Subj : Flood Potential SoCalif To : All From : Mike Powell Date : Fri Nov 21 2025 09:38:12 AWUS01 KWNH 211245 FFGMPD CAZ000-211830- Mesoscale Precipitation Discussion 1239 NWS Weather Prediction Center College Park MD 744 AM EST Fri Nov 21 2025 Areas affected...Southern California Concerning...Heavy rainfall...Flash flooding possible Valid 211245Z - 211830Z SUMMARY...Risk of slow moving, narrow updrafts capable of ..75"-1"/hr rates likely to continue to a few more hours. Isolated 1-2" totals in/near urban locations in SoCal suggest localized flash flooding remains possible. DISCUSSION...A well-defined closed low is parked directly over southern California with an upstream highly anomalous shortwave/vorticity center descending southward along the western periphery of the low. This and favorable cyclonically curved geography of the coast and mountain ranges will help to keep surface to boundary layer cyclone relatively stationary for the next few hours just along/south of Long Beach, CA. The cold front and associated warm conveyor have pressed eastward into far NW Baja California (state) of Mexico before angling through Imperial Valley and lower Colorado River Valley. However, the western branch of the TROWAL and occluded front remain banked up against the Orange county and San Diego county beaches. GOES-W WV suite shows the core of the upper-level jet remains south near the San Diego country border with Mexico, allowing for solid cyclonically curved left exit ascent across much of SoCal providing solid ascent for updrafts that do develop with the solid surface/low level moisture convergence. The limiting factor will likely be unstable air/vertical ascent through convective processes. MUCAPEs have dropped to around 500 J/kg but are now mostly driven through cold advection aloft. The upstream shortwave will dull this advection for a few hours but may allow the lapse rates to maintain this weak 250-500 J/kg instability. As such, updrafts are likely to remain isolated and generally narrow, though with isallobaric response to the updraft, moisture convergence should allow for the .75-.9" total PWats (loaded mainly below 700mb) to support rates of .75-1"/hr. As such, a localized 1-2" total still remains possible for the next few hours. Naturally low FFG and/or urban hydrophobic conditions will result in solid run-off and maintain a risk of widely scattered incident or two of possible flash flooding through the morning. It is also possible (more likely toward 16-18z) that a few showers/cells may try to develop with some weak clearing through the Imperial Valley along the western branch of the TROWAL. These cells would be also similarly slow moving but likely translating NW rather than NE as with the coastal cells; but there is less certainty with that evolution and a secondary MPD may be required if trends continue to improve. Gallina ATTN...WFO...LOX...SGX... ATTN...RFC...RSA...NWC... LAT...LON 34551850 34481788 34071704 33471650 32801624 32581627 32531672 32561724 32981753 33301781 33581827 33971908 34331893 $$ --- SBBSecho 3.28-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (618:250/1) .