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

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000
FXUS66 KMTR 240558
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
1058 PM PDT Sat Mar 23 2024

...New AVIATION, MARINE...

.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...
(06Z TAFS)
Issued at 1055 PM PDT Sat Mar 23 2024

Rain showers will continue to decrease in coverage and intensity
through the night with chances becoming unmentionable by tomorrow
afternoon. While chances for thunderstorms (30%) still exist through
Sunday morning, only a few lightning strikes were recorded within
the area today and today`s environment was supposed to be the more
favorable of the two days. VFR conditions prevail through the TAF
period with reductions in flight category possible if a shower
passes directly over a terminal. Winds tomorrow will be gusty out of
the W/NW with gusts of 20-30 knots to be expected.

Vicinity of SFO...Currently VFR with breezy westerly flow. Rain
shower activity will continue to diminish through the TAF period.
Winds tomorrow will be gusty out of the W/NW with gusts up to 30
knots to be expected.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Currently VFR with breezy southwesterly
flow at MRY and MVFR with a rain shower passing over SNS. Rain
shower activity will continue to diminish through the TAF period.
Winds will be gusty (20-25 knots) out of the W/NW at both
terminals by late-morning tomorrow.

&&

.MARINE...
(Tonight through next Friday)
Issued at 1055 PM PDT Sat Mar 23 2024

Scattered showers with slight chance for thunderstorms continues
overnight tonight into Sunday morning across the coastal waters.
If  a thunderstorm develops, winds will become locally gusty which
will  cause dangerous conditions for small crafts. Generally,
westerly  winds will become more northerly overnight tonight and
increase to  become fresh to strong. Moderate period westerly
swell and elevated  wave heights will persist before diminishing
Sunday into next week.  Additional northwest swell trains will
propagate through the coastal  waters next week. Rain chances
decrease moving into Sunday afternoon  with calmer weather for the
beginning of the work week as high  pressure briefly builds.

&&

.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...Sarment
MARINE...Kennedy

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