Area Forecast Discussion

KEY MESSAGES

Updated at 1229 PM PDT Sat Sep 19 2026

- Warmer temperatures today

- Brief cooling Sunday through Monday

- More substantial warming trend Tuesday through Thursday

SHORT TERM

Issued at 1229 PM PDT Sat Sep 19 2026 (This evening through Sunday night)

The marine layer is around 1,500 feet deep and the morning clouds have pulled back to the coast. There is a weak offshore gradient (SFO-WMC -3mb) that caused some moderate NE winds across the North Bay and East Bay mountains early this morning. The sea breeze is now taking over, flipping winds back onshore as the mesoscale gradient weakens. A 500 mb short wave ridge axis will move over the Bay Area this afternoon. This building ridge is causing subsidence and warmer conditions in the lower atmosphere. Surface temperatures are around 5 degrees warmer than this time yesterday outside of the cloudy coast. That puts us right around normal for this time of year.

A weak cut-off low will start to move in from the west Sunday. This will reverse the warming trend and bring temperatures around 5-10 degrees below normal again. It will also encourage the the marine layer to expand a bit.

LONG TERM

Issued at 1229 PM PDT Sat Sep 19 2026 (Monday through next Friday)

The cut-off low will move overhead Monday. This will keep the cooler temperatures in place, deepen the marine layer, and may bring some morning drizzle to the coast and windward slopes. The ECMWF shows some decent 850 mb vorticity, which will help create the lift necessary to form drizzle drops within the deeper cloud layer. These are still tiny drizzle drops though, so any accumulation will be very light.

By Tuesday we will be on the backside of the low and a more substantial warming trend will begin. A relatively low-amplitude 500 mb ridge will build through the middle of the week, but 850 temperatures will climb to 20 to 23C by Wednesday and Thursday. That range is approximately the 75th to 95th percentile for this time of year. Our current forecast has near normal temperatures across the interior Tuesday, steadily building to 10 to 15 degrees above normal by Thursday. With no sign of strong offshore winds, a shallow marine layer will likely survive this warm-up, at least through Wednesday. Heat Advisories are possible, but we're getting to the time of year where the nights are just as long as the days, which really helps dull the accumulating impacts.

The ridge will start to break down Friday as a 500 mb trough moves over the Pacific Northwest. This will bring temperatures back down. There's still no real chance for rain until the following week.

AVIATION

(00Z TAFS) Issued at 437 PM PDT Sat Sep 19 2026

VFR prevails except for coastal stratus and mist/fog /IFR/. SFO-SAC pressure gradient is 2.4 mb with onshore winds bringing stratus and mist/fog /IFR-LIFR/ inland tonight and Sunday morning. Conditions improve to MVFR-VFR near the coastline Sunday afternoon while VFR continues farthest inland.

Vicinity of SFO...VFR and a west wind 20 to 25 knots during the evening, west wind then diminishing to near 10 knots tonight and Sunday morning. MVFR stratus ceiling forecast 06z-19z Sunday. West wind 10 to 15 knots Sunday afternoon and evening.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Stratus and mist/fog /IFR-LIFR/ are nearby and will move inland tonight and Sunday morning. Conditions improve to MVFR-VFR by late Sunday morning and afternoon. Mainly onshore winds 5 to 15 knots.

MARINE

(Tonight through next Thursday) Issued at 428 PM PDT Sat Sep 19 2026

Moderate northwest winds will continue tonight into Sunday then increase Sunday afternoon and evening as a weak upper low approaches the region. Fresh wind wave seas will continue over a long period southerly swell. High pressure builds Tuesday through Thursday with winds easing near shore.

FIRE WEATHER

Issued at 1229 PM PDT Sat Sep 19 2026

The marine layer is around 1,500 feet deep and compressing. There were some offshore winds this morning, but the sea breeze is taking over as the offshore gradient relaxes. Today will be warmer and slightly drier than recent days, although winds will be lighter through the peak burn period. Cooler and more humid conditions arrive Sunday-Monday before a longer warming trend Tuesday through Thursday.

MTR WATCHES / WARNINGS / ADVISORIES

CA...None. PZ...Small Craft Advisory until 9 AM PDT Sunday for Pt Arena to Pt Reyes 0-10 nm.

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

Small Craft Advisory from 3 PM to 9 PM PDT Sunday for Pigeon Pt to Pt Pinos 0-10 nm.

Small Craft Advisory until 3 AM PDT Monday for Pigeon Pt to Pt Pinos 10-60 NM-Pt Pinos to Pt Piedras Blancas 0-10 nm.

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