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

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000
FXUS66 KMTR 241753
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
1053 AM PDT Sun Mar 24 2024

...New AVIATION, MARINE...

.SYNOPSIS...
Issued at 1223 AM PDT Sun Mar 24 2024

Unsettled weather continues through this afternoon with rain
showers and perhaps an isolated thunderstorm. A bit drier for
Monday into Tuesday before rain chances return for mid week into
the weekend.

&&

.UPDATE...
Issued at 856 AM PDT Sun Mar 24 2024

The morning KOAK sounding paints a decent picture of the current
atmospheric environment over the region. The sounding reveals
moderate instability with (SFC CAPE 300+ J/kg) and little to no
convective inhibition (CINH). Additionally, PWATs are sitting
near 0.6", while not crazy moist it`s still around the 75
percentile. Lastly, lapse rates are moderate to moderate/high at
7.5 C/km or conditionally unstable. So what does this all mean?
Unstable atmosphere that can support convective showers and
possibly a thunderstorm or two. Looking at KMUX radar confirms the
atmospheric environment with widespread shower activity across
the region tracking NW to SE. Haven`t observed any lightning yet,
but given the set up it`s possible. Probabilistic guidance
continues to show a 25% chc of lightning with the stronger cells.
A little bit of daytime heating may be enough to tip the chances
for lightning higher. One thing that has been observed are higher
precip rates with the stronger showers. These brief heavy showers
may lead to excessive runoff with localized ponding on area
roadways. Finally, yesterday featured a waterspout over Monterey
Bay. Today`s set up shows marginal low-level shear 0-1km. Have
already seen very weak rotation over the coastal waters with more
developed cells this morning. Will be monitoring closely for any
stronger/further development.

No updates planned. Showers and isolated thunderstorms through
early this afternoon before tapering off from N to S.

&&

.SHORT TERM...
(Today and tonight)
Issued at 1223 AM PDT Sun Mar 24 2024

A closed upper low over SW Oregon will gradually devolve to an open-
wave trough as it drops southeast through NorCal today. The
associated surface cyclone will dissipate with remnant troughing
locating just offshore from NorCal. The combination of steep
mid/upper lapse rates and the nearby surface trough will lead to a
continuation of scattered instability showers across the region
primarily during the first half of today. Like yesterday there
remains a little instability so can`t rule out an isolated
thunderstorm or two, but by and large showers are the most likely
forecast outcome for most. The primary weather hazards for today are
brief locally heavy rainfall, small hail, and perhaps a lightning
strike or two. Flooding impacts are unlikely as the steering flow
remains progressive and northwesterly. Readings will remain cool
with highs mostly in the 50s to around 60. Lows tonight will dip
into the 40s, with some upper 30s in southern Monterey County.

&&

.LONG TERM...
(Monday through Saturday)
Issued at 1223 AM PDT Sun Mar 24 2024

High pressure will prevail aloft for Monday and Tuesday with drier
conditions and a slight warming trend.

A cold front attendant to low pressure over the northeast Pacific
will bring renewed rain chances for Wednesday into Thursday. Rain
amounts with this system appear beneficial and not overly impactful.

An upper low looks to evolve somewhere in the vicinity for late week
into the weekend. Deterministic models and their ensembles are in
good agreement with the general pattern, but differ somewhat in the
strength and placement of the upper low. It does appear that a
better moisture tap will accompany this system with the potential
for coastal ranges to receive 1-2" of rainfall. However there are
still some details to resolve so keep up with forecast updates.

&&

.AVIATION...
(18Z TAFS)
Issued at 1052 AM PDT Sun Mar 24 2024


Scattered showers continue to move through the region through the
first half of the TAF period, bringing at times moderate rainfall to
terminals. Isolated thunderstorms are still a possibility this
morning, though chances diminish into the early afternoon of Sunday.
Winds are likely to be the biggest impact, as gusty northwesterly
winds up to around 20-25 knots generally impact terminals through
the evening of Sunday. Although gusts diminish into the overnight
hours of Sunday into Monday, winds remain somewhat elevated for most
terminals at around 10-12 knots. Most terminals will see VFR
conditions lasting through the TAF period, though Monterey Bay
may see lowered CIGs and MVFR conditions in the early morning of
Monday. However, confidence on this is low-moderate. Although
models at this time do not hint at a return of fog to KSTS
terminal, ample clearing of high clouds and residual moisture from
recent rainfall may lend to fog development Monday morning. At
this time, have kept KSTS VFR though this will be something to
keep an eye on.


Vicinity of SFO...Scattered shower chances last through the
afternoon, though quickly abate beyond about noon. Highest
confidence is in VFR conditions lasting through the TAF period,
though a few low clouds may form over the terminal in the morning of
Monday. Winds will be the largest concern today with gusts up to
around 30 knots out of the northwest, peaking in the late afternoon
today. Towards sunset, some directional wind shear develops over the
terminal as gusts begin to ease into the night to become breezy.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Showers will continue to intermittently
impact the terminal today through the early afternoon, at times
bringing reductions in visibility. However, conditions should
largely remain VFR through the evening today. Winds out of the NW
and gusting to around 20 knots this afternoon. In the early morning
of Monday, MVFR CIGs develop and last just beyond sunrise. Though,
there is disagreement amongst models as to CIG development
whatsoever. At this time, moderate confidence in MVFR CIGs
developing in the early morning of Monday.

&&

.MARINE...
(Today through Friday)
Issued at 1052 AM PDT Sun Mar 24 2024

Scattered rain showers continue through the late morning today,
becoming more sparse into the late afternoon. Still cannot rule
out the chance for an isolated thunderstorm or two, though best
chances for any formation of thunderstorms continue to be in the
morning hours today. Fresh and gusty northwesterly winds continue,
leading to hazardous conditions for small craft. Come the early
morning of Monday, and winds ease to become more moderate out of
the northwest. Larger northwest swell abates through the day of
Monday, with a new and longer period northwest swell arriving
behind it.

&&

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

     Small Craft Advisory until 9 AM PDT Monday for Pigeon Pt to Pt
     Pinos 0-10 nm-Pigeon Pt to Pt Pinos 10-60 NM.

     Gale Warning until 3 AM PDT Monday for Pt Pinos to Pt Piedras
     Blancas 0-10 nm.

     Small Craft Advisory from 3 AM to 3 PM PDT Monday for Pt Pinos
     to Pt Piedras Blancas 0-10 nm.

&&

$$

SHORT TERM...SPM
LONG TERM....SPM
AVIATION...AC
MARINE...AC

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