Subj : Flood Potential SoCA To : All From : Mike Powell Date : Thu Jan 01 2026 09:23:10 AWUS01 KWNH 010958 FFGMPD CAZ000-011800- Mesoscale Precipitation Discussion 0001 NWS Weather Prediction Center College Park MD 457 AM EST Thu Jan 01 2026 Areas affected...Southern CA Concerning...Heavy rainfall...Flash flooding possible Valid 011000Z - 011800Z SUMMARY...Flash flooding is possible from the Coastal Range to the Transverse Ranges where soils remain sensitive and saturated. Localized urban flash flooding around the greater Los Angeles metro area is also possible this morning. DISCUSSION...GOES-19 satellite imagery shows a compact 500mb low embedded within an increasingly negative 200-500mb mean trough located west of CA. This upper trough is working in concert with a 700mb ridge near Cabo San Lucas to direct a highly anomalous plume of moisture into not only CA but much of the western U.S.. PWATs along the CA coast this morning are topping 1.25" and are above the 99th climatological percentile. IVT is also topping 500 kg/m/s and winds are out of the SW, which is supportive of some upslope enhancement along orthogonally-oriented terrain from the Coastal Range on south and east through the Transverse Ranges. As the triple point of an occluded low approaches, so will the nose of a 500mb jet streak and low-level winds will strengthen off the coast. Steepening mid-level lapse rates are expected as the upper-low approaches and 00Z HREF guidance does show as much as 250 J/kg of MUCAPE potentially available as far north as Big Sur this morning as a result. 06Z HREF guidance shows high chance probabilities (>70%) for 6-hr rainfall totals >2" between 12-18Z along the San Bernadino Mountains and low-to-moderate chances (30-50%) along the San Gabriel. These are the mountain ranges most susceptible to potential flash flooding in wake of last week's significant flood event and lingering burn scars. As the the dry slot quickly moves in by 18Z, the core of the heaviest rainfall should move north and east with only lingering upslope flow keeping periods of rain around the Transverse and Peninsular Ranges. Given the low FFG's and sensitive soils in the higher terrain, as well as locally heavy rainfall rates around the highly urbanized Los Angeles metro area, flash flooding is possible this New Year's Day morning. Note that rock slides and debris flows are also possible in the Transverse Ranges where soils and burn scars are highly sensitive. Mullinax ATTN...WFO...HNX...LOX...MTR...SGX... ATTN...RFC...RSA...NWC... LAT...LON 36632190 36542164 36222137 35922107 35642076 35252039 35022004 34881962 34851903 34941860 34781831 34491824 34481790 34491738 34371706 34221696 34061748 33891770 33651837 33821908 34241954 34332017 34392067 35062099 35792164 36092200 36412207 $$ --- SBBSecho 3.28-Linux * Origin: Capitol City Online (618:250/1) .