Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Dec 10 2022 10:29:39 AWUS01 KWNH 101029 FFGMPD CAZ000-101900- Mesoscale Precipitation Discussion 1148 NWS Weather Prediction Center College Park MD 529 AM EST Sat Dec 10 2022 Areas affected...Northern to Central California... Concerning...Heavy rainfall...Flash flooding possible Valid 101030Z - 101900Z SUMMARY...Atmospheric River along/ahead of cold front will slowly slide southward from NW CA toward San Francisco Bay by late morning/early afternoon. Rates up to .75"/hr and totals of 2-4" by 18z pose flooding concerns esp. near fresh burn scars. DISCUSSION...A broad longwave pattern dominates the GOES-W WV imagery across the Northeastern Pacific. Very strong deep layer fetch across the subtropical Pacific has pulled a moderately wide moisture plume along its southwest leading edge. CIRA LPW and TPW values are average to slightly above average with .6-.75" & .2 to ..3" aligned in the sfc-850mb and 850-700mb layers respectfully and totals of 1-1.2". The strength of the atmospheric river is the strength of the flow and flux given strong 850mb winds of 60-70 kts already analyzed by VWP from BHX up to 70kts at 7H combined with fairly solid directional convergence. This results in a strong IVT response peaking around 700 kg/m/s along the Northwest CA coast over the next few hours, which is favorably oriented to the orographics for additional ascent/convergence.=20 An embedded shortwave is pressing eastward along the interface of the broad shield of mid to upper level stratus with some transverse banding and cauliform nature suggesting vertical ascent further supported by occasional GLM optical energy signals.=20 Favorable mid-level cold advection is helping to provide some weak mid-level instability to the moisture plume...with 200-300 J/kg MUCAPEs with potential up to 500 J/kg over the next few hours with the best PVA as the base swings through and northward. The 3H jet will continue to maintain broad diffluence to help any verticality to showers. This embedded enhanced shower/thunderstorm activity will support short-term rates of .5-.75"/hr as the traverse the mountain ranges of NW CA, generally below freezing levels at 5-6Kft, this after persistent 4-6hrs of broad ascent at the leading edges of the moisture plume supporting .25-.3"/hr rates.=20 The combination will support pockets of 2-3" with isolated maxima of 4" through the early morning hours across the Coastal Range (reducing through the valley in totals, but perhaps a bit less in those rates associated with embedded cyclical convective cores), before reaching similar overall totals on the lower slopes of the Sierra Nevada Range from Shasta to Placer counties with time. It will remain difficult to precisely forecast these embedded cores with respect to recent burn scars, but there may be opportunities for quick .5" totals to intersect these areas, suggesting debris flows/flash flooding may be possible through morning, though may increase further later toward afternoon as the next stronger jet streak/shortwave feature digs the trough further after 18z directed south of San Francisco Bay toward the Santa Cruz/Santa Lucia Ranges and lower slopes of the Sierra in Placer to Calavaras county.=20=20 Gallina ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!5xfE_E5AspV5WMEPN5luQ9DBLFuwjyYD2HtMHku_WA6uy8jU22e9wbnmQoDS7qbRHxz4= uWcGQaKweEtXhc4XAeD5Cvc$ for graphic product... ATTN...WFO...EKA...MTR...STO... ATTN...RFC...CNRFC...NWC... LAT...LON 41742378 40962373 40662362 39872332 39632291=20 39952268 40622265 40912210 40332169 39752132=20 39022063 38322041 38122058 37952115 37582156=20 37052162 36592154 36002100 36062188 36542228=20 37452286 38412352 39322406 40912465 41712433=20 =20=20=20=20=20=20=20=20=20=20=20=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) .