National Weather Service Raw Text Product

Displaying AFOS PIL: AFDMTR Received: 2018-03-13 10:28 UTC


388 
FXUS66 KMTR 131028
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco Bay Area
328 AM PDT Tue Mar 13 2018

.SYNOPSIS...An active weather pattern will continue for the rest 
of the week. Expect cool temperatures with periods of rainfall 
along with breezy and gusty winds at times.

&&

.DISCUSSION...as of 3:30 AM PDT Tuesday...Upper level low is
centered near 40/135 while a 985 mb low is 380 miles west of the
Oregon coast and moving north. This has generated gusty winds
along the coast and over the hills. Strongest winds have been over
the North Bay and SFO Bay Area hills where gusts to 40 mph have
reported. Higher gusts are being reported at the very highest
peaks like Mt Diablo and Atlas Peak. 

The warm front moved through Monday afternoon and our district
remains in the warm sector with scattered light rain. The cold
front will come onshore over the North Bay after 12Z and will
spread through the SFO Bay Area by midmorning and the MRY Bay Area
early afternoon. Light to moderate rain will spread over the area
through the morning hours. Rain will turn to scattered showers 
this afternoon and continue through Wednesday as the trough axis 
remains offshore. A cooler airmass will allow snow levels to drop
to 4000 feet so there could be some snow on the highest peaks of
Monterey and San Benito Counties. Models indicating shower 
activity could pick up over most areas Wednesday afternoon as the
trough axis moves onshore. There is a slight chance for weak 
thunderstorms Wednesday as the greatest instability occurs during 
trough passage. 
 
A break in the weather is expected Wednesday night before another
upper low approaches the northern California coast. A warm front 
will bring a chance of light rain to the area Thursday morning and
afternoon but southeast winds will result in a lot of rain 
shadowing inland of the coastal ranges. The cold front will move 
fairly quickly through the North Bay late Thursday afternoon and 
the SFO Bay Area Thursday night reaching the MRY Bay Area early 
Friday morning bringing about a 3-6 hour period of light to 
moderate rain. Timing of the frontal passage is a little uncertain
as the NAM is a few hours faster. In either case there will be 
showers behind the front that will last through Friday night. 
Colder air will be ushered in with this system and snow levels may
drop to 2500 feet in the North Bay and 3000 feet in the Santa 
Lucias Friday night. Isolated thunderstorms are a possibility as 
well.

Additional rain amounts through Saturday are expected to be 1-2 
inches in the lower elevations except 1/2 to 1 inch over Monterey
and San Benito counties...and 2-3 inches in the hills except
locally 4 inches in the Santa Cruz Mountains.

Shower activity will diminish Saturday afternoon with dry weather
is expected Sunday. Medium range models indicate unsettled weather
returning around Tuesday and Wednesday of next week. 

&&

.AVIATION...as of 11:02 PM Monday...Subtropical origin air with
milder conditions has arrived, warm air advection rain is ongoing
in spots. Conditions are VFR/MVFR and locally IFR. Echo tops are
recently lower this evening; decided to leave VCTS in KSTS taf 
tonight as earlier forecast soundings had indicated some convective
potential specifically more robust in the North Bay. Still no sign
of lightning yet, but a cold front will be arriving Tuesday morning
setting the stage for possible additional convection. Also decided
to leave in VCTS for Bay Area tafs for Tuesday afternoon. A steepening
contrast in air mass characteristics plus daytime heating if there
are sunny breaks Tuesday could provide an extra boost to instability
and isolated thunderstorm development.

Vicinity of KSFO...MVFR cig tonight, MVFR/VFR Tuesday. Downpours
possible near cold frontal passage and maybe an isolated thunderstorm
in the vicinity of KSFO Tuesday. Gusty SE winds near frontal passage
at about 16z.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...VFR/MVFR with tempo light rain this evening
then moderate to locally heavy rain possible Tuesday morning near cold
frontal passage. Strong and gusty SE winds possible especially in the
Salinas Valley. Cigs Tuesday improve to VFR by either late morning
or early afternoon, still some lingering late day showers possible
long after the cold front has moved by Tuesday.

&&

.MARINE...as of 8:50 PM PDT Monday...Gusty southerly winds will 
continue over the coastal waters for most of tonight into Tuesday 
morning. A cold front will move eastward over the coastal waters 
and bays Tuesday morning causing more wet weather. Wet and breezy 
weather will continue for much of this week.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tday...SCA...SF Bay
             SCA...Mry Bay
             SCA...Pt Arena to Pt Reyes 0-10 nm
             SCA...Pt Reyes to Pigeon Pt 0-10 nm
             SCA...Pigeon Pt to Pt Pinos 0-10 nm
             SCA...Pt Arena to Pigeon Pt 10-60 nm
             SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm
             SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm

&&

$$

PUBLIC FORECAST: W Pi
AVIATION: Canepa
MARINE: Canepa

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