574 FXUS66 KMTR 162005 AFDMTR Area Forecast Discussion National Weather Service San Francisco Bay Area 105 PM 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 01:05 PM PDT Sunday... Today and Tonight: A closed upper low will progress through the Desert Southwest as upstream troughing locates well offshore. Between these features look for mid-level height rises across our area as transient upper ridging takes hold. This will support the poleward extension of subtropical surface ridging from the eastern Pacific towards the CA coast. A moist layer was 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. Given this clouds should be slow to clear towards the coast today despite any influence from the nearby ridge. In fact locations near the immediate shoreline may see very little, if any, sunshine given the pattern. With steady onshore winds it will be a cool afternoon area-wide with high temperatures mostly in the 60s to lower 70s. Even the warmest inland spots should only top out around 75 or so. By tonight upper heights will begin falling slightly as the offshore trough progresses slowly eastward. This should maintain the deep marine layer with clouds quickly spilling inland from the coast during the first portion of the night. Given the depth of the marine layer expect some uniformity in low temperatures with even the higher elevations dropping into the 40s and 50s. Readings along the coast will generally be in the 50-55 degree range, with mid to upper 40s for the inland valleys. Monday and Tuesday: High pressure aloft will strengthen over the Intermountain West as the offshore trough edges slightly closer to the coast. This should maintain a similar pattern of onshore winds, cool temperatures, and plentiful cloud cover into Monday. By Tuesday energy consolidates in the base of the upper trough with a closed low evolving offshore from SoCal. As this occurs heights will begin rising across the Bay Area as the upper ridge flexes back in. This will promote the beginning of a warming trend across the interior with high temperatures reaching the mid 70s to mid 80s. Readings will remain a bit cooler along the coast however given morning clouds followed by afternoon sea breeze cooling. Overnight temperatures should remain seasonal and between 45 and 55 degrees with the warmest temperatures along the coast and bays. Wednesday through Friday: The upper ridge will remain prominent across much of the west through Wednesday before weakening in response to upper troughing dropping into the northern Rockies and High Plains by Friday. Meanwhile the closed upper low should remain offshore from SoCal with our only local impact being some potential increase in mid to high level cloud cover. The greatest influence from the upper ridge should be felt on Wednesday with far inland temperatures warming into the 80s to perhaps around 90. Thereafter some cooling is possible on Thursday and becomes likely by Friday as the upper ridge further weakens. Even so it's still looking warm for interior areas with 70s to perhaps some lower 80s in the warmest spots. Some erosion/compression of the marine layer appears possible during this time with the potential for earlier daytime mix out of clouds for coastal areas. This should promote warming of high temperatures there as well, with readings in the mid 60s to lower-mid 70s possible. Lows should also be a bit warmer with 50s in the lower elevations and some lower 60s in the hills. Next Weekend: A more progressive flow pattern should evolve aloft with upper troughing digging into the Pacific Northwest and Intermountain West. Of less confidence is whether the trough's influence could extend into NorCal. Comparing model ensemble members it's noted that a few do bring very small rain chances into the Bay Area. However the majority keep us dry and this is the most likely forecast outcome. Otherwise look for cooler temperatures with a deepening marine layer and more coastal/valley clouds expected. && .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 01:02 PM PDT Sunday...Light southwesterly winds will become occasionally breezy this afternoon. Mixed northwesterly and southerly seas prevail. Winds become northwesterly towards mid week with stronger gusts and higher seas developing through next weekend. && .MTR WATCHES/WARNINGS/ADVISORIES... .Tday...None. $$ PUBLIC FORECAST: 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