Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Jan 14 2023 21:16:26 AWUS01 KWNH 142116 FFGMPD CAZ000-150900- Mesoscale Precipitation Discussion 0042 NWS Weather Prediction Center College Park MD 415 PM EST Sat Jan 14 2023 Areas affected...Southern CA Concerning...Heavy rainfall...Flash flooding possible Valid 142115Z - 150900Z SUMMARY...Heavy rains associated with the atmospheric river impacting the West Coast will continue to settle south and overspread southern CA going through the evening hours. Areas of flooding will be a concern given the wet antecedent conditions, and an isolated threat of flash flooding will be possible for the burn scar locations over the Transverse and Peninsular Ranges. DISCUSSION...Surface observations and satellite imagery show a cold front advancing inland across central and northern CA as the main axis of the attendant atmospheric river advances farther south down the coast into much of southern CA. A southwest low-level jet of 30 to 40 kts ahead of the cold front continues to favor robust warm air advection and moisture transport into the coastal ranges, along with southern portions of the San Joaquin Valley and the adjacent foothills of the Sierra Nevada. The IVT values are expected to remain relatively strong heading into the evening hours despite some expected weakening of the low-level jet, and the 12Z NAM/GFS solutions support IVT magnitudes reaching 500 to 750 kg/m/s over the next several hours across the Transverse and Peninsular Ranges with diminishing values farther inland. Rainfall rates though will remain rather high with widespread 0.25" to 0.50"/hour rates expected to peak locally to as high as 0.75"/hour along and just ahead of the approaching cold front. The orthogonal nature of the low to mid-level flow to the terrain and the incorporation of moisture offshore with some subtropical origins will be a key facilitator of these heavier rates for the remainder of the day and heading into the evening hours. By late this evening, the advance of the cold front farther inland should shunt the atmospheric river axis far enough south that the organized heavy rainfall threat will begin to diminish. However, there will still be sufficiently moist onshore post-frontal flow for additional showers to persist over the upslope areas of the higher terrain. Going through midnight, additional rainfall amounts may reach as high as 2 to 4 inches, with isolated heavier amounts possible. The coastal ranges will see the heaviest overall totals. These additional rains with this atmospheric river evolution will foster concerns for more runoff problems and flooding given the wet antecedent conditions. An isolated threat of flash flooding is expected for the more sensitive burn scar locations as well where some of these heavier rainfall rates materialize. Orrison ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!4TWwITg0tKajdz0HmTbkrF-PIFzV_-S0_qf0l42GYyC-KSYuFGC1HYdsEeXnfW4qWfTk= wzFyajRBAXe8pGwiisRnXHY$ for graphic product... ATTN...WFO...HNX...LOX...MTR...SGX... ATTN...RFC...CNRFC...NWC... LAT...LON 37151903 36181865 35281833 34681790 34331697=20 33431631 32711622 32551716 33461800 34171938=20 34372020 34512058 34972071 35272060 35822025=20 36481999 37121968=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) .