443 FXUS66 KMTR 092214 AFDMTR Area Forecast Discussion National Weather Service San Francisco Bay Area 314 PM PDT Tue Oct 9 2018 .SYNOPSIS...Onshore flow will continue through Wednesday with cooler temperatures. Weak offshore flow will then likely develop late in the week, resulting in warmer and drier conditions from Friday on through the weekend. Dry weather conditions will persist through at least the middle of next week. && .DISCUSSION...as of 03:10 PM PDT Tuesday...Afternoon visible satellite imagery shows coastal clouds lingering along the Marin and Sonoma County coastlines and nosing in through the Golden Gate. This is a result of onshore flow dominating the Bay Area region. Onshore flow will continue through the night as a broad deep trough persists over the Intermountain West. A shortwave is forecast to ride down the western flank of this trough tonight, bringing a pulse of NNE winds to the North Bay Mountains. Some peak in Napa County could gust into the 40 mph range overnight with an outside chance of reaching 50 mph in brief gusts. Humidity at the time is expected to be in the 25% range. At this time there is no Red Flag Warning in place. The Fire Weather Forecast highlights the gusty winds, but conditions are not expected to meet RFW criteria. Either way, diligence and vigilance is always encouraged when conditions are even remotely close to carrying fires. Going for a tale of two halves, drizzle will be an issue along the immediate coast tonight. With the shortwave we'll be looking at a deepening marine layer and should be able to squeeze out abundant moisture from the onshore flow. As such, the afternoon package did expand the reach of drizzle all the way up the Sonoma coast and down to Monterey. Temps across the region will remain seasonable through tomorrow before the shortwave along the broad trough pinches off along the California coast. This will induce some weak offshore flow and warming conditions. Therefore, look for a warming and drying trend for the second half of the week. Overall the forecast remains on track with limited changes. Confidence remain generally high in the pattern for the week with a cutoff low along the coast for the second half of the week. If along the coast or the immediate shoreline, be ready for some wet roadways, otherwise enjoy the fair fall weather. && .AVIATION...as of 10:50 AM Tuesday... Marine stratus surged up the coast last night and into this morning, making slight inroads inland through this morning. VFR prevailing across the inland regions except for a few patches of stratus over the Monterey Bay incl KMRY. Light to locally breezy onshore winds are forecast for most terminals today. For tonight, the marine stratus returns and surges slightly deeper inland, bringing local LIFR to MVFR cigs to most coastally influenced terminals while KLVK and KSJC are left mostly clear. Some offshore winds aloft will be possible overnight at KLVK KAPC and especially KOAK, with NE winds 15-25kt possible at around 1500-2500 ft AGL and calm winds at the sfc. Drizzle is possible along the coast overnight. Vicinity of KSFO...VFR. Light wind this morning shifts to become breezy and onshore by the afternoon and into the evening. Low to med confidence for tonight for patchy stratus cigs around 1000 ft, with highest chance of BKN-OVC cigs from 08-14Z WED. SFO Bridge Approach...Similar to SFO. Monterey Bay Terminals...Patches of stratus linger along the Monterey Bay late this morning. Expect to see KMRY clear out within the next 30 to 45 minutes. Light to occasionally, locally breezy onshore winds into the early afternoon. LIFR to IFR cigs return as early as 00Z but definitely by 02Z for KMRY and KSNS. && .FIRE WEATHER...As of 3:30 AM PDT Tuesday...The general trend through Wednesday is for increasing onshore flow and a deeper marine layer across the district, and thus cooling temperatures and better nighttime humidity recoveries in the hills. However, the exception is possible localized dry and gusty north winds in the North Bay Mountains late tonight and Wednesday morning. Strongest winds are expected to be across the higher hills of eastern and northern Napa County, as well as extreme northeast Sonoma County. In these areas wind gusts of up to 35 mph are possible late tonight through Wednesday morning. Because this is expected to be a short-duration and localized offshore wind event, Red Flag Warnings are not currently anticipated. Will headline local gusty offshore winds in the Fire Weather Forecast. More widespread light offshore flow is forecast to develop late in the week which will result in warm and dry conditions across most of the district from Friday into the weekend. && .MARINE...as of 02:39 PM PDT Tuesday...Split flow across the waters through the next few days with stronger northwest winds in the northern and outer waters and southerly winds along the coast. Occasional to infrequent gale force gusts are possible in the outer waters north of Point Reyes through this evening. Mixed swell with small to locally moderate northwest and southerly swells. Southerly swell peaks later this week due to Hurricane Sergio west of Southern Baja. && .BEACHES...Tropical storm Sergio will bring moderate period and height swell to the Central California and Bay Area coastlines beginning Thursday morning. Exposed south facing beaches will be at highest risk for building surf. Some breakers may reach as high as 10 feet with 10 to 20 minute lulls between sets. All beaches will experience an increase in rip current activity during the second half of the week as this swell arrives and transits the area. && .MTR WATCHES/WARNINGS/ADVISORIES... .Tngt...SCA...Pt Arena to Pigeon Pt 10-60 nm SCA...Pt Arena to Pt Reyes 0-10 nm until 4 AM SCA...SF Bay until 11 PM && $$ PUBLIC FORECAST: BFG AVIATION: DRP MARINE: DRP FIRE WEATHER: Dykema 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