180
FXUS66 KMTR 020902
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
202 AM PDT Tue Sep 2 2025

...New SHORT TERM, LONG TERM, FIRE WEATHER...

.KEY MESSAGES...
Updated at 156 AM PDT Tue Sep 2 2025

 - A 15-20% chance of isolated showers and thunderstorms through
   the early afternoon along the interior eastern portions of
   Contra Costa, Alameda, Santa Clara, San Benito, and Monterey
   counties.

 - Gradual cooling trend through the remainder of the week.

&&

.SHORT TERM...
Issued at 156 AM PDT Tue Sep 2 2025
(Today and tonight)

Today`s forecast is interesting as we have an upper level low just
off to our west, which will slowly make its way towards our coast
today. While that is occuring, monsoonal moisture surges northward
across the Golden State. What we`ve seen so far, is convection
flaring across the southern San Joaquin Valley and just to our
south, along San Louis Obispo`s interior mountains. Expect this
trend to continue with storms drifting northward this morning and
chances gradually increasing to 15-20% around daybreak. We`ll have
lift from either the upper low or the terrain and decent moisture as
PWATs should be around 0.75 to 1.25 inches today. The limiting
factor should CAPE as models tend to keep amounts light, around a
couple hundred J/kg or less and there should be some CIN. Mid level
lapse rates today favor around 7-8C, total totals around 44-58, and
LI`s around 0 to -3. If we`re able to overcome any drier air and
bust the cap, a few showers and isolated thunderstorms will be
possible through the early afternoon hours. Chances then begin to
decrease mid to late afternoon as the upper low traverses north and
we lose daytime heating.

Outside of the thunderstorms, expect fairly quiet conditions today,
with temperatures starting their gradual cooling trend today. &&

.LONG TERM...
Issued at 156 AM PDT Tue Sep 2 2025
(Wednesday through Monday)

Not much change in the extended as the gradual cooling eventually
steadies by the weekend. Cluster analysis shows upper level troughing
holding over meandering over the E PAC and gradually approaching the
PacNW late in the weekend or early next week. We can expect the
marine layer to deep and as a result, we`ll see stratus developing
each evening and then spreading inland overnight. The CPC continues
to show near normal temperatures and above average precipitation.
Note: Above average precipitation this time of year does not amount
to much and may be in the form of coastal drizzle and/or light rain.
Thus, widespread rainfall is not expected.


&&

.AVIATION...
(06Z TAFS)
Issued at 949 PM PDT Mon Sep 1 2025

Currently VFR at all terminals with the exception of SNS. With the
exception of the Monterey Bay terminals of MRY and SNS, moderate to
high confidence on VFR prevailing through the afternoon. There`s a
non-zero chance for elevated convection beginning tonight - while I
don`t expect the ingredients to align and impact a terminal, some
rain showers may be seen in the air.

Vicinity of SFO...Currently VFR with northwesterly flow. High
confidence in VFR through the afternoon with a ceiling (likely IFR)
returning to the terminal tomorrow night. Westerly winds will
prevail through the TAF period.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Currently a generous VFR with westerly flow
at MRY and IFR with northerly flow at SNS. A low confidence forecast
due to the uncertainty on if dry air will advect into the region and
dissipate the stratus or if stratus can sustain itself via Otter
Eddy within the Monterey Bay. The trend will likely be realized
within the next hour or so - best case scenario: VFR through the
afternoon, worst case scenario: LIFR/IFR through the morning.
Westerly winds will prevail through the TAF period.

&&

.MARINE...
(Tonight through next Sunday)
Issued at 849 PM PDT Mon Sep 1 2025

Northwesterly breezes will diminish through the night, with
moderate to fresh breezes prevailing through Friday. Strong gusts
and thus hazardous conditions for small craft will return to the
outer waters and coastal jet regions by Wednesday. Moderate seas
will prevail through Friday with occasional rough seas in the
outer waters.

&&

.FIRE WEATHER...
Issued at 156 AM PDT Tue Sep 2 2025

An upper level low continues to move northeastward passing over
the region today. The low is surrounded by some drier air off
shore, but has started to tap into residual mid level moisture
this morning. The primary concern is there is a low, 15-20%,
chance of high impact weather if any elevated showers, isolated
dry lightning and storm associated gusty outflow winds develop.
The best chances look to be across our interior and most eastern
regions, favoring Contra Costa, Alameda, Santa Clara, San Benito, and
Monterey counties. For interior portions of the North Bay, chances
are less than 10%, but will still be monitored.

Otherwise a cooling trend sets in Tuesday and will continue through
the remainder of the extended forecast. Daily highs and lows will
be closer to normal for early September.


&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory until 3 AM PDT early this morning for
     Pigeon Pt to Pt Pinos 10-60 NM-Pt Arena to Pt Reyes 0-10 nm.

     Small Craft Advisory until 9 PM PDT this evening for Pt Arena to
     Pt Reyes 10-60 NM.

&&

$$

SHORT TERM...KR
LONG TERM....KR
AVIATION...Sarment
MARINE...Sarment

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