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

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FXUS66 KMTR 221702
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco Bay Area
902 AM PST Thu Feb 22 2018

.SYNOPSIS...A weak weather system will impact the area today
bringing widely scattered showers, a slight chance of
thunderstorms in the afternoon, and lowering snow levels. This
system will also bring gusty winds and colder temperatures by
Friday morning. Dry weather and slightly warmer temperatures are
expected for the weekend. Cooler, unsettled weather to return
early next week.

&&

.DISCUSSION...as of 09:00 AM PST Thursday...Unsettled weather
continues today as a 531dm 500mb upper low presently centered
over eastern Washington is set to rapidly descend southward into
the Golden State over the next 24 hours. The San Francisco and
Monterey Bay areas will primarily be on the drier/windier side of
this storm system as it descend into the area.

As a result, look for winds rapidly increase through the next few
to several hours, particularly along the coast and higher
elevations. Widespread northwest sustained winds of 20 to 30 mph
will be possible, with local gusts at favored locations of 40 to
55 mph possible. Precipitation will fall from convective post
frontal showers, so amounts will not be uniform across the area,
with areas under heavier showers seeing the most rain, and some
areas seeing none at all. Generally speaking, accumulations will
be very light and range from a few to several hundredths, with
locally higher amounts of up to 0.25" where the strongest storm
cells develop. An isolated thunderstorm or two are possible over
the area as the coldest air advects in aloft later today. Snow
levels will be down to around 2500 feet as the convective snow
showers move through, meaning a dusting of snow is possible down
to these elevations.

Finally, much colder air will advect in with the core of the upper
low tonight... resulting in another round of near to subfreezing
temperatures for the area tonight/tomorrow morning. These
temperatures will not be quite as cold as Monday night/Tuesday
morning, but widespread upper 20s to upper 30s are forecast. As a
result, preparing any vulnerable plants, pets, and populations
ahead of this cold is recommended.

Looking ahead, temperatures rebound slightly over the coming days
as a weak shortwave ridge develops over the area late tomorrow
through the upcoming weekend. Forecast models show a pair of more
organized but still relatively dry storm systems moving through
the forecast area through the duration of next week. This means
that this cool, unsettled weather is not going anywhere anytime
soon. Precipitation amounts with the storm systems next week are
likely to exceed those of this week, however, these storms
presently do not appear to be fueled by extremely wet moisture
plumes (generally .50-.66" of TPW -- we usually want to see >1.0"
for wetter events). Stay tuned as we track these upcoming storms.


.PREVIOUS DISCUSSION...As of 3:13 AM PST Thursday...KMUX radar is
already showing some weak echoes over the coastal waters off of
the San Mateo coast in advance of an approaching low pressure
system approaching the area from the north. This system is not
expected to have much moisture to work with as it comes from
Canada. Thus, only scattered showers are expected to occur this
afternoon and evening with a few hundredths of an inch to around
0.15 total, and the bulk of that expected over the Santa Lucias.
With the cold air, a slight chance of thunderstorms is possible
this afternoon and evening, mainly over the north and east bay
interior. Snow levels are forecast to drop to under 2000 feet by
this afternoon with only a dusting of snow expected at higher
elevations. Showers are expected to end overnight.

Winds are also expected to ramp up by this afternoon with this
system. Northwest winds are forecast to gust as high as 40 mph
along the coast and in the hills, and locally higher in the winder
locations. Breezy conditions will persist into the early evening
and then winds will subside overnight.

The cold air with this trough will result in chilly overnight low
temperatures. Look for temperatures to drop to freezing, or
slightly below, across inland areas by Friday morning, with
similar readings possible again by Saturday morning. Dry
conditions and cool conditions are forecast over the weekend. Cool
and unsettled weather is expected to continue into next week.
Medium range models bring a better chance of rain to the area
early in the week with another possible system later in the week.

&&

.AVIATION...as of 3:51 AM PST Thursday for 12Z TAFs...VFR
conditions are generally expected to prevail this morning and
afternoon at San Francisco Bay and Monterey Bay Area terminals.
Have seen some temporary MVFR ceilings reported around KSFO this
just prior to the 12Z TAF issuance. Could see some tempo
SCT/BKN030 at the terminal through sunrise, but think the BKN/OVC
decks will remain above 3000 ft. Strong west to northwest winds
will develop through the day at the terminals, with sustained
winds ranging from 15 to 25 kt, and gusts over 30 kt possible
(with locally higher gusts).

Vicinity of KSFO...Expect mostly VFR conditions today, though
can`t rule out temporary MVFR ceilings through about 14 or 15Z
this morning. Think most likely scenario this morning will see
BKN/OVC decks around 3-4k ft AGL, with SCT/BKN decks around 4-5k
ft after mid-morning. Strong west winds will develop through the
day, increasing to around 20 kt sustained by midday, and near 30
kt by mid/late afternoon. Gusts around 35 kt seem quite likely.
Will closely monitