Area Forecast Discussion
Issued by NWS San Francisco Bay Area, CA
Issued by NWS San Francisco Bay Area, CA
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860 FXUS66 KMTR 151819 AFDMTR Area Forecast Discussion National Weather Service San Francisco CA 1119 AM PDT Sun Sep 15 2024 ...New AVIATION... .SYNOPSIS... Issued at 203 AM PDT Sun Sep 15 2024 Gusty winds and cooler temperatures today as a potent upper low digs into the west coast. Below normal temperatures last through mid week with a second upper low moving in. Gradual warmup into next weekend. && .UPDATE... Issued at 911 AM PDT Sun Sep 15 2024 Widespread stratus continues across the inland valleys, with the colder temperatures and deeper marine layers slowing the dissipation of the stratus, perhaps sometime in the afternoon if at all. The cold front is making its way through the SF Bay Area, with gusty winds already observed and continuing to build through the day. A few hundredths of an inch of drizzle have already fallen in terrain-favored locations in the Bay Area. More rain is expected through Monday morning. For more information, see the previous discussion. DialH && .SHORT TERM... (Today and Monday) Issued at 203 AM PDT Sun Sep 15 2024 Hints of the approaching system beginning to show up this morning in the form of gusty winds and very light, isolated showers. As of writing, the initial cold front is located over Mendocino county, and will continue to move southward through the Bay Area by about midday today. There is some evidence of light showers with rain making it to the ground as some Alert CA cams in Mendocino county show a few drops on the lenses. Current thinking for rainfall across the Bay Area hasn`t changed much. Still on the order of a few hundredths to a tenth or so for those that are lucky enough to see rain (generally coastal and terrain enhanced areas). Winds will continue to increase through the day today, and should peak by late tonight/early Monday morning as the trough axis swings inland. Most areas will likely see gusty winds to an extent through this afternoon and evening, but the strongest winds will be in the favored NW flow coastal areas (e.g. Sonoma coast, Golden Gate, and Santa Cruz Co coast west of Capitola) and NW/SE oriented valleys and gaps (e.g. Salinas Valley, East Bay Valleys, and the San Bruno Gap near SFO). Will other locations generally see 25-30 mph winds, these favored areas have to potential to see 35-40 mph, with occasional gusts of 45-50 mph. We are holding off on a Wind Advisory on this shift since we will only touch the lower criteria in a few isolated areas for a relatively short period of time. Winds begin to diminish early Monday morning, and will give way to what should be a very pleasant, cool day across much of the region with highs ranging from the upper 50s to mid-70s. && .LONG TERM... (Tuesday through Saturday) Issued at 203 AM PDT Sun Sep 15 2024 By midweek, we could be looking at a deja vu situation, but with slightly less wind. Another cold-core system is poised to slide down the west coast and basically follow in the footsteps of the system that is moving in today (as far as we`re concerned for our region). A bit less dynamic in the upper levels, we wouldn`t expect as much wind from the midweek system, but we do have another shot for some light rainfall Wednesday. Still nothing astonishing as far as rainfall totals go. Perhaps a few hundredths here and there. Nevertheless, great for putting a slight damper on our local fire season. After the Wednesday system departs, the pattern begins a swing back towards slight ridging with temperatures increasing to around normal by the weekend. && .AVIATION... (18Z TAFS) Issued at 1117 AM PDT Sun Sep 15 2024 An early season cold front ahead of an anomalously low upper-level low will bring a tale of two hazards, wind and precipitation. The cold front will continue to support gusty winds at all terminals through the early morning hours of Monday. It isn`t until the anomalously low upper-level low drops down from the Pacific Northwest tomorrow morning that the best precipitation chances emerge. The TAFs were constructed with a four hour timeframe where probabilities of -SHRA were highest, -DZ is possible preceding and succeeding that timeframe. Ceilings will be transient between MVFR and VFR through the TAF period. Vicinity of SFO...Currently MVFR with gusty westerly flow. Westerly winds will strengthen with gusts up to 40 knots expected this afternoon through the early morning hours of Monday. MVFR ceilings will impact the terminal through most of the TAF period as it is still not scattered out and ceilings are expected to make an early return tonight with another late clearing slated for tomorrow. Best timeframe for precipitation (-SHRA) is 09Z-13Z with -DZ possible on either side of that timeframe. SFO Bridge Approach...Low clouds will filter in by 03Z and linger through the TAF period. Monterey Bay Terminals...Currently MVFR with westerly flow at both terminals. Both terminals are expected to briefly improve to VFR this afternoon with a quick return of MVFR ceilings by this evening. Winds will prevail out of the west through the TAF period, becoming gusty this afternoon. Best timeframe for precipitation (-SHRA) is 12Z-16Z with -DZ possible on either side of that timeframe. && .MARINE... (Today through Friday) Issued at 911 AM PDT Sun Sep 15 2024 Back to back early season cold fronts will move through the coastal waters today and Wednesday resulting in widespread strong northwesterly breezes with near gale force gusts. In addition, there is also up to a 10% chance for thunderstorms which could produce lightning, locally heavy rainfall, and locally stronger winds. Seas will remain rough outside of protected waters through the forecast period. && .MTR WATCHES/WARNINGS/ADVISORIES... CA...None. PZ...Small Craft Advisory until 3 AM PDT Monday for Mry Bay-SF Bay N of Bay Bridge. Gale Warning until 3 AM PDT Monday for Pt Arena to Pt Reyes 0-10 nm. Gale Warning until 9 PM PDT this evening for Pt Pinos to Pt Piedras Blancas 0-10 nm-Pt Reyes to Pigeon Pt 0-10 nm. Small Craft Advisory until 9 AM PDT Monday for Pigeon Pt to Pt Pinos 0-10 nm. Gale Warning until 3 PM PDT Monday for Pt Arena to Pt Reyes 10- 60 NM. Small Craft Advisory until 9 PM PDT Monday for Pigeon Pt to Pt Pinos 10-60 NM. && $$ SHORT TERM...Behringer LONG TERM....Behringer AVIATION...Sarment MARINE...Sarment 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