FXUS66 KSGX 151042 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 242 AM PST Thu Feb 15 2024 .SYNOPSIS... Dry and fair weather will continue through the weekend. An incoming Pacific storm system will bring cool and wet weather Monday through Wednesday. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... Low clouds in the coastal basin are again noncommittal this morning, with fairly patchy and shifting coverage. Today through the weekend, we'll have a mix of these nocturnal and matutinal low clouds in the coastal basin while occasional bands of high clouds drift across the sky. A weak trough of low pressure will enhance our onshore flow today to keep temperatures in check. On Friday a high pressure ridge builds slightly and there is a touch of offshore flow. These factors will make Friday our warmest day in the coming week, with temperatures reaching into the 70s in parts of the lower elevations. An impressive jet stream stretches across most of the Pacific Ocean and will strengthen over the next few days as it approaches California. Over the weekend, a couple shortwaves in the stream will break down the weak ridge along the West Coast. The jet buckles on Sunday, allowing a low pressure trough to amplify and deepen off the coast, but that serves to stall the trough. Meanwhile, southwest flow increases into SoCal, tapping the subtropics and forming an atmospheric river that points a firehose of rain into the Point Conception region, as far east as L.A. Orange County will be on its periphery for increasing chances of rain late Sunday. Eventually, the big trough marches forward Monday and Tuesday spreading rain across all of SoCal, but it rapidly weakens as it does. The trough slowly trudges through SoCal Tuesday before the final trough axis lifts through SoCal Wednesday morning, with precipitation ending shortly thereafter. Interestingly, model guidance is better agreed on the timing of the system's exit in seven days than its entrance in four days. We're still fuzzy on when the rain will start and the times when it will be heaviest. But we do have high confidence that overall rainfall will be much higher north (Orange-San Bern Counties) rather than south (San Diego). More and more it's looking like less and less for San Diego. This system does not have the strongest winds, but southerly winds Monday and again Wednesday will be brisk, and strongest and in mountains and deserts. The snow level will remain above 6,500 feet through Tuesday, so accumulations will be modest, a few inches, for places like Big Bear Lake, but over a foot above 8,000 feet elevation. Heavy rain leading to localized flooding is our biggest concern with this storm, especially Orange County and southwest San Bern County. Right now, storm totals Monday through Wednesday look like this: 1.50 to 2.00 inches in Orange County 1 to 2 inches in the Inland Empire 0.50 to 1.30 inches in western San Diego County 0.50 in southern San Diego County's mountains ranging to 4.00+ inches in the San Gabriels 0.10 to 0.50 in the high desert 0.20 or less in the low desert With so much uncertainty, just plan on these numbers changing as fresh guidance and analysis prompts us to adjust in coming days. Also plan on adjustments to onset times, like in fits and starts. Rain rates appear highest any time from Monday night through Tuesday night. The jet stream remains strong and active, so the dry weather expected next Thursday and Friday could be fleeting. && .AVIATION... 151030Z...Coast/Valleys: SCT-BKN020-025 through 17Z with unrestricted vis except 3-5 miles in HZ at KONT and KSBD this morning. Aft 17Z...SCT-BKN250. Mountains/Deserts: SCT-BKN250 with unrestricted vis today and tonight. && .MARINE... No hazardous marine weather conditions through Sunday. A Pacific storm will bring a large, long-period swell Sunday, strengthening southerly winds Sunday night and Monday, and scattered showers Monday and Tuesday. && .BEACHES... A large (8-10 feet) long-period (16-18 seconds) west swell (270-280 degrees) is expected to arrive Sunday morning, producing surf of 7- 10 feet or more on west-facing beaches. Tidal overflow and minor beach flooding is possible Sunday and Monday during the early morning highs tides of 5.0 ft. A second long-period swell could bring more high surf Tuesday. Stay tuned for updates. && .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...MM AVIATION/MARINE/BEACHES...Moede