FXUS66 KMTR 240446
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
946 PM PDT Wed Sep 23 2026

...New AVIATION, MARINE...

.KEY MESSAGES...
Updated at 1103 AM PDT Wed Sep 23 2026

 - Warming trend continues into Thursday bringing pockets of
   moderate HeatRisk across parts of the Bay Area and Central
   Coast.

 - Cooler conditions arrive Friday into the weekend.

 - Near seasonal temperatures early next week.

&&

.SHORT TERM...
Issued at 223 PM PDT Wed Sep 23 2026
(This evening through Thursday night)

Our marine layer will continue to degrade off the coast with low 
expectations for it to rebuild significantly overnight. Persistent 
onshore winds remain light into Thursday with a weak push of 
offshore flow overnight across the higher elevations. Due to the 
lack of low clouds, temperatures climb into the mid 80s to lower 90s 
across the interior North/East/South Bays with the Central Coast 
experiencing inland temperatures up to the mid 90s. As a result, 
pockets of moderate HeatRisk persist today into tomorrow afternoon, 
specifically along the San Pablo Bay shoreline, interior East/South 
Bay and Central Coast valleys, as well as the Big Sur coastline. 
Remember to stay hydrated by drinking plenty of water, wearing 
sunscreen and light clothing. The Pacific coastline along the Bay 
Area and Monterey Bay regions remain cooler in the 60s to lower 70s. 
Similar conditions are expected to continue Thursday morning as the 
marine layer is expected to remain confined to the coast with poor 
humidity recoveries overnight. Thursday afternoon, however, marks 
the beginning of a transition period towards cooler conditions due 
to an increased push of strong onshore winds ahead of an incoming 
dry cold frontal passage.

&&

.LONG TERM...
Issued at 223 PM PDT Wed Sep 23 2026
(Friday through next Tuesday)

After a couple of days of above normal temperatures, things will
begin to transition as we round out the end of the work week and
venture into the weekend. On the synoptic scale the region will be
in the wake of an upper trough that is forecast to swing eastward
through the Pacific NW. Largely NW breezes are anticipated as the
diffuse frontal boundary slides southward, however, portions of 
the Central Coast (largely the Santa Lucia Range) may experience 
brief periods of N to even NNE'ly breezes as surface pressure 
rises across the northern Sac Valley late Friday into Saturday. 
Fortunately, the probability for widespread wind gusts exceeding 
30 to 35 mph remains under 10%, except across Pacific Coast 
waters.

The upper air pattern will remain somewhat amplified this weekend
and into early next week. Broad/diffuse troughing along the 
Pacific Coast should translate to some degree of onshore flow. 
It doesn't appear that the marine layer will deepen through 3,000
feet (or at least deepen it quickly) with the tail end of some of
the hi-res guidance suggesting around 1500-2000 ft. For 
elevations toward the higher end of this range, cross-sections do 
indicate RH potentially as low as the mid-teens which may set the 
stage for extended periods of dryness, particularly during the 
overnight hours. Should this signal in the NWP persist, fire 
weather headlines for poor overnight humidity may be warranted
this weekend and into early next week. Additionally, we'll need 
to monitor the progression of the marine layer as it'll have
ramifications on the temperature forecast as we progress through 
the weekend. Should the marine layer not deepen as much, it'll be 
highly probable that upward adjustments to MaxT (and downward
adjustments to RH) will be needed. For now, the official forecast
will roll with the deterministic NBM which keeps temperatures in 
the 60s along the coast to the low to mid 80s across the interior.
Outside of occasional coastal drizzle/mist/fog, there doesn't 
appear to be any real opportunity for widespread rainfall in the 
next week or so. 

&&

.AVIATION...
(06Z TAFS)
Issued at 934 PM PDT Wed Sep 23 2026

A relatively weak but compressed marine layer continues to
maintain VFR conditions across our area. Coastal sites are
expected to see MVFR/IFR ceilings develop after midnight with
interior locations like KSTS and KSJC possibly not seeing
stratus/fog until closer to sunrise. VFR is expected area wide by
mid/late Thursday morning.

Vicinity of SFO...MVFR ceilings are expected to develop during the
overnight hours, with high confidence in VFR conditions by mid-
morning Thursday. Gusty onshore flow develops in the afternoon
and will continue into the late evening hours. A fetch of weak
offshore flow late in the forecast period may limit stratus
development into early Friday morning.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...IFR/LIFR ceilings are expected to develop
around or shortly after midnight and persist through mid-morning
Thursday with VFR conditions expected through the remainder of the
TAF period into late Thursday evening.

&&

.MARINE...
(Tonight through next Tuesday)
Issued at 934 PM PDT Wed Sep 23 2026

North to northwest breezes will continue tonight, with strong
gusts developing Thursday afternoon that will persist through
Friday, especially Friday afternoon and evening from nearshore
Santa Cruz to Big Sur with seas responding and becoming rough into
the weekend.

&&

.FIRE WEATHER...
Issued at 440 AM PDT Wed Sep 23 2026

Marine layer returned again impacting lower portions of the
district this morning with excellent RH recovery. Similar to
yesterday morning patchy fog will impact the N Bay Valleys, 
Monterey Peninsula and the Salinas Valley. Unlike yesterday two
other notable differences: the exact footprint of the marine 
layer is slightly different with less coverage over the E Bay
Valleys and along the Big Sur coastline and moderate to poor
recoveries above the marine layer. Speaking of the drier 
conditions aloft, RH recoveries are 15 to 50 pct drier depending 
on locations. In other words, nocturnal drying returned. 
Otherwise, warmer and drier across the board, especially interior 
locations.

MM

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory until 5 AM PDT early 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 Thursday for Pt Arena to Pt 
     Reyes 10-60 NM.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory from 9 AM to 9 PM PDT Friday for Mry Bay.

     Small Craft Advisory from 3 PM Thursday to 9 AM PDT Saturday for 
     Pigeon Pt to Pt Pinos 0-10 nm-Pt Arena to Pt Reyes 0-10 nm.

     Small Craft Advisory from 9 PM Thursday to 9 AM PDT Saturday for 
     Pt Pinos to Pt Piedras Blancas 0-10 nm.

     Small Craft Advisory until 3 AM PDT Thursday for Pt Arena to Pt 
     Reyes 10-60 NM.

     Small Craft Advisory from 3 AM Friday to 3 PM PDT Saturday for 
     Pigeon Pt to Pt Pinos 10-60 NM-Pt Arena to Pt Reyes 10-60 
     NM.

&&

$$

SHORT TERM...Navarrete
LONG TERM....Bain
AVIATION...JM
MARINE...JM

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Prepared by Boulder-Creek.com Weather at: Wed Sep 23 22:30:04 PDT 2026