FXUS66 KMTR 282350 AFDMTR Area Forecast Discussion National Weather Service San Francisco Bay Area 450 PM PDT Tue Mar 28 2023 .SYNOPSIS...A cold front is presently moving southward through the Santa Cruz Mountains, lying in the middle of a broad band of rain and showers. Somewhat of a break in the precipitation appears on tap for tonight, but with the next and more convective round moving in Wednesday as the cold upper low itself approaches. Mostly dry weather is forecast for Thursday through Saturday, but then more unsettled conditions look to return beginning the latter part of the weekend and continuing into next week. && .DISCUSSION...As of 02:30 PM PDT Tuesday...Latest satellite imagery shows a broad cold frontal cloud band extending NE - SW through our forecast area. Wind shift with the frontal passage occurred at both KHAF and KSFO right about 19Z (Noon PDT). Winds with and ahead of it got pretty strong and gusty, though not quite to the magnitudes associated with last week's system. The peak gust at KSFO was 48 mph, right at the time of frontal passage and 51 mph at KOAK. Up in the hills it was even stronger, with speeds getting up to 65 mph at the Las Trampas RAWS site in the East Bay Hills. Largest rainfall total noted thus far is 2.96" at Venado in NW Sonoma County. Post-frontal scattered showers are now moving in to northern Sonoma County, while at the same time the leading edge of the frontal precip band hasn't yet reached the far southern portion of the district. Will note that to this point there have been no satellite detections or surface reports of lightning. As the evening progresses, an interval of drier conditions looks to spread southward over the area, but then quickly be followed by the next approaching band of rain. This looks to reach the central Bay Area right around the time of the morning commute and be more showery in nature, and also with the possibility of a thunderstorm and even some small hail as 500 mb temps fall to around -30 deg C and positive surface-based CAPEs begin to develop. This occurs in association with the approach of the postfrontal cold core upper level low, forecast to progress southward down through the northern and central California coastal waters Wednesday and Wednesday evening. The net result will be a cool and showery day, with thunderstorm/small hail chances increasing somewhat as the day progresses, given the combination of a bit of additional midtropospheric cooling in conjunction with late March diurnal surface heating. Snow levels look to be in the 3000 to 3500 ft range, so could see some snowfall on the highest peaks and ridges. Thursday then looks to be dry, aside perhaps from a few residual showers in our southern interior, as the upper low progresses down into Southern California and high pressure at the surface and aloft builds into our area. Ensemble solutions are in good agreement that cool and dry conditions will continue to prevail through Saturday, but with rain chances returning in a Saturday evening to Sunday morning time frame and continuing into next week. && .AVIATION...As of 04:52 PM PDT Tuesday....For the 00Z TAFs. Cold front is currently pushing SE through the South Bay and will exit the terminals within the next couple of hours. A relative lull is expected following this frontal passage, with a general improvement in CIGS and resultant transition to MVFR/VFR territory for the remainder of the afternoon and evening. A few isolated SHRA will still be possible at any time, with brief CIG/vis reductions. Winds largely SE and will remain so in the post frontal environment. Expect an increase in intermittent shower and isolated TS activity after midnight and throughout the AM hours Wednesday. Vicinity of SFO...Southerly winds near or slightly above 10 kt expected to persist much of the afternoon and evening today, with overall break in precipitation and shift to MVFR/VFR conditions. Early morning, increasing potential for showers and TS to continue through the day Wed, with brief MVFR/IFR conditions possible during any heavier showers. SFO Bridge Approach...Similar to SFO. Monterey Bay area terminals...Back end of cold front currently moving through the area, with IFR-MVFR conds and localized heavy rain at times through 01-02Z before CIGS and vis improve and rain moves out. Still potential for isolated brief showers anytime this evening, but chances will ramp up mainly closer to sunrise and during the day Wed. TS will be possible as well, with brief MVFR/IFR conds possible during heavier SHRA/TS. Current W winds will diminish following frontal passage, with general shift to S or SE flow thereafter. && .MARINE...As of 2:18 PM PDT Tuesday...A cold front will reach the southern California waters tonight, post frontal winds decreasing below gales through the afternoon and evening. A low center while gradually weakening will move southward across the offshore waters resulting in showers and a slight chance of thunderstorms tonight and Wednesday. Northwest swell continues to decay but a larger northwest swell builds into the waters tonight into Wednesday, bringing steep and hazardous seas. && .MTR WATCHES/WARNINGS/ADVISORIES... .Tday...Wind Advisory...CAZ006-508>510-512>518-528>530 SCA...SF Bay SCA...Mry Bay SCA...Pt Arena to Pt Reyes 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 SCA...Pt Reyes to Pigeon Pt 0-10 nm && $$ PUBLIC FORECAST: Blier AVIATION: Rodriguez MARINE: Canepa 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