Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Dec 11 2022 05:55:44 AWUS01 KWNH 110555 FFGMPD CAZ000-111500- Mesoscale Precipitation Discussion 1153 NWS Weather Prediction Center College Park MD 1255 AM EST Sun Dec 11 2022 Areas affected...Coastal Central/Southern California & Southern San Joaquin Valley Concerning...Heavy rainfall...Flash flooding possible Valid 110600Z - 111500Z SUMMARY...Strong Atmospheric River Plume sliding south into SoCal. A secondary front brings another shot to Central CA coast maintaining possible debris/flash flooding risk. DISCUSSION...The strong atmospheric river along and ahead of leading well defined cold front continues to slide southward given further digging long wave trough in the Northeast Pacific west of Northern California. This leading moisture plume is starting to reduce in width and overall strength and deep layer moisture dropping to about a max total of 1" total PWAT as it crosses SLO county and rounds Point Conception into southern California.=20 Convergence angle has further reduced as well upon the 40-50kt low to mid-level southwesterly flow, below 45 degrees to more around 20-30 degrees. Further downstream across the Southern San Joaquin Valley, the angle of deep layer flow is also reducing orthogonality to the slope of the southern Sierra Nevada/Greenhorn ranges. Still, this remains potent and with 400-500 kg/m/s IVT values and the still remains favorably oriented to the coastal ranges to support a narrow ribbon of .5-.75"/hr embedded within the broaden longer term .25-.33"/hr rates. Timing/progression of the cold front should reach LA county and NW Orange county toward 12-15z and therefore will support 2-3.5" totals across the Transverse Ranges. The cold front should bank up against the southern Sierra and limit showers/post-frontal scattered cells by 12z allowing for an additional 2-3" across the southern slopes of the Sierra Nevada Range. Intersection with burn scars that dot the region are near/slightly above the rates required for potential debris flows and so risk of flash flooding remains possible. Upstream, GOES-W WV suite denotes a strong inner shortwave is rounding the base of the larger parent synoptic scale trough near 28N125W with a slight negative tilt toward the Bay Area and Central CA coastal range. Cold air advection aloft is steepening lapse rates, while supporting FGEN for a secondary cold front formation from Monterrey Bay westward. The backing sfc to boundary layer flow is strengthening convergence and moisture pooling for a .7-.8" total PWat Max with some 350kt 850mb flow increasing to near 45kts orthogonal to the Santa Lucia Range.=20 Recent heavy rainfall already resulted in localized flash flooding/debris flow, so this secondary shot (though weaker and shorter in duration) may support another 1hr total up to .5" and up to an additional 1.5" as it presses southward. As such, have pulled the MPD area of possible FF, back northward into Monterrey County through 12z, as it is expected to enter/translate through SLO county as well.=20 Gallina ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!7r7hqPZ0BEu3nv0lr4CUMB_1M86hBEUGdVYv_AmlX1XyqH7R5Xsho7mYT5Vts4gaVsEy= ZBZDHuV-RWpwXng8dfle7Tg$ for graphic product... ATTN...WFO...HNX...LOX...MTR...SGX... ATTN...RFC...CNRFC...NWC... LAT...LON 37271973 37261942 37051913 36571877 36021859=20 35361816 34921841 34641833 34301787 34221712=20 33801682 33481698 33101735 32791786 32791857=20 33121950 33912043 34792081 35392111 36032170=20 36442211 36602196 36482152 36002108 35742083=20 35522043 35831997 36571985=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) .