Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Dec 11 2022 15:22:54 AWUS01 KWNH 111522 FFGMPD CAZ000-120100- Mesoscale Precipitation Discussion 1155 NWS Weather Prediction Center College Park MD 1022 AM EST Sun Dec 11 2022 Areas affected...Southwest California Concerning...Heavy rainfall...Flash flooding possible Valid 111520Z - 120100Z Summary...Localized rainfall rates of up to 0.5-1.0"/hr will be possible along upslope regions in southwestern California through this morning and into the afternoon. Localized totals as high as 2-3" (in as little as 3-6 hours) are most likely along the southern faces of the San Gabriel and San Bernadino Mountains. Flash flooding and debris flow are possible, particularly in and near recent burn areas. Discussion...A highly anomalous longwave trough continues to dig southward along the western U.S. coast early this morning, driving a cold front and associated atmospheric river south and eastward into Southern California. The best low-level moisture transport and flux convergence are situated immediately ahead of the front, pushing inland from the southwest and even resulting in some limited instability (with MU CAPE of up to ~100 J/kg). This is allowing for a fairly broad area of moderate to heavy rainfall (rates generally a 0.10-0.25"/hr) with embedded elements of convection capable of 0.25-0.50"/hr rates. Precipitable water values along the landfalling portion of the atmospheric river are indicated to be near 1.0" per CIRA advected layer precipitable water imagery, which is close to record levels (and well above the 90th percentile) for this time of year (via San Diego, NDX, sounding climatology). This should allow for rates along the upslope regions (primarily the southern faces of the San Gabriel and San Bernadino Mountains) to reach as high as 0.5-1.0"/hr over the next 6 or so hours, before gradually weakening and shifting south into the San Jacinto Mountains and far southwestern coastal regions of CA (San Diego Metro area). Rainfall rates in the greater Los Angeles metro and populated inland valleys will tend to max out near 0.25"/hr, which should primarily keep the flash flood threat confined to the upslope mountain regions where lift is maximized. Conditions may become particularly dangerous where 0.5"+/hr rates are realized in the vicinity of recently burned areas (i.e. the Fish and Lake burn scars), resulting in potential debris flows. Churchill ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!7k8K6fbXJE__ptrnIKXZXJonGqJc7DEJINON4LL79LUVIWUqyOe6DXf0kJgfWc2i9qjy= e_RH0wZt8Dv07z55Y8k55ew$ for graphic product... ATTN...WFO...LOX...SGX...VEF... ATTN...RFC...CNRFC...NWC... LAT...LON 34651815 34531771 34531729 34381678 34181645=20 33941654 33751645 33511647 33151636 32821621=20 32561622 32521667 32481723 32811743 33251778=20 33711853 33811872 34351858=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) .