876
FXUS66 KMTR 140352
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
852 PM PDT Sun Jul 13 2025

...New UPDATE...

.KEY MESSAGES...
Updated at 1250 PM PDT Sun Jul 13 2025

 - Temperatures near to slightly below seasonal averages with a
   more noticeable cooling trend beginning Tuesday.

 - Localized elevated fire weather threat continues across the
   higher elevations.

&&

.UPDATE...
Issued at 849 PM PDT Sun Jul 13 2025

No updates to the forecast this evening. Marine stratus has begun
encroaching farther inland with patchy fog and drizzle expected
overnight into the Monday morning commute. Temperatures tomorrow
will be right around to slightly below normal with more cooling
through the week.

&&

.SHORT TERM...
Issued at 1250 PM PDT Sun Jul 13 2025
(This evening through Monday)

Temperatures this afternoon will be similar to those yesterday.
Generally expecting the coastal areas to be in the upper 50s to
lower 70s where low stratus looks most likely to prevail. The
interior will warm into the upper 70s to lower 90s and the far
inland areas of the North Bay, East Bay, South Bay and interior
Monterey/San Benitio County reaching or exceeding 100 degrees F (but
only in isolated spots).

Stratus will return back inland into the coastal valleys tonight and
into early Monday morning. There is also the potential for coastal
drizzle again tonight and has been added to the official forecast.
Low clouds retreat back to the coast by mid/late Monday morning
resulting in sunny skies across the inland areas. Meanwhile, coastal
locations may very well remain under cloudy or mostly cloudy skies.

Monday afternoon will feature similar temperatures as today!

From previous forecaster: "Localized elevated fire weather threat
persists across areas above and inland of the marine layer`s
influence. The combination of dry daytime humidities of around 20-
35%, poor overnight recoveries of 25-40%, and localized gusts to 25
mph will be the main factors behind the elevated threat. However,
the winds will remain onshore, leading to the fire weather threat
being diurnally driven, especially in the foothills where lighter
winds and good overnight recoveries are expected each night."

&&

.LONG TERM...
Issued at 1229 AM PDT Sun Jul 13 2025
(Monday night through Saturday)

Late on Monday, a shortwave trough, or perhaps a weak cutoff low,
develops into the Pacific Northwest, pushing the ridge axis
towards the west and north and causing a noticeable cooling trend
to begin on Tuesday and lasting for at least the following two
days. High temperatures drop into the middle 70s to middle 80s
inland and the upper 60s to the middle 70s along the Bayshore,
with the coast remaining rather stable at the upper 50s to lower
60s.

Towards the end of the forecast period, the forecast becomes a
little more uncertain. Ensemble model cluster analysis points to
weak ridging (i.e. warmer temperatures) and weak troughing (i.e.
cooler temperatures) by Friday, with the differences compounding
through the upcoming weekend into the early part of the following
week, when a significant ridge and a significant trough are possible
across the western United States. With the two scenarios having
nearly equal probabilities, there is not enough confidence at this
time to deviate from the default NBM forecast, which depicts a
gradual warming trend heading into the upcoming weekend. CPC
outlooks suggest a slight lean towards temperatures above seasonal
averages in the 8-14 day period (July 20-26).

&&

.AVIATION...
(00Z TAFS)
Issued at 541 PM PDT Sun Jul 13 2025

The more localized onshore SFO-SAC 2.8 mb and southerly STS-UKI
2.8 mb and SNS-SJC 2.6 mb pressure gradients predominate across
our forecast area early this evening, though because of the current
depth of the marine layer, surface winds are primarily northwesterly
across the San Francisco Bay and the bay shoreline. Over the CA
coastal waters and offshore waters stratus clouds highlight air
motion within a weak and nearly stationary surface trough. Along
the coast the profilers from Bodega Bay to Point Sur show the marine
layer depth varies only a little from 1300 to 1500 feet.

Only minor temperature fluctuations are forecast aloft specifically
in the vicinity of 925 mb (~ 2500 feet) tonight and Monday. Thermal
ridging aloft otherwise continues in the lower to mid levels tonight
and Monday. The 00z TAFs lean toward a persistence forecast, expect
an inland intrusion of stratus, patchy fog and redevelopment of at
least patchy light coastal drizzle /IFR-LIFR/ tonight and Monday
morning. Lower level temps at ~ 2500 feet begin to cool Monday night
with 2 Celsius to 3 Celsius cooling by 12z Tuesday morning per 18z
NAM output. Lower level cool air advection should begin to deepen
the marine layer setting up for a deeper inland stratus intrusion
Monday night and Tuesday morning.

Vicinity of SFO...310 degree surface wind direction and current
marine layer depth resulting in a moderate to high confidence VFR
forecast through the evening; if the northerly component to the
wind continues, may be able to amend the forecast to extend VFR
conditions a little later than 06z MVFR ceiling forecast this
evening. So far the high resolution models are not quite capturing
the extent of 310 degree wind direction, there`s still the onshore
SFO-SAC gradient so it`s still possible stratus could spread toward
the terminal post sunset surface pressure gradient/winds easing.
Conditions lifting to MVFR-VFR late Monday morning. Northwest wind
easing and becoming more west-northwesterly by late evening. West
to northwest wind redeveloping and becoming gusty to 25 knots
Monday afternoon and evening.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Satellite and surface observations show
stratus over the Monterey Bay moving into the northern Salinas Valley.
Wind flow across the Monterey Bay and the Monterey Peninsula favor
stratus first reaching KSNS tempo IFR 01z-03z then prevailing IFR-
LIFR tonight and Monday morning. Stratus is forecast to reach KMRY
tempo IFR 04z-06z then prevailing IFR-LIFR tonight and Monday morning.
Light patchy drizzle and fog developing tonight and Monday morning
as well. Conditions lifting to MVFR-VFR late morning and/or early
afternoon Monday. Onshore winds 5 to 15 knots.

&&

.MARINE...
(Tonight through next Friday)
Issued at 441 PM PDT Sun Jul 13 2025

Localized hazardous marine conditions in the form of strong
northerly breezes and very rough seas will be present Monday and
Tuesday for the northern outer waters. Aside from that, a gentle
to moderate breeze with moderate to rough seas will prevail
through Thursday.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory until 9 PM PDT this evening for SF Bay N of
     Bay Bridge.

     Small Craft Advisory from 3 PM Monday to 3 AM PDT Tuesday for Pt
     Arena to Pt Reyes 10-60 NM.

&&

$$

SHORT TERM...RGass
LONG TERM....DialH
AVIATION...Canepa
MARINE...Canepa

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