Area Forecast Discussion
Issued by NWS San Francisco Bay Area, CA
Issued by NWS San Francisco Bay Area, CA
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992 FXUS66 KMTR 151048 AFDMTR Area Forecast Discussion National Weather Service San Francisco CA 348 AM PDT Sat Jun 15 2024 ...New SYNOPSIS, SHORT TERM, LONG TERM, MARINE, FIRE WEATHER... .SYNOPSIS... Issued at 254 AM PDT Sat Jun 15 2024 Dry and windy with elevated fire concerns into early next week. Seasonal temps and quiet weather midweek. Potential warming trend for late next week. && .SHORT TERM... Issued at 254 AM PDT Sat Jun 15 2024 (Today and tonight) What a difference 24 hours makes...June-Gloom is all but gone. The longwave pattern over the West remains relatively unchanged with an upper low anchored off the BC Coast and an upper level trough covering the PacNW into NorCal. Additionally, a weak upper level boundary pushed through the region on Friday. The passing boundary helped to set the stage for the much talked about burst of northerly winds. The SFO-ACV gradient ramped up to over -6mb and the SFO-SAC gradient topped out at over 4mb. This pressure gradient set up is perfect for gusty northerly winds and stronger onshore flow. A sampling of winds over the last 12 hours shows gusts 40-60 mph, with the strongest winds over the coastal waters, immediate coastline, higher peaks, and any inland gap/pass. The stronger N-S gradient helped to mix out the marine layer (June- Gloom)for the most part. Latest satellite fog product does show some patchy stratus trying to develop along the SF Peninsula coast, Pt Reyes, and East Bay Hills. That will be it, patchy at best through sunrise. Lastly, the better mixed low levels has also led to slightly warmer overnight temperatures. Rest of today and tonight - breezy to gusty winds will persist thanks to the stronger N-S and W-E gradients. Still not strong enough or widespread enough for a Wind Advisory, but strong enough for minor impacts like blowing small unsecured items around. The biggest impact will be to the marine environment with steeper wind waves and hazardous conditions. Interestingly enough, a very pronounced coastal jet forms south of Pt Sur. In fact, latest forecast has winds approaching Storm Force conditions with a few gusts flirting with the 48 kt (55mph) mark. Moderate to high confidence on these stronger coastal waters winds as ensemble guidance indicate high exceedance values (80+ percent) greater than 50 mph. Additionally, the ECMWF EFI shows how unusually strong the winds are for this time of year and a good portion of the ensemble members are favoring the "extreme" side. One other impact for the persistent northerly winds over the waters will be effective Ekman transport and increased upwelling. In other word, colder water along the coast. The change in airmass associated with stronger northerly flow will lead to cool temperatures today, especially over the interior. && .LONG TERM... Issued at 335 AM PDT Sat Jun 15 2024 (Sunday through Friday) No big changes with the overall sensible weather for Sunday and Monday. Not much in the way of night/morning clouds and associated marine layer thanks to persistent breezy/gusty northerly flow. Temperatures at night will be milder thanks to better mixing and seasonably cool during the day. By Tuesday northerly flow will begin to slowly ease as the upper trough weakens. In fact, the longwave pattern aloft begin to become more zonal and then favors a more ridge like pattern for the second half of the week into the following weekend. So what does this pattern shift mean? A gradual warming trend with a potential for much warmer weather by next weekend. While tonight`s guidance may have backed off from the more "extreme heat" around June 21/22 it is still plenty warm across the interior. Both CPC and WPC continue to highlight portions of the Bay Area and Central Coast for excessive heat from June 21-26. Stay tuned... && .AVIATION... (06Z TAFS) Issued at 1026 PM PDT Fri Jun 14 2024 VFR conditions throughout the region, generally through the TAF period. Model output has some probability of stratus development tonight at the immediate coast, at the East Bay Hills, and near MRY, but confidence is low and strong winds aloft may keep the skies clear through the nighttime. Strong northwest winds will diminish through the evening, with LLWS concerns developing along the coast this evening as strong winds aloft decouple from the surface layer. Strong northwest winds expected to resume Saturday afternoon. Wind speeds become somewhat uncertain towards the end of the 24-hour TAF period, with some models showing a slower decline in speed than the forecast. Vicinity of SFO... VFR through the TAF period. Strong west-northwest winds continue through the rest of the evening. Winds will taper off to around 10-15 knots overnight, with marginal LLWS concerns. Strong gusts resume Saturday afternoon. Current forecast calls for gusts up to 30 knots, but gusts at or exceeding 35 knots are still very much in the picture. SFO Bridge Approach... Similar to SFO. Monterey Bay Terminals... Model output shows some probability of IFR ceilings at MRY overnight both tonight and Saturday evening, but confidence is low (around a 30-40% probability) with winds aloft remaining strong. Otherwise the region remains VFR through the TAF period Lights winds continue through the night with breezy northwest winds resuming Saturday afternoon. && .MARINE... (Today through Thursday) Issued at 254 AM PDT Sat Jun 15 2024 Expect strong northwest winds with widespread gale force gusts along with wave heights up to around 12 to 15 feet in the outer waters and 10 to 14 feet in the inner waters. Hazardous conditions continue early next week as winds remain strong and seas remain elevated. Seas start to diminish in the middle of the work week. && .FIRE WEATHER... Issued at 345 AM PDT Sat Jun 14 2024 ...Elevated Fire Weather Conditions Through The Weekend... *Increasing northerly winds, especially higher terrain *Lowering relative humidity values day and night Forecast remains on track as northerly flow ramps up across the district. Gusts of 30-50 mph will be more common along the coast, higher terrain, and inland gaps/passes. Have already seen a few isolated inland passes reach close to 60 mph as well. These stronger winds will persist through early Monday. It should be noted that they will not be strong the entire time, more like bursts of stronger winds. The northerly flow has also ushered in much drier air across the region too. 24 hour trends show some locations 40-70% drier than 24 hours ago. While there are a few isolated stations that may "technically" reach Red Flag criteria conditions are not widespread enough to warrant a fire weather zone wide Red Flag warning. Therefore, still best to message elevated fire weather conditions through the weekend. Regardless, individuals with outdoor activities planned this weekend should be fire weather aware. Be mindful and don`t be "that spark". MM && .MTR WATCHES/WARNINGS/ADVISORIES... CA...None. PZ...Small Craft Advisory until 9 PM PDT this evening for SF Bay N of Bay Bridge. Small Craft Advisory from 3 PM Sunday to 3 AM PDT Monday for SF Bay N of Bay Bridge. Small Craft Advisory until 3 AM PDT Monday for Mry Bay. Gale Warning until 3 AM PDT Monday for Pigeon Pt to Pt Pinos 0- 10 nm-Pigeon Pt to Pt Pinos 10-60 NM-Pt Arena to Pt Reyes 0- 10 nm-Pt Arena to Pt Reyes 10-60 NM-Pt Pinos to Pt Piedras Blancas 0-10 nm-Pt Reyes to Pigeon Pt 0-10 nm. && $$ SHORT TERM...MM LONG TERM....MM AVIATION...DialH 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