Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Mar 14 2023 21:43:33 AWUS01 KWNH 142143 FFGMPD CAZ000-150900- Mesoscale Precipitation Discussion 0107 NWS Weather Prediction Center College Park MD 542 PM EDT Tue Mar 14 2023 Areas affected...Foothills of the Central and Southern Sierra Nevada into the Transverse Range of Southern California Concerning...Heavy rainfall...Flash flooding likely Valid 142140Z - 150900Z SUMMARY...Concentrated areas of heavy rainfall combined with snowmelt over the higher terrain, and especially the foothills of the central and southern Sierra Nevada will foster locally significant runoff and flash flooding concerns going through the afternoon and evening hours. DISCUSSION...The latest GOES-W satellite imagery shows robust atmospheric river activity surging across California, with the latest surface observations showing the heaviest rainfall rates focused across the upslope areas of the central to southern Sierra Nevada and into the Transverse Range of southern California. All of this is in association with a strong shortwave trough and associated area of low pressure quickly moving into northern California. Strong deep layer southwest flow around the southern flank of the low center continues to favor enhanced IVT values with magnitudes still on the order of 500 to 750 kg/m/s focused across southern parts of the Central Valley and into the adjacent foothills of the Sierra Nevada along with the Transverse Range. These values are expected to gradual decrease with time as the wind fields slowly weaken, but the moisture anomalies are still forecast to remain very high. In fact, the PW anomalies from the 12Z GFS are progged to be a solid 4+ standard deviations above the mean by 00Z across much of this region. A major driver of this is the deep layer trans-Pacific fetch of subtropical moisture associated with this particular atmospheric river event. The 12Z/18Z HREF guidance favors a transition in the heavy rainfall mode for especially the foothills of the central and southern Sierra Nevada with the hires CAMs indicating a strong likelihood for seeing several semi-organized and linear bands of convection developing over eastern portions of the Central Valley this evening and lifting up into the adjacent foothills of the high terrain. This will be a consequence of steepening lapse rates, modest low-level instability and moist low-level flow working in tandem with upslope flow for heavy shower activity. Heavy rainfall rates of 0.50" to 1"/hour are likely with the more organized convective cells, and some cell-training will be possible. Meanwhile, farther south into the Transverse Range of southern California, the conveyor belt of stronger moisture transport and warm air advection will still be in place and conducive for generating heavy rainfall with the aid of upslope flow over the high terrain and approach of the offshore cold front. Rainfall rates here occasionally approaching and locally exceeding a 0.50"/hour are expected. The latest HRRR guidance supports as much as 3 to 5 inches of additional rain over the next 12 hours going past midnight for the foothills of the Sierra Nevada, with lesser amounts of 2 to 4 inches for the Transverse Range of southern California. The additional rainfall coupled with areas of additional snowmelt over the higher terrain should facilitate concerns for locally significant runoff and flash flooding. Orrison ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!-vjPQC_isQwSN36OFP07C3lRMigsAc3gLxXiwp-KKJTIDAVZLB5CF6Ky1QhA-Kx2f0Li= Vdk7px838d3PhjwwwM6AOuk$ for graphic product... ATTN...WFO...HNX...LOX...SGX...STO... ATTN...RFC...CNRFC...NWC... LAT...LON 38242014 38061965 37741936 37231886 36771851=20 36461829 35821810 35281818 34841835 34561805=20 34381710 33971716 33741766 33671835 33651869=20 33621926 33762011 34112053 34592061 34892024=20 35051956 35411925 36191934 36711957 37362028=20 37982039=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) .