Area Forecast Discussion
Issued by NWS San Diego, CA
Issued by NWS San Diego, CA
667 FXUS66 KSGX 140928 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 228 AM PDT Sat Sep 14 2024 .SYNOPSIS... High temperatures will remain below normal through the weekend, with night and morning coastal low clouds extending inland to the valleys and foothills. A stronger low pressure system moving inland through central California on Monday will bring a slight chance of light precipitation for the mountains westward as well as gusty winds in the mountains and deserts. High temperatures will increase a few degrees Tuesday, but remain well below average through next week. A second low pressure system will bring additional chances of light precipitation by Thursday. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... Marine layer low clouds have spread into the inland valleys in San Diego County and are slowly spreading into the Inland Empire this morning. Elsewhere they are clear skies outside of smoke from the ongoing wildfires. Low clouds will clear from the inland areas by late morning, but may cling to portions of the coast through the afternoon. The marine layer deepens slightly tonight into Sunday morning, filling in across the coastal basin with limited clearing at the coast again Sunday afternoon. A few ensemble members from both the EC and GEFS show light precipiation west of the mountains on Sunday morning. Introduced patchy drizzle for these areas, though the chance of measurable precipitation remains below 10%. Weak troughing remains across the Southwest this weekend with highs as much as 10-15 degrees below normal each day and gusty southwest to west winds across the mountains and deserts each afternoon into late night, strongest through the passes. On Monday, an upper level closed low digging south along the Pac NW Coast progresses inland across Central California. This will bring greater deepening of the marine layer and a 15-25% chance of precipitation for the coast to the lower coastal slopes of the mountains. Given that moisture only extends up to about 5,000 ft, higher elevations of the mountains - including portions of the Bridge and Line Fires - may not see much if any precipitation, though they will benefit from higher humidity. Any rainfall is forecast to be light, generally less than one-tenth inch, though local higher amounts are possible on the coastal slopes. Winds also peak on Monday with gusts 35-50 mph along the desert mountain slopes and deserts. Isolated gusts in excess of 50 mph are likely through the San Gorgonio Pass and along I-8 near the Imperial County border. High temperatures will be as much as 15-20 degrees below normal: generally in the upper 60s to low 70s across the coastal areas, valleys, and high desert, mid 50s to mid 60s in the mountains, and upper 80s to low 90s in the low desert. The closed low lifts out on Tuesday with long-wave troughing remaining over the Western US. Tuesday and Wednesday will be slightly warmer though highs remain around 10-17 degrees below normal inland. The marine layer is forecast to be around 4000-5000 ft deep these days, but with a weak or non-existent inversion once the trough passes, low cloud coverage will be much patchier. Another closed low develops within the mean trough and drops south and inland across Central and Southern CA sometime late Wed into Thu. Ensembles are in relatively good agreement with the strength and track of this low, with most of the uncertainty lying in the timing of the trough. This will bring another slight (15-25%) chance of rainfall for the coasts to the mountains sometime late Wednesday or Thursday, cooler weather, and more gusty winds in the mountains and deserts. The low lifts out with the mean trough shifting east for the remainder of the week as an upper level ridge nudges in from the west. This will bring gradual warming and dry weather for Friday into next weekend. && .AVIATION... 140900Z...Coasts/Valleys...Marine stratus with bases 2000-2200ft MSL and tops near 3000ft MSL have pushed in 30-35mi inland, and will continue to fill in across the Inland Empire through 12-13z. Obscured visibility where clouds intersect highest terrain with the only VIS reductions below cloud bases due to local FU trapped in the marine layer, especially in the northern Inland Empire near the Line or Bridge fires. Stratus will generally clear from southeast to northwest later this morning around 15-17z, with the Inland Empire and Orange County clearing closer to 17-19z. Some areas along the coasts may struggle to clear at all, with lingering stratus expected through the afternoon, especially for coastal San Diego County. Marine stratus surges back inland again this evening starting 23-02z with similar bases/tops. Mountains/Deserts...Local VIS restrictions will continue through Sat evening due to FU over the San Bernardino County Mountains near the Line Fire and Bridge Fire and the Santa Ana Mountains near the Airport Fire. Otherwise, mostly clear skies with unrestricted VIS prevails through Sunday morning. && .MARINE... Stronger winds will occur in the outer coastal waters Monday and Monday night with gusts 20-25 knots likely from the W/NW. Otherwise, no hazardous marine conditions are expected through Wednesday. && .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...SS AVIATION/MARINE...Munyan