Area Forecast Discussion
Issued by NWS San Diego, CA
Issued by NWS San Diego, CA
357 FXUS66 KSGX 040935 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 235 AM PDT Sat May 4 2024 .SYNOPSIS... Mostly cloudy cool weather will prevail this weekend with gusty winds in the mountains and deserts and periods of showers over and west of the mountains. Southwest to west winds will strengthen through the day today, peaking tonight and early Sunday. Patchy drizzle may occur this morning, but the best chances of accumulating rain will be tonight and early Sunday. Dry and warmer conditions will prevail Monday through most of next week. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... .SHORT TERM (Today-Monday)... Marine layer low clouds have filled in west of the mountains and have spread into the Cajon Pass. Elsewhere skies are clear. The marine layer cloud deck may be thick enough for some patchy light drizzle again this morning, though little in the way of accumulation is expected. A large upper level low currently positioned off the Oregon coast near 44.2N, 131.5W will progress east-southeast into the northern Great Basin this weekend. The trough axis and associated surface cold front will pass through So Cal tonight into Sunday. Both the GFS and EC show IVT of over 400 kg/m/s and a quick-hitting weak atmospheric river tonight into Sunday morning in mostly west- southwesterly flow. Despite the higher IVT, most of the moisture will be confined below about the 750-800 mb level. Given this and the short duration, rainfall amounts will be somewhat limited - generally less than 0.15 inch for the coasts/valleys with local amounts around 0.25 inch near the foothills. Orographics will enhance precipitation along the coastal slopes of the mountains with amounts of 0.25-0.50 inch, upwards of 0.75 inch on the southwest facing slopes of the San Bernardino Mountains. Amounts in the high desert, if any, will be a couple hundredths of an inch, with no precipitation expected in the low deserts. Precipitation will come to an end by early Sunday afternoon. Snow levels will begin near 7500-8000 ft tonight, falling to around 5500 ft behind the cold front as precipitation tapers off. Any snow accumulation will be limited to an inch or less. In addition to precipitation, this system will generate breezy southwest to west winds across the mountains and deserts this afternoon into Sunday, strongest this evening into tonight. Highest wind gusts will be around 50-60 mph along the desert mountain slopes and locally into the deserts with isolated gusts to around 70 mph through the San Gorgonio Pass. Winds slowly weaken late Sunday afternoon into Monday morning. Another round of weaker but still gusty west winds will occur Monday afternoon and evening. Significant cooling occurs through the weekend. Today, highs will be around 3-7 degrees below normal for most areas, near normal in the low deserts. Sunday is even colder with highs around 15-20 degrees below normal inland and 5-10 degrees below normal near the coast. This puts us at highs in the 60s for the coastal areas/valleys and high deserts, 40s in the mountains, and 70s to around 80 in the low desert. Temperatures rebound quickly for Monday, though highs will remain a few degrees below normal. && .LONG TERM (Tuesday-Friday)... The slow warming trend continues into Tuesday as the upper low moves out. Beyond Tuesday is a little less uncertain, however, as ensemble solutions begin to diverge with regards to a second low dropping out of Canada and setting somewhere into the Western US while a ridge sets up to our west. For Wednesday the ensembles are pretty much split half and half on warmer vs cooler scenarios. By Thursday, the cooler scenario with the low retrograding much further SW is the outlier containing only 7 percent of global ensemble members. Given the large uncertainty left NBM for temperatures which shows a very subtle warming trend through the week. This uncertainty also has implications on the depth of the marine layer and the strength of the marine inversion which would affect how far inland any clouds would extend and how much clearing we would have each day. && .AVIATION... 040835Z...Coasts/Valleys/Foothills...Low clouds cover the region west of the mtns, with bases 1800-2200 FT MSL and tops to 3000 ft MSL. VIS reduced to 1-3SM where low clouds and terrain intersect, obscuring higher terrain. Expect clearing 17z-20z inland, with partial clearing near the coast and intermittent CIGs into the afternoon. Elsewhere...Clear skies with unrestricted VIS this morning, with increasing high clouds AOA 15,000 FL MSL later today. Mountains/Deserts...W-SW winds developing after 20z, with the strongest winds after 00z Sun. Expect W-SW winds 20-35 kt with gusts of 45-60 kt. Areas of MOD-STG up/downdrafts and LLWS over/east of mtns. && .MARINE... No hazardous marine conditions are expected through this morning. Gusty northwest wind gusts of 25 to 30 knots will occur this evening through Sunday evening, which will generate hazardous boating conditions, especially in the outer waters. Northwest wind gusts up to 20 knots will be possible over the outer waters each afternoon and evening for Monday through the middle of next week. && .SKYWARN... Skywarn activation is not requested. However weather spotters are encouraged to report significant weather conditions. && .SGX WATCHES/WARNINGS/ADVISORIES... CA...Wind Advisory from noon today to 8 PM PDT Sunday for Apple and Lucerne Valleys-San Bernardino County Mountains-San Gorgonio Pass Near Banning. Wind Advisory from 3 PM this afternoon to 8 PM PDT Sunday for Coachella Valley-Riverside County Mountains-San Diego County Deserts-San Diego County Mountains. PZ...Small Craft Advisory from 3 AM to 10 PM PDT Sunday for Coastal Waters from San Mateo Point to the Mexican Border and out to 30 nm. Small Craft Advisory from 6 PM this evening to 3 AM PDT Monday for Waters from San Mateo Point to the Mexican Border Extending 30 to 60 nm out including San Clemente Island. && $$ PUBLIC...SS AVIATION/MARINE...PG