874 FXUS66 KSGX 090402 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 902 PM PDT Sun Jun 8 2025 .SYNOPSIS... A warming trend continues through midweek, peaking Tuesday and Wednesday for inland and desert areas, before a very slight cooldown towards the end of the week. Above normal temperatures may return by next weekend. The marine layer becomes shallower through mid week with night and morning low clouds for the coastal areas and western portions of the inland valleys. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... This evening...The marine layer is about 1500 ft deep, several hundred feet shallower than at this time yesterday. At this hour, low clouds cover the coastal areas of San Diego County and southern Orange county as well as portions of the San Diego County valleys. The shallowness of the marine layer will inhibit its ability to extend as far inland tonight as the last several nights. It will also reduce the potential for drizzle but makes it more likely that we could see reduced visibility in fog on elevated coastal terrain. High-resolution models still show widespread low clouds over Orange County, the coastal areas and western portions of the inland valleys of San Diego County, although little cloud cover in the Inland Empire. From previous discussion... Water vapor imagery currently shows a weak Rex block with a closed upper low over the coast of central CA and a high over OR. The block, such as it is, will quickly dissolve into a ridge over the western states as the low moves inland and becomes an open wave over AZ by late Monday. High temperatures on Monday will likely be similar to highs today, with only slight warming by a degree or two for the deserts and Coachella Valley. Tuesday through Thursday, the ridge shifts slightly northeast and a quick warm up ensues for nearly all locations east of the coasts. One noticeable change in the models compared to previous runs is the indication of some gulf moisture trying to sneak up into the deserts and Coachella Valley on Tuesday and moreso on Wednesday, which would severely limit the warming potential there. Should this occur, highs in the low deserts and Coachella valley may be cooler by around 3-7 degrees compared to the current forecasted highs for both Tuesday and Wednesday. At this point, chances of exceeding 105F in the Coachella Valley on Tuesday are around 70% while the chance for exceeding 110F is around 40%. Elsewhere, the shift of the high to the north has encouraged significant heating from the previous forecast, with highs for many spots in the Inland Empire now expected to be well over 90F, with around a 60% chance of hitting or exceeding 95F both Tuesday and Wednesday for locations like San Bernardino and Hemet. For the coastal regions, a shallower marine layer would support a slightly quicker burn off and warmer afternoons, but at this point the moderate onshore flow looks to help it persist along the direct coast through at least mid week, helping hold temperatures near normal for mid June while other locations heat up. There is still strong agreement between the global models with an upper low moving south along the Canadian coastline, breaking down the ridge and zonal flow aloft settles in over the region. Newest guidance slows down this low and shifts the high into Baja late week and eventually into the Four Corners this weekend, with weak ridging over SoCal for the end of the week and stronger ridging for the weekend. Currently, ensemble members support this pattern compared to the more aggressive troughing, and this would prevent much cooling off for inland areas and the deserts through the end of the week. Should this pan out, there may be more stagnant temperatures or only a slight cooldown into the end of the week with a quick warm up this weekend. There remains a lot of uncertainty with the placement of the high as well as the Canadian low, but have generally adjusted temperatures to match this warmer solution in the long term. && .AVIATION... 090345Z....Coast/Valleys...Low marine layer clouds (based largely at 700-1000ft MSL) have been filling back in this evening across San Diego County and into southern Orange County. Clouds will continue to spread through Orange County through 06-09z with patchy coverage expected for the Inland Empire by 09-12z. There`s about a 70 percent chance of CIGs at KONT and a 40 percent chance of CIGs to KSBD overnight. VIS restrictions to 2-5 SM in BR for elevated inland valleys and coastal higher terrain. Low clouds expected to clear to the coasts by 17-18z Monday morning, with partial and intermittent clearing possible along the immediate coasts of San Diego County between 21-00z Monday afternoon. Better confidence in clearing through coastal Orange County. Low clouds fill back inland after 00z Tuesday with lower bases and likely less inland extent than tonight. Mountains/Deserts...Mostly clear skies and unrestricted VIS through Monday night. && .MARINE... No hazardous marine conditions are expected through Friday. && .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...Munyan