Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Dec 20 2023 22:06:56 AWUS01 KWNH 202206 FFGMPD CAZ000-210400- Mesoscale Precipitation Discussion 1209 NWS Weather Prediction Center College Park MD 506 PM EST Wed Dec 20 2023 Areas affected...Portions of the Central and Southern California Coast Concerning...Heavy rainfall...Flash flooding possible Valid 202205Z - 210400Z SUMMARY...A slow-moving front tapping abundant Pacific moisture and instability will draw storms northward into the western Transverse Ranges, resulting in enhanced rainfall rates and an increasing threat of flash flooding through this evening. DISCUSSION... A slow-moving vertically-stacked low off the coast of Monterey will gradually shift south through Thursday. The occluded front wrapping around the low will be nearly stationary...only slowly drifting east through this evening. Ample Pacific moisture and instability are present ahead of the front, resulting in a corridor of heavy rain, with embedded convective storms. The storms are racing northward with the broad southerly wind flow. As the storms reach the western Transverse Ranges this afternoon and evening, their northward movement will be orthogonal to the east-west orientation of the Ranges. This will locally enhance upslope lift, resulting in heavier rain along the south-facing slopes of the mountains. Up to 1.25 inch per hour rainfall rates will be possible with the stronger storms and upslope flow, with the most persistent heavy rainfall rates in those favored upslope areas. The storms are encountering an area where the soils are a bit drier than normal, so it may take a few hours of these heavier rates before flash flooding can commence. Thus, for this initial period of heavier rain, flash flooding concerns should be isolated to widely scattered. There are several burn scars from recent years into the Transverse Ranges, which are locally prone to flash flooding and debris flows and will flash flood more easily. Heavy rain is expected to continue into the overnight hours beyond the duration of this MPD, which will likely enhance the coverage and severity of flash flooding in the area by then. An updated MPD will be sent around 04Z. Wegman ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!8TSCo2vcaftTqN8Wyp1PJmplEQPepUqLY1BoKQJI-fzEG31h8yNjUzOZs9Ma2r6nZD8K= 2Sibj8VHKQSd31q6uFEtNNE$ for graphic product... ATTN...WFO...LOX...MTR... ATTN...RFC...CNRFC...NWC... LAT...LON 36362115 36112070 35882049 35622022 34901950=20 34751919 34391904 34141923 34391955 34462049=20 34602066 35172086 35932147=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) .