Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Jan 27 2025 02:06:58 AWUS01 KWNH 270206 FFGMPD CAZ000-270805- Mesoscale Precipitation Discussion 0004 NWS Weather Prediction Center College Park MD 906 PM EST Sun Jan 26 2025 Areas affected...Southern California Concerning...Heavy rainfall...Flash flooding possible Valid 270205Z - 270805Z SUMMARY...An uptick in shower and thunderstorm activity is expected through the evening hours across coastal portions of southern California. This 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 continues to show a deep layered low dropping south just off the southern CA coast. Some cooling of cloud tops is noted over coastal Santa Barbara county, resulting in a modest uptick in rainfall rates. As of 01z, water vapor imagery continues to depict mid and upper level dry air further south over Los Angeles county, likely helping limit shower coverage and intensity. However, as the low continues to drop south, we should see a gradual moistening of the column, along with a steepening of lapse rates. These factors should promote an uptick in shower (and isolated thunderstorm) activity over coastal areas of Ventura, Los Angeles and Orange counties as the evening progresses. In fact as of 02z just beginning to see an uptick in shower activity and slight cooling in IR imagery over Los Angeles County. Recent HRRR runs and the 18z HREF are supportive of an uptick in shower coverage and rainfall rates between 02z and 12z. HREF probabilities of exceeding 0.5" in an hour increase into the 20-40% range. The 23z HRRR depicted hourly rainfall around 0.75" just offshore, although the 00z HRRR is back closer to 0.5" an hour for peak rates. Both the HREF and HRRR focus the majority of these higher rates just offshore where the weak instability should stay focused. However, while the better coverage of these higher rates should remain just offshore, do anticipate we will see some 0.5"-0.6" an hour rainfall make it onshore on a localized basis anytime between ~02z and 12z. For the most part this forecast rainfall will only result in localized minor flooding of urban and low lying areas. However, more significant impacts are possible over recent burn scar areas, particularly over Los Angeles County. Confidence on these more significant impacts remains low, however with the expected uptick in shower coverage and intensity this evening, the threat of significant impacts is higher than it was earlier this afternoon. The Eaton, Palisades, Hurst, Franklin, Bridge and Hughes burn scar areas in particular will need to be closely monitored for debris flow impacts this evening into the overnight hours. Chenard ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!4uDbQG2HQ3AXj8bza6JbxE_3NsjrpFL5VCim8O4HzhHqpTV4u8UDgWZJQs1a_ZIc2wmp= mkTgB9Us3LpwC15hDi3sH1k$ for graphic product... ATTN...WFO...LOX...SGX... ATTN...RFC...CNRFC...NWC... LAT...LON 34651835 34431817 34301774 33981760 33631762=20 33451786 33571821 33631832 33991925 34322034=20 34382049 34642044 34551947 34561934 34611884=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 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .