Area Forecast Discussion
Issued by NWS San Diego, CA
Issued by NWS San Diego, CA
260 FXUS66 KSGX 222033 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 133 PM PDT Sun Sep 22 2024 .SYNOPSIS... Warming trend for early this week. The marine layer will become shallower over the next two to three days, becoming confined to the coast and portions of the western valleys. For the middle to end of the week, minor daily fluctuations in high temperatures are expected. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... This afternoon...The marine layer low clouds have mostly cleared except for the beaches in south San Diego County. Cumulus clouds are forming over the mountains as the precipitation that fell a few days ago evaporates in the sunshine. Temperatures are almost universally higher than at this time yesterday, especially in the mountains where some locations are 10-15 degrees warmer. From previous discussion... Numerical models are in good agreement through Wednesday with respect to the synoptic pattern. Cyclonic flow aloft in a stretched trough will evolve in a relatively weak Rex Block by Tuesday, with a closed upper low centered about 100 miles west of San Diego and an upper high centered just off the southern Oregon coast. By Wednesday, a low/trough deepens off the west coast as a strong low pressure system moves into the Gulf of Alaska. This will displace the upper high to a position near the Four Corners. Solutions begin to diverge on Thu and the spread increases significantly as we approach next weekend. However, it seems likely that some form of low/trough will persist near SoCal through the forecast period. High temperatures today will reach the mid to upper 70s in the coastal areas, the 80s to low 90s in the valleys, 70s to low 80s in the mountains, low 90s in the High Desert, and 100 to 105 degrees in the low desert. Additional warming is expected for Monday, with most places 3 to 5 degrees warmer than today. For Tuesday, temps will be similar to Monday with only a degree or two difference in most locations. At this time, it`s most likely that there will be only slight day-to-day temp variations from Wed through Friday with more of a cooling trend for next weekend. However, the spread in model solutions continue to inject significant uncertainty in the forecast. The marine layer will become shallower through Wednesday, with low clouds and fog becoming mostly confined to the coastal areas, inland Orange County and the western portions of the San Diego County valleys. The marine layer may recover slightly (or significantly) for the middle to end of the week if - as some model solutions suggest - the trough deepening off the west coast were to shift eastward even a little. This would put Socal under southwest winds aloft in cyclonic flow. && .AVIATION... 222015Z...Coasts/Valleys...Low marine stratus (based around 1000- 1500ft MSL, tops near 2300ft MSL) mainly over the coastal wates this afternoon. Low stratus builds in again for coastal sites around 03-06z this evening with similar bases and tops. Local vis 1-3SM in BR for higher coastal terrain and valleys. Confidence in return time of around 23/05Z at KSAN is moderate. Mountains/Deserts...Mostly clear skies with unrestricted VIS expected through Sunday evening. && .MARINE...No hazardous marine conditions are expected through Thursday. && .SKYWARN... Skywarn activation is not requested. However weather spotters are encouraged to report significant weather conditions. && .SGX WATCHES/WARNINGS/ADVISORIES... CA...None. PZ...None. && $$ PUBLIC...PG AVIATION/MARINE...Small