FXUS66 KMTR 312347 AFDMTR Area Forecast Discussion National Weather Service San Francisco CA 447 PM PDT Sat Aug 31 2024 ...New AVIATION, MARINE... .SYNOPSIS... Issued at 135 PM PDT Sat Aug 31 2024 A weak upper level low will gradually drift towards Northern California over the next 24 to 36 hours, before moving inland on Monday. As a result, the marine layer may deepen a bit, with some late night or early morning drizzle possible near the immediate coast. Otherwise, expect dry conditions will prevail, with temperatures remaining below normal through our holiday weekend. A warming trend will develop for the work week. && .SHORT TERM... (This evening through Sunday) Issued at 135 PM PDT Sat Aug 31 2024 Water vapor imagery continues to show a weak upper level low spinning 38 North and 133.8 West this afternoon. This upper level low will gradually dig towards Northern California over the next 24 to 36 hours, and be the primary influencer of our weather through the remaining portion of the holiday weekend. As a result, onshore flow will prevail, with breezy west to northwest winds developing each afternoon and evening. At this time, temperatures are running similar to or slightly warmer than this time yesterday. That said, they are still running 3 to 5 degrees below normal. The marine layer did pull back nicely this afternoon, with just a few coastal locations somewhat socked in. That said, expect the marine layer to push inland once again this evening and into the overnight hours. It should also deepen from between 1500 and 1600 feet this morning to around 2000 feet by Sunday morning. While not expecting much in the way of drizzle tonight, cannot completely rule it out along the immediate coast. Otherwise, expect Sunday to be a repeat of today, with inland areas potentially another degree or two cooler than today in response to the deepening trough. Let's talk Labor Day weekend safety. While the weather is relatively quiet, it does not mean that there are not other hazards out there. Water safety: -Whenever possible, swim at beaches with lifeguards. The chances of drowning at a beach with lifeguards are 1 in 18 million. -Do what experienced surfers and lifeguards do: watch the ocean for at least 20 minutes. Study its wave patterns. Get a feel for the pattern of the waves before relaxing on the beach or engaging in recreational activities. -Cold water shock can be just as severe and dangerous from water temperatures of 50-60F as it is from water at 35F. Wearing a life jacket significantly increases chances of survival. -Never turn your back on the ocean. Fire safety: -Use grills/smokers on gravel or paved surfaces. -Keep water stored near campfires, fire pits, grills, smokers, burning brush, etc. -Maintain vehicle brakes and tires, and secure tow chains to avoid dragging. Don't drive on dry grass or brush. && .LONG TERM... (Sunday night through next Friday) Issued at 135 PM PDT Sat Aug 31 2024 This upper level trough will continue to dominate our weather through the remainder of the holiday weekend, before kicking inland along the California and Oregon border on Monday. Therefore, expect the onshore flow to continue, with near to below normal temperatures to prevail into the day on Monday. There are indications that the marine layer will mix out on Monday, so only expect a somewhat patchy return Monday night. High pressure will then build into the region for the work week, with drier and warmer conditions prevailing. At this point in time, it looks like Wednesday may be the peak of the warming trend, as another weak trough starts to dig off the West Coast. That said, inland areas of San Benito and Monterey County may peak on Thursday. One other thing that we will need to watch closely is that winds may turn weakly offshore across portions of the North and East Bay on Tuesday and Wednesday. For now, the winds look relatively week, but it bears watching. Otherwise, expect another minor cooling trend to develop once again for late in the work week and next weekend. && .AVIATION... (00Z TAFS) Issued at 446 PM PDT Sat Aug 31 2024 VFR expected to become MVFR-IFR overnight. Pushed back the arrival of stratus for most airports with current satellite conditions appearing fairly similar to this time yesterday. Ensemble guidance suggests an earlier arrival for stratus, but, they continue to overforecast stratus coverage in comparison to observations which lowers confidence in an early stratus return. Currently anticipating widespread stratus to return later this evening, based on a mix of persistence and GFS guidance, with conditions primarily staying MVFR but some potential for IFR-LIFR closer to the coast. One potential hitch to this forecast is that stratus coverage returned far later than expected last night (generally between 10-11Z) so based solely on persistence, stratus may return slightly later than currently forecast. We will continue to monitor offshore stratus as it approaches the coastline and update the forecast as needed. Moderate northwest winds continue during the day with locally higher gusts possible at OAK and SFO. Winds weaken and become more variable overnight before moderate northwest winds return during the day. Vicinity of SFO...VFR becoming MVFR overnight. Currently expecting stratus to return later this evening around/after 06Z but confidence remains low to moderate given low confidence in ensemble guidance. Once stratus returns, it is expected to persist through mid morning before VFR conditions return. Moderate northwest winds continue into the evening with stronger gusts up to 28 to 29 knots possible. Moderate winds weaken slightly overnight but are expected to strengthen again by tomorrow afternoon with gusts up to 26 knots possible. SFO Bridge Approach...Similar to SFO. Monterey Bay Terminals...VFR becoming MVFR to LIFR overnight. Moderate confidence that stratus will return later this evening with CIGs gradually expected to lower overnight. Low to moderate confidence in exact timing of stratus return given issues with ensemble guidance. Looking at persistence, stratus could return closer to 10Z but current thinking is still leaning towards 07-08Z as the most likely time frame. Moderate northwest winds continue during the day before weakening and becoming more southwesterly to variable overnight. By tomorrow afternoon winds will again become more northwesterly and strengthen to 12 to 15 knots. && .MARINE... (Tonight through next Thursday) Issued at 446 PM PDT Sat Aug 31 2024 Expect the pattern of afternoon gusty, westerly winds trough the Golden Gate and into the northern San Francisco Bay into the upcoming work week. Northwesterly winds will strengthen over the southern coastal zones, specifically near Point Sur this weekend and into early next week resulting in building moderate seas. By early next week stronger synoptic northwest winds will build rough seas in the northern zones. && .MTR WATCHES/WARNINGS/ADVISORIES... CA...None. PZ...Small Craft Advisory until 9 PM PDT this evening for Pigeon Pt to Pt Pinos 0-10 nm-SF Bay N of Bay Bridge. Small Craft Advisory from 3 PM to 9 PM PDT Sunday for Pigeon Pt to Pt Pinos 0-10 nm-SF Bay N of Bay Bridge. Small Craft Advisory until 9 AM PDT Sunday for Pt Pinos to Pt Piedras Blancas 0-10 nm. Small Craft Advisory from 3 PM Sunday to 3 AM PDT Monday for Pt Pinos to Pt Piedras Blancas 0-10 nm. && $$ SHORT TERM...Palmer LONG TERM....Palmer AVIATION...Kennedy 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