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

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000 FXUS66 KMTR 231151 AFDMTR Area Forecast Discussion National Weather Service San Francisco Bay Area 451 AM PDT Fri Jun 23 2017 .SYNOPSIS...Cooling trend starts today for most areas as onshore flow returns. The far interior valleys will remain seasonably warm through this evening. The overall trend this weekend and into next week will be a return to more seasonable temperatures along with more extensive night and morning low clouds followed by sunny afternoons. && .DISCUSSION...as of 3:34 AM PDT Friday...All signs point to a significant cooling trend today and for the coastal valleys these transitions are rarely gradual. The marine layer has deepened to around 1200 feet around Monterey Bay and trending deeper with a southerly surface wind component as the southerly wind reversal is now approaching Cape Mendocino. 24 hour trends for the hills show as much as 10-20 degrees of cooling at this hour due to a deepening marine layer and onshore winds. The gradients from Arcata to SFO have gone flat while the SFO to Sac is 3.3 mb onshore at this early hour. Wind out in the Delta are already gusting to 25 kt as cooler marine air oozes inland. Given all this will maintain the current heat advisories for some of the far interior zones and hills. This is mainly being done for consistency of message and lingering heat impacts for heat sensitive populations. Its expected that any remaining heat headlines for our office will be allowed to expire by 9 pm this evening if not earlier. Looking at the 06z nam graphical and mos output numbers confidence is growing that the overall trend this weekend will be continued cooling back to or even slightly below normal by Sunday afternoon. In general it looks like a more normal summer time weather pattern this weekend across the Bay Area with night and morning low clouds pulling back to the coast and followed by clear and warm afternoons. Latest ecmwf keeps a zonal or slightly cyclonic flow aloft off the coast for next week implying near normal temperatures with dry weather forecast. Longer range solutions later next week or towards the end of the month show more pronounced ridging with potential for another round of weak offshore flow and associated warming. && .AVIATION...
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As of 4:55 AM PDT Friday...For 12z Tafs. Compressed but relatively deeper marine layer offshore pushing further inland this morning bringing VLIFR-IFR cigs to low lying areas along the coast this morning. Expect to see further expansion of marine stratus/low clouds through the early morning hours before retreating in the 17Z hour. Winds generally light today, except breezy onshore winds through coastal gaps, including near KSFO, by this afternoon and evening. Vicinity of KSFO...Stratus in the Bay Area will need to wrap clockwise around the Bay before reaching KSFO. More likely to see low clouds near the bridge/KSMB rather than the tower/KSFO this morning. Low confidence this morning with forecast counting on VFR conditions at KSFO but possible impacts near bridge. SFO Bridge Approach...Similar to KSFO with higher chance of LIFR- IFR cigs at bridge versus tower. Monterey Bay Terminals...VLIFR TO IFR cigs through 17Z hour. Early return of low clouds/stratus tonight. Generally light winds.
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&& .MARINE...
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as of 04:43 AM PDT Friday...Generally light southerly winds over the coastal waters today. Onshore winds increase later today and tonight through coastal gaps such as the Golden Gate gap and across the northern San Francisco Bay. Northwest winds return this weekend. Generally decreasing seas through the coming days.
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&& .MTR WATCHES/WARNINGS/ADVISORIES... .Tday...Heat Advisory...CAZ510-511-517-518 til 9 pm SCA...SF Bay from 2 PM && $$ PUBLIC FORECAST: RWW AVIATION: DRP MARINE: DRP 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

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