237
FXUS66 KMTR 081836
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
1136 AM PDT Sat Aug 8 2026

...New AVIATION...

.KEY MESSAGES...
Updated at 1206 AM PDT Sat Aug 8 2026

 - Warming trend through the weekend will result in moderate to
   major HeatRisk for the interior

 - Near-critical fire weather conditions in the higher terrain
   through Sunday

 - Minor coastal flooding for bayshore locations along the San Francisco
   Bay, San Pablo Bay, and Monterey Bay through Thursday morning

&&

.UPDATE...
Issued at 918 AM PDT Sat Aug 8 2026

The marine layer was deeper than previously anticipated with the
OAK 12Z upper air sounding showing it around 1,600 feet in depth.
This allowed for widespread stratus to push inland into the
interior valleys this morning, but is now showing signs of
retreating to the coastline. Mid-to-upper level moisture wrapping
around the western periphery of the high pressure over the Four
Corners region is bring mid-to-high level clouds as well. A Heat
Advisory will go into effect at 10 AM this morning and through 10
PM Sunday across much of the interior Bay Area and Central Coast.
Areas under the Heat Advisory will warm into the mid 90s and up to
105 deg F in the warmest interior locations. That said, the
ongoing forecast remains on track at this time with no updates
anticipated at this time.

RGass

&&

.SHORT TERM...
Issued at 1206 AM PDT Sat Aug 8 2026
(Today through Sunday)

Upper-level ridging across the Four Corners will expand westward
Saturday bringing widespread moderate to areas of major HeatRisk to
the interior over the weekend. This will support temperatures 10-15
degrees above normal and a compressed marine layer. While messaging
remains the same, the ridge is forecast to be slower to break down
with northerly/offshore flow developing at 925 mb down the Northern
Sacramento Valley on Sunday. This will make Sunday the hottest of
the two days in some locations, namely the North Bay Interior
Valleys, San Francisco Bayshore, and San Francisco. Have opted to
leave them out of the Heat Advisory still; however, they may need to
be included in subsequent forecasts. Near-critical fire weather
conditions persist through the weekend across the interior due to
very hot and dry conditions. Minor coastal flooding is expected
during the highest high tide (evening/overnight) for bayshore
locations along the San Francisco Bay, San Pablo Bay, and Monterey
Bay through Thursday morning. The Pacific Coast may need to be added
Sunday through Tuesday. Tonight`s forecast was overdone by 0.1 ft
and while that is not a lot, it is the difference of whether or not
the Pacific Coast gets included. We will wait to see how our
forecast performs and what the trend is after Saturday night`s high
tide before we make a decision one way or the other.

&&

.LONG TERM...
Issued at 1206 AM PDT Sat Aug 8 2026
(Monday through Friday)

Global ensemble clusters are in agreement that upper-level shortwave
troughing will develop Monday off the West Coast between subtropical
high pressure across the Eastern Pacific Ocean and the Four Corners
high. This will result in temperatures moderating to near normal and
the return of a marine layer around 1,000 feet. Even with the
cooling trend and the deepening of the marine layer, the increase in
onshore wind will support elevated fire weather conditions into next
week. The upper-level pattern along with a resurgence in monsoonal
moisture may be enough to bring elevated rain showers/thunderstorms
to the forecast as early as Thursday and into next weekend. Whether
or not the aforementioned trough pinches off to become a low or not
will be important for the lifting mechanism factor. As far as
instability and moisture go, conditionally unstable lapse rates and
sufficient MUCAPE will overlap with PWAT values in excess of an
inch. While there`s no mention in the official forecast now, it may
be warranted as we get closer.

