Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Jan 10 2023 07:59:02 AWUS01 KWNH 100758 FFGMPD CAZ000-101500- Mesoscale Precipitation Discussion 0035 NWS Weather Prediction Center College Park MD 258 AM EST Tue Jan 10 2023 Areas affected...portions of central and north-central CA Concerning...Heavy rainfall...Flash flooding possible Valid 100752Z - 101500Z Summary...A renewed round of heavy rain will move into portions of the central CA coast beginning 09-11Z, quickly spreading east and south through 15Z. Peak rainfall rates over 0.5 in/hr are expected with an additional 1-3 inches in the favored upslope terrain through 15Z. Given recent heavy rain and ongoing areas of flooding, renewed areas of flooding will be possible. Discussion...07Z water vapor imagery showed two vorticity maxima approaching the West Coast, part of a negatively tilted mid-upper level trough axis crossing just south of 40N 130W. RAP analysis data showed a mid-upper level jet max of 110 kt located on the south side of the upper trough with diffluent and divergent flow immediately downstream. Surface observations and satellite imagery helped place an occluded/cold front at the leading edge of the mid/upper trough, rapidly approaching the West Coast. While CIRA Layered PW imagery showed the deeper and more anomalous moisture axis pointed into southern CA, just ahead of a dissipating cold front, a secondary surge of moisture with PW values of 0.9 to 1 inch was located with the upstream cold front 150 miles west of San Francisco. As the mid to upper-level trough axis continues to advance toward CA over the next 6-9 hours, a narrow plume of 500 to 600+ kg/m/s IVT is forecast to swing across central CA just ahead of the frontal boundary. A relatively narrow axis/band of heavy rain should follow the plume of IVT into CA with intense rain over a short period of time. While precipitable water values will only peak near 1 inch near the coast, 850-700 mb winds of 50-60 kt and increased ascent at the leading edge of the mid/upper level jet streak should help to support localized rainfall rates up to and just over 0.5 in/hr, especially where orographic ascent becomes maximized from the Coastal Ranges into the upslope regions of the Sierra Nevada. These higher rates should be fairly quick hitting, lasting for 1-2 hours at most for any given location due to the progressive nature of the storm system. However, many locations across CA are already experiencing flooding due in part to an anomalous rainfall event over the past 24 hours with 1-3" reported in many locations, 3-5" for the central Coastal Ranges and 5-15" for the southern Coastal Ranges into the Transverse Mountains. The forecast of an additional 1 to 3 inches with peak rates near 0.5 in/hr will act to renew or exacerbate ongoing flooding across the region. In the wake of the cold front, colder 500 mb temperatures tied to the core of the mid-level low will support increasing 700-500 mb lapse rates of 7-8 C/km. Corresponding increases in instability and sufficient mid-level shear will support some stronger cells, but the storm mode should be scattered and showery in nature compared to the surge tied to the front. Otto ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!9fjHJXLtAIThnFJOE9UUh7troyrpEWRBf4LUJAvPdT3SbKJ2nn_e5O7qmU1bFbR80umx= j1nj0mqouROAdZFRinY_ucE$ for graphic product... ATTN...WFO...EKA...HNX...LOX...MTR...STO... ATTN...RFC...CNRFC...NWC... LAT...LON 39992142 39002042 37761956 37311914 36721870=20 36291858 36201864 36201890 36581927 36651954=20 36261989 35971994 35601981 35271991 35102032=20 35122098 35972186 37202265 37822320 38682381=20 39502419 39932388 39982238=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) .