289
FXUS66 KMTR 130416
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
916 PM PDT Mon May 12 2025

...New UPDATE, MARINE...

.SYNOPSIS...
Issued at 121 PM PDT Mon May 12 2025

Isolated showers continue through the early evening, with a warming
trend following into the middle and latter part of the week.

&&

.UPDATE...
Issued at 914 PM PDT Mon May 12 2025

Quick update to the evening forecast to keep shower chances
through the night. KMUX radar remains in precip and continues to
detect scattered showers mainly south of the Golden Gate over
both the coastal waters and land areas. Automated gages have
tipped a few hundredths over the last few hours. So why the
continuing shower activity? Post-frontal regime and an unstable
airmass. Latest surface analysis puts the cold front that moved
through earlier today over SoCal. Behind the front is a weak
surface trough just off the Bay Area Coast. KOAK 00Z, NUCAPS
satellite soundings, and ACARS soundings all shows some
instability, but vary on CINH or inhibition. Post-frontal surface
features and meager instability has led to the ongoing shower
activity. Based on latest CAMS and observational data decided to
keep scattered showers through early Tuesday morning. Not
expecting a ton of precip, but showers dropping a few hundredths
seems plausible nonetheless. In addition to lingering precip,
winds remain breezy and onshore. A quick scan of the latest obs
show gusts 20 to 30 mph with a few isolated 40 mph gusts.

One other adjustment to the forecast was to include some scattered
showers over the S Gabilan Range Tuesday afternoon. This location
is always favored in these regimes for afternoon pop up showers.
00Z CAMS show a few showers firing up over the Sierra Crest,
Central Valley, and lastly over the interior Central Coastal Mts.
No mention of thunder at this time, but a showers seem plausible.

MM

&&

.SHORT TERM...
(This evening through Tuesday)
Issued at 121 PM PDT Mon May 12 2025

Radar and satellite imagery showed the main rain band practically
fall apart as it went through the Central Coast, and at the moment,
isolated showers continue across the Bay Area. Most of the region
saw around a tenth of an inch, with as much as a quarter to a half
an inch in the Bay Area and Santa Cruz mountains, while the interior
Central Coast did not see any rain. Isolated showers and perhaps a
few rumbles of thunder in the North Bay will continue through the
early evening with any additional accumulation up to a few
hundredths of an inch. Any rain chances for tomorrow will mainly be
limited to coastal and orographically driven drizzle, with the main
concentrations of accumulating precipitation off to our east in the
Sierra Nevada range.

Temperatures across the region remain cool with today`s highs
reaching the lower to middle 60s in the inland valleys, into the
upper 60s to the lower 70s in the warmest spots, and around the
middle to upper 50s in the coastal locations. Highs in the inland
valleys reach the upper 60s to lower 70s on Tuesday, but this is
still around 5 to 10 degrees below seasonal averages, while lows on
Tuesday morning hover in the middle 40s to lower 50s in the lower
elevations, down to the upper 30s to the lower 40s in the higher
elevations.

&&

.LONG TERM...
(Tuesday night through next Sunday)
Issued at 121 PM PDT Mon May 12 2025

As upper level ridging builds through the middle and latter part of
the week, inland temperatures will begin to return to seasonal
averages as the inland valleys reach the middle 70s to middle 80s
while the Bayshore sees highs in the upper 60s to middle 70s. Highs
along the coastal regions remain relatively constant and cool, owing
to the sea breeze influence.

With an upper level trough coming through the western United States
later this week into the weekend, the potential for an weak inside
slider continues. Analysis of the global ensemble model clusters
shows that the majority of the model ensembles are pointing towards
a open wave trough this weekend, around 30-45% of the model
ensembles -- mainly driven by those from the American GEFS and
Canadian GEPS models -- continue to hint at a potential closed low
developing across the Intermountain West. Such a low could drive
dry, offshore (at this stage, more northerly instead of easterly(
flow over our region, helping to enhance the fire weather risk.
Without a firm track and intensity for the upcoming low pressure
system, such talk remains something to keep in the back of your mind
rather than something to take immediate action on. Keep an eye out
for further forecast updates as the system`s evolution continues
through the week.

&&

.AVIATION...
(00Z TAFS)
Issued at 515 PM PDT Mon May 12 2025

Light scattered shower activity across our area is expected to taper
off by sunset. VFR is expected to prevail across the North Bay, with
MVFR cigs expected to develop later tonight for the Monterey Bay
terminals. The Bay Area and South Bay terminals will likely see VFR
prevail through the late evening with periods of MVFR cigs during
the overnight into mid morning Tuesday.

Vicinity of SFO...Light shower activity will taper off by early
evening with VFR expected to prevail through the forecast period,
with occasional cig drops into MVFR possible if stratus develops
overnight.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...The strongest signal for MVFR cigs
overnight is expected for KMRY and KSNS, mostly likely to set in
after midnight and persist through late morning Tuesday. Winds will
increase out of the west during the overnight as an upper level
system exits to the east.

&&

.MARINE...
(Tonight through next Sunday)
Issued at 851 PM PDT Mon May 12 2025

Showers continue to linger off our coastal waters this evening
with little to no impacts expected. Fresh northwest breezes are
expected to be strong by Tuesday, along with building seas. Gales
are expected by Tuesday evening, leading to hazardous marine
conditions.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory from 9 AM to 9 PM PDT Tuesday for Mry Bay.

     Small Craft Advisory until 3 AM PDT Wednesday for Pigeon Pt to
     Pt Pinos 10-60 NM-Pt Arena to Pt Reyes 0-10 nm.

     Small Craft Advisory from 3 AM Tuesday to 3 AM PDT Wednesday for
     Pt Pinos to Pt Piedras Blancas 0-10 nm-Pt Reyes to Pigeon
     Pt 0-10 nm.

     Small Craft Advisory from 9 AM Tuesday to 3 AM PDT Wednesday for
     Pigeon Pt to Pt Pinos 0-10 nm.

     Small Craft Advisory until 3 PM PDT Tuesday for Pt Arena to Pt
     Reyes 10-60 NM.

     Gale Warning from 3 PM Tuesday to 3 AM PDT Wednesday for Pt
     Arena to Pt Reyes 10-60 NM.

&&

$$

SHORT TERM...DialH
LONG TERM....DialH
AVIATION...JM
MARINE...JM

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