877
FXUS66 KMTR 261806
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
1106 AM PDT Sat Apr 26 2025

...New AVIATION...

.SYNOPSIS...
Issued at 1240 AM PDT Sat Apr 26 2025

Isolated showers will continue today, mainly focused on the
Central Coast and North Bay. Skies will start to clear Sunday as a
pattern change brings weak offshore winds with warmer and drier
conditions expected next week.

&&

.UPDATE...
Issued at 908 AM PDT Sat Apr 26 2025

Light rain continues across southern Monterey County and San Benito
County with a few wrap around showers located to the north over the
Bay Area. Over the last 12 hours, up to 0.04" of rain has fallen
over the Central Coast. Across the majority of the Bay Area,
rainfall has been light (generally a few hundredths of an inch). The
exception to this is in northeast Contra Costa County where
localized wrap around showers produced up to 1/4" of rain within the
last two hours. No reports of lightning so far but guidance
continues to indicate up to a 15% chance of thunderstorms across the
Central Coast through this afternoon.

&&

.SHORT TERM...
(Today and tonight)
Issued at 1240 AM PDT Sat Apr 26 2025

An upper level low off the coast is moving toward Point Conception
early this morning. This cold-core low is dropping the 500 mb
temperature as low as -27C, which is in the bottom 5% for this
time of year. With cold air aloft, the atmosphere will be unstable
(relatively warm air near the surface will be buoyant and
accelerate upward). This effect is most pronounced when the
maximum surface heating in the afternoon lines up with the coldest
air aloft. In this case, the timing doesn`t line up. The coldest
air is moving in early this morning, well before the maximum
surface heating this afternoon. Nonetheless we are still expecting
isolated showers to continue through the day, and there is still
a slight chance for thunderstorms, mainly over the Central Coast.
There are 2 windows that are more favorable for stronger
convection. The first is in the pre-dawn hours this morning over
the coastal waters (which are 5-7 degrees F warmer than the land
at the moment). The second is over southern Monterey County this
afternoon between 11 AM and 3 PM due to enhanced surface heating.
For what it`s worth, the higher resolution models are more
aggressive than the global models (HRRR brings the surface CAPE
above 200 J/kg to areas south of San Jose). The latest satellite
imagery suggest overcast skies are moving in across the interior
Central Coast and will likely stick around for most of the day.
This will reduce the surface temperature, limit the instability
and decrease thunderstorm chances.

&&

.LONG TERM...
(Sunday through Friday)
Issued at 1240 AM PDT Sat Apr 26 2025

As the bowling ball of cold air aloft moves further inland, it
will eventually be picked up by a positively tilted trough early
in the work week. This will cause a pretty stark change in the
weather pattern as moist, cool onshore flow this weekend flips to
warm, dry, offshore wind by Monday. Sunday will serve as a
transition day with light showers lingering in the morning and
skies clearing through the afternoon. Fortunately the offshore
winds look pretty weak and diurnal wind shift will still dominate
along the coast. The SFO- WMC gradient is only expected to drop
somewhere between neutral and -6 mb. This is the type of pattern
that brings fantastic weather to the Bay Area this time of year.
Inland highs will be in the mid 70s with coastal areas reaching
the mid 60s. The weather will remain pretty consistent through the
week as the positively tilted trough fades into a pure ridge by
Thursday. Ensemble clusters suggest this ridge will break down
next weekend, although the exact pattern is still uncertain. Some
solutions bring another cut-off low through, while other have more
straight-forward troughing. Either way, this looks like our next
chance for rain. Both GEFS and ECMWF ensemble means show a modest
amount around 1/10-1/4", but there are a few outliers among the
members of both ensembles that suggest up to 1" is a possible
scenario.

&&

.AVIATION...
(18Z TAFS)
Issued at 1106 AM PDT Sat Apr 26 2025

Convective clouds starting to rapidly develop over higher terrain
with upper low nearby. Most terminals are forecast to remain
mainly dry but tafs will show vicinity showers. Most cigs should
remain mvfr outside of heavier downpours. Cant rule out isolated
lightning chances but best chances remain away from terminals
over higher terrain and out towards the Central Valley. Best
chance of showers will be afternoon hours, roughly 21-00z and then
a final shot 02-06z as final shortwave rotates down the coast
from North Bay to Central coast with most likely terminals to see
showers being Half Moon Bay and Monterey under post frontal
favorable NW wind flow pattern. Skies to quickly trend VFR after
sunrise Sunday with drying trend building in behind upper trof.

Vicinity of SFO...WNW winds mainly under 15 kt with cigs mainly
MVFR. Nearby showers this afternoon and into this evening. Drying
trend returns by 12z Sunday.

SFO Bridge Approach...Similar to SFO with showers passing over the
Bay possibly impacting visuals of the runways at times this
afternoon and evening.

Monterey Bay Terminals...Building cumulus over the higher terrain
around MRY and SNS with prevailing NW winds this afternoon and
evening. Nearby showers this afternoon then better chances for
light rain and lowering cigs for KMRY between 02-07z as final
disturbances pushes through. Drying trend with VFR skies
developing 13-17z Sunday.

&&

.MARINE...
(Today through Thursday)
Issued at 421 AM PDT Sat Apr 26 2025

Showers will continue today due to a low pressure system moving
southeastward over the coastal waters. Tonight and Sunday the low
will move eastward with a few lingering showers possible over the
coastal waters and bays. Breezy northwest winds will develop
across the northern outer waters from later today to Sunday. High
pressure will bring dry weather next week.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory from 9 PM this evening to 9 AM PDT Sunday
     for Pt Arena to Pt Reyes 0-10 nm-Pt Reyes to Pigeon Pt 0-10
     nm.

     Small Craft Advisory from 3 PM this afternoon to 9 PM PDT Sunday
     for Pt Arena to Pt Reyes 10-60 NM.

     Small Craft Advisory from 9 PM this evening to 9 PM PDT Sunday
     for Pigeon Pt to Pt Pinos 10-60 NM.

&&

$$

SHORT TERM...Flynn
LONG TERM....Flynn
AVIATION...RW
MARINE...RW

Visit us at www.weather.gov/sanfrancisco

Follow us on Facebook, X, and YouTube at:
www.facebook.com/nwsbayarea
x.com/nwsbayarea
www.youtube.com/nwsbayarea