textproduct: San Francisco Bay Area

KEY MESSAGES

Updated at 1206 PM PDT Mon Sep 14 2026

- Cooling trend and below normal temperatures through mid-week; return to seasonal temperatures late week into weekend

SHORT TERM

Issued at 1204 AM PDT Tue Sep 15 2026 (Today and tonight)

Interesting to see some high clouds continue to stream over the heart of the Bay Area early this morning. In fact, the stream of clouds have been like a conveyor belt of upper level moisture over the last 36-48 hrs. Why the conveyor belt like feed? While the longwave pattern shows broad troughing over the West (including CA) it also shows a weak upper level disturbance parked well NE of the Hawaiian Island. The sub-tropical jet is the connection between that weak disturbance and CA. Impactful? No. Interesting to see a feed for a longer period of time? Yes. Now onto the forecast.

Marine layer struggled to fully form last night due to dry air and offshore flow. Tonight we're dropping the offshore flow, but dry air remains. As of midnight stratus still remains patchy, but as the night moves on there is higher conf that stratus will become more widespread over the coastal waters and move locally inland. The limiting factor will be the lingering dry air.

Monday was a warm up day, but Tuesday will be a transition day in the other direction. Broad upper trough will get a boast from a highly amplified jet nosing into AK and the downstream trough deepening. Onshore flow will kick a little more today as well. Winds will be strongest along the coast, inland valleys, and inland gaps/passes (Altamont). Onshore flow and dropping 500mb heights will bring a general cooling of 3 to 5 degrees nudging much of the region to below normal for this time of year.

Moistening in the low level and falling 500mb heights will once again promote better stratus development Tuesday night into Wednesday with the depth increasing of 1000-1500 ft for the marine layer.

LONG TERM

Issued at 1204 AM PDT Tue Sep 15 2026 (Wednesday through Monday)

How a about a little taste of late fall to begin the Long Term. The aforementioned amplified jet will to drive another upper low down the PacNW coast and into NorCal/OR. Latest guidance actually cuts off the low from the main flow pattern. Not only are we getting another upper low, but this one will be chilly for this time of year with 850mb temps dropping close to 10C, which is an anomaly of 5 to 7. So what does this mean for overall sensible weather? The cooldown in temperatures will continue with highs dropping another 3 to 8 degrees. Highs will be mainly 60s coast and upper 60s to mid 80s interior. Onshore flow will bring gusty conditions again. The marine layer will be a tricky one. Generally speaking one would expect a deeper marine layer and that's what the forecast has Wednesday into Thursday. However, one always has to watch stratus development as the airmass aloft begins to approach the current SST. If they're too close, stratus production generally declines. Confidence is too low at this point to remove stratus, but will monitor nonetheless. Given that the stratus mid- week is tricky and not classic, impacts from extreme nocturnal drying events are less likely.

The upper level low departs eastward late Thursday into Friday with shortwave ridging to follow. Subtle warming trend develops for next weekend with interior locations solidly returning to the 80s and far interior mid 90s.

AVIATION

(06Z TAFS) Issued at 1007 PM PDT Mon Sep 14 2026

Gentle to moderate onshore breezes continue this evening, becoming light overnight. Above the surface, a weak offshore flow continues to keep stratus out of most terminals this TAF period but will gradually diminish by Tuesday morning. Wednesday night looks more promising for widespread stratus due to the absence of an offshore flow and the passage of an upper-level trough, which will allow the marine layer to deepen. That being said, VFR prevails this evening except at HAF where MVFR ceilings have already formed. Medium confidence for APC to develop borderline MVFR-IFR ceilings early Tuesday morning and scatter out by mid Tuesday morning. Diurnal onshore breezes increase Tuesday afternoon into the evening.

Vicinity of SFO...VFR with gentle onshore breezes through the night. Low confidence on the development of MVFR ceilings tonight, therefore the TAF advertises SCT decks. If ceilings become robust overnight, they will likely be short-lived and scatter out by late Tuesday morning. Wednesday has a higher chance of developing MVFR ceilings, likely after the current TAF cycle. Diurnal onshore breezes prevail through the TAF period.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Gentle onshore winds continue through the night and increase by Tuesday morning. High confidence for IFR ceilings to develop around midnight, filling in over MRY first followed by SNS. Stratus is expected to scatter out by late Tuesday morning resulting in a short period of VFR conditions. An earlier onset of MVFR stratus is expected tomorrow evening around sunset.

MARINE

(Today through Sunday) Issued at 248 AM PDT Tue Sep 15 2026

Northwesterly breezes will diminish across the inner coastal waters and the southern coastal waters today. Hazardous conditions for small craft will linger across the northern outer waters through Wednesday morning. Moderate to rough seas will prevail through today before subsiding to become slight to moderate Wednesday through Friday.

FIRE WEATHER

Issued at 345 AM PDT Tue Sep 15 2026

The transport of cooler air on northwest winds relative to sea surface temperatures in the upper 50s to lower 60s continues to help produce coastal stratus early this morning. The marine layer depth varies from 1500 to 2000 feet. Above the marine layer temperature inversion, humidities are currently in the mid 20% to 30% range. The depth of cool air transport will increase which will gradually increase humidities at higher elevations during mid to late week. Before humidities reach a maximum, there may be temporary, small areas of nocturnal drying at highest elevations, coverage though should be minimal.

MTR WATCHES/WARNINGS/ADVISORIES

CA...None. PZ...Small Craft Advisory until 9 AM PDT this morning for Pigeon Pt to Pt Pinos 10-60 NM-Pt Arena to Pt Reyes 0-10 nm.

Small Craft Advisory until 3 AM PDT early this morning for Pt Pinos to Pt Piedras Blancas 0-10 nm.

Small Craft Advisory until 9 AM PDT Wednesday for Pt Arena to Pt Reyes 10-60 NM.