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

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FXUS66 KMTR 291154
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
454 AM PDT Fri Mar 29 2024

...New AVIATION, MARINE...

.SYNOPSIS...
Issued at 230 AM PDT Fri Mar 29 2024

A weather system brings wind, rain, and a few thunderstorms to the
region later today through Saturday. Moderate impacts are
anticipated including minor flooding and potential tree and power
line damage. Stay weather aware and prepare for longer afternoon
and evening commute times today.

&&

.SHORT TERM...
(Today and tonight)
Issued at 230 AM PDT Fri Mar 29 2024

Key Points:
* Impactful weather system today into Saturday
* Moderate wind and water impacts anticipated
* Strong wind gusts may cause tree and power line damage
* Minor flooding potential from locally heavy rainfall
* Isolated thunderstorms with lightning and small hail
* Peak impacts this afternoon into Saturday evening

Weather Overview:

A cyclonic flow pattern prevails aloft across the northeast Pacific
early this morning. Two low pressure systems are evident -- one west
of Washington and another located around 400 nm west of the Redwood
Coast. A consensus of the forecast models suggest the lower latitude
system will become the prevailing low as it drops southeast towards
the northern/central CA coast. The surface low will subsequently
deepen to around 995 mb as it locates just east of the Bay Area by
this evening. This dynamic system will bring impacts to the
region in the form of strong gusty winds, periods of moderate to
heavy rainfall, and thunderstorms through the forecast period.
Below is a timeline of our expectations for today into tonight.

This Morning:

Scattered showers will increase in coverage across the Bay Area
during the mid to late morning hours as warm advection aloft becomes
the primary forcing mechanism for ascent. Breezy southerly winds
will begin to pick up as well, especially along the coast and within
the coastal ranges of the Bay Area. Showers should be light to
moderate through most of this period, with heavier showers
approaching the Bay Area as afternoon approaches. The primary
impacts during this period should be wet roadways along the with
the potential for a few branches down due to the breezy winds.

This Afternoon and Evening:

This will be prime time for the greatest impacts. Look for the
deepening surface low to wobble towards the coast as a surface warm
front lifts north early in the period before a cold front moves
onshore during the late afternoon to early evening. Coverage and
intensity of showers should increase by early afternoon with
elevated instability providing for isolated thunderstorm potential
as well. A 50 kt southerly low-level jet (LLJ) will impinge on
coastal portions of the region as well with an uptick in strong
and gusty gradient winds occurring. In addition the higher
resolution convection allowing models are suggestive of a
conditional risk for mixing these stronger winds to the surface in
convection particularly as the main frontal band moves onshore
during the early to mid afternoon hours. As mentioned instability
is sufficient for thunderstorm development as early as this
afternoon, but actually peaks within the colder and unstable
airmass following the cold frontal passage. Regardless,
thunderstorm hazards will exist in the form of occasional
lightning, brief heavy rain, gusty to perhaps locally damaging
winds, and small hail. Given the strong low-level wind fields and
sufficient low-level directional shear can`t rule out the
potential for a landfalling waterspout as well, especially this
afternoon. Scattered showers and isolated thunderstorms will
continue within the post-frontal environment overnight as the
cold-core low remains in the vicinity. Now that we`ve outlined
the weather setup here`s a quick breakdown on potential hazards
for today and tonight:

* Strong gusty winds with tree and power line damage possible
* Locally heavy rainfall leading to urban/street flooding
* Isolated thunderstorms with lightning, wind, and small hail
* Conditional risk for landfalling waterspout

Stay weather aware today and keep up with forecast changes.

&&

.LONG TERM...
(Saturday through Thursday)
Issued at 230 AM PDT Fri Mar 29 2024

Saturday into Sunday morning:

While the weakening surface low will depart to our south the region
remains under the influence of the cold-core upper low. This means
we`ll see plentiful showers and isolated thunderstorms on Saturday.
The day won`t be a total washout (we`ll probably even see some
sunshine at times), but watch out because when it rains, it pours
(as they say). So watch out for lightning, brief locally heavy
rainfall, and small hail as potential hazards. This risk is greatest
on Saturday afternoon, with coverage continuing overnight. By Sunday
morning look for precipitation to have largely ended for most areas
outside of perhaps the Santa Lucias and southern Diablo range.
Overall amounts should be lighter compared to during Friday/Friday
night, but locally heavy amounts could cause minor flooding concerns
if a heavier shower or storm traverses an urban or hydrologically
sensitive area. Winds should be quite a bit lower as well as the
pressure gradient relaxes. For temperatures, they`ll be a little on
the cool side with highs in the upper 50s to lower 60s and lows
mostly in the 40s.

Late Sunday through Thursday:

High pressure builds into the region with dry conditions and a
warming trend through mid week. Expect a cooling trend by late week
as upstream troughing traverses the Pacific Northwest states. A
little light precipitation may accompany this feature as well but it
doesn`t appear to be anything noteworthy at this point.

&&

.AVIATION...
(12Z TAFS)
Issued at 454 AM PDT Fri Mar 29 2024

Increasingly strong and gusty southeasterly winds aloft resulting
in low level wind shear, otherwise moderate to heavy rain including
periodic gusty southerly surface winds also developing today. Windy
conditions continuing tonight along with moderate to heavy showers
and a slight chance of thunderstorms. Winds easing somewhat by early
Saturday morning. MVFR-IFR conditions during the period.

Vicinity of SFO...Southerly to southeasterly winds increasing today
with gusts 25 to 30 knots, possibly a few higher gusts during the
afternoon. Low level wind shear developing by late morning, continuing
through the afternoon. Rain developing today, showers along with a
slight chance of thunderstorms tonight and Saturday morning.

SFO Bridge Approach... Similar to SFO.

Monterey Bay Terminals...Southerly to southeasterly winds increasing
today, especially gusty in the Salinas Valley. Localized low level
wind shear possible during the afternoon. Otherwise rain developing
today, showers along with a slight chance of thunderstorms tonight
and Saturday morning.

&&

.MARINE...
(Today through Wednesday)
Issued at 445 AM PDT Fri Mar 29 2024

A strengthening low pressure system over the eastern Pacific will
continue moving toward California resulting in southerly gales and
moderate to heavy rain developing today. Cold, unstable air aloft
with the low will also result in a slight chance to chance of
thunderstorms later today, tonight and Saturday. A high pressure
system will build in behind the low late in the weekend and early
next week bringing drier, milder conditions to the area.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Wind Advisory from 11 AM this morning to 5 AM PDT Saturday for
     CAZ006-504-509-510-512-514>516-518-528>530.

     Wind Advisory from 8 AM this morning to 3 AM PDT Saturday for
     CAZ502-503-505.

     High Wind Warning from 11 AM this morning to 9 PM PDT this
     evening for CAZ517.

     Wind Advisory from 9 PM this evening to 5 AM PDT Saturday for
     CAZ517.

PZ...Small Craft Advisory from 3 PM this afternoon to 9 PM PDT this
     evening for SF Bay N of Bay Bridge.

     Small Craft Advisory from 9 AM this morning to 3 PM PDT this
     afternoon for Mry Bay.

     Gale Warning from 3 PM this afternoon to 3 AM PDT Saturday for
     Mry Bay.

     Small Craft Advisory until 9 AM PDT this morning for Pigeon Pt
     to Pt Pinos 0-10 nm-Pigeon Pt to Pt Pinos 10-60 NM-Pt Arena
     to Pt Reyes 0-10 nm-Pt Arena to Pt Reyes 10-60 NM-Pt Pinos
     to Pt Piedras Blancas 0-10 nm-Pt Reyes to Pigeon Pt 0-10 nm.

     Gale Warning from 9 AM this morning to 3 PM PDT this afternoon
     for Pt Arena to Pt Reyes 0-10 nm-Pt Arena to Pt Reyes 10-60
     NM-Pt Reyes to Pigeon Pt 0-10 nm.

     Gale Warning from 9 AM this morning to 9 PM PDT this evening for
     Pigeon Pt to Pt Pinos 0-10 nm-Pigeon Pt to Pt Pinos 10-60
     NM-Pt Pinos to Pt Piedras Blancas 0-10 nm.

&&

$$

SHORT TERM...SPM
LONG TERM....SPM
AVIATION...Canepa
MARINE...Canepa

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