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000
FXUS66 KMTR 191136
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco Bay Area
436 AM PDT Mon Apr 19 2021

.SYNOPSIS...A cooling trend begins today with breezier onshore
winds and a deepening marine layer. More widespread cooling is
forecast for Tuesday as temperatures return to seasonal averages.
Dry and seasonable conditions then persist through Friday. The
weekend will bring cooler temperatures and increasing chances for
rain late Saturday and Sunday.

&&

.DISCUSSION...as of 03:35 AM PDT Monday...The marine layer has
deepened to around 1000 ft, as the upper ridge begins to weaken
its grip over our area. Stratus has developed along the coast from
Sonoma through the Central Coast and will advance farther inland
as the morning progresses. Temperatures are running a few degrees
warmer than 24 hours ago at most sites, as a result of the much
above normal temperatures experienced yesterday. Today will be
another above normal day away from the coast, as a weak ridge
remains over our area and 850 mb temps peak. Areas closer to the
ocean and bays will cool by a couple to perhaps up to 12 degrees,
as stronger onshore flow returns. This will translate to 50s and
60s along the immediate coast, upper 60s to low 70s along the SF
Bay shoreline, and low to mid 80s in the inland valleys. Winds may
also become pretty gusty in the late afternoon and evening as an
upper low forms off the Oregon coast and moves over northern CA.

Tuesday, the area will experience more widespread cooling under
the influence of the upper low, with the most significant cooling
occuring inland. This basically means a return to near-normal
temperatures region-wide. Unfortunately, models keep all precip
associated with the low to the north and east of our area.

Wednesday through Friday do not bring any changes to our area in
terms of sensible weather. As the low moves east, we become
situated between a trough over the inter-mountain west and a ridge
several hundred miles off the coast. Temperatures will be near
normal, and a marine layer will provide continued night and
morning low clouds.

Saturday, an upper low approaches the PacNW, bringing cooling to
the coast. Both the ECMWF and GFS bring precip to northern CA
Saturday afternoon, but leave our area dry until Sunday morning.
There is some disagreement on the path and timing of the low at
this point. The ECMWF develops a deep trough off the northern CA
coast, which pivots over our area late Sunday, bringing wetting
rain to much of the state. The GFS keeps the closed low off the
northern coast until Monday afternoon with wetting rain preceding
it Sunday afternoon and evening. Ensemble members are also coming
together for light to moderate precip in the late Sunday to early
Tuesday timeframe. Our forecast reflects this increasing
confidence, with chance pops and light qpf across the region
Sunday and Monday. Guardedly optimistic at this point, as we`re
still six days out.

&&

.AVIATION...As of 04:36 AM PDT Monday...For the 12Z TAFs. Low
clouds have filled in along the coast as profilers show the marine
layer has deepened to to about 1200 ft AGL. Stratus has also
pushed through the Golden Gate Gap and made its way around to
Oakland. Clouds expected to continue to fill into the Bay and
towards SFO this morning. Current observations record cig heights
between 300 and 800 ft AGL with conditions ranging from VFR to
LIFR. Expect low clouds to persist through mid to late morning
(~15z-18z) with later clearing times around the Monterey Bay.
Slight chance of fog around KSTS early this morning. VFR
conditions this afternoon before low clouds return this evening.
W/NW winds at or below 10 kt this morning increasing this
afternoon and evening. Models and guidance continue to suggest
gusts between 20-25 kt possible, generally, through early tomorrow
morning with stronger gust potential for SFO.

Vicinity of KSFO...Satellite shows low clouds slowly expanding
south and westward towards the terminal. Intermittent IFR
conditions anticipated until ~16z before VFR conditions prevail.
Low clouds forecast to return tonight. W/NW winds throughout to
increase this afternoon to 20-25+ knots lasting through mid to
late tomorrow morning.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...The marine layer has deepened to about
1200 ft AGL as stratus has filled into the Bay and expanded down
the Salinas Valley. IFR/LIFR conditions currently, later clearing
times expected today compared to yesterday (~17z-19z). Still a
slight chance of fog early this morning. VFR conditions expected
this afternoon before low clouds return this evening and tonight.
Light winds this morning increasing this afternoon to around 15
kt. Breezy conditions may linger into the evening.

&&

.MARINE...as of 02:02 AM PDT Monday...Northwest winds will
increase through the day as a disturbance moves southward from the
Pacific Northwest into northern California. Gale force gusts are
expected to develop over portions of the coastal waters starting
with the Big Sur Coast by late this afternoon before winds
increase over the northern waters this evening and persist into
Tuesday. These winds will produce steep wind waves resulting in
hazardous seas conditions, particularly for smaller vessels.
Moderate northwest swell through the period along with a lighter
longer period southerly swell.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tday...SCA...Mry Bay from 2 PM
             SCA...Pigeon Pt to Pt Pinos 0-10 nm from 2 PM
             SCA...Pt Arena to Pt Reyes 0-10 nm
             SCA...Pt Arena to Pigeon Pt 10-60 nm
             SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm until 3 PM
             GLW...Pt Pinos to Pt Piedras Blancas 0-10 nm from 3 PM
             SCA...Pt Reyes to Pigeon Pt 0-10 nm
             SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm

&&

$$

PUBLIC FORECAST: Lorber
AVIATION: AS
MARINE: AS

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