FXUS66 KMTR 020345 AFDMTR Area Forecast Discussion National Weather Service San Francisco CA 845 PM PDT Fri Nov 1 2024 ...New UPDATE, MARINE... .SYNOPSIS... Issued at 115 PM PDT Fri Nov 1 2024 Cold front this evening bringing widespread rain to the region. Drying trend by late weekend through next week with strong offshore winds and elevated fire weather conditions likely. && .UPDATE... Issued at 834 PM PDT Fri Nov 1 2024 The frontal band has narrowed leading to slightly higher rain rates, but only from light to more moderate for most areas. KMUX is showing more of a defined edge of where the main rain band ends over the last few hours, however post-frontal showers and drizzle could still linger through much of the night. Rainfall totals so far seem on track with most areas in the North Bay falling in the 0.30" to 0.50" range, and around 0.70" on the highest peaks. && .SHORT TERM... (This evening through Saturday) Issued at 115 PM PDT Fri Nov 1 2024 Cold front currently located up around Eureka at the time of writing is making its way southward and is expected to move through the Bay Area late this evening. There is high confidence in most locations seeing some measurable rainfall, but portions of inland southern Monterey county may end up with only a few hundredths of an inch. Elsewhere, generally a tenth or two can be expected, up to a quarter of an inch for higher elevations, and locally up to a half inch for coastal ranges. Timing looks to be well after sunset, with some light showers entering Sonoma county on the leading edge of the front by about 5-6 PM. After midnight for the Monterey Bay southward. Overnight temps tonight will be a few degrees warmer than previous simply due to the insulating effects of the cloud cover and warm sector moisture advection ahead of the front. By sunrise Saturday, most shower activity will have moved out of the region with some lingering light showers for southern zones through the morning. && .LONG TERM... (Saturday night through next Thursday) Issued at 115 PM PDT Fri Nov 1 2024 By Sunday, the upper trough shifts into the Great Basin while additional vorticity associated with a vigorous shortwave trough moving through the PNW will be absorbed and result in a further deepening of the upper low. The positioning of this occurrence will promote widespread strong northerly winds from Sunday morning into early Monday morning. High confidence in this scenario at this point with solid agreement among ensemble members at least through Monday. The good news here is that we will be dealing with recent rainfall at that point, as well as decent lingering moisture from the cold frontal passage set to occur tonight. Drying out of RH is expected, but we aren't quite seeing critical fire weather conditions at this juncture. Per usual with this setup, the highest winds gusts can be expected in the highest terrain of the North Bay interior, with gusts potentially reaching up to 45-50 mph...more like 25-30 mph in the valleys. The offshore pressure gradient weakens slightly Monday, promoting a decrease in winds and potentially restored order by Monday afternoon (weak onshore flow and less dangerous fire weather conditions). The middle of the week presents a potentially more volatile setup based on current guidance. Another vigorous upper low moves through the PNW and digs deep into the Desert SW, where it closes off and lingers a big longer than the early week system. Current guidance advertises more robust surface high pressure over the PNW and northern Rockies, promoting a very strong offshore-oriented surface pressure gradient. In fact, the current best forecast for the SFO-WMC and the RDD-SAC gradients approach the 99.5th percentile for this time of year, peaking during the early half of Wednesday. Once again, the good news that we have for now is that we still aren't forecasting critical dryness, but will certainly need to adjust the forecast and pay close attention to RH as the event comes closer. Refer to the FIRE WEATHER section below for more information. && .AVIATION... (00Z TAFS) Issued at 535 PM PDT Fri Nov 1 2024 VFR conditions deteriorating to MVFR-IFR tonight due to an incoming cold front and