900 FXUS66 KMTR 081131 AFDMTR Area Forecast Discussion National Weather Service San Francisco Bay Area 431 AM PDT Fri Oct 8 2021 .SYNOPSIS...The first of two disturbances moving through a long wave upper level trough will bring a chance of some light showers this morning, mostly south and east of San Francisco Bay. Then the second one, and a bit wetter, will spread shower chances south to around the Monterey Peninsula this evening and overnight. Otherwise dry conditions look to prevail through the forecast period. Unseasonably cool temperatures today, then moderating over the weekend. A strong weather system dropping into the Great Basin early next week looks to produce periods of gusty north winds Monday into Tuesday that will increase fire weather concerns. && .DISCUSSION...as of 03:15 AM PDT Friday...Latest IR satellite imagery shows the axis of a long and wide band of mid and high cloudiness extending NE-SW through the center of our forecast area, in association with a weak upper level disturbance passing through. Just some modest returns have been evident on radar however, and thus far haven't noted any reports of precipitation. That said, can't rule out the possibility of it bringing a few light showers the rest of the night and Friday morning as it continues to propagate southeastward. Then by afternoon, it should be out of our district entirely with dry and mostly sunny conditions generally prevailing. Temperatures will be on the cool side however, reflecting the unseasonably chilly air mass that will then be over us, with 850 mb temps down to around 5 deg C. Even usually warmest inland locations will generally be confined to the 60s. Friday night, a second and a bit stronger and wetter disturbance will rapidly move in from the northwest and spread a somewhat greater chance of showers southward through most of the CWA. That said, have noted just received 06Z model output has shifted in the direction of more of the shower activity being out over the waters. On the other hand, the latest (03Z) SREF (SPC Short Range Ensemble Forecast System) PoPs are still up in the likely range from Marin County down through the shoreline of SF Bay to Santa Cruz County. High confidence that precip totals will be quited limited, generally less than 0.1 inches with even wettest spots receiving no more than perhaps 0.2 inches. But that said, there is a potentially significant associated hazard: for many places the first chance of roadways, and especially freeways and highways, having wet surfaces for the first time in many months. The leaching out of accumulated oils, and it doesn't take much rain to do this, can quickly make them very slick and slippery. The weekend will bring a return to very pleasant autumn weather conditions, with temperatures rebounding as an upper level ridge temporarily builds in along with warming of the air mass aloft. By Sunday, they should be back to near or even a bit above seasonal norms. All attention turns to increasing northerly winds beginning Monday morning, as a strong "inside slider" type upper level short wave trough moves rapidly southward to our east. North winds look to rapidly pick up behind it, especially over more interior portions of the North and East Bay. At the same time, the air mass is projected to get progressively drier. The net result is heightened fire weather concerns and a Fire Weather Watch remains in effect for the aforementioned areas. In the longer range, 00Z ECMWF, GFS and Canadian Ensemble output all indicate dry conditions and generally seasonal temperatures then continuing through the end of next week. && .AVIATION...as of 04:31 AM PDT Friday...For the 12z TAFs. VFR in the North Bay, while MVFR stretches from the San Francisco Bay Area down the Central Coast. Lightly scattered showers have developed over the East Bay by KLVK along the elevated boundary passing through, but little to no precip is likely falling. High clouds will stick around on Friday, but VFR and breezy onshore winds are expected in the afternoon. Isolated stronger northwest wind gusts are possible for coastal terminals. While mid level clouds move back in Friday night with a return of chances for MVFR conditions and lightly scattered showers Friday night into Saturday morning. Vicinity of KSFO...MVFR with a slight chance for patchy drizzle Friday morning. Breezy westerly winds prevail leading toward stronger gusts between 20 to 25 knots expected Friday afternoon. Lower cigs clear by 16Z for VFR skies despite mid level clouds sticking around. Another weak boundary passes over the terminal Friday night leading to a better chance for scattered showers passing near the terminal. These showers will bring clouds with MVFR cigs back to the terminal Friday night into Saturday morning. Winds will remain onshore and breezy through the night. KSFO Bridge Approach...Similar to KSFO. Monterey Bay...Chance for patchy drizzle this Friday morning as a weak elevated boundary exits to the east. Cigs remain at MVFR levels and are expected to remain through 16Z. VFR forecast for Friday with west winds increasing in the afternoon to 10 to 15 knots. MVFR cigs return Friday evening with a chance for weakly scattered showers late in the TAF period. && .MARINE...as of 02:37 AM PDT Friday...Gusty northwest winds persist over the northern outer waters. Generally speaking winds will subside through the day, but isolated stronger gusts are possible Friday night into Saturday morning as a weak boundary passes over the waters with a slight chance for light showers. Another strong front approaches late Sunday night into early next week that has the possibility to have gale force gusts and steep seas associated with it. && .MTR WATCHES/WARNINGS/ADVISORIES... .Tday...SCA...Pt Arena to Pt Reyes 0-10 nm SCA...Pt Reyes to Pigeon Pt 0-10 nm SCA...Pt Arena to Pigeon Pt 10-60 nm SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm from 9 AM SCA...SF Bay from 9 AM && $$ PUBLIC FORECAST: Blier AVIATION: DK MARINE: DK 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