FXUS66 KMTR 061801
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
1101 AM PDT Thu Aug 6 2026
...New AVIATION...
.KEY MESSAGES...
Updated at 1248 AM PDT Thu Aug 6 2026
- Elevated fire weather conditions in the higher terrain Thursday
- Warming trend through Saturday will result in moderate to major
HeatRisk for the interior through Sunday
- Near-critical fire weather conditions in the higher terrain
Friday through Sunday
- Minor coastal flooding for bayshore locations along the San Francisco
Bay, San Pablo Bay, and Monterey Bay Saturday evening through
Thursday morning
&&
.UPDATE...
Issued at 1012 AM PDT Thu Aug 6 2026
Morning satellite looks a lot like Fogust - solid marine layer
covering all coastal waters and inland valleys. The depth this
morning per soundings and profilers is near 1800 feet. Latest
trends on satellite already show inland treat of the marine layer
back to the coast.
No update needed in the near term as the forecast is on track. A
slight warm up is on tap for today, especially outside of the
marine layer foot print.
Highlights for afternoon forecast package:
Fine tuning heat for Friday through Sunday. Still looking like the
weekend will be the hottest days and advisories will be issued
this afternoon.
Moonsonal moisture streams in from the south. Can
already see a few clouds over SoCal. Still not expecting a
convective threat for the Bay Area. Better forcing over the
Sierra.
Given the hot and dry set up fire weather conditions will return
to near critical for the weekend. Each afternoon will feature an
onshore push of breezy conditions.
MM
&&
.SHORT TERM...
Issued at 1248 AM PDT Thu Aug 6 2026
(Today and tonight)
Longwave upper-level ridging will drift in from the Nevada and the
Desert SW today, compressing the marine layer to near 1,500 feet
in the process. Temperatures will be near to slightly above normal
with the diurnal sea breeze. A surge of monsoonal moisture
arrives today, increasing surface dew points and relative humidity
in the process. Sensible weather wise, this will make it feel
hotter and more uncomfortable than what the thermometer reads.
Areas of moderate HeatRisk are expected in the interior with
pockets of major in the higher terrain of Monterey and San Benito
Counties. Stagnant air from the ridge may support haze from
wildfire smoke. Elevated fire weather conditions continue today
above the marine layer.
&&
.LONG TERM...
Issued at 1248 AM PDT Thu Aug 6 2026
(Friday through Wednesday)
Surface high pressure over the Four Corners will build and expand
westward Friday and into the weekend. This will bring the hottest
conditions of the week and compress the marine layer further. Areas
of moderate HeatRisk across the interior on Friday will expand to
become widespread on Saturday with areas of major. To put this into
context: 850mb temperatures, 500mb heights, and PWAT values are all
forecast to exceed the 90th percentile Saturday. No records are
forecast with temperatures 10-15 degrees above normal for the
hottest spots. A potential wild card in the precision and subsequent
impacts of the forecast is the aforementioned surge of monsoonal
moisture. Mid-to-high level clouds would limit solar insolation
during the day and radiational cooling at night, potentially
resulting in cooler highs and warmer lows than the official
forecast. Even though the ridge will begin to break down and dry air
will begin to get filtered in from the northwest, cumulative impacts
from the heat and humidity will likely still be felt on Sunday. Near-
critical fire weather conditions are expected above the compressed
marine layer Friday through the weekend due to hot and dry
conditions with the diurnal sea breeze. Global ensemble clusters are
in agreement that upper-level shortwave troughing off the West Coast
will prevent the aforementioned ridge and subtropical high pressure
across the Eastern Pacific Ocean from joining forces and building
out of control across our area. Sensible weather wise, temperatures
will moderate to near normal with onshore flow Monday through
Wednesday. 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 Saturday evening
through Thursday morning.
&&
.AVIATION...
(18Z TAFS)
Issued at 1101 AM PDT Thu Aug 6 2026
Satellite is showing stratus receding to the coastline where it'll
remain for the rest of the day. Typical diurnal onshore breeze
pattern is expected where winds will increase to 10-15 kt through
the afternoon and ease to 5-8 kt by sunset. Widespread stratus
coverage expected again tonight which will bring a mixed bag of low-
end MVFR to IFR ceilings. Medium confidence on whether LVK will be
included in the stratus coverage tonight. If there is a sufficient
onshore breeze, an MVFR ceiling may develop so TAF hints at the
possibility around 12Z. Overall, medium confidence on the exact
arrival of stratus tonight.
Vicinity of SFO...VFR through the afternoon as onshore winds
increase. With a depth of around 1000-1500 feet, the marine layer
will bring MVFR ceilings (~OVC010-015) over SFO and OAK this evening
around 04-06Z. Medium confidence on the exact timing of ceilings as
they may arrive a couple hours later than specified. Stratus should
mix out by 17-18Z Friday morning as onshore winds increase.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...Stratus should remain confined to the
coastline through the afternoon, resulting in VFR conditions.
Anticipated stratus arrival is currently around 03Z, though it may
arrive as late as 06Z. Prevailing MVFR ceilings are expected for
SNS, meanwhile MRY will drop to IFR. SNS may intermittently drop to
high-end IFR ceilings overnight. Coastal drizzle associated with
these low ceilings are possible.
&&
.MARINE...
(Today through Tuesday)
Issued at 1012 AM PDT Thu Aug 6 2026
Gentle northwest winds continue to increase to strong by Saturday
morning across the outer Northern coastal waters. Wind-driven
moderate seas build to rough (9-12 feet) Saturday night in
response to strengthening winds. A long period southwesterly
swell of 15 to 17 seconds approaches our coastline Saturday
morning and persists through the weekend.
&&
.FIRE WEATHER...
Issued at 1248 AM PDT Thu Aug 6 2026
Elevated fire weather conditions continue Thursday with hot and dry
conditions alongside the diurnal sea breeze. PSAs of Mid Coast to
Mendocino, Diablo/Santa Cruz Mountains, and Central Coast Interior
are all currently in the 97th percentile for ERC with Mid Coast to
Mendocino and Central Coast Interior forecast to reach daily record
values this weekend. This indicates potential for extreme burning
conditions. Even the more marine layer influenced PSAs of Bay Marine
and Central Coast are forecast to peak in the 80th-90th percentile.
Building high pressure will bring near-critical fire weather
conditions Friday through Sunday. Temperatures will be 10 to 15
degrees above normal with a shallow marine layer in place. Poor
minimum daytime relative humidity as low as 10% is expected in the
afternoons with little-to-no recovery expected overnight. The one
missing piece preventing this from being a Fire Weather Watch/Red
Flag Warning as of now is wind, it's expected to be light. The
exception being through gaps/passes (namely Altamont Pass, the
Delta, and Pacheco Pass) and down the Salinas Valley. To add onto
this, the critical conditions are not expected to overlap spatially
(majority of a zone) or temporally (for at least 8 hours) to warrant
a product.
Sarment
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...None.
&&
$$
SHORT TERM...Sarment
LONG TERM....Sarment
AVIATION...Navarrete
MARINE...Navarrete
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Prepared by Boulder-Creek.com Weather at: Thu Aug 6 12:30:02 PDT 2026
From the National Weather Service
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