rain. Post frontal cool air advection resulting in patches of fog /LIFR-IFR/ overnight and Saturday morning. Conditions improving to MVFR-VFR by late Saturday morning and afternoon. Vicinity of SFO...VFR-MVFR, lowering to IFR 1030-1730z Saturday. Rain developing by 02z this evening, decreasing to showers early Saturday morning with cold frontal passage. Prefrontal surface wind is forecast to shift to 170 degrees 8 knots early this evening. Half Moon Bay recently reporting 140-150 degree wind direction. Cold frontal wind shift to west-northwest by 1030z Saturday morning, showers decreasing thereafter. Wind west to northwest 12 to 15 knots Saturday afternoon, possibly a few higher gusts nearing 20 knots in the evening. SFO Bridge Approach...Similar to SFO. Monterey Bay Terminals...VFR-MVFR, rain developing by late evening and continuing Saturday morning. VFR Saturday afternoon. Winds onshore becoming southeasterly tonight and continuing to late Saturday morning. Winds shifting to northwest either late Saturday morning or early Saturday afternoon. && .MARINE... (Tonight through next Thursday) Issued at 834 PM PDT Fri Nov 1 2024 Showers are spreading across the waters from the north and will continue to do so through the night and into Saturday. Winds increase through the night and will become gusty from the northwest with gales- force gusts developing over the outer waters Saturday afternoon to Sunday night. This will result in very rough seas in the outer waters lasting into early next week. Long period northwest swell arrives Sunday night and Monday. && .FIRE WEATHER... Issued at 115 PM PDT Fri Nov 1 2024 Elevated fire weather conditions expected from Sunday through midweek as a pair of strong upper lows move into the Great Basin and Desert SW. Live fuels have generally responded well to the recent cool weather and rainfall, and will get another dose of moisture tonight into Saturday morning as another cold front moves through with widespread rainfall. However, as the low moves inland, offshore winds are expected to increase quickly Sunday morning and last through Monday morning as part of the first wave of this two-part offshore wind event. As it is early in the season, we do expect live fuels to respond rather quickly to the drier conditions. In fact, the current forecast advertises the energy release component of live fuels around the region to increase dramatically above the 60th percentile going into the middle of this week. The big question mark that hangs over us right now in how much rain we see overnight, and if any areas can hang on to some lingering scattered showers Saturday morning. By Saturday afternoon, we will see how this has played out and perhaps have a better idea of what the full fire weather picture will look like going into Sunday/Monday. By the middle of the week, we are expecting the second and potentially more impactful offshore wind event, but some uncertainty remains on the duration and moisture retention. Will stay focused on the near-term event for now and increase messaging on the mid-week event as confidence increases. Behringer && .MTR WATCHES/WARNINGS/ADVISORIES... CA...Beach Hazards Statement from Sunday afternoon through Monday evening for CAZ006-505-509-530. PZ...Small Craft Advisory until 9 AM PDT Saturday for SF Bay N of Bay Bridge. Small Craft Advisory from 9 PM Saturday to 9 AM PDT Sunday for SF Bay N of Bay Bridge. Small Craft Advisory from 9 AM Saturday to 3 AM PDT Sunday for Mry Bay. Small Craft Advisory until 9 AM PDT Sunday for Pt Arena to Pt Reyes 0-10 nm-Pt Reyes to Pigeon Pt 0-10 nm. Small Craft Advisory from 9 AM Saturday to 9 AM PDT Sunday for Pigeon Pt to Pt Pinos 0-10 nm-Pt Pinos to Pt Piedras Blancas 0-10 nm. Small Craft Advisory until 3 PM PDT Saturday for Pt Arena to Pt Reyes 10-60 NM. Gale Warning from 3 PM Saturday to 3 AM PDT Monday for Pt Arena to Pt Reyes 10-60 NM. Small Craft Advisory until 9 PM PDT Saturday for Pigeon Pt to Pt Pinos 10-60 NM. Gale Warning from 9 PM Saturday to 9 PM PDT Sunday for Pigeon Pt to Pt Pinos 10-60 NM. && $$ SHORT TERM...Behringer LONG TERM....Behringer AVIATION...Canepa MARINE...Murdock 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