&&

.AVIATION...
(18Z TAFS)
Issued at 1135 AM PDT Sat Aug 8 2026

Tricky forecast this TAF period. The marine layer overperformed this
morning at a depth of 1600 feet. Majority of model guidance kept
signaling a compression below 1000 feet, but considering the recent
observations and expected onshore wind support, it will likely be
closer to 1200-1500 feet tonight. That being said, a mixed bag of
borderline IFR-LIFR ceilings are expected after 02Z Sunday for
coastal sites and after 04Z Sunday for inland sites. SJC is the only
inland site that will see low-end MVFR ceilings this TAF period. Low
confidence on whether LVK will develop a brief MVFR-IFR ceiling as
it is dependent on how far inland the marine stratus travels. If a
ceiling does develop, it will likely be sometime after 10Z Sunday.
Overall, medium confidence on stratus arrival for Bay Area sites.
Aside from stratus, typical diurnal onshore wind pattern prevails
through the TAF period with most sites shifting to VFR by the early
afternoon.

Vicinity of SFO...VFR with northwest winds increasing to 12-18 kt
this afternoon and ease to 7-10 kt overnight. Marine stratus returns
again tonight with IFR ceilings. In terms of timing, relied on
persistence for SFO but expect a delayed arrival for OAK (~04Z
Sunday). Medium confidence on exactly when they will arrive, though
ceilings are expected to persist until 17-18Z tomorrow.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Stratus has receded to the coastline where
the otter eddy resides. VFR through the afternoon with high
confidence for IFR ceilings to roll in around 02-03Z this evening.
Overnight, ceilings may drop to LIFR (OVC003-004) though there is
low confidence on when and how long those conditions will last.

&&

.MARINE...
(Today through Thursday)
Issued at 918 AM PDT Sat Aug 8 2026

Fresh to strong northwest winds continue through the weekend into
the work week with building rough seas up to 12 feet across the
outer coastal waters. The northern coastal waters particularly
will remain hazardous to small craft with occasional near gale
force gusts through the middle of next week. Gusty onshore winds
are forecast through Sunday across the San Francisco Bay north of
the Bay Bridge to the Delta. A long period southerly swell of 15
to 17 seconds prevails through the weekend.

&&

.FIRE WEATHER...
Issued at 1206 AM PDT Sat Aug 8 2026

Near-critical fire weather conditions persist through the weekend
across the interior due to very hot and dry conditions. Strong
thermal belting, extended burn periods, elevated PIG, and near or
record BI/ERC values are expected. Temperatures will be 10 to 15
degrees above normal with a compressed marine layer. Poor minimum
daytime relative humidity as low as 10% in the afternoons with
little-to-no recovery overnight is expected with nocturnal drying in
the highest terrain. Even with critically dry conditions, wind is
the limiting factor preventing this from being a Fire Weather
Watch/Red Flag Warning event. Outside of the diurnal sea breeze that
will bring breezy conditions in the afternoons and evenings through
gaps and passes, onshore flow will be light. Additionally, critical
conditions are not expected to meet coverage or duration
requirements to warrant a product. Elevated fire weather conditions
are expected into next week as onshore flow increases on the heels
of the near-critical hot and dry event this weekend. The upper-level
pattern along with a resurgence in monsoonal moisture may be enough
to bring elevated rain showers/thunderstorms to the forecast as
early as Thursday and into next weekend.

Sarment

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Coastal Flood Advisory until 2 AM PDT Thursday for CAZ006-506-
     508-529-530.

     Heat Advisory until 10 PM PDT Sunday for CAZ503-504-510-512>518.

PZ...Small Craft Advisory until 9 PM PDT this evening for SF Bay N of
     Bay Bridge.

     Small Craft Advisory from 9 AM to 9 PM PDT Sunday for Pt Arena
     to Pt Reyes 0-10 nm-SF Bay N of Bay Bridge.

     Small Craft Advisory from 3 PM this afternoon to 3 AM PDT Monday
     for Pt Arena to Pt Reyes 10-60 NM.

&&

$$

SHORT TERM...Sarment
LONG TERM....Sarment
AVIATION...Navarrete
MARINE...Navarrete

Visit us at www.weather.gov/sanfrancisco

Follow us on Facebook, X, and YouTube at:
www.facebook.com/nwsbayarea
x.com/nwsbayarea
www.youtube.com/nwsbayarea