National Weather Service Raw Text Product

Displaying AFOS PIL: AFDMTR Received: 2018-03-13 11:55 UTC


772 
FXUS66 KMTR 131155
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco Bay Area
455 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 4:55 AM Tuesday...For 12z Tafs. Forecast 
confidence is fairly low through this TAF period. A cold front 
will be passing through the district this morning, bringing a 
brief period of moderate to heavy rain along the cold front. Light
to moderate rain is currently affecting the North Bay and will 
impact the SF Bay Area by 12-13z. Current observations have been 
borderline VFR/MVFR across the Bay Area, anywhere from BKN/OVC 
020-040 agl. 

Forecast model guidance has not been capturing winds very will 
with this storm system. Current thinking is gusty SE winds can be
expected along/ahead of the cold front, with winds turning more 
SW behind the front and becoming less gusty. Nonetheless, winds 
will have to be monitored closely, especially over the next few 
hours as the front passes through. As far as thunderstorm chances
today, there were a few lightning strikes over the open ocean, 
behind the cold front earlier this morning. Decided to keep VCTS 
in the SF Bay Area/North Bay terminals for this afternoon. 
Forecast models and soundings show the best available convective 
energy for thunderstorms to be around the SF Bay Area and North 
Bay starting mid afternoon through early evening.

Vicinity of KSFO...Rain/showers will wet runways through much of
the forecast period. MVFR cigs will dominate this morning, with 
VFR cigs possible by early afternoon. Downpours possible near 
cold frontal passage and maybe an isolated thunderstorm in the 
vicinity of KSFO this afternoon. Gusty SE winds ahead of the cold 
front, turning SW around 16z.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...VFR/MVFR through the day today. Showers
likely ahead of the cold front, with heavier rain along the front.
Breezy and gusty SE winds possible especially in the Salinas 
Valley through the morning. Cigs improve to VFR by either late 
morning or early afternoon, still some lingering late day showers 
possible long after the cold front.

&&

.MARINE...as of 3:21 AM PDT Tuesday...Southerly winds will 
decrease slightly through the morning, but will remain gusty as a 
cold front passes through from the west. Small craft advisories 
will continue for all ocean zones and for the northern San 
Francisco Bay and West Delta for hazardous seas and wind gusts 
over 20 knots. 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: BAM
MARINE: BAM

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