Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Jan 26 2025 19:06:52 AWUS01 KWNH 261906 FFGMPD CAZ000-270105- Mesoscale Precipitation Discussion 0003 NWS Weather Prediction Center College Park MD 205 PM EST Sun Jan 26 2025 Areas affected...Southern California Concerning...Heavy rainfall...Flash flooding possible Valid 261905Z - 270105Z SUMMARY...Locally heavy showers and a few thunderstorms arriving over the next several hours may result in localized areas of burn scar flash flooding, including debris flow activity. This will include the Eaton, Palisades, Hurst, Franklin, Bridge and Hughes fire areas. DISCUSSION...GOES-W satellite imagery shows an upper-level low continuing to drop south toward southern CA, with coastal surface low pressure helping to facilitate an increase in low-level onshore flow into the Transverse and Peninsular Ranges. The flow is modest, but the uptick in Pacific moisture coupled with gradually steepening mid-level lapse rates and divergent flow aloft via DPVA is driving broken coverage of moderate to locally heavy shower activity. Additional shortwave energy rounding the base of the upper low will overspread the coastal ranges this afternoon, including much of the broader Los Angeles Basin. This coupled with a slight increase in diurnally driven instability and orographic ascent should help facilitate an increase in rainfall rates. In fact, there has already been some lightning activity noted with recent low-topped convection that has impacted Ventura County, and radar imagery shows convection tending to intensify just offshore of Los Angeles County which will be moving inland soon. This is where some MUCAPE values of 250+ J/kg are noted in the latest RAP analysis. The 12Z HREF guidance favors occasional rainfall rates locally reaching or exceeding a 0.25"/hour with some of the stronger convective elements that materialize over the next several hours. However, with the slight increase in instability and pulse nature of the convective threat, it is possible that there could be as much as a 0.25" of rain in as little as 15 to 30 minutes. The latest guidance suggests some spotty 6-hour rainfall totals reaching upwards of 1 inch where some of this activity persists over the foothills of the terrain including the San Gabriel and San Bernadino Mountains. Given the significant sensitivities on the ground with the ongoing wildfire activity and/or recently burned areas, these rains may be sufficiently heavy enough, at least on a localized basis, to result in some debris flow/mudslide activity and related flash flooding concerns. The Eaton, Palisades, Hurst, Franklin, Bridge and Hughes burn scar areas in particular will need to be closely monitored for impacts. Orrison ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!53YZ0QmbT34wxoA1C2YMl_sXNG14x0HdATKan4Qquj7yxKUoUmHjETLGk1wc_3hwLdq4= tI_pP8L1bTMokH8WkTqy3os$ for graphic product... ATTN...WFO...LOX...SGX... ATTN...RFC...CNRFC...NWC... LAT...LON 34861989 34761923 34681885 34521836 34381780=20 34271702 33761663 33271688 33101720 33241756=20 33491792 33601830 33841860 34041918 34291960=20 34422014 34662028=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) .