Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Feb 19 2024 05:19:22 AWUS01 KWNH 190519 FFGMPD CAZ000-191600- Mesoscale Precipitation Discussion 0064 NWS Weather Prediction Center College Park MD 1218 AM EST Mon Feb 19 2024 Areas affected...Central and Southern California Concerning...Heavy rainfall...Flash flooding likely Valid 190515Z - 191600Z SUMMARY...Heavy rainfall arriving across the coastal ranges of central to southern CA, including portions of the Transverse Range, will couple with wet antecedent conditions to result in areas of flooding and flash flooding. DISCUSSION...An atmospheric river of Pacific moisture focused around the southeast flank of an upper-level trough offshore of the West Coast will be focusing a heavy to excessive rainfall threat overnight and into Monday morning across the coastal ranges of central to southern CA. The latest CIRA-ALPW data products in conjunction with GOES-W WV satellite imagery show a relatively concentrated axis of mid-level moisture already streaming inland across the terrain with the axis of deeper layer moisture transport extending well southwest and offshore of southern CA. IVT magnitudes nosing toward the Santa Lucia Range and extending south down toward the Santa Ynez Range are already approaching 500 kg/m/s, and localized rainfall rates across these areas have been approaching a 0.50"/hour over the last couple of hours. The latest GOES-W IR satellite imagery shows some cloud top cooling noted offshore of Monterey, San Luis Obispo, and Santa Barbara County with a more focused batch of heavier showers quickly approaching and this was confirmed by a 0253Z GPM/GMI overpass which showed multiple bands of broken convection and heavier rainfall rates. This activity is being aided by a combination of some offshore instability and also the nose of an increasing southwest low-level jet which is yielding an axis of stronger low-level speed convergence. A cold front offshore of the West Coast will be gradually settling southeast overnight and will be crossing over the coastal ranges. However, the front will also be slowing down as it becomes more aligned with the deeper layer steering flow. This coupled with strengthening IVT magnitudes approaching 750 kg/m/s in the 06Z to 09Z time frame in association with the low-level jet should focus enhanced rainfall rates into the orographically favored terrain along the coast. Given the orthogonal orientation of the deeper layer IVT axis, the rates should be maximized and occasionally capable of reaching 0.75" to 1.0"/hour, and especially with any more organized convective elements that advance inland. Rainfall amounts overnight and through Monday morning are expected to be on the order of 3 to 6 inches, with isolated heavier amounts possible. The heaviest rains should gradually focus over the Transverse Range in particular, with Santa Barbara County and eventually Ventura County likely to see enhanced rainfall rates and corresponding totals with this event. Given the sensitive/wet antecedent conditions on the ground already, these rains with this latest atmospheric river event are likely to cause areas of flooding, including a threat for flash flooding. Debris flow and landslide activity will also be a notable concern at least locally as these heavier rains arrive. Orrison ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!87K6utbkLzkeH6djxlX7TIA2Y98wsIDgtaW_id6rdzf90m5K6DEcGEcmmr7mJQpTKqAi= OeBQL1UWAiTTtUOAxsfQfqA$ for graphic product... ATTN...WFO...HNX...LOX...MTR... ATTN...RFC...CNRFC...NWC... LAT...LON 36942093 36072004 35261962 34751858 34381845=20 34011895 34201973 34282032 34552069 35322112=20 35582139 36172184 36632192 36822169=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) .