Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Dec 21 2023 15:31:10 AWUS01 KWNH 211531 FFGMPD CAZ000-212130- Mesoscale Precipitation Discussion 1212 NWS Weather Prediction Center College Park MD 1030 AM EST Thu Dec 21 2023 Areas affected...Central and Southern California Coast and Adjacent Mountains Concerning...Heavy rainfall...Flash flooding likely Valid 211530Z - 212130Z SUMMARY...Heavy rain redeveloping offshore will move into the coast through this morning. Flash flooding likely as up to 1 inch per hour rainfall rates move over the same areas hit with 2 to 6 inches of rain last night. Urban/small stream flooding is likely with possible debris flows near burn scars. DISCUSSION...An upper-level vorticity maximum well southwest of the Catalina Islands is advancing northward towards the California coast this morning. It has begun to increase rainfall rates around the Channel Islands, which will subsequently push north-northwest into the coast and adjacent mountains. MU layer instability of 500 to 1,000 J/kg has developed offshore based on the SPC mesoanalysis, which will further support heavier rainfall rates as cold air associated with the upper low rotates above much warmer air near the surface. The lull in the rainfall early this morning will be ending shortly as impulses of heavy rain redevelop. 2 to 6 inches of rain have fallen along the coast and adjacent ranges so far, with an additional 1 to 4 inches likely through midday. The highest totals are expected along south-facing slopes. The latest consensus of CAMs guidance suggests most, if not all the rainfall forecast through this morning will impact Oxnard and points west, with relatively little forecast for the L.A. Basin. That may change late today into tonight, but for now, few impacts are expected for the L.A. Basin. Meanwhile, flash flooding impacts are likely for Oxnard and points north and west, with some uncertainty as to how far north into SLO/Monterey Counties the heaviest rainfall extends. This is primarily due to the increasing easterly/offshore component to the wind that will develop with latitude, which will work to limit the northward extent of the rainfall. Thus, there is more certainty that the further north up the coast you go, the more likely any significant rainfall this morning will remain near the coast. Urban/small stream flooding will likely worsen or redevelop in the impacted areas, with possible debris flows near burn scars. Wegman ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!-mIPHyGGjDhxehuU0K-XIq0kRl6RsOFCtFbwM8Q4MG9J_DXh9y9CYxLBPmjFnna7z5kd= tjyLt40BNiQa4vXFfrfo2YA$ for graphic product... ATTN...WFO...LOX...MTR... ATTN...RFC...CNRFC...NWC... LAT...LON 36322180 36312126 36012068 35802029 35562021=20 35271993 35041958 34901953 34781929 34761888=20 34321862 34001899 33971905 34291955 34422060=20 35082082 36052186=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) .