FXUS66 KMTR 061124
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
423 AM PDT Thu Aug 6 2026
...New AVIATION, MARINE...
.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
&&
.SHORT TERM...
Issued at 1248 AM PDT Thu Aug 6 2026
(Today and tonight)
Longwave upper-level ridging will drift in from the Eastern Pacific
Ocean 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...
(12Z TAFS)
Issued at 423 AM PDT Thu Aug 6 2026
Strong 500 mb high pressure continues while coastal stratus and
patchy mist/fog /MVFR-IFR/ are moving inland on onshore winds.
Onshore winds are supported by a 2.4 mb SFO-SAC pressure gradient.
Stratus, mist/fog will mix out to VFR by late morning and early
afternoon. Coastal stratus, mist/fog /MVFR-IFR/ return inland on
onshore winds tonight and Friday morning.
Vicinity of SFO...Stratus /MVFR/ mixing out to VFR 17z today.
Stratus returns 06z tonight. West to northwest wind 5 to 15 knots.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...Stratus /IFR/ until late morning then
mixing out to MVFR-VFR. Stratus /IFR/ returns this evening and
overnight. Mainly northwest winds 5 to 15 knots.
&&
.MARINE...
(Today through Tuesday)
Issued at 412 AM PDT Thu Aug 6 2026
Northwest winds will increase over the outer coastal waters Friday
through the weekend resulting in hazardous seas conditions for
small craft. A long period southwesterly swell of 15-17sec begins
Saturday, peaks on Sunday then begins to subside by the beginning
of next week.
&&
.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...Canepa
MARINE...Canepa
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Prepared by Boulder-Creek.com Weather at: Thu Aug 6 06:30:03 PDT 2026
From the National Weather Service
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