, Issued at 106 PM PDT Thu Oct 9 2025 (This evening through Friday)
Satellite imagery depicts extensive cloudiness over the North Bay, some cumulus clouds over the higher elevations of the Bay Area and Central Coast, and lingering clouds over the Big Sur coastal region. Radar returns show a narrow stationary boundary extending south from Marin County to the inner waters off the San Mateo Peninsula and the outer waters off the Central Coast. Our colleagues at the WPC are analyzing this as a stationary front on land associated with a surface low pressure system in the North Coast and a weakening cold front offshore. Any remaining rainfall totals from this system will be very light, a few hundredths of an inch at most. Another shot of light rain comes through Friday, generally limited to Sonoma County where a few hundredths of an inch will fall in the valleys, and a tenth to two tenths of an inch in the coastal ranges. Otherwise, the weather remains remains dominated by an upper level low currently meandering off the Pacific Northwest, leading to cool conditions with breezy and gusty winds each afternoon and evening along with periods of clouds as weak cold fronts pass through the region. High temperatures today and Friday range from the lower to middle 70s in the interior valleys of the central bay Area, the South Bay, and the Central Coast, along with the Bayside regions, to the upper 60s in the North Bay valleys and the lower to middle 60s along the Pacific coast.
..issued at 106 PM PDT Thu Oct 9 2025 (Friday night through next Wednesday)
The chance for rain clears out Friday night as the low pressure system moves eastward into the Pacific Northwest, and leads into a dry, but cool, weekend with highs broadly similar to the previous couple of days, except in the North Bay where temperatures warm to the lower to middle 70s on Sunday. Incidentally, around this time, the remnants of Typhoon Halong in the northwestern Pacific will begin to dissipate into the jet stream circulation to the south of the western Aleutians and lose any sense of identity through the weekend as its remnants make their way towards Alaska. Sometimes, the remnants of western Pacific typhoons will recurve and impact the West Coast, but in this specific instance, it looks like any impacts will be well to our north.
Confidence is increasing in some form of rainfall, particularly significant rainfall, for the early part of the next work week. As the current low pressure system begins to dissipate heading into the Northern Rockies, a second trough will start to develop over British Columbia, gravitate offshore, and deepen in to a new low pressure system that descends parallel to the West Coast, eventually reaching the coast off central California. The result will be a rather fast moving storm, but one which will likely be our first significant rainmaker since the previous winter season. Probabilities of precipitation in the Monday to Tuesday timeframe top out around 60- 80% across the forecast area. A preliminary estimate of potential rainfall totals suggests that 1 inch of rain is possible in the lower elevations with rainfall totals in the coastal ranges reaching the 2-3 inch range. Please note that there is still a fair bit of uncertainty with the rainfall totals at present. Taking the National Blend of Models as a baseline, from Monday at 5 AM to Wednesday at 5 AM, there is an 80% chance that the rainfall total in downtown San Francisco falls between 0.0" and 2.4", and a 50% chance that the total falls between 0.09" and 1.65". For Monterey Airport, those ranges are 0.01"-2.2" and 0.58"-1.68" respectively, while at downtown Santa Rosa, the respective ranges are 0.0"-2.1" and 0.01"- 1.50". Right now, a significant rain event is more likely than not, but the forecast does have time to evolve.
Wind threats will also arrive as the storm system comes through the region, with strong gusts potentially developing on Monday and Tuesday as the descending low causes a strong pressure gradient and a jet streak comes through the region with 40-50 kt winds at 500 mb. It is a little far out to mention any specifics, but gusts reaching or exceeding 30 mph can not be ruled out. In addition, model data is also suggesting a slight (10-20% probability) chance for thunderstorms Monday night and Tuesday. This is when the region would sit on the left exit region of the jet streak, a favored region for divergent flow that would support a chance for convection. Again, too early to say what the specifics will be. We will continue to follow the system as it evolves and refine the forecast as more model data arrives into the weekend.
(18z TAFS) Issued at 1045 AM PDT Thu Oct 9 2025
Generally VFR at terminals this morning, but pockets of MVFR are passing through as well. MVFR and precip is most likely over the North Bay as a weak boundary is stalled in that area through this afternoon. Convective temps will be met leading to some strato-cu this afternoon, which will briefing a SCT-BKN deck for portions of the Bay Area. Despite some clouds heights should be VFR. ANother system will approach late tonight and more so on Friday bring some clouds/precip back to the North Bay toward the end of the TAF pd. Overall conf is medium.
Vicinity of SFO, VFR with a few cu popping. Cigs will be in the 4-5k ft range. Lower cigs and VCSH still west of the San Bruno Gap and over coastal waters.
SFO Bridge Approach, Same as SFO. Cig at the wrong place wrong time could impact visuals occasionally in the afternoon.
Monterey Bay Terminals, VFR, but monitoring some cu popping to the SW moving north. Cigs heights still look in the VFR range.
(today through Tuesday) Issued at 852 AM PDT Thu Oct 9 2025
Light precipitation is expected over the coastal waters, especially south of Point Reyes. Light to locally moderate winds will be shifting through tonight. Light rains build into the waters through Friday and exit into that night. Northwesterly winds arrive Saturday and increase to a strong breeze that night, building rough seas by Sunday. Disturbed conditions with periods of rain and gusty winds are expected across the waters early next week.
Ca, None. PZ, None.
