Area Forecast Discussion
Issued by NWS San Francisco Bay Area, CA

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721 FXUS66 KMTR 042153 AFDMTR Area Forecast Discussion National Weather Service San Francisco Bay Area 153 PM PST Sun Dec 4 2016 .SYNOPSIS...A mainly dry cold front will approach northern California Monday and Tuesday with seasonably cool temperatures. There will be a slight chance of showers on Tuesday with the front. Wednesday morning may be the coldest morning so far this season with inland valleys around 30 degrees. Warm frontal rains will be possible later Thursday into Friday. && .DISCUSSION...as of 1:53 PM PST Sunday...Some high clouds over the Bay Area this afternoon with afternoon highs in the upper 50s to around 60. The high clouds will keep overnight lows from dropping too much as a mainly dry cold frontal boundary pushes into northern California. Daytime highs will cool into the mid 50s for Monday with high clouds and a cooler air mass in place. A secondary cold front/short-wave will drop down on Tuesday with steady rains confined to north of Cape Mendocino. There may be just enough moisture and cold instability aloft to generate some isolated showers across the area on Tuesday so slight chance pops have been expanded for the Tuesday time frame. Any qpf with these will be light and widely scattered in nature. The coldest airmass of the season will be left in the wake of that boundary and overnight lows by sunrise Weds morning could be the coldest so far this season. Still a few days out so will hold off on any frost/freeze type headlines as the leftover low clouds or incoming high clouds could limit the amount of cooling. Brief ridging will return on Wednesday with highs in the 50s as high clouds begin to increase ahead of a warm advection pattern. Confidence is increasing for warm advection rains to develop later Thursday into Friday as a pacific jet approaches the region. Early qpf numbers from the rfc shows 1-2.5 inches of rain potential but at this time the best chances look to be focused from the north bay southward to the Santa Cruz Mtns. Still a lot of time to sort out timing and rainfall totals with this event but the ecmwf has been consistent for at least the last four model runs. With no strong cold advection not expecting heavy rain rates but rather a prolonged period of soaking light to moderate rains sometime later Thursday into Friday. Low confidence beyond that with some type of break likely Friday night into Saturday but then the models diverging on possible continued systems later next weekend or early next week. Either way no blocking ridges in sight and a nice moderately active start to the rainy season. && .AVIATION...As of 10:00 AM PST Sunday...VFR through the day due to offshore flow at the surface. Moisture will return tonight as a system approaches from the north. This will lead to MVFR CIGs returning to portions of our region. High confidence through 04Z with moderate confidence after that. Vicinity of KSFO...VFR through 05Z with the potential for MVFR conditions after that point. Winds generally 280 to 300 through the day with speeds up to 15 KT. High confidence through 05Z. Moderate confidence after that. SFO Bridge Approach...Similar to ksfo. Monterey Bay Terminals...VFR through 05Z with IFR CIGs expected after that point. Winds mostly 280 to 300 up to 10 KT. High confidence to 03Z. Moderate confidence after that. && .MARINE...as of 01:38 PM PST Sunday...Moderate northwesterly winds will continue over the next several days. in addition...northwest swell will gradually subside going into the work week. && .MTR WATCHES/WARNINGS/ADVISORIES... .Tngt...SCA...Pigeon Pt to Pt Pinos 0-10 nm SCA...Pt Arena to Pigeon Pt 10-60 nm SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm SCA...Pt Arena to Pt Reyes 0-10 nm SCA...Pt Reyes to Pigeon Pt 0-10 nm SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm SCA...Rough Bar Advisory for SF Bar until 3 AM && $$ PUBLIC FORECAST: RWW AVIATION: Bell MARINE: Bell Visit us at www.weather.gov/sanfrancisco Follow us on Facebook and twitter at: www.Facebook.com/nwsbayarea www.twitter.com/nwsbayarea

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