Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Mar 11 2023 06:02:27 AWUS01 KWNH 110602 FFGMPD CAZ000-111500- Mesoscale Precipitation Discussion 0095 NWS Weather Prediction Center College Park MD 100 AM EST Sat Mar 11 2023 Areas affected...Foothills of the Central/Southern Sierra Nevada Concerning...Heavy rainfall...Flash flooding possible Valid 110600Z - 111500Z SUMMARY...Heavy shower activity is expected to continue overnight across the eastern portions of the Central Valley and into the foothills of the central and southern Sierra Nevada which will maintain concerns for some enhanced runoff and flash flooding. DISCUSSION...The latest GOES-18 WV suite shows the main core of this most recent atmospheric river gradually settling south and weakening with time. However, there continues to be the intrusion of sufficient Pacific moisture and jet energy aloft working in tandem with convergence near a quasi-stationary front for there to be areas of heavy showers impacting eastern portions of the Central Valley and the adjacent foothills of the Sierra Nevada. Radar imagery over the last few hours has been showing repeated development of heavy shower activity impacting portions of Tuolumne, Mariposa, Madera, Fresno and Tulare counties. Aside from forcing associated with proximity of the stalled front, and the intrusion of Pacific jet energy aloft, the latest RAP analysis does show a pool of MUCAPE values of 100 to 250+ J/kg pooled over the Central Valley and this coupled with somewhat elevated vertical shear profiles is facilitating some of this repeated convective development. The deeper layer flow remains largely orthogonal to the terrain as well, and so there is a persistent orographic forcing component to the ongoing shower activity which should largely remain intact going through the overnight hours. Somewhat stronger upper-level jet dynamics offshore are forecast to overspread the region overnight as the left-exit region of a 100+ kt 250 mb jet arrives. Given a combination of modest thermodynamics, and the persistence of dynamical and mechanical forcing for pockets of stronger vertical ascent, the ongoing shower activity should persist through the night, and be capable of producing additional areas of heavy rain. Rainfall rates with the additional convective elements should still occasionally approach or exceed a 0.50"/hour. Additional rainfall totals going through 1500Z (7AM PST) may reach 2 to 3 inches locally. Snow levels remain rather high and generally between 7000 and 8000 feet going from north to south across the MPD area. There continues to be locally significant snowmelt concerns, and the melting snow combined with the additional heavy rainfall, especially in the foothills of the Sierra Nevada, will maintain a threat for enhanced runoff and areas of flash flooding. Orrison ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!9NxJvQMEG4RC3WNDKxTl0q18dNO3T9bhVhX6d3anInjFD64HaRyvjx053BcdkzUXiL27= CBIKwUwX60P-xc5fx_PPXpM$ for graphic product... ATTN...WFO...HNX...REV...STO...VEF... ATTN...RFC...CNRFC...NWC... LAT...LON 37961967 37741911 37251863 36691832 35851820=20 35471840 35491887 35721919 36701963 37192007=20 37712025=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) .