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

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FXUS66 KMTR 261129
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
429 AM PDT Tue Mar 26 2024

...New AVIATION, MARINE...

.SYNOPSIS...
Issued at 309 AM PDT Tue Mar 26 2024

Unsettled conditions return for Wednesday and Thursday as a weak
weather system moves through. A stronger system brings rain, wind,
and perhaps a few thunderstorms on Friday into the weekend.

&&

.SHORT TERM...
(Today and tonight)
Issued at 309 AM PDT Tue Mar 26 2024

High pressure at the surface and aloft will result in benign
conditions with onshore breezes and near to slightly below average
temperatures. Highs away from the coast will generally be in the low
to mid 60s, with lows tonight generally in the 40s.

&&

.LONG TERM...
(Wednesday through Monday)
Issued at 309 AM PDT Tue Mar 26 2024

Wednesday and Thursday:

An upper circulation will progress from the Gulf of Alaska into the
northeast Pacific with an occluding surface low off the Pacific
Northwest coast. This will bring a decaying cold front through our
area in the Wednesday into Thursday timeframe. Rainfall amounts from
this system appear beneficial and unchanged with amounts up to 1" in
the coastal ranges with 0.25-0.5" elsewhere. Breezy southwest winds
will precede the frontal passage with high elevation and coastal
gusts in the 25-40 mph range. Instability showers will follow the
frontal passage into Thursday.

Friday through Sunday:

A strong and dynamic low pressure system will drop south along the
California coast. This will bring more impactful weather to the
region during this time. Showers begin early Friday morning within a
warm advection regime with PM coverage increasing as a surface front
nears into early Saturday. This will maximize forcing for ascent as
a focused plume of moisture arrives via a 45 knot low-level jet
(LLJ). Precipitable water values are modest (~.75") but should be
sufficient to provide for periods of light to moderate rainfall.
Isolated thunderstorms are possible late Friday into Saturday with
increasing instability. Occasional lightning, gusty winds, and brief
heavy rainfall are the primary hazards. Shower coverage looks to
wane somewhat by Sunday as the low pressure wobbles farther away
towards SoCal. While deterministic models and their ensembles are in
relatively good agreement on the large-scale pattern there remains
some differences in forecast rain amounts across the region. Taking
a look at global ensemble members there is medium confidence (40%)
in seeing moderate rain amounts averaging 1-3". This solution is
slightly favored by a majority of the ensemble members. However
alternate, somewhat lower confidence, solutions include a 30%
potential for amounts of 1-2" or less on the lower end and a 20%
potential for 2-5" on the higher end. So there remains a range of
possible outcomes at this juncture. It`s worth noting that we have
high confidence in everyone getting a soaking as almost none of the
ensemble members suggest little to no rainfall -- even within the
generally drier inland portions of our area. Keep up with forecast
changes as we fine tune details in the days ahead. What about
impacts? Well, if we end up with the "high amounts" scenario (20%
potential) minor flooding impacts are possible. However the "most
likely" forecast outcome at the moment suggests ponding of water and
impacts to commutes are the most likely water-related impacts.
Depending upon the LLJ strength gusty winds could become a concern
as well, particularly in the hills and along the coastal interface.
As mentioned previously thunderstorm-related hazards are possible as
well depending upon the degree of instability that develops. So all-
in-all it`s looking like an active start to the weekend with wind,
rain, and even a bit of lightning possible. Stay weather aware!

Monday and Beyond:

Global models suggest small chances for a few showers around the
Central Coast. Otherwise expect a drying trend with northwest winds
and warming temperatures.

&&

.AVIATION...
(12Z TAFS)
Issued at 411 AM PDT Tue Mar 26 2024

Currently seeing a mix of IFR-VFR conditions at the terminals.
Widespread VFR and breezy westerly winds will prevail by this
afternoon. Towards the end of the TAF period, winds become
southerly ahead of the cold front that will move through the area
on Wednesday.

Vicinity of SFO...Currently MVFR with breezy westerly flow.
Patchy stratus of FL030-FL050 will impact the terminal through
the morning hours, potentially developing a ceiling at times.
Winds will be breezy out of the west through this afternoon before
becoming light and transitioning to a southerly heading ahead of
the cold front that will move through the area on Wednesday.

SFO Bridge Approach...Low clouds will clear the San Mateo Bridge
Approach by this afternoon.

Monterey Bay Terminals...Currently IFR with breezy southwesterly
flow at MRY and MVFR and calm at SNS. VFR and breezy W/NW winds
will prevail at both terminals by this afternoon. MVFR conditions
look to return to MRY towards the end of the TAF period.

&&

.MARINE...
(Today through Sunday)
Issued at 411 AM PDT Tue Mar 26 2024

Moderate northwesterly winds will be enhanced in the coastal jet
regions this afternoon. By Wednesday, an approaching cold front
will cause winds to shift to a fresh southerly breeze as rough
seas begin to build. A stronger low pressure system arrives off
the coast on Friday, further deteriorating marine conditions. Long
period northwesterly swell will continue to abate through the
waters through the end of the month.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory from 3 PM this afternoon to 9 PM PDT this
     evening for Mry Bay-Pt Arena to Pt Reyes 0-10 nm.

     Small Craft Advisory until 3 AM PDT Wednesday for Pt Pinos to Pt
     Piedras Blancas 0-10 nm.

     Small Craft Advisory until 9 AM PDT this morning for Pt Arena to
     Pt Reyes 10-60 NM.

&&

$$

SHORT TERM...SPM
LONG TERM....SPM
AVIATION...Sarment
MARINE...Sarment

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