Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Mar 31 2024 23:25:46 AWUS01 KWNH 312325 FFGMPD CAZ000-010520- Mesoscale Precipitation Discussion 0122 NWS Weather Prediction Center College Park MD 725 PM EDT Sun Mar 31 2024 Areas affected...southern CA Concerning...Heavy rainfall...Flash flooding possible Valid 312323Z - 010520Z Summary...A localized flash flood threat will continue across southern CA through 05Z, from near Los Angeles/San Bernardino into the San Diego metro areas, with potential for 0.5 to 1 inch of rain in an hour or less. Discussion...GOES West visible imagery at 23Z showed a persistent axis of surface convergence that was located west-east through the Channel Islands, just north of San Clemente Island before turning southward and parallel to the coast, roughly 10-20 miles west of the San Diego County coastline. Recent outflow has been noted to be pushing across San Clemente Island on visible imagery but some degree of convergence remained to its north. This feature has been an active focus for showers and thunderstorms for the past several hours, located just northeast of a surface low, located roughly 150 miles west of the northern Baja Peninsula via visible satellite imagery. This area of southern CA was beneath the center of a mid to upper-level low/trough with weak storm motions, ~5 kt, using 0-6 km AGL mean layer winds as a proxy for cell motions. As the southern portion of the parent upper trough slowly edges southeastward over the next 6 hours, low level onshore flow from the south to southwest will continue to favor the likelihood of cells containing heavy rain between the coast and the Peninsular Ranges over the next few hours. It is unclear the future location or existence of the surface convergence axis just offshore, but given its proximity to the coast, it seems reasonable that showers and embedded thunderstorms will continue to impact coastal locations of Orange into northern San Diego County in the short term, focusing near an estimated wave along the boundary west of NFG within an axis of instability containing a few hundred J/kg of MLCAPE. Forecasts of MLCAPE from the RAP support values up to ~500 J/kg lingering just offshore of San Diego County through 06Z with low level onshore flow (weak as it may be) maintaining a fetch from the instability reservoir onto land. Slow moving to nearly stalled showers and thunderstorms will have the potential to produce high rainfall rates of 0.5 to 1 inch in an hour or less, supporting a lingering but localized flash flood threat into the night for southern CA. The focus is expected to be in Orange and San Diego counties, but cannot rule out some activity farther north into Los Angeles County as well. Otto ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!42gXXv2miJOjdDFu1m5uuOVep67SRnO_x-w476PQ-WNv5L3ZwGaatosN0jHHnwW-pSxz= aL2z0gJ5CM3eF_mRlZ03lkg$ for graphic product... ATTN...WFO...LOX...SGX... ATTN...RFC...CNRFC...NWC... LAT...LON 34371803 34111742 33731690 33291659 32681644=20 32411645 32261692 32391758 33161814 33661886=20 34271864=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) .