255
FXUS66 KMTR 220458
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
958 PM PDT Mon Jul 21 2025

...New AVIATION, MARINE...

.KEY MESSAGES...
Updated at 206 PM PDT Mon Jul 21 2025

 - Below normal temperatures continue through the end of the week.

 - Localized elevated fire weather threat for the East Bay Hills
   through this evening due to gusty onshore winds.

 - Gusty onshore winds continue through this evening along the
   coast, ridgetops, and gaps/passes before easing overnight.

&&

.UPDATE...
Issued at 815 PM PDT Mon Jul 21 2025

Strong onshore flow continues to impact the Bay Area this
evening. The SFO-SAC gradients peaked over 4 MB earlier in the day
and has since eased. However, we`re still observing some
impressive winds across the East Bay with gusts still exceeding 50
mph at Altamont Pass with many other locations in the 30-40 mph
range. Latest guidance continues to show these winds will slowly
ease overnight. Until that happens, high profile vehicles passing
through Altamont are in for a bumpy ride.

The other item of note is that KMUX radar was briefly switched to
precip mode earlier in the evening. The left over pieces from a
boundary had enough juice for a high based virga to touch northern
Napa county.

Otherwise, another night with a solid marine layer developing
along the coast and inland.

Lastly, a Coastal Flood Advisory remains through midnight for San
Francisco, North Bay Interior Valleys (Bay Shoreline) and San
Francisco Bay Shoreline.

MM

&&

.SHORT TERM...
Issued at 206 PM PDT Mon Jul 21 2025
(This evening through Tuesday)

Stop me if you`ve heard this one before - upper level troughing and
below normal temperatures continue across the West Coast through the
duration of the extended forecast. The high pressure that brought
our temperatures closer to seasonal averages over the weekend has
pushed eastward while upper level troughing deepens over the West
Coast. This will bring us a rinse and repeat of No Sky July with
overcast conditions returning overnight and dissipating again by
late morning. High temperatures will be in upper 60s to 70s across
the interior with the higher elevations reaching the upper 70s to
low 80s.

Gusty onshore winds persist along the coast, ridgetops, and mountain
gaps/passes through tonight before diminishing Tuesday morning. Peak
gusts between 30 to 40 mph are expected across the East Bay Hills
with locally higher gusts to around 45 mph across the Altamont Pass
region. As has been discussed for the past few days, these strong
winds will result in an increased risk of grass fires across the
East Bay. The SFO-SAC gradient looks to peak around +4.6 hPa between
4PM to 8PM tonight with guidance indicating the gradient will relax
overnight. By Tuesday morning, winds will have diminished across the
region and we will see a return to our normal diurnal pattern of
breezy afternoon/evening winds gusting between 20 to 30 mph.

&&

.LONG TERM...
Issued at 206 PM PDT Mon Jul 21 2025
(Tuesday night through next Sunday)

Not too many differences in the Long Term forecast as upper level
troughing and a deep marine layer continue. Below normal
temperatures in the 70s continue across the interior with the
warmest locations in the far interior East Bay and interior Central
Coast reaching the 80s. Coastal areas will stay much cooler in the
mid 50s to mid 60s. Expect a continuation of diurnally breezy
onshore winds gusting between 20 to 30 mph in the afternoon/evening
and the return of overcast skies each night with clearing expected
by late morning. The upper level trough continues to develop a cut-
off low just offshore of the Bay Area. This will result in an
increased chance for thunderstorm for our neighbors in Eureka and
Medford but the threat is confined to far northern CA/OR and does
not impact our CWA. NBM guidance does show a slight warming trend
starting next Sunday with highs rising into the upper 70s to mid 80s
across the interior.

The question on everyone`s mind, when will we see more summer
like weather? Well, CPC guidance indicates below normal
temperatures are likely to persist through the end of July with a
switch to temperatures leaning near to above normal at the
beginning of August. Long range guidance does show upper level
ridging pushing into the West Coast at the start of August which
would support temperatures warming up. However, it is important to
note that this is well over ten days out and we have to keep in
mind that model accuracy degrades the longer in time you go out.
Models are most accurate within the first 3 days of the forecast,
accuracy decreases past this point but models remain decent
through about 7 days out. Anything past the day 7 mark should be
used for trend guidance and not taken as a representation of what
will exactly happen. So is it guaranteed we will see warmer
temperatures come August? No, but it`s worth keeping an eye on the
forecast to see how guidance evolves and if models are
persistently showing ridging or troughing over the West Coast.

&&

.AVIATION...
(06Z TAFS)
Issued at 957 PM PDT Mon Jul 21 2025

MVFR-IFR stratus extends inland from the coast, into the Bay Area
and Monterey Bay regions, and is expected to continue developing
inland through the rest of the night. Stratus retreats to the
immediate coast through Tuesday morning, with breezy onshore winds
returning in the afternoon. Stratus should begin developing again
Tuesday evening, with coverage continuing to increase after the end
of the 24-hour TAF period.

Vicinity of SFO... IFR conditions continue through early Tuesday
afternoon. High resolution model data does not depict a situation
where stratus flows through the Golden Gate, but if it does,
confidence in clearing time will decrease and the terminal could end
up socked in through the day. Stratus should return to the terminal
Tuesday evening. Breezy west winds should resume Tuesday afternoon,
but should not be as gusty as those seen today (Monday).

SFO Bridge Approach... Similar to SFO.

Monterey Bay Terminals... IFR-LIFR ceilings through the night into
early Tuesday afternoon. High confidence that SNS clears out, but
with possible lingering stratus at the immediate coast, confidence
is lower for VFR conditions at MRY. Stratus returns to the terminals
early Tuesday evening. Breezy west-northwest winds are expected on
Tuesday afternoon and evening.

&&

.MARINE...
(Tonight through next Sunday)
Issued at 957 PM PDT Mon Jul 21 2025

Winds are easing across the waters and will remain gentle to
moderate into the upcoming weekend. Slight to moderate seas
persist through the remainder of the forecast period.

&&

.CLIMATE...
Issued at 1221 AM PDT Mon Jul 21 2025

This Summer has been cooler than average and that trend will
continue for at least another week. I decided it was a good time
to add a climate section here to compare just how different this
Summer has been than last year. I created a simple head-to-head
scoring system to add days above/below normal weighted by how far
above/below normal they were. For example, if the maximum
temperature was 2 degrees below normal on Saturday and 3 degrees
above normal on Sunday, the score would be 2-3. I focused on max
temperature at San Jose from June 1 - July 20. Meteorological
Summer starts June 1st and San Jose is a good mixture of some
marine layer influence and inland heat depending on the day.
Again, I just made this scoring system up tonight, so hopefully it
makes sense. The results are pretty interesting, particularly
when compared with last year.

2025: Cold: 168, Warm:  36
2024: Cold:  30, Warm: 302

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Coastal Flood Advisory until midnight PDT tonight for CAZ006-506-
     508.

PZ...None.
&&

$$

SHORT TERM...Kennedy
LONG TERM....Kennedy
AVIATION...DialH
MARINE...DialH

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