FXUS66 KMTR 081205
AFDMTR

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

...New AVIATION, MARINE...

.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

&&

.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...
(12Z TAFS)
Issued at 505 AM PDT Sat Aug 8 2026

A strong 500 mb high pressure system and large scale compression 
continue to slowly decrease the marine layer depth. At the same 
time, satellite shows widespread stratus and fog over the coastal 
and offshore waters with onshore winds transporting stratus, fog 
and mist /MVFR-IFR-LIFR/ inland underneath the high and across low
lying areas of the Bay Area and north Central Coast. Otherwise it
is VFR. In the marine layer temperature inversion across the hills
and mountains it's much warmer and dry. The SFO-SAC pressure gradient
is 3.0 mb and it is forecast to reach near 4 mb this afternoon. 
Stratus and fog have a solid start, however diurnal surface warming
will connect with the lower level temperature inversion and raise the
temperatures and mix out the stratus and fog to the coastline.

Recent high resolution model output has been showing drier northwest
winds arriving later today, tonight and Sunday eroding the coastal
stratus north-south, perhaps leaving a narrow channel of stratus and
fog /IFR-LIFR/ along the immediate coastline along with an inland
intrusion possible tonight and Sunday morning. The high resolution
rapid refresh model leans less stratus and fog and the NAM leans more
stratus and fog remaining; 12-24 hours from now it's a low confidence
forecast.

Vicinity of SFO...Stratus /IFR/ until 17z today then VFR. Stratus
/IFR/ is forecast 10z Sunday. West to northwest wind 5 to 15 knots
except 15 to 25 knots from late morning through mid evening.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Stratus, patchy fog and mist /IFR-LIFR/ 
lifts to MVFR-VFR by late morning. Stratus, patchy fog and mist 
/IFR-LIFR/ return tonight and Sunday morning. West to northwest 
winds 5 to 15 knots.

&&

.MARINE...
(Today through Thursday)
Issued at 426 AM PDT Sat Aug 8 2026

Northwest winds will increase to fresh to strong across the
coastal waters with seas in the northern waters becoming hazardous
to small craft beginning today and lasting to the middle of next
week. Occasional gale force gusts are possible across the outer
northern coastal waters. Expect gusty onshore winds across the San
Francisco Bay north of the Bay Bridge to the Delta today and
Sunday. A long period southerly swell at 15 to 17 seconds persists
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 from 10 AM this morning to 10 PM PDT Sunday for 
     CAZ503-504-510-512>518.

PZ...Small Craft Advisory from 9 AM this morning to 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...Canepa
MARINE...Canepa

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Prepared by Boulder-Creek.com Weather at: Sat Aug 8 06:30:02 PDT 2026