Area Forecast Discussion
Issued by NWS San Francisco Bay Area, CA

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000
FXUS66 KMTR 240201
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
701 PM PDT Sat Mar 23 2024

...New UPDATE...

.SYNOPSIS...
Issued at 1207 AM PDT Sat Mar 23 2024

Unsettled weather continues today into Sunday morning with breezy
winds, rain showers, and even a few thunderstorms. A bit drier for
Monday into Tuesday before rain chances return for mid week into
next weekend.

&&

.UPDATE...
Issued at 656 PM PDT Sat Mar 23 2024

Scattered showers continue this evening. The convection never
really became organized enough for widespread thunderstorms today,
despite the 00Z sounding from Oakland finding 455 J/kg of surface
based CAPE supported mainly by a nearly dry adiabatic lapse rate
from the surface to 850 mb. Showers will gradually become more
isolated and weaker overnight, but linger into Sunday morning
before finally tapering off.

&&

.SHORT TERM...
(This evening through Sunday)
Issued at 1256 PM PDT Sat Mar 23 2024

Pretty active weather day around the Bay Area and Central Coast
with scattered showers and thunderstorms. An already unstable
airmass got a boost from some daytime heating, which helped to
increase coverage and intensity of the shower activity. Some of
the highlights since this morning: a few automated rain gages have
eclipsed one half inch in the last six hours, stronger cells
resulted in rice to bb size hail, lightning flash observed near
Half Moon Bay, and a weak rotating cell over Monterey Bay spawned
a brief waterspout.

Rest of this afternoon through Sunday afternoon: One of the main
forcing mechanisms for the weather today is an overhead upper
level trough that is associated with an upper level low near the
Oregon coast. The upper trough will remain over the region as the
upstream upper low drifts southward tonight through early Sunday.
In fact, the latest guidance has the upper low becoming an open
wave by early Sunday as it drifts southward through eastern CA. So
what does all of that mean for our forecast area? Scattered
showers and embedded thunderstorms will still be possible through
at least early Sunday. The most dynamic period will be this
afternoon through this evening when the most instability is
present. Weather impacts continue to be: brief heavy rain, small
hail, gusty winds, and lightning. Not seeing much in the way of
any low level shear for additional spin ups, but we`ll be
monitoring nonetheless. As always in these set ups, additional
rainfall amounts will vary greatly due to scattered nature. As
noted on previous AFDs, snow levels have dropped and some snow
will be possible over the highest peaks later tonight/early
Sunday.

By Sunday afternoon, the open wave will be marching its way
southward. As a result, any lingering showers will be taper off
from N to S.

&&

.LONG TERM...
(Sunday night through next Friday)
Issued at 140 PM PDT Sat Mar 23 2024

Sunday night through Tuesday: Dry weather returns weak ridging
over the West Coast including the Bay Area and Central Coast.
Previous forecast did have a brief mention of showers on Monday,
but that has now been removed. Given the drier weather and weak
ridge do expect an upward trend with regards to temperatures.
Daytime temperatures upper 50s to upper 60s (higher peaks 40s and
50s) and nighttime temperatures 40s to low 50s (interior
valleys/higher peaks mid 30s to lower 40s).

Wednesday and Thursday: High confidence for a pattern shift mid-
week as noted on WPC clusters. The ridge becomes replaced by a
developing upper low/upper trough. The low itself looks to be
placed near the PacNW coast Wednesday. However, an associated
cold front trailing to the south will sweep through CA Wednesday
into Thursday. This passing front will bring another round of
widespread rain initially over the North Bay early Wednesday
before spreading S and E Wednesday afternoon into Thursday. Next
round of rain still looks beneficial rather than hazardous.
Rainfall amounts: North Bay and Santa Cruz Mts 0.25-1.00",
elsewhere 0.10-0.25" and less than 0.05" interior Central Coast.

Friday into next weekend: Another upper low will round the base of
the mid-week trough and take aim at CA. Once again decent
agreement on WPC cluster analysis. There are some differences with
timing and strength, which is understandable since it`s still
several days out. Next weekend system does appear to have a better
moisture regime with early rainfall amounts of 1-3" for the
coastal mountains. Stay tuned...

&&

.AVIATION...
(00Z TAFS)
Issued at 442 PM PDT Sat Mar 23 2024

Scattered showers across the region continue through Sunday morning.
Most convective activity has initiated in the Central Valley to the
east and the chances for thunderstorms in the forecast region have
decreased. VCTS has been removed from LVK due to lower probability
of occurrence. Breezy and gusty west-southwest flow continues
through the day with a lull in wind speeds overnight, turning to the
northwest by the late morning of Sunday. Generally VFR conditions
prevail with transitory MVFR possible in the most intense showers.

Vicinity of SFO... Generally VFR through the TAF period, MVFR
possible if an intense shower comes over the terminal. Shower
activity continues and will diminish through Sunday morning. Breezy
and gusty west-southwest winds continue overnight, turning to the
northwest late on Sunday morning. Model output suggesting gusts up
to 30 knots on Sunday, will monitor for the possibility of gusts
over 35 knots with updated information.

SFO Bridge Approach... Similar to SFO.

Monterey Bay Terminals... Showers continue through the TAF period,
but coverage decreases through the day on Sunday. A west-
southwesterly flow continues through the night and shifts more to
the northwest Sunday morning, gusting up to 20-25 knots. VFR
conditions prevail with perhaps a spot of MVFR where the showers
develop.

&&

.MARINE...
(Tonight through next Thursday)
Issued at 442 PM PDT Sat Mar 23 2024

Scattered showers with slight chance for thunderstorms continues
overnight tonight into Sunday morning across the coastal waters.
Locally gusty winds possible near a thunderstorm should they
develop. Generally, westerly winds will become more northerly
overnight tonight and increase to become fresh to strong. Moderate
period westerly swell will persist before diminishing Sunday into
next week. Additional northwest swell trains will propagate
through the coastal waters next week.

&&

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

     Small Craft Advisory until 9 PM PDT Sunday for Pt Arena to Pt
     Reyes 0-10 nm-Pt Arena to Pt Reyes 10-60 NM.

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

     Gale Warning from 9 AM to 9 PM PDT Sunday for Pt Pinos to Pt
     Piedras Blancas 0-10 nm.

&&

$$

SHORT TERM...MM
LONG TERM....MM
AVIATION...DialH
MARINE...McCorkle

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