Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Mar 13 2023 21:25:15 AWUS01 KWNH 132125 FFGMPD CAZ000-140315- Mesoscale Precipitation Discussion 0105 NWS Weather Prediction Center College Park MD 524 PM EDT Mon Mar 13 2023 Areas affected...central to northern CA Concerning...Heavy rainfall...Flash flooding possible Valid 132123Z - 140315Z Summary...Isolated areas of flash flooding will be possible across the Sacramento Valley into the northern San Joaquin Valley and adjacent lower elevations of the Sierra Nevada through at least 02Z as shower/thunderstorm coverage increases. Hourly rainfall totals of 0.5 to 1 inch will be possible in the strongest cells and area-wide sensitive soils may support areas of flooding developing more quickly compared to normal. Discussion...GOES West visible imagery at 21Z showed expanding cumulus/developing cumulonimbus occurring along the northern ends of the Diablo Range and into portions of the central Valley. Locations just east of these developing showers were mostly clear with the exception of some of the lower elevations of the Sierra Nevada which were experiencing scattered shower activity. Farther north into the northern Sierra Nevada, showers were ongoing and a bit more expansive in coverage compared to locations farther south and there was also greater cloud cover upstream into the northern Sacramento Valley. 21Z SPC mesoanalysis data showed weak MLCAPE of 250-500 J/kg extending across the Valley from east of San Francisco Bay into the northern Sacramento Valley. Precipitable water values were 0.7 to 0.9 inches across the Valley and south to southwest low level flow was helping with upslope enhancement to showers across the Sierra Nevada with 30-40 kt across northern locations but only 10-20 for the central Valley (per VAD wind and RAP short term forecast data). While mid-level lapse rates of ~6 C/km are weaker compared to the weekend, steepening low level lapse rates due to diabatic heating at the surface and modest moisture will likely help to support the expansion of showers and thunderstorms into the late afternoon as activity moves eastward into an increasing field of instability. Recent RAP forecasts support MLCAPE growing into the 500-750 J/kg range by 00Z for some locations across the Valley. Kinematic profiles suggest cell movement will be fairly steady off toward the east at 20-30 kt (in general) and shear profiles support at least some loosely organized thunderstorms though limited instability will be a hindrance to more organization. Despite some of these mitigating factors, hourly rainfall of 0.5 to 1.0 inches will be possible in any of the more developed cells as well as with cell mergers from expanding coverage toward the east into the lower elevations of the Sierra Nevada. This region is fairly sensitive to flooding given recent precipitation and ongoing areas of snowmelt and saturated soils. While cell coverage isn't expected to be widespread, some localized areas of flash flooding will be possible through 03Z. Otto ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!_L18Hgm2m5GLzyRwN8XxtYUo3Dc5t2A3d-Jdyf35xAHyebGBr5HNDMFn4YU_XDYCJx-n= L3PacoxN1b-nqe4yKjV-CWI$ for graphic product... ATTN...WFO...HNX...REV...STO... ATTN...RFC...CNRFC...NWC... LAT...LON 40422140 40122111 39582057 39042028 38462011=20 37771972 37031960 36722007 36772052 36982087=20 37552108 38242142 38972179 39752197 40362190=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 3.14-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .