Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Mar 11 2023 18:50:47 AWUS01 KWNH 111850 FFGMPD CAZ000-120400- Mesoscale Precipitation Discussion 0096 NWS Weather Prediction Center College Park MD 149 PM EST Sat Mar 11 2023 Areas affected...central to northern CA Concerning...Heavy rainfall...Flash flooding possible Valid 111847Z - 120400Z SUMMARY...Showers and eventual thunderstorms will continue a flood/flash flood threat into the afternoon and evening hours. Peak rainfall rates over 1 in/hr will be possible with an additional 1 to 2+ inches of rain through 04Z. These additional rainfall totals may contribute to new or renewed areas of flooding. DISCUSSION...GOES West water vapor imagery showed a zonally oriented upper level jet across the eastern Pacific into the West Coast with Derived Motion Winds showing a 110-120 kt core focused from roughly 30N/140W to the south-central coast of CA at 18Z. On the cyclonic shear side of this jet were numerous vorticity maxima tracking eastward within the westerly flow aloft. Regional radar imagery at 18Z showed a relative lull in precipitation intensity across much of CA compared to yesterday but mean westerly flow in the 850-700 mb layer of 15-25 kt was allowing showers with brief surges in intensity for the south-central Sierra Nevada while more stratiform precipitation was falling across the northern Sacramento Valley. Abundant rainfall has fallen over CA during the past 48 hours with 1-3 inches in the Valley and 5-10 inches reported in the central/southern Sierra Nevada, translating into areas of flooding which are ongoing with saturated soils and creeks/streams/rivers at or above their banks. Despite abundant cloud cover noted on visible imagery this morning, estimated MLCAPE from the 17Z SPC mesoanalysis was 100-300 J/kg across the San Joaquin Valley owing in part due to relatively steep mid-level lapse rates. 12Z soundings from OAK, VBG and REV showed 700-500 mb lapse rates of roughly 6.5-7.0 C/km and these values are not expected to change much over the next 12 hours given no appreciable changes in mid-level heights forecast. Daytime heating is expected to support an increase in MLCAPE into the 500-1000 J/kg range for 20-22Z. Precipitable water values are likely to increase slightly from just under 1 inch to just over 1 inch for the Valley, remaining fairly anomalous for early March. Expect continued showers into the afternoon, with orographic enhancement into the upslope regions of the Sierra Nevada with mean westerly flow aloft to continue throughout the day into the evening hours. Between 20-21Z, as instability increases, showers and perhaps some organized thunderstorms with sufficient speed shear aloft are expected to form from the Sacramento into the San Joaquin Valleys with a general west to east movement. Brief training cannot be ruled out with rainfall rates peaking above 1 in/hr at times. Snow levels are expected to range from ~6000-8000 ft, highest to the south. Areas of snowmelt continue to contribute to areas of ongoing flooding and the addition of an additional 1 to 2+ inches through 04Z is expected to only exacerbate flooding concerns. Otto ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!9UsYnhW6W1m25L0We8jZRwNMk7bCw5bSuT-AtHa5TFJ2OjCvXN5iXbDagoVDKI6g23wP= MOHciG5COBLTjLFL9AtetF0$ for graphic product... ATTN...WFO...HNX...STO... ATTN...RFC...CNRFC...NWC... LAT...LON 39872094 39642066 39282048 38942026 38562016=20 38111992 37471952 37461932 37331921 37151916=20 37061909 36961898 36761879 36461868 35911830=20 35181839 35101879 35491907 35911930 36452005=20 37082062 37712099 38422130 39062152 39522156=20 39782143=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) .