, Issued at 1240 AM PDT Mon Sep 14 2026 (Today and tonight)
Longwave pattern over the West is heavily focused on the wound up upper low sweeping through the N Rockies. Why is that important? Behind this upper level feature surface high pressure is slowly building across the Pac NW and into the Great Basin. Pattern recognition in the fall-ish months leads to offshore flow signals. As such, latest sfc pressure gradients from SFO-WMC reveals a flip from onshore Sunday to trending offshore overnight. While latest guidance has cut way back on offshore flow potential from a few days ago to today, it is still offshore nonetheless. The offshore gradient is projected to be -5ish mb, which is on the lower end. Regardless current overnight observations show a switch at Mt St Helena with gusts to 35 mph and lower RH. Not expecting a big impact given the weakness of the offshore flow, but will drive sensible weather with breezy, mild, and drier conditions for N Mts and E Bay Hills through early Monday. Elsewhere, mostly clear skies prevail overnight. The exceptions are few high clouds passing overnight and some patchy stratus along the coast/coastal waters from San Francisco Peninsula south to Monterey Bay.
Speaking of pressure gradients, the N-S gradient has ramped up while the W-E gradient has eased. As such, winds too will be less than what was observed on Sunday. The stronger winds will shift back over the coastal waters. That being said, still expecting some breezy conditions for Monterey Bay, Pt Sur, and the Salinas Valley. Temperatures today will rebound slightly with highs in the 60s/70s coast and 80s to lower 90s inland, still a few degrees below normal for mid-September.
Monday night - offshore flow eases as onshore flow returns. As such, the marine layer will have a better shot at returning. Latest guidance shows a better marine layer/stratus picture by Tuesday morning with coastal clouds push locally inland into Monterey Bay and Salinas Valley.
..issued at 140 AM PDT Mon Sep 14 2026 (Tuesday through Sunday)
Interesting longwave pattern develops heading into mid-week as another upper low cuts off of the main flow aloft and drifts into OR/NorCal. Overnight ensemble guidance shows the upper low is pretty anomalously low for this time of year and packs a cold punch too. Overall cooling trend is expected Tuesday through Thursday. In fact, 850mb temps will drop down to 11 to 12 C, which is an anomaly of -5 to -7. The record heat from last week will be a distant memory as highs on Wednesday will be locked in the 60s and 70s, with a few interior spots reaching into the mid 80s. That's about 5 to 15 degrees below normal. The cold advection will cause an uptick in winds too. Winds on Wednesday will be strongest through the Delta, East Bay gaps/passes. The lower 500mb heights and colder air will help to re-establish a more robust marine layer Wednesday and Thursday with some guidance suggesting drizzle along the coast. It does come with a price, nocturnal drying above the marine layer may return over the highest peaks Thursday morning.
Heading into next weekend the upper low fades and 500mb heights rise and 850mb temps warm. Therefore the marine layer will begin to compress and temperatures will trend back toward seasonable levels.
(12z TAFS) Issued at 507 AM PDT Mon Sep 14 2026
It's VFR except for patchy coastal stratus and fog /MVFR-IFR/. A few additional patches of stratus and fog /MVFR-IFR/ will develop during the morning hours then mix out by late morning. Coastal stratus and fog /MVFR-IFR/ redevelop tonight and Tuesday morning.
Vicinity of SFO, VFR during the 12z TAF except BKN007 ceiling forecast 10z Tuesday. West wind 5 to 10 knots except 15 to 25 knots from this afternoon to mid evening.
SFO Bridge Approach, Similar to SFO.
Monterey Bay Terminals, VFR except tempo stratus /IFR/ at KMRY 13z-16z in the morning. A few patches of morning fog are also possible. Coastal stratus /MVFR-IFR/ redeveloping tonight and Tuesday morning. Light and variable winds in the morning becoming onshore 7 to 15 knots in the afternoon to early evening, then light onshore winds tonight and Tuesday morning.
(today through Saturday) Issued at 436 AM PDT Mon Sep 14 2026
Hazardous conditions for small craft will continue for the coastal waters and Monterey Bay early in the week. Northwest winds will ease by mid-week. Moderate to rough seas will prevail through Tuesday before abating Wednesday.
Ca, None. PZ, Small Craft Advisory from 3 PM this afternoon to 9 PM PDT this evening for Mry Bay-Pigeon Pt to Pt Pinos 0-10 nm.
Small Craft Advisory until 3 AM PDT Tuesday for Pt Arena to Pt Reyes 0-10 nm-Pt Pinos to Pt Piedras Blancas 0-10 nm.
Small Craft Advisory until 3 AM PDT Wednesday for Pt Arena to Pt Reyes 10-60 NM.
Small Craft Advisory until 9 AM PDT Tuesday for Pigeon Pt to Pt Pinos 10-60 NM.
