763 FXUS66 KMTR 161807 AFDMTR Area Forecast Discussion National Weather Service San Francisco Bay Area 1107 AM PDT Sun Oct 16 2022 .SYNOPSIS...A deep marine layer brings widespread cool temperatures and low clouds Sunday. Warming trend begins Monday and continues through midweek, before moderating at the end of the week. Dry conditions continue through the week. && .DISCUSSION...as of 09:16 AM PDT Sunday... A closed upper low is evident via moisture channel imagery this morning over the Desert Southwest with troughing located well offshore from CA. Between these features weak mid-level ridging exists across our area with modest height rises taking place. This is supporting weak high pressure at the surface along the CA coast. A moist layer is evident on the 16.12Z KOAK sounding with near saturation between 2.5-3.5 kft and this is consistent with area observations showing cloud bases in the 2.2-2.5 kft range this morning. Clouds should be slow to clear towards the coast today as a result, with areas along the shore possibly seeing no (or very little) sunshine today. Given steady onshore winds it will be fairly cool area-wide with highs only reaching the 60s and 70s. This is all reflected in the going forecast which is in good shape; so no updates are planned for this morning. && .PREV DISCUSSION...as of 03:49 AM PDT Sunday...Night satellite imagery shows widespread stratus once again, reaching into higher terrain as well. Coastal profilers earlier this afternoon were reporting a marine layer depth around 2500 feet, before they stopped reporting. A look at the 00Z KOAK sounding from this evening shows an inversion layer around 2700 feet. Cloud bases are being reported mostly around 2000 feet from surface stations. As a result of the higher bases, not seeing reports of fog or low visibilities. There has also been some warming at the surface, with most sites reporting temperatures in the upper 50s to low 60s, around 4 to 7 degrees warmer than 24 hours ago. The exception to this trend is the higher elevations in the hills, which are now several degrees cooler from the marine layer influence. Stratus will take a while to erode today, given the deep marine layer, and coastal areas may once again have a mostly cloudy day. While interior areas see clearing by afternoon, temperatures will be cool and below normal area-wide. The warmest interior locales may only reach the mid 70s, while along the coast 60s will be prevalent. Thus, similar temperatures to yesterday, or slightly cooler. The cooling trend is a result of the upper level ridge that was situated over the eastern Pacific being pushed inland by an upstream trough, now several hundred miles offshore. The leading edge of this trough is observed on water vapor imagery. As it approaches the coast this afternoon, we can expect increasing high level clouds. These clouds, along with an invading cooler airmass, will help moderate surface temperatures. The incoming trough and cool air advection may help to partly disrupt the marine layer tonight, though ensembles and hi-res models still show stratus re-forming. Thus, expect another night of low clouds with some patchy fog possible. The incoming trough is projected to stall before reaching the West Coast, and spawn a cut-off low, which will meander off the SoCal coast through much of the week. Meanwhile, the aforementioned upper level ridge will expand over the Intermountain West, leading to a warming trend over much of CA through midweek. Temperatures will likely be 5 to 15 degrees above normal by Wednesday, before moderating by the end of the week. Thus, expect 70s at the coast and 80s inland, perhaps low 90s in the warmest spots Wednesday. Global models are still projecting a trough moving down the coast next weekend along with some moisture. But it seems unlikely that it will dig deep enough to reach the Bay Area, as most ensemble members keep the area dry. The Euro still seems to be the most aggressive model for precip, but even that is not too promising. && .AVIATION...As of 11:07 AM Sunday... For the 18Z TAFs. MVFR throughout the entire CWA as clearing is forecasted to take place around 19Z-22Z. There is a higher chance that inland sites will clear sooner but moderate confidence on timing for all TAF sites. High confidence that VFR conditions will start taking place into the afternoon/early evening, but MVFR will dominate once again throughout the remainder of the TAF period. Possible chance for ceilings to come in before 10Z for the Bay Area, but most likely to arrive after 10Z. Little chance of visibility issues as the marine layer sits about ~2500 feet. There is a slight chance that the marine layer may compress but very low confidence it will lower the ceilings to IFR. Winds showed a southwesterly flow in the morning, but turns onshore into the afternoon. Vicinity of SFO... A mix of MVFR and VFR throughout the TAF period with onshore winds. Some models vary on clearing time and current satellite shows thick stratus flowing over the terminal, therefore moderate confidence that it will clear by 21Z but high confidence that it will clear later into the afternoon, cigs will be VFR. KSFO Bridge Approach...Similar to SFO. Monterey Bay...MVFR conditions as satellite shows some pockets of clearing south of the terminals. Moderate confidence that it will clear by 20z for most areas with greater uncertainty around KMRY. && .MARINE...as of 09:16 AM PDT Sunday...Light southwesterly winds will become occasionally breezy this afternoon. Mixed northwesterly and southerly seas prevail. Winds become northwesterly next week, with the chance for stronger gusts along the immediate coast. && .MTR WATCHES/WARNINGS/ADVISORIES... .Tday...None. $$ PUBLIC FORECAST: Lorber/SPM AVIATION: SO MARINE: SPM Visit us at www.weather.gov/sanfrancisco Follow us on Facebook, Twitter, and YouTube at: www.facebook.com/nwsbayarea www.twitter.com/nwsbayarea www.youtube.com/nwsbayarea