Area Forecast Discussion
Issued by NWS San Diego, CA
Issued by NWS San Diego, CA
300 FXUS66 KSGX 100943 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 243 AM PDT Fri May 10 2024 .SYNOPSIS... There is a slight chance of showers over the San Bernardino and Riverside County mountains this afternoon and evening. Areas of night and morning low clouds and fog will continue across portions of the coastal areas and valleys through the week. Gradual warming inland through Sunday followed by minor cooling Monday and Tuesday. Inland warming trend will resume on Wednesday. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... Marine layer low clouds are struggling to organize over San Diego County this morning, but have filled in across Orange County with some patchy development in the Inland Empire. Elsewhere skies are clear. Clouds will gradually fill in across the valleys by sunrise, then slowly clear back towards the coast by the early afternoon. Water vapor imagery shows an upper level low centered over NV with a trough axis extending west to the Central CA coast. This wave will rotate around the base of the low through tonight, pulling the low further southwest towards So Cal. There is marginal mid- level moisture with this low and High Level Total Totals around 34-36 for the San Bernardino Mountains northward. This should be sufficient for at least isolated showers over the higher peaks of the mountains Riverside and San Bernardino Counties this afternoon and evening. Elsewhere dry weather will prevail with highs a few degrees below normal. The upper low drifts east through the weekend with an upper level ridge setting up over the Southwest. This will bring steady warming inland through Sunday with highs likely reaching the triple digit mark in the low deserts. By Sunday highs will be around 5-9 degrees above normal inland, but the persistent marine layer will keep temperatures west of the mountains closer to normal. The marine layer will become more shallow over the weekend with less inland extent of cloud cover. The strengthening marine inversion will make it harder to get clearing at the coast during the afternoons. A weak closed low will slowly move across the region Monday and Tuesday, bringing minor cooling and allowing the marine layer to deepen once again. Beyond about Tuesday ensemble spread increases considerably regarding the position of the E Pac upper high and the placement of any downstream troughing. It`s currently around a 50/50 split on a stronger ridge into the Pac NW and warmer weather here versus weak troughing across the Pac NW or a western displacement of the high, resulting in cooler weather for So Cal. These differences continue through the end of the week. The range of potential high temperatures is quite massive - around a 20 degree spread for the inland valleys to the deserts, but only around 5-10 degrees for the coastal areas and western valleys since the marine layer will stick around either way. Temperature forecast left with deterministic NBM which closely follows the 50th percentile. && .AVIATION... 100930Z...Coast/Valleys...Areas of low clouds with bases 1800-2600 ft MSL and tops to 3500 ft will occur overnight, though some areas may have only brief/intermittent CIGs. Local VIS 1-4 miles will occur in BR, mainly in the valleys through 16Z, with local terrain obscurations in clouds. The valleys will clear 16Z-18Z, with partial clearing near the coast 18Z-21Z as some locations will have a BKN CIG 2100-2700 ft MSL lasting through Fri afternoon. Low clouds will spread farther inland Fri evening. Mountains/Deserts...SCT/BKN clouds will develop again Fri afternoon over the mountains with bases around 9000 ft MSL with local TCU possible. Otherwise, mostly clear skies will prevail through Fri evening with unrestricted VIS. && .MARINE... No hazardous marine conditions are expected through Tuesday. && .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...Adams