Issued at 902 PM PDT Wed Sep 16 2026
The advertised cooldown for today definitely verified. Not only did highs remain well below seasonal averages they also came in under forecast values as well. Max temps reached the 60s along the coast and 70s inland with a handful of 80s well interior. Cold upper low coming down the coast, strong onshore flow, and lingering stratus clouds contributed to the cooler temps.
For this evening, stratus is already making an appearance across the region. Expect coverage to increase overnight. That being said, this is not a "classic" marine layer setup thanks to the nearby upper low. Definitely some strato-cu vibes as inland clouds are popping off over terrain features. No update is needed to the forecast this evening.
Thursday AM is still on track to start off cool, damp, and cloudy with drizzle.
, Issued at 110 PM PDT Wed Sep 16 2026 (This evening through Thursday night)
The marine layer was measured to be 2,400 feet deep by the 12Z sounding from Oakland. Surface observations show it's closer to 3,000 feet deep along the Central Coast, where all of Santa Cruz County remains under overcast skies. The NW wind direction created some downslope dry air that managed to keep Silicon Valley clear, but that was the exception. The morning stratus reached inland to Healdsburg, Dublin, and Paso Robles. As a cut-off low over Northern California continues to drift south, the marine layer will expand over the next 24 hours. The deeper cloud layer will be enhanced by some 700 mb vorticity and typical orographic lift to support some drizzle overnight through Thursday morning. The signal is better over the Bay Area than the Central Coast, but all of the typical drizzle locations have a chance. In fact, all 50 of the ECMWF ensemble members have some precipitation reaching SFO Thursday morning. This is still drizzle though, so the accumulation will range from a trace to a few hundredths before the atmosphere mixes in some drier air by midday.
In addition to drizzle, the cut-off low will bring some strong onshore winds this evening. The SJSU 2km WRF ensemble shows high confidence in a onshore 8-10 mb SFO-WMC gradient developing quickly this afternoon. This is a result of northerly winds west of the low cooling the coast, while warm southerly winds east of the cut-off support thermal exhaust and surface low pressure over northern Nevada. The RRFS shows gusts up to 40 mph this evening in favored gaps such as Pacheco Pass, Altamont Pass, and the Carquinez Straight. Gusts up to 25 mph are likely in both the San Francisco and Monterey Bays later today as well. These winds will peak in the early evening, but continue well into the overnight hours. The strongest winds are not widespread enough to warrant a wind advisory, but expect to feel them while driving through the areas mentioned.
Outside of drizzle and wind, the cut-off low will bring cool, humid conditions to the entire Bay Area. Coastal temperatures will be in the 60s along the coast and 70s inland. Some of the warmer places will reach the upper 70s, but that's still roughly 10 degrees cooler than normal for this time of year. We'll get a repeat of these cool temperatures on Thursday before a slight warming trend kicks off Friday.
..issued at 110 PM PDT Wed Sep 16 2026 (Friday through next Tuesday)
The cut-off low will have weakened and start to be reabsorbed into the jet stream by Friday. This will open the door for a short wave ridge to briefly build through Saturday. While short lived, this feature will cause the marine layer to compress and temperatures to return back to normal. We may even see some weak offshore winds at this time. The SFO-WMC gradient is expected to flip negative by Saturday morning, but there is no indication it will be very strong. By Sunday a much weaker cut-off low will move in from the west. This feature will likely keep conditions pretty consistent and relatively benign through mid week. The 850 mb temperature is expected to hover around 20C early next week, which is around the 75th percentile for this time of year. By mid week the uncertainty balloons. Since the pattern depends on multiple, hard to track cut-off lows, chaos theory goes into full swing quickly. Ensembles shows an equal chance of 850 temps reaching 5C or 25C next Thursday, which literally spans the entire range of historical possibilities for this time of year. While I like to look for signs of early rain or strong offshore winds this time of year, with the high uncertainty it's not really
(06z TAFS) Issued at 933 PM PDT Wed Sep 16 2026
Currently a mixed bag of MVFR-VFR. Transient TAF period on tap thanks to an upper-level low to our north that is mixing up the environment. As a result, ceilings on the cusp of MVFR/low-end VFR are expected through tomorrow morning for most terminals. Drizzle will lower ceilings and visibilities; the best chances are in the Bay Area with chances diminishing southward. Diurnal winds will prevail.
Vicinity of SFO, Currently VFR with southwesterly flow. Transient TAF period on tap with clouds on the cusp of MVFR/VFR expected through tomorrow morning. Drizzle will be possible overnight, resulting in a lower ceiling/visibility. Diurnal winds will prevail.
SFO Bridge Approach, The San Mateo Bridge Approach will likely not be as impacted as SFO; however, clouds at or below FL055 should be expected in the vicinity through tomorrow morning with a chance that they linger into the afternoon.
Monterey Bay Terminals, Currently VFR with southerly flow at MRY and VFR with southwesterly flow at SNS. Once stratus reaches the terminals, MVFR conditions will likely prevail through the morning. Lower probability for drizzle, but if it occurs, lower ceilings and visibilities are expected. VFR is expected by late-morning. Diurnal winds will prevail.
(tonight through next Tuesday) Issued at 933 PM PDT Wed Sep 16 2026
Conditions will improve tonight as northwesterly breezes diminish to become gentle to moderate. Hazardous conditions for small craft will return Friday into the weekend due to fresh to strong northwesterly breezes. Slight to moderate seas will prevail through Sunday.
Ca, None. PZ, None.
