651
FXUS66 KMTR 140511
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
1011 PM PDT Sun Jul 13 2025

...New AVIATION...

.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...
(06Z TAFS)
Issued at 1011 PM PDT Sun Jul 13 2025

The onshore SFO-SAC 3.2 mb predominates with decent inland
stratus and fog intrusion potential tonight and Monday morning.
Over the CA coastal waters and offshore waters a weak and nearly
stationary surface trough persists. Coastal profilers from Bodega
Bay to Point Sur show very little change in the marine layer
depth, varying from 1300 to 1500 feet. Recent air temps at San
Francisco downtown and Oakland downtown are ~ 1/2 degree
Fahrenheit cooler than this time 24 hours ago, it may not sound
like much and it isn`t, but it may represent a slight change in
surface air mass characteristics advected in from the coastal
waters. The overall combination of a clear sky above the marine
layer with this evening`s 00z Oakland sounding precipitable water
lower at 0.51" (10th percentile for time of year) supports
improved nocturnal radiational cooling which while there is a
surface influx of slightly cooler air within the marine layer may
set up for a longer duration stratus and fog intrusion to mix out
Monday. For the 06z TAFs decided to slightly extend ceiling
forecasts over model output by an hour or two.

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 06z TAFs still mainly lean toward persistence, expect
an ongoing 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...Amended the earlier TAF forecast to extend VFR
conditions just a little longer tonight, satellite imagery shows
stratus curling around from the Golden Gate to Oakland, a classic
summer set up for later arrival at SFO. Forecast tempo IFR 08z-10z,
then IFR prevailing. RAP model is indicating high humidity, low
ceiling and fog potential tonight/Monday morning. Conditions may
not lift to MVFR-VFR until Monday early afternoon. West-northwest
wind tonight. West to northwest wind becoming gusty to 25 knots
Monday afternoon and evening. Stratus returns Monday evening and
night.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Stratus, fog and drizzle /IFR-LIFR/ tonight
and Monday morning. Conditions lifting to MVFR-VFR Monday afternoon.
Stratus returns early Monday evening and night. 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 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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