FXUS66 KMTR 152015 AFDMTR Area Forecast Discussion National Weather Service San Francisco CA 115 PM PDT Tue Oct 15 2024 ...New SYNOPSIS, SHORT TERM, LONG TERM... .SYNOPSIS... Issued at 114 PM PDT Tue Oct 15 2024 Mild weather through midweek, critical fire weather conditions expected by the end of the week. Fire Weather Watch has been upgraded to a Red Flag Warning, in effect Thursday night through Saturday. && .SHORT TERM... (This evening through Wednesday) Issued at 114 PM PDT Tue Oct 15 2024 Mild and fairly quiet conditions continue through the middle of the week. A shortwave trough out ahead of the main upper low is progged to move across the region Wednesday morning, which will result in a slight chance of drizzle across the Bay Area, North Bay, and coastal areas. A few lucky locations in the North Bay and around San Francisco may see a passing light shower through midday Wednesday, but most places are not expected to see much in the way of beneficial wetting rain. && .LONG TERM... (Wednesday night through next Monday) Issued at 114 PM PDT Tue Oct 15 2024 Thursday is the transition day where things start to become more interesting. Following the passage of the weak shortwave Wednesday, a deep upper low is progged to move into the Great Basin from the northwest. Winds are set to increase as the surface front approaches through the day Thursday, but humidity will remain relatively high as winds will be out of the northwest initially. By Thursday evening, the rather vigorous trough axis sweeps through the state by around sunset, which is when we should see a more substantial increase in winds. Strong surface high pressure will quickly build in the wake of the front overnight Thursday, promoting a more north-northeasterly wind component. This will be the defining moment when humidities will start to drop quickly to critical levels through Friday morning. The offshore-oriented pressure gradient from Redding to Sacramento is expected to peak Friday morning near the 99th percentile, further bolstering confidence in a potentially high impact event for the North Bay interior mountains. On a more broad scale, the pressure gradient from San Francisco to Winnemucca is forecast to be offshore-oriented from Friday morning until Saturday night, peaking around Friday afternoon. Nothing particularly notable on the extreme scale, but there is reasonable agreement among guidance...once again increasing the confidence in the large scale impact of this offshore wind event. As it stands with current guidance, the most worrisome areas are likely to be the North Bay interior mountains, the East Bay hills and Diablo Range, and the SF Peninsula. Higher terrain and ridges will be especially vulnerable, with gusts up to 65 mph possible. Otherwise, winds will be in the 25-35 mph range, with gusts to 45. The offshore gradient weakens and order is restored by late Saturday into Sunday as the upper low weakens and moves inland. && .AVIATION... (18Z TAFS) Issued at 1050 AM PDT Tue Oct 15 2024 Mostly VFR conditions across the region expect near-term around the Monterey Bay Terminals which are IFR/LIFR expected to clear by late this morning. Onshore winds increase this afternoon and will diminish by late evening. High clouds will begin to roll in towards the end of the TAF period, signaling a disturbance that will cause the marine layer to expand and should improve aviation weather conditions tonight. The Monterey Bay Terminals are most likely to see the return of low clouds late this evening and persist into the overnight. Vicinity of SFO...VFR, moderate to high confidence. Light and variable winds this morning will increase and become onshore by this afternoon. Wind speeds diminishes overnight, yet are expected to remain out of the west-northwest as an incoming trough approaches from the northwest. This should allow conditions to remain VFR through the TAF period. SFO Bridge Approach...Similar to SFO. Monterey Bay Terminals...IFR/LIFR conditions this morning improving to VFR through the evening. Winds will increase out of the west- northwest this afternoon before diminishing by early evening. Low clouds are expected to return early this evening as a moderate marine layer remains in place with conditions lowering to IFR/LIFR, medium confidence. && .MARINE... Issued at 1050 AM PDT Tue Oct 15 2024 Rough to very rough seas continue to subside across the exposed waters with fresh to moderate NW breeze. Conditions will gradually improve through Wednesday as the long period swell abates. This reprieve will be short lived as conditions deteriorate again by Thursday. A stronger system will bring the possibility for gale force gusts and rebuild rough seas across the coastal waters. && .FIRE WEATHER... Issued at 149 AM PDT Tue Oct 15 2024 A Fire Weather Watch is in effect from 11 AM Thursday until 8 PM Saturday. Normal temperatures, excellent relative humidity recoveries, and onshore flow will keep fire weather concerns at ease through Wednesday. Fire weather concerns will be high Thursday through the weekend as an inside slider event comes to town. While fuels are near average, they are expected to dry out as the week progresses. Northerly winds will develop Thursday as a deep upper-level low digs into the Great Basin. As this digs further south and becomes a cutoff low, winds will become northeasterly/offshore. These winds will lead to rapid drying, compressional warming, poor relative humidity recovery and retention as low as 15%, and a nonexistent marine layer. The windiest timeframes will be Thursday night into Friday morning and Friday night into Saturday morning with winds largely on the order of 20-30 mph with gusts to 40 mph, isolated gusts to 50 mph across the highest terrain and ridgetops and through gaps and passes. && .BEACHES... Issued at 1050 AM PDT Tue Oct 15 2024 Long period northwesterly swell of 13-17 seconds with wave heights approaching 10 feet will result in a moderate risk of sneaker waves across all Pacific Coast beaches through at least Wednesday. Large waves can sweep across the beach without warning, pulling people into the sea from rocks, jetties, and beaches. Beachgoers should always remember to observe the ocean for 20 minutes before relaxing near the water, keep your pets on a leash and away from the water, and never turn your back on the ocean. && .MTR WATCHES/WARNINGS/ADVISORIES... CA...Beach Hazards Statement through Wednesday evening for CAZ006-505- 509-529-530. Red Flag Warning from 11 PM Thursday to 5 PM PDT Saturday for CAZ006-502>504-506-508>510-512>518-528. PZ...Small Craft Advisory until 3 AM PDT Wednesday for Pt Pinos to Pt Piedras Blancas 0-10 nm. && $$ SHORT TERM...Behringer LONG TERM....Behringer AVIATION...RGass MARINE...RGass 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