Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Sep 10 2023 19:12:33 AWUS01 KWNH 101912 FFGMPD NYZ000-PAZ000-MDZ000-VAZ000-WVZ000-110100- Mesoscale Precipitation Discussion 1053 NWS Weather Prediction Center College Park MD 312 PM EDT Sun Sep 10 2023 Areas affected...Interior Mid-Atlantic States Concerning...Heavy rainfall...Flash flooding likely Valid 101910Z - 110100Z Summary...Showers and thunderstorms will become increasingly widespread this afternoon and then train to the northeast. Rainfall rates of 1-2"/hr are likely, resulting in 1-3" of rain with locally higher amounts. Flash flooding is likely. Discussion...The GOES-E visible imagery this afternoon shows breaks in mid/high level cloud cover developing across MD/DE/PA, within which Cu development is rapidly progressing. Some of this deeper Cu is producing convection with radar-estimated rainfall rates already eclipsing 1"/hr. As the cloud cover continues to erode, forcing will intensify though SBCAPE rising to 1500-2000 J/kg in conjunction with subtle height falls downstream of an opening positively tilted mid-level trough, weak PVA ahead of embedded shortwave impulses, and modest upper level diffluence within the tail of a 70 kt poleward arcing jet streak. PWs across the region are 1.7-2.0 inches as measured by GPS, well above the 90th percentile according to the SPC sounding climatology, and characterized by deep warm cloud depths with weak moist-adiabatic lapse rates indicating efficient warm rain processes. As instability continues to climb and forcing intensifies, there is good agreement among the various high-res members that convective coverage will increase. This will likely be accompanied by convective intensification as noted by HREF 2"/hr rain-rate probabilities reaching 20-30% in conjunction with the HRRR 15-min rainfall product peaking near 0.75" (brief 3"/hr rain rates). Nearly unidirectional flow from the S/SW evident in morning U/A soundings downstream of the primary trough axis indicates training of storms is likely, which is further reflected by Corfidi vectors aligned to the mean 0-6km wind at 10-15 kts. This should result in stripes of heavy rainfall where training occurs, which is most likely along weak convergent differential heating boundaries and in the vicinity of a stationary front draped across the region. Both the HREF and RRFS TL ensembles forecast a 20-40% chance of 3" of rain in some areas during the next 6 hours, with locally higher amounts possible in the most robust training. FFG across this area is severely compromised in some areas, especially from the Laurel Highlands into the Poconos and near the Catskills, to as low as 0.75-1"/3hrs from 7-day rainfall according to AHPS that has been 150-300% of normal. Additionally, MRMS 24-hr rainfall has been locally as high as 4", creating extremely vulnerable 40cm soil moisture that is above the 95th percentile according to NASA SPoRT. The HREF FFG exceedance probabilities rise to above 40% this evening, and thus it is likely that training of these heavy rain rates will result in scattered instances of flash flooding. Weiss ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!5T9j9m-Ehcrr_jqMbdConz1yKBxXhKv25ckomrgY69Z7fOEGZrc2KAUJsS6ClBV9ZWdh= JrwCaOwFiaYmNpDfh9MhB5c$ for graphic product... ATTN...WFO...ALY...BGM...CTP...LWX...PBZ...PHI... ATTN...RFC...MARFC...NERFC...OHRFC...NWC... LAT...LON 42897433 42657340 42117358 41667462 40847536=20 39787594 39177662 38997715 39127812 39527871=20 40047905 40717892 41887785 42307706 42707590=20 =20=20=20=20=20=20=20=20=20=20=20=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) .