San Mateo, California 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

443
FXUS66 KMTR 260826
AFDMTR

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

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

.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.

&&

.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...
(06Z TAFS)
Issued at 1008 PM PDT Fri Apr 25 2025

Light rain activity has diminished somewhat late this evening,
however scattered light rain will linger across the region
overnight as an upper level low continues moving south down the
California coast. VFR is expected to prevail through the forecast
period with occasional MVFR cigs possible when showers move over
terminals.

Vicinity of SFO...VFR conditions are expected to prevail through
the overnight with occasional MVFR cigs when showers are in
vicinity of the terminals. Shower activity has diminished over
the Bay Area but is expected to increase in coverage once again
early Saturday morning, remaining light and scattered with little
to no impacts expected.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Light rain will remain in vicinity of the
Monterey Bay most of the overnight through Saturday morning. Rain
coverage is expected to diminish by early afternoon with breezy
westerly winds easing after sunset. VFR is expected to prevail
through the TAF period.

&&

.MARINE...
(Today through Wednesday)
Issued at 842 AM PDT Fri Apr 25 2025

A chilly upper level low arriving from the northwest will result
in scattered showers across the coastal waters and bays today
through Sunday morning. Gusty northwest winds and rough seas
return across the northern outer coastal waters late Saturday. Dry
weather returns early next week due to an eastward moving high
pressure system over the Pacific.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory from 3 PM this afternoon to 9 PM PDT this
     evening for Pt Arena to Pt Reyes 10-60 NM.

&&

$$

SHORT TERM...Flynn
LONG TERM....Flynn
AVIATION...JM
MARINE...JM

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