textproduct: San Francisco Bay Area

KEY MESSAGES

Updated at 1056 AM PDT Sun Sep 13 2026

- Gustier, dry offshore winds across the Vaca Range and Altamont Pass tonight into Monday

UPDATE

Issued at 846 PM PDT Sun Sep 13 2026

Mostly sunny skies blanketed the Bay Are and Central Coast to round out the weekend. Despite some sunshine a dry cold front last night keeping temps in check. Highs only reached the 60s and 70s...a few 80s far interior. Those temperatures were running 5 to 15 degrees below normal for mid September. In other words, "cool" day despite the sunshine. It was also a breezy afternoon with gusts of 20 to 30 mph being pretty common with a few 40-50 mph in the windier gaps/passes.

Noteworthy weather item for tonight will be two fold as noted below: patchy stratus and developing offshore flow. Already started to see some patchy stratus develop around Monterey Peninsula and the San Francisco Peninsula coast. The larger scale onshore flow is also is beginning to switch to offshore. Not expecting to be a big offshore push, but offshore nonetheless.

No updates needed this evening.

MM

SHORT TERM

Issued at 1056 AM PDT Sun Sep 13 2026 (This afternoon through Monday)

Troughing continues to dominate the forecast as a deep upper level low continues to move through the PNW and into the Intermountain West. The marine layer remains at a depth of approximately 1500 ft but dry air in the wake of last night's dry cold frontal passage prevented stratus from redeveloping across the interior last night. The drier airmass is expected to remain in place through at least midweek with another night of largely clear skies expected tonight. Patchy stratus is possible directly along the coastline where conditions are more supportive for stratus development. Wondering why? Buoys are reporting warmer ocean temperatures than air temperatures above it. This indicates an upwards transfer of heat/moisture from the ocean to the air, resulting in a warming and saturating layer of air where stratus is able to develop. Any coastal stratus that does develop will be patchier with the San Mateo coastline and coastal Monterey Peninsula the most likely areas to see at least temporary cloud cover overnight.

Another factor in tonight's stratus forecast is the wind. Winds through this evening will be breezy and onshore with the SFO-WMC gradient forecast to peak around +9 to +10 mb today. This largely correlates to wind gusts between 20 to 35 mph with gusts up to 45 mph across the favored windy spots. By tonight the wind setup changes from onshore to offshore. Offshore winds should remain on the lighter but two locations, the highest ridgelines of the Vaca Mountains and the Altamont Pass, will experience gustier offshore winds between 20 to 35 mph overnight tonight through Monday. Offshore winds will keep the region slightly drier overnight which increases confidence that stratus will struggle to redevelop/spread across the interior tonight. That being said, not anticipating any major fire weather concerns given the short duration and localized nature of the stronger offshore.

A slight warming trend will kick off Monday as the center of the upper low moves into the Intermountain West and more zonal flow dominates Central California. This will see a return of near normal temperatures for much of the region with interior highs in the 80s and coastal areas in the 60s to 70s. The hottest locations (far interior East Bay and interior Central Coast) will reach the upper 80s to potentially the 90 degree mark. Winds to decrease throughout the day with light to moderate onshore winds returning during the day.

LONG TERM

Issued at 1056 AM PDT Sun Sep 13 2026 (Monday night through next Saturday)

Zonal flow to slight troughing continues through midweek before another deeper trough pushes into the Oregon and Northern California border. Temperatures remain relatively seasonal on Tuesday with highs in the upper 70s to 80s across the interior and 60s along the coastline. The arrival of the upper level trough will bring a cooler airmass into the Bay Area and Central Coast with 850 mb temperatures peaking around 12 C during the day. That is roughly between the 10th and 25th percentiles for this time of year with the median 850 mb temperature ~17 C. The NBM was running a bit warmer than other models for Wednesday/Thursday but the latest run has started to lower temperatures, coming into better agreement. A reasonable lower end temperature forecast for Wed/Thurs would be interior highs in the low to mid 70s while the higher end forecast (the current forecast) keeps high temperatures in the mid 70s to low 80s. Given the arrival of the much cooler airmass, would not be surprised if we saw the forecast high temperatures for Wed/Thurs to decrease by a few more degrees (slightly closer to the lower end forecast). The caveat to this being temperatures may be warmer if the trough/cold air mass slows down and arrives later than currently forecast. Regardless, the cool down will be most evident Wednesday and Thursday with near normal temperatures in the upper 70s to mid 80s Friday into the weekend. The arrival of the trough should allow the marine layer to deepen enough that stratus will become more widespread mid to late week. Diurnally breezy winds continue across mountain gaps and passes, the coast, and along the highest ridgelines. Northern California and the Sierra Range have some potential for thunderstorms mid to late week as the trough moves in but chances are negligible across our region (<5%) with thunderstorms not expected.

AVIATION

(06Z TAFS) Issued at 926 PM PDT Sun Sep 13 2026

Currently VFR. MVFR stratus along the San Francisco Peninsula Coast and Monterey Peninsula will impact HAF, MRY, and SNS at least intermittently through mid-to-late morning. Otherwise, VFR and diurnal winds will prevail.

Vicinity of SFO...Currently VFR with westerly flow. High confidence on VFR and diurnal winds prevailing through the TAF period.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Currently VFR and calm at MRY and VFR with southwesterly flow at SNS. MVFR stratus has already impacted MRY and is lingering within the vicinity of the terminals; as such, expect at least intermittent MVFR ceilings through mid-to- late morning. Diurnal winds will prevail.

MARINE

(Tonight through next Saturday) Issued at 926 PM PDT Sun Sep 13 2026

Hazardous conditions for small craft will continue for the coastal waters and Monterey Bay through Monday. Conditions begin to improve Tuesday as northwesterly breezes diminish with that trend continuing through Thursday. Moderate to rough seas will prevail through Tuesday before abating Wednesday.

FIRE WEATHER

Issued at 422 AM PDT Sun Sep 13 2026

Patchy coastal stratus has developed overnight. 925 mb relative humidities are higher over the Timber and Plaskett fires early this morning. Tonight into Monday night, a light to gentle offshore breeze (with occasionally moderate gusts) is forecast to develop in the higher terrain as the mid/upper level trough axis shifts into the northern Rockies. As such, areas above the marine layer often experience nocturnal drying that will likely continue through early this upcoming week.

MTR WATCHES/WARNINGS/ADVISORIES

CA...None. PZ...Small Craft Advisory from 3 PM to 9 PM PDT Monday for Mry Bay- Pigeon Pt to Pt Pinos 0-10 nm-Pt Reyes to Pigeon Pt 0-10 nm.

Small Craft Advisory until 3 AM PDT Tuesday for 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.

Small Craft Advisory until 3 AM PDT Monday for Pigeon Pt to Pt Pinos 0-10 nm-Pt Reyes to Pigeon Pt 0-10 nm.