211 FXUS66 KMTR 061807 AFDMTR Area Forecast Discussion National Weather Service San Francisco Bay Area 1007 AM PST Wed Jan 6 2021 .SYNOPSIS...Some patchy valley fog early this morning otherwise increasing mid and high clouds ahead of the next front. Some light rain for the North Bay later this morning through this afternoon but little or no rain will make it south of the Golden Gate. Drying trend with high pressure overnight into Thursday. Another weak front approaches Thursday night into Friday morning with another shot of light rain but again mainly focused over the North Bay. Rapid drying by midday Friday as dry high pressure builds through the weekend into next week. && .DISCUSSION...as of 08:40 AM PST Wednesday...A cool and cloudy start to the day for the Bay Area and Central Coast with high clouds overhead and temps in the 30s/40s. The most notable weather item in the short term will be an approaching cold front that is lurking offshore. KMUX radar continues to show rain increasing over the northern outer waters. GLM has also detected some lightning strikes due west of Pt Reyes roughly 100 miles out. Fortunately, models indicate that instability will gradually decrease through the day. Will watch the convection closely, but current thinking is it will likely dissipate before land. Otherwise, light to locally moderate rain will develop over the North Bay the next few hours and then gradually spread southward to San Francisco. North Bay burn areas appear to be under any threshold from a debris flow standpoint as well. Not expecting much in the way of precip south of the Golden Gate - possibly a few showers may trickle down to the South Bay. No update needed this morning, but will watch the offshore storms closely. && .PREV DISCUSSION...as of 2:38 AM PST Wednesday...Fog is less widespread this morning with only Santa Rosa and Novato reporting 1/4 mile fog so far early this morning. High clouds are more extensive and conditions are less ideal for widespread fog through sunrise though still expect to see some more fog, especially out in the Delta and eastern Contra Costa county as tule fog oozes into the region. For today, the main focus will be on the next incoming weak cold front. The trend for days now has been less precip with this boundary even though things look impressive when looking at offshore satellite imagery. Mesoscale models suggest light rain should develop in northwest Sonoma county by 18z this morning with light rain gradually overspreading Sonoma county this afternoon as well as Marin and Napa. Little or no rain is expected south of the Golden Gate though a few sprinkles or light showers cant be ruled out. Rain totals for the North Bay generally a tenth or less except up to 0.25 for the hills of western Sonoma county. The South Bay and Central Coast will remain dry with just some increased clouds this afternoon and evening. Any lingering shower activity across the Bay Area quickly ends by around 03z tonight. Then high pressure builds overnight into Thursday. Conditions will be prime for overnight dense fog for the North Bay valleys as fresh boundary layer moisture will get trapped by the building ridge and overnight inversions. Other than morning fog no weather concerns for Thursday with lingering high clouds and seasonal temps from the mid 50s North Bay to mid 60s Central Coast. Next weak frontal boundary quickly approaches by Thursday evening. Once again the best precip chances will be focused over the North Bay, mainly during the overnight hours into sunrise Friday morning. The front may be slightly wetter and some light precip could make it onto the Peninsula and portions of the East Bay Friday morning but amounts look light with 0.10-0.25 North Bay and a tenth or less Bay Area with little or no rain south of Santa Cruz. The Weds and Friday light rain events will represent an unceremonious end to what initially looked like a wet week of weather for the Bay Area. Alas our percent of normal rainfall remains in the 20-30% range and falling. The long range trends look dry this weekend through MLK weekend. If some of the longer range models verify we could see some record warmth later next week with widespread 70s for portions of the South Bay and Central Coast. In the uber long range the models still suggest a West Coast trough could set up beyond Jan 20th. && .AVIATION...As of 9:35 AM PST Wednesday...For the 18z TAFs. VRF conditions prevail under a blankets of high clouds as a weak cold front approaches area terminals. The front will bring light rain to North Bay terminals by early afternoon with little to no rain south of KSFO. MVFR and local IFR conditions expected in North Bay with VFR elsewhere. Light winds expected throughout the day. Patchy fog possible overnight into Thursday. Vicinity of KSFO...VRF conditions will prevail under a blankets of high clouds as a weak cold front approaches. Light showers expected to pass over the Bay in the afternoon with tempo IFR cigs possible. Winds should remain light as the front will be weak. SFO Bridge Approach...Similar to KSFO. Monterey Bay Terminals...VRF conditions will prevail under a blankets of high clouds as a weak cold front approaches. Light to moderate winds. && .MARINE...as of 09:00 AM PST Wednesday...Southerly winds will prevail across the northern waters ahead of an approaching weak frontal boundary. Winds will become breezy ahead of the front, particularly over the northern waters, and rain is likely during the day in this area. Once the front passes this afternoon, winds will return briefly to the north and weaken before veering once again to the south as yet another system approaches Thursday, with possible rain. A large, long period northwest swell will continue through the week, resulting in hazardous seas conditions. The next northwest swell will arrive towards the end of the week. && .MTR WATCHES/WARNINGS/ADVISORIES... .Tday...SCA...Mry Bay SCA...Pt Arena to Pt Reyes 0-10 nm SCA...Pt Reyes to Pigeon Pt 0-10 nm SCA...Pigeon Pt to Pt Pinos 0-10 nm SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm SCA...Pt Arena to Pigeon Pt 10-60 nm SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm && $$ PUBLIC FORECAST: RWW AVIATION/MARINE: CW 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