Area Forecast Discussion
Issued by NWS San Francisco Bay Area, CA
Issued by NWS San Francisco Bay Area, CA
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862 FXUS66 KMTR 191757 AFDMTR Area Forecast Discussion National Weather Service San Francisco CA 1057 AM PDT Thu Sep 19 2024 ...New AVIATION... .SYNOPSIS... Issued at 239 AM PDT Thu Sep 19 2024 There is a slight chance of showers and even a couple rumbles of thunder over southern Monterey County later this afternoon and early evening, with the best chances farther inland you go into higher elevations. Locations under the influence of the marine layer along the coast will be in the 60s and low 70s. Interior locations away from the marine layer will be in the 70s to low 80s. A warming trend for this weekend into the beginning of next week remains on track. && .UPDATE... Issued at 907 AM PDT Thu Sep 19 2024 Showers and thunderstorms occurred and continue over the interior Central Coast with rainfall amounts of 0.36" near Greenfield and 0.47" at Mustang Ridge in the past 12 hours. Those are just sites that happened to be under the rainfall and up to 0.75" may have occurred in areas without rain gauges. There remains the potential for additional showers and thunderstorms through the afternoon across this region, but current radar trends show this ongoing convection diminishing. That said, the ongoing forecast remains on track with no updates anticipated this morning. && .SHORT TERM... (Today and tonight) Issued at 239 AM PDT Thu Sep 19 2024 A positively tilted upper level low currently situated offshore in the vicinity of Big Sur will continue to track south along the California coastline toward Los Angeles today and eventually begin to move inland over San Diego by tomorrow afternoon and evening. The best chance for showers and/or thunderstorms will be farther inland where orographic upslope flow enhances an otherwise weak thermodynamic environment for convection. Highs today will generally be 5-10 degrees below normal, and slightly warmer tomorrow. && .LONG TERM... (Friday through Wednesday) Issued at 239 AM PDT Thu Sep 19 2024 The upper level trough moving across our area today and tomorrow will eventually shift inland over SOCAL by tomorrow evening. Increasing H50 heights and thickness values over the weekend will result in temperatures rebounding back up above normal by the end of the weekend into the beginning of next week. A weak upper level disturbance interrupts the ridging pattern off the coast of central California by late Sunday into early Monday morning, while the northern extent of the ridging amplifies over the Pacific Northwest. The net result is warmer than normal temperatures and increasing heat risk concerns the farther inland and north you go for the beginning of next week. The warming trend may result in the need for a heat advisory for those locations as soon as Sunday, but more likely Monday and Tuesday. && .AVIATION... (18Z TAFS) Issued at 1057 AM PDT Thu Sep 19 2024 Mix of VFR and IFR-LIFR CIGs across the board. The upper level low that disrupted the marine layer and brought light rain to our CWA has moved to the south of us with a slightly more typical stratus pattern expected tonight. Thunderstorm chances continue to decrease along the Central Coast but a slight chance persists through the afternoon. Moderate confidence that stratus will continue to clear throughout the Bay Area with all sites to return to VFR by 20Z. Low to moderate confidence in clearing across the Central Coast where scattered convection continues across southern Monterey County. Stratus is expected to return early this evening along the Central Coast and by mid to late evening throughout the rest of the Bay Area. Low to moderate confidence that MVFR CIGs will reach LVK overnight with any ceilings that do develop expected to occur after 09Z. Clearing is expected by mid tomorrow morning with most sites clearing 16-17Z. Vicinity of SFO...Stratus is clearing out of SFO with northwesterly winds to pick up over the next few hours. MVFR CIGs are expected to prevail tonight with ensemble guidance suggesting some potential for IFR CIGs to develop during the late evening/early morning hours, however, confidence remains low on IFR development. Stratus is expected to clear by mid morning with moderate northwest winds between 12-15 knots expected. SFO Bridge Approach...Similar to SFO. Monterey Bay Terminals...Patchy IFR to LIFR CIGs continue with low to moderate confidence that CIGs will fully clear around 20Z. Scattered convection associated with the upper level low is still located in southern Monterey County and is adding additional uncertainty to time of stratus clearing at MRY and SNS this morning. Current thinking is CIGs will at least temporarily clear out this afternoon with a brief period of VFR conditions. Stratus will return late this afternoon/early this evening between 00-03Z and persist through the remainder of the TAF period with MVFR to IFR CIGs. A slight chance (generally less than 10%) of thunderstorms continues for SNS through this afternoon. Confidence is too low to include VCTS in TAFs given that convection is weakening in southern Monterey county and lightning probabilities are continuing to diminish. && .MARINE... (Today through Tuesday) Issued at 907 AM PDT Thu Sep 19 2024 Moderate northwesterly winds continue over the majority of the coastal waters. Northwesterly winds are expected to strengthen to fresh to strong and seas will become rougher in the northern outer waters through the day. Winds and seas remain elevated through the weekend but ease into the next work week. && .MTR WATCHES/WARNINGS/ADVISORIES... CA...None. PZ...Small Craft Advisory from 3 PM this afternoon to 9 AM PDT Saturday for Pt Arena to Pt Reyes 10-60 NM. && $$ SHORT TERM...JM LONG TERM....JM AVIATION...Kennedy MARINE...Kennedy 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