583
FXUS66 KMTR 162031
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
131 PM PDT Sat Aug 16 2025

...New SHORT TERM, LONG TERM...

.KEY MESSAGES...
Updated at 130 PM PDT Sat Aug 16 2025

 - Cool and cloudy through Tuesday, especially along the coast

 - Patchy drizzle or very light rain along the Pacific coast on
   Sunday

 - A warming trend is forecast after Tuesday and into next weekend

&&

.SHORT TERM...
Issued at 130 PM PDT Sat Aug 16 2025
(This evening through Sunday)

Continued northwest to west onshore flow today has resulted in
cloud cover blanketing most areas, with the exception of the North
Bay and East Bay interior, as well as central/southern parts of San
Benito and Monterey counties. Drizzle and very light rain have
resulted in areas along the Pacific Coast picking up measurable
rainfall, with the big winner being Half Moon Bay with 0.15" over
the last 24 hours. While coastal drizzle isn`t that uncommon
across our area, low level moisture convergence and perhaps
greater ascent may be the result of a diffuse frontal boundary
currently draped across the region. It`s certainly "humid" for a
good portion of our region this afternoon.

Through tonight, this frontal boundary will sag southward through
the Bay Area and likely stall and become very ill-defined along
the Central Coast. Near and just south of this feature is where I
would anticipate the greatest opportunity for areas of drizzle
and/or very light rain to shift a little farther south with the
Central Coast perhaps being more of the epicenter for measurable
rainfall. The intensity of drizzle/light rain should be less than
what we saw this morning given that frontolysis will translate to
less favorable precipitation development. Still, drizzle/very
light rain will be advertised across portions of the San Mateo
Peninsula and Monterey Bay regions. Cloud cover is not anticipated
to be quite as expansive compared to today, with the exception
being along the immediate coastline, where high-resolution MTRWRF
output indicates that RH in the lowest few hundred meters of the
boundary layer will remain above 95%. Even here, there`s potential
that a very brief period of more sun than clouds could
materialize. Moisture through the 1km depth does appear to be less
available on Sunday as well which may also mean a "thinner" cloud
depth. As a result, Sunday MaxTs are anticipated to be a few
degrees greater, with areas in the 60s to mid 70s along the coast
to mid to upper 80s elsewhere. Some far interior regions may see
highs in the low to mid 90s if onshore flow is weaker than
currently anticipated.

The only other item in the short term period will be the
potential for very minor coastal flooding along the SF
bayshore line. High tides approach thresholds for minor coastal
flooding, but at this time, confidence in widespread above normal
tidal activity isn`t high enough for any coastal flood headlines.
Still, some low-lying coastal spots may be prone to very minor
flooding over the next several high tide cycles through at least
Monday. Visit tide and current predictions at
tidesandcurrents.noaa.gov or our surf forecasts for the latest
information.

&&

.LONG TERM...
Issued at 130 PM PDT Sat Aug 16 2025
(Sunday night through next Friday)

The longer term forecast will be characterized by a transition
from widespread cooler than normal conditions, to high
temperatures climbing 5 to 10 degrees above typical values for
this time of year (at least away from the coast). Our persistent
summertime troughing is expected to be nudged back to the west as
the Four Corners high pressure cell starts to assert itself
across the Pacific Southwest. While this years` theme of longer
term guidance being a overly aggressive with the westward
progression of the high, there`s remarkable agreement among the
several hundred ensemble members for the synoptic picture next
week. This does yield higher than normal confidence that it`ll get
hot across parts of the area, though it`s not a guarantee as
there`s still some time for things to change.

At any rate, as the ridge inches closer to the west, our
predominantly northwest to westerly mid-level onshore flow will
switch to more southwesterly flow. While still onshore, there`s
more in the way of warm advection with this wind direction and the
proximity of the H5 ridge will also serve compression of the
marine layer. While areas along the coast are likely to benefit
from the marine influence, interior sections are anticipated to
lose favorable wind trajectories for cooler weather. In addition,
less in the way of cloud cover will mean more optimal solar
insolation. In fact, by Tuesday and Wednesday, the probability of
high temperatures above 90F exceed 70% for portions of the North
Bay and East Bay Interiors, as well as across Monterey and San
Benito Counties, including Pinnacles NP. Pockets of `Moderate`
HeatRisk do appear across these areas as well and we`ll continue
to update/fine tune the forecast as we get closer.

&&

.AVIATION...
(18Z TAFS)
Issued at 1104 AM PDT Sat Aug 16 2025

Generally IFR/MVFR conditions across much of the region this morning
with the North Bay terminals at VFR. However, LIFR conditions
prevail at HAF with high confidence to remain LIFR/IFR throughout
the TAF period. Moderate confidence for Bay Area terminals to see
ceilings lift this afternoon, but generally remain MVFR at OAK with
SFO seeing conditions returning to VFR this evening. The Monterey
Bay Terminals are MVFR and with moderate to high confidence for
IFR/MVFR conditions to return this evening. A west to northwest
breeze will continue this afternoon, yet slightly weaker than
yesterday. Moderate confidence for IFR/MVFR conditions to return to
most TAF sites this evening and potentially lowering to LIFR early
Sunday morning around the Monterey Bay terminals.

Vicinity of SFO...IFR/MVFR. Moderate (50% probability) confidence for
ceilings to lift with SFO becoming VFR this evening before lowering
to IFR/MVFR once again tonight. High confidence for west to
northwest winds to increase this afternoon with at or above 30kt.
Winds will then ease into early Sunday morning.

SFO Bridge Approach...40% probability that low stratus clouds linger
across the San Mateo Bridge Approach through the TAF period. Then
earlier clearing by mid-morning on Sunday.

Monterey Bay Terminals...MVFR. Moderate to high confidence for MVFR
ceilings to remain through much of the TAF period. Then moderate
confidence for IFR/MVFR to return this evening and potentially
lowering to LIFR early Sunday morning. Westerly to northwesterly
winds will prevail through the TAF period.

&&

.MARINE...
(Today through Thursday)
Issued at 922 AM PDT Sat Aug 16 2025

The overall sea state will be dominated by moderate to fresh
northwest breezes, with northwesterly seas of 4 to 6 feet. Periods
are anticipated to hover around 5 to 7 seconds through tonight.
Hazardous boating conditions, due to steep to very steep waves are
likely to ensue, largely for smaller vessels and crafts across
area waters, including the bays. After tonight, periods are
anticipated to increase closer to 10 seconds which should help
decrease the overall steepness of waves, though boating conditions
may still remain hazardous. Otherwise, secondary southerly swell
will persist, courtesy of recent tropical activity in the eastern
Pacific. Southerly swell periods are anticipated to average
between 12 and 16 seconds with wave heights around 2 feet or less.

&&

.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 until 9 PM PDT this evening for Mry Bay.

     Small Craft Advisory until 9 AM PDT Sunday for Pt Arena to Pt
     Reyes 0-10 nm-Pt Arena to Pt Reyes 10-60 NM-Pt Pinos to Pt
     Piedras Blancas 0-10 nm.

     Small Craft Advisory until 3 AM PDT Sunday for Pt Reyes to
     Pigeon Pt 0-10 nm.

&&

$$

SHORT TERM...Bain
LONG TERM....Bain
AVIATION...RGass
MARINE...Bain

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