FXUS66 KMTR 240701
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
1201 AM PDT Mon Aug 24 2026
...New SHORT TERM, LONG TERM...
.KEY MESSAGES...
Updated at 1200 AM PDT Mon Aug 24 2026
- Temperatures near to slightly below seasonal averages persist
within the marine layer through the rest of the week
- Warm and dry conditions continue above 1000 feet
- Pattern change Friday into the weekend brings cooler
temperatures and possible tropical moisture
&&
.SHORT TERM...
Issued at 1200 AM PDT Mon Aug 24 2026
(Today and tonight)
For the last couple of days we've written the tale of a battle
between the eastern Pacific trough and the Desert Southwest ridge
that has dominated our weather pattern. Today it's the troughing
that will take the upper hand as a cutoff low inches towards the
Pacific Northwest, leading to slightly cooler temperatures and
cloudier mornings across the region. Another interesting factor
today is a weak shortwave trough coming into the region through the
morning. The two main global weather models, the European ECMWF and
the American GFS, are showing that there could be enough
instability, moisture, and lift to maybe, just maybe, support a few
high-based thunderstorms developing across the North Bay,
particularly over Napa County. This is a very low probability
forecast (around 5% chance through around 11 AM), along with a low
confidence for storm development. The higher resolution NAM, HRRR,
and RRFS models do not show any signs of developing storms, lapse
rates aloft are marginal at best, and K-Index values below 20
degrees Celsius suggest no chance for developing thunderstorms. Any
precipitation that does develop is also likely to end up as virga,
evaporating within the vast dry low layer where relative humidity
values as of the 0Z (5 PM PDT) OAK sounding fell into the single
digits.
Today's highs range from the 80s into the lower 90s for the inland
valleys, the middle 90s to the triple digits across the warmest
interior spots, the upper 60s to the upper 70s near the Bays, and
the upper 50s to the middle 60s along the Pacific coast. The higher
elevations above the marine layer influence will remain rather day,
especially during the afternoon and evening hours. Breezy onshore
pattern winds will develop this afternoon and evening with wind
gusts reaching 20 to 30 mph along coastal jet regions, through
favored gaps and passes, and within the northern Salinas Valley.
Smoke from the Timber Fire will continue impacting the immediate
area around the actively burning fire through the day, with winds
aloft lofting the smoke plume over Salinas and Hollister. For air
quality information, refer to products issued by the Monterey Bay
Air Resources District.
&&
.LONG TERM...
Issued at 1200 AM PDT Mon Aug 24 2026
(Tuesday through Sunday)
Temperatures rebound Tuesday and Wednesday as the ridge reasserts
itself, with the inland valleys reaching highs in the middle 80s to
the middle 90s on Wednesday and Thursday while the Bays reach the
lower 70s to the lower 80s. A pattern change will begin later on
Thursday as a deep trough builds into the West Coast while the ridge
begins to inch its way eastwards towards the Southern Plains. It
will be interesting to see what the trough will do as the upcoming
weekend comes closer and we are better able to refine the forecast.
Also worth a mention is the possibility of tropical moisture coming
into the region, with our colleagues at the National Hurricane
Center tracking Tropical Storm Iselle and three other areas of
interest off the coast of Mexico. While the circulations remain far
to the south of our waters, the resultant moisture will be captured
by the developing trough with a wide variation in just how far north
the moisture goes. By way of example, the deterministic European
ECMWF model brings a swath of tropical moisture into the San
Francisco Bay Area by Friday morning, whereas the deterministic GFS
keeps the moisture plume to the south of Monterey County. In
addition, wave models are also showing an increase in southerly
swells as the tropical eastern Pacific remains active into the early
part of next week.
&&
.AVIATION...
(06Z TAFS)
Issued at 919 PM PDT Sun Aug 23 2026
VFR continues except for areas of coastal stratus and mist/fog
/MVFR-IFR-LIFR/. Mid and high clouds, including wildfire smoke
over the north Central Coast, are moving northeastward over the
forecast area. Coastal stratus and mist/fog /MVFR-IFR-LIFR/
redevelop and move inland tonight and Monday morning. Conditions
improve to MVFR-VFR along the coast late Monday morning and
afternoon otherwise VFR Monday. Coastal stratus and mist/fog
/MVFR-IFR-LIFR/ redevelop and move inland Monday night and early
Tuesday morning.
Vicinity of SFO...VFR prevails until stratus /MVFR/ develops 12z
Monday. VFR returns 18z Monday. Stratus /IFR/ develops Monday evening
and night. West wind 5 to 15 knots.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...Stratus and mist/fog /IFR-LIFR/ move
inland mid to late evening to Monday morning. Conditions improve
to MVFR-VFR late Monday morning and afternoon. Stratus and mist/fog
/IFR-LIFR/ redevelop and move inland Monday night. West to northwest
winds 5 to 15 knots.
&&
.MARINE...
(Tonight through next Saturday)
Issued at 836 PM PDT Sun Aug 23 2026
Moderate northwest breezes gradually diminish this evening and
become gentle by tomorrow. Occasional strong gusts are possible
this evening, particularly across the Northern outer waters and
near the Big Sur coast. Slight to moderate wind driven seas
prevail into the work week.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory until 3 AM PDT early this morning for Pt
Arena to Pt Reyes 10-60 NM.
&&
$$
SHORT TERM...DialH
LONG TERM....DialH
AVIATION...Canepa
MARINE...Canepa
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Prepared by Boulder-Creek.com Weather at: Mon Aug 24 04:30:04 PDT 2026
From the National Weather Service
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