Technical NOAA Weather Discussion

FXUS66 KMTR 080708
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
1208 AM PDT Sat Aug 8 2026

...New SHORT TERM, LONG TERM, FIRE WEATHER...

.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...
(06Z TAFS)
Issued at 952 PM PDT Fri Aug 7 2026

IFR-LIFR stratus is expanding into the Sonoma County valleys, the 
SF Bay, the Monterey Bay region, and the Salinas Valley with 
expansion expected to continue into the night. The current forecast 
calls for gradual compression of the marine layer through the night 
as an upper level ridge expands over the region. Confidence in 
stratus impacts at SJC has lowered dramatically, and not expecting 
any stratus to make it into the interior East Bay. Stratus will 
retreat to the immediate coast through Saturday morning with breezy 
onshore winds resuming in the afternoon. Most stratus development on 
Saturday evening falls after the end of the 24-hour TAF period.

Vicinity of SFO... Moderate confidence that an IFR-LIFR ceiling will 
develop over the terminal through the night, with some high 
resolution model output depicting the stratus deck deflected to the 
north of the terminal. Confidence is higher at OAK. Stratus 
dissipates over the post-sunrise hours Saturday morning and breezy 
west-northwest winds develop in the afternoon and evening hours. Low 
confidence of stratus impacts to the terminal Saturday night through 
Sunday morning.

SFO Bridge Approach... Lower confidence of stratus impacts 
compared to the immediate terminal area. Otherwise similar to SFO.

Monterey Bay Terminals... IFR-LIFR stratus persists through the 
night and into Saturday morning. Stratus will retreat to the 
immediate coast around 16-18Z and breezy northwest winds develop in 
the afternoon hours. Moderate confidence that stratus returns early 
Saturday evening.

&&

.MARINE...
(Tonight through next Thursday)
Issued at 952 PM PDT Fri Aug 7 2026

Moderate seas gradually build to rough seas up to 12 feet as
northwest winds increase to fresh to strong by Saturday into the
middle of the week. Seas and winds remain elevated through the
middle of next week. Embedded near gale force gusts are possible
across the outer northern coastal waters. 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 3 PM this afternoon to 9 AM PDT Sunday 
     for Pt Arena to Pt Reyes 10-60 NM.

&&

$$

SHORT TERM...Sarment
LONG TERM....Sarment
AVIATION...DialH
MARINE...DialH

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Prepared by Boulder-Creek.com Weather at: Sat Aug 8 00:30:03 PDT 2026
From the National Weather Service