow off the very moist Northwest Atlantic will increase total moisture across the Delaware/Hudson Valley into New England with 1.75 increasing to 2"+ by midday. In response a surface low and associated cold front (and inverted trof across NY) should support strong moisture flux convergence along its length by mid-morning (if not already ongoing by 09.12z) across NY, central PA to Western VA/NC.=20 Efficient rainfall production should result in localized rain-rates to 2"/hr and possible instances of flash flooding, deep layer steering will support northward moving cells supporting short-term training as the front slowly progresses eastward.=20 As the afternoon evolves, upper-level divergence increases along with heating to increase instability across the eastern US while the surface low strengthens in N VA. This will back the local flow across the Delaware Valley into the Hudson Valley, increasing moisture flux and FGEN ascent through E PA, further slowing forward progress of the convective line while cells still train/repeat to the north. By evening instances of 3-6" locally will become increasingly plausible with 00z HREF probability fields greater than 60% from DC to N VT (with spots near 90-100% for 3" and 30-60% of 5" across NE PA/N NJ to S VT. 00z Hi-Res CAMs have trended slightly eastward to align more favorably to the greatest 14-day precipitation over 300% of climatological normal axis extending from near Baltimore to Philly to N NJ and W MA, suggesting increased runoff potential for these. As the surface wave advances toward the New York Bight by early morning, increased low level flow, will advect unstable across across S NY/New England and with continued isentropic ascent through warm conveyor belt along/north of the surface low, additional efficient thunderstorms a likely to linger overnight, in proximity to SE NY/SW New England as well as into south facing terrain making a more likely scenario for flash flooding. As such, the Moderate Risk of excessive rainfall was shifted eastward slightly to account for the guidance trends. ....Eastern North Carolina... At the tail end of the cold front, the Slight Risk was expanded south and west to account for lower FFG over recently affected areas of west-central VA. Some consideration was made toward including the NC Fall Line/Piedmont region including Charlotte as the southern end of thunderstorm activity may lay out outflow boundaries for late evening/early overnight redevelopment of thunderstorms on increased orthogonal ascent of LLJ across the boundaries. The signal in guidance has increased for this thunderstorm development, but remain generally too isolated/scattered with only isolated enhanced rainfall totals to expand the Slight Risk at this time. ....Southern Plains to Central Gulf Coast... Like prior days, there is likely to be an ongoing MCS across Oklahoma at the start of the forecast period from prior night's upslope flow. Current RADAR and satellite imagery trends denote some increased in elongation of the wave/convective line from west to east with weaker isentropic ascent, though the length should maintain duration for modest rainfall crossing saturated grounds from multiple prior days' complexes, there remains a slightly faster trend toward the east. By mid-day, insolation and convergence in proximity to the MCV across LA/S AR should spur an additional round of stronger, moderately organized thunderstorms.=20 00z Hi-res guidance trends depict a more loosely organized clusters with some weak southwesterly isentropic ascent with cells moving off/away from the boundary into weaker elevated cells across LA/MS into SW AL. This is a general reduction of repeating/training environment expanding the potential for clusters than one or two broader heavy rainfall signatures/footprints. As such, the broad Slight has reduced in confidence for number of potential flooding incidents but remains generally broad enough to maintain, with a reduction of the western extent to account for the faster cell motions of the initial MCS this morning. Gallina=20 Day 2 The Day 2 outlook will be updated by 0830Z. Day 3 The Day 3 outlook will be updated by 0830Z. Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!9g0NAxSp4UMGIYlQd4cfivnk2axXzlOXaPtUt5kOnw3a= 8a5646BIFlweRzmImm_IC0ped-ikevOZpFQHiNoCMGjTMzs$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!9g0NAxSp4UMGIYlQd4cfivnk2axXzlOXaPtUt5kOnw3a= 8a5646BIFlweRzmImm_IC0ped-ikevOZpFQHiNoCqdh7V_c$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!9g0NAxSp4UMGIYlQd4cfivnk2axXzlOXaPtUt5kOnw3a= 8a5646BIFlweRzmImm_IC0ped-ikevOZpFQHiNoCI7vhuNg$=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) .