Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Dec 01 2023 22:44:25 AWUS01 KWNH 012244 FFGMPD MSZ000-LAZ000-TXZ000-020430- Mesoscale Precipitation Discussion 1184 NWS Weather Prediction Center College Park MD 543 PM EST Fri Dec 01 2023 Areas affected...Southern LA Concerning...Heavy rainfall...Flash flooding possible Valid 012230Z - 020430Z Summary...Recent radar and IR imagery depict intensifying thunderstorm clusters just southwest of HGX. Continued development and training of this activity over the next several hours along a slow moving cold front could lead to isolated- scattered flash flooding given saturated antecedent conditions.=20=20=20 Discussion...Trends in radar mosaic and IR imagery within the past hour suggest a gradual uptick in thunderstorm coverage and intensity just southwest of HGX, which were lifting to the northeast around 30-40 kts. This activity appears to be mainly forced along a slow moving cold front and frontal wave analyzed at 21z just offshore the Texas coastline, by RAS. Downstream of these storms, weak southerly flow and filtered sunlight beneath a shield of high cirrus has allowed for modest 1000-1500 J/kg MLCAPE within a "skinny" profile to develop across LA, with 45-50 kts of effective bulk shear to support storm organization and maintenance. Within the warm sector of the front, recent ALPW also highlights a plume of moisture pooled from the surface through 700 mb to further enhance rainfall efficiency. 0 hour forecast soundings in LA and MS depict a lingering inversion above 700 mb which could initially dampen convective coverage and intensity through the next 2-3 hours. However, strengthening right entrance forcing going into tonight combined with embedded shortwave perturbations within the southern stream are expected to remove the lingering cap and promote expanding thunderstorm coverage in the vicinity of the cold front, which is forecast to meander southeast tonight. Thus, the concern is for this activity to redevelop and train across southern LA as the mean storm motions align with the front, with rainfall rates upwards of 2-3" possible per recent runs of the HRRR. The last several runs of the HRRR have trended toward a more narrow, focused band of 3-4" of rainfall through 4z across southern LA as the front sinks southward. This will possibly support a threat of isolated to scattered flash flooding going into tonight, especially over areas which saw 3-6" of rainfall yesterday along a similar band of heavy rainfall.=20=20 Asherman ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!6KnrGLi3iZrbz08Zz1q01Aupb2yjE0XFK50jS_o0pjlJsormQwEAOu3K03Tiot4YEwiI= DB7XjIBctofvlIRqWvzgUFI$ for graphic product... ATTN...WFO...JAN...LCH...LIX... ATTN...RFC...LMRFC...WGRFC...NWC... LAT...LON 31178991 30598944 29979011 29559139 29439244=20 29579359 29759405 30329370 31039166=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) .