Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Feb 04 2024 21:01:03 AWUS01 KWNH 042100 FFGMPD CAZ000-050900- Mesoscale Precipitation Discussion 0047 NWS Weather Prediction Center College Park MD 400 PM EST Sun Feb 04 2024 Areas affected...Transverse Range and Los Angeles Basin Concerning...Heavy rainfall...Flash flooding likely Valid 042100Z - 050900Z SUMMARY...High-impact rainfall with dangerous and life-threatening flash flooding is likely across portions of the Transverse Range and the Los Angeles Basin going through tonight as strong atmospheric river activity arrives. DISCUSSION...The latest GOES-W Airmass RGB satellite imagery in conjunction with dual-pol radar and passive microwave data shows strong atmospheric river activity offshore of southern CA advancing inland with locally very heavy rainfall rates. Enhanced IVT magnitudes continue to gradually slide south down across the Transverse Range and will be heading into the Los Angeles Basin this evening as a cold front gradually approaches the region. Low pressure currently offshore of central CA will be lifting off to the north through this evening and the overnight hours which will allow for this trailing cold front and corridor of stronger IVT values along it to tend to slow its advance down the coast with time. This will facilitate a degree of atmospheric river persistence for southern CA that will likely drive high-impact rainfall and concerns for significant flash flooding heading into the overnight hours. IVT magnitudes aiming into the Transverse Range and the Los Angeles Basin should tend to peak in the 500 to 800 kg/m/s range over the next 6 to 12 hours which will be driven by strong low to mid-level southwest flow with 850/700 mb moisture flux anomalies of +3 to +5 standard deviations above normal. This enhanced Pacific fetch of moisture will be oriented orthogonal to the terrain which coupled with large scale forcing/divergent flow aloft and strong frontal convergence should yield enhanced rainfall rates. The 12Z/18Z HREF guidance and recent runs of the HRRR favor very heavy bands of showers with some stronger convective elements producing rainfall rates as high as 1" to 1.5"/hour, and the localized persistence/training of some of these rates should yield highly excessive rainfall totals. Additional rainfall totals going through 09Z (4AM PST) may reach 4 to 8 inches, which will bring some storm totals by later in the night as high as 10+ inches. The heaviest rains should be over the windward slopes of Santa Barbara, Ventura, and Los Angeles Counties. However, even areas in the lower elevations including the Los Angeles Basin are expected to see high-impact rainfall that may reach 2 to 4 inches by late tonight. These rains are expected to result in numerous to widespread instances of dangerous and life-threatening flash flooding, and especially with lingering sensitivities in the wake of the most recent atmospheric river event. Impacts will likely include significant urban and small stream flooding, debris flows, and landslides. Orrison ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!4WqIhIf0U1Bi0RxF7lsnGuCM-Yn0Sx8SOaWcoP32H0ESbP4SuPFPdrGNJ-Nf2tZa6AfR= CgkcA7Aw4D0gybf0nF9NXnc$ for graphic product... ATTN...WFO...HNX...LOX...SGX...VEF... ATTN...RFC...CNRFC...NWC... LAT...LON 35491919 35201861 34981810 34781724 34481670=20 33871658 33641671 33511697 33331749 33501800=20 33711861 34031923 34181959 34221996 34452051=20 34652070 35132064 35362018=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) .