175
FXUS66 KMTR 300346
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
846 PM PDT Sun Jun 29 2025

...New UPDATE...

.SYNOPSIS...
Issued at 145 PM PDT Sun Jun 29 2025

The marine layer is around 1000 feet this afternoon and will
spread into the coastal valleys tonight while inland areas will
see a warm Sunday evening. An upper low offshore will deepen the
marine layer the next 24 hours and lead to slightly stronger
onshore winds along with an inland cooling trend. Instability
associated with the upper low looks to remain north and east of
the Bay Area through midweek. Another trough will approach by
Thursday and Friday keeping a deep marine layer along with inland
temperatures running near or slightly below normal.

&&

.UPDATE...
Issued at 846 PM PDT Sun Jun 29 2025

The upper ridge is trying to hang on for dear life. As of about
830 PM, observations above about 1500 feet are still reading in
the 70s with some even in the 80s. The stand out to me is Middle
Peak, Mt Tam, @ 2339ft and reading 81 degrees at the time of this
writing. All that said, drop below 1500 feet and you have to go
deep into the recesses of the interior to find warm temps. Most
low lying areas are already in the 50s and low 60s due to the
marine layer undercutting the upper ridge. Through the dark hours
tonight the upper trough, just offshore, will shove the ridge out
and the marine layer will deepen through the day on Monday. By
this time Monday evening, expect the marine layer to be in the
2000 - 3000 foot depth. This means a cool down for everyone and
increased moisture. Wouldn`t be surprised to get some more drizzle
out of this upper trough as it could provide just enough lift of
moisture, then let the CCN with moisture and gravity do the rest.

Going back to what RW was talking about earlier in the AFD
regarding thunderstorms. Looking at the latest model data, there
is really no change. Odds of thunderstorms occurring are slim to
none for our service area. That said, there will be just a hair of
lift, which means we`ll probably see some fluffy white cumulus
across East and North Bays tomorrow.

Have a pleasant evening to all.

&&

.SHORT TERM...
(This evening through Monday)
Issued at 145 PM PDT Sun Jun 29 2025

A sunny and warm Sunday afternoon across the Bay Area with mainly
80s inland except widespread 90s interior Monterey county. The
marine layer is currently around 1000 feet and confined to the
coast. SFO-Sac gradient currently 2.4 mb but forecast to increase
this afternoon in response to inland heating and the offshore
upper low that should induce moderate seabreeze winds through the
Golden Gate and into the coastal valleys allowing for low clouds
to push locally inland overnight. Synoptic pattern features an
upper low offshore that may squeeze out some drizzle over the
ocean and along the coast late tonight into Monday morning.

Models show a slug of mid level instability (MUCape rotating
around offshore low) passing over the North Bay tonight but not
expecting any precip associated with this tonight.

Would expect marine layer to deepen slightly by Monday morning as
the offshore low gets a little closer to the coast. This should
help to increase onshore winds and keep inland temps mainly in the
80s once again for the interior Bay Area with 60s and 70s
coast/bays.

The upper low will bring some interesting weather to the state but
it looks to stay north and east of the Bay Area with thunderstorms
and associated fire weather/lightning concerns across the
Northern Sierra and the coastal ranges from roughly Clear Lake
northward. Models still show 2-5% probs of thunder for northern
Sonoma/Napa so cant completely rule threat out but climatology and
pattern recognition suggests the main threat remains to our
north, nonetheless we will continue to monitor.

&&

.LONG TERM...
(Monday night through next Saturday)
Issued at 145 PM PDT Sun Jun 29 2025

Upper low of interest should be over Big Sur by Tuesday and lead
to a deep marine layer locally from the Golden Gate to Big Sur.
Instability associated with the upper low will be over the Sierra
and northern mountains from the coastal ranges up towards Mt
Shasta. The low will keep winds onshore and along with the deep
marine layer no real hot weather is forecast for the region.

The main trough axis finally pushes inland and the upper flow will
turn WSW witch will end a lot of the convective threat across the
state (except east of the Sierra crest).

Looks like another trough arrives by Thursday or Friday. This one
looks more progressive with some cool (in relative terms) air
aloft. This suggests no hot temp concerns locally for the start of
the holiday weekend. The trough may be strong enough to mix out
the marine layer or at least allow for partial clearing each
afternoon and evening. Main message then for the holiday weekend
looks to be dry with near or below normal temps.

Some hint of more significant ridging and inland heat by around
July 7-8th which would match climatology as the 4-corners ridge
starts to build but far enough away to keep confidence low to
medium as several 500 mb clusters still show troughing solutions.

&&

.AVIATION...
(00Z TAFS)
Issued at 414 PM PDT Sun Jun 29 2025

IFR-LIFR stratus lingers at the immediate coast, with the interior
remaining VFR through the rest of the day. Breezy winds continue
through the evening with southerly flow along the immediate coast,
turning to the northwest across the inland terminals. Stratus will
begin to build into the Monterey Bay and Salinas Valley, and through
the Golden Gate this evening and overnight, before retreating back
to the immediate coast Monday morning. Breezy onshore winds resume
on Monday afternoon with more of a westerly flow across the coastal
waters, especially in the Central Coast.

Vicinity of SFO... VFR conditions continue with moderate to high
confidence that they persist overnight. If stratus does form at the
terminal, it will be brief and quick to dissipate in the couple of
hours after sunrise. Breezy northwest flow continues into the
evening hours, with light winds overnight before the northwest winds
resume Monday afternoon.

SFO Bridge Approach... Similar to SFO.

Monterey Bay Terminals... VFR conditions with breezy onshore winds
through the next couple of hours. LIFR stratus returns to the
terminals early this evening and persists through Monday morning,
with breezy onshore winds resuming Monday afternoon.

&&

.MARINE...
(Tonight through next Friday)
Issued at 414 PM PDT Sun Jun 29 2025

Significant wave heights and winds continue to ease through early
Tuesday morning. Locally breezy, fresh to strong, northwesterly
gusts continue across the outer coastal waters with emphasis on
the far northern outer waters north of Point Reyes. South to
southwest winds continue across the inner coastal waters north of
Point Pinos. Significant wave heights build again on Tuesday with
strong northwesterly breezes and moderate to rough seas that will
persist into the later part of the week.

&&

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

&&

$$

UPDATE...BFG
SHORT TERM...RW
LONG TERM....RW
AVIATION...DialH
MARINE...DialH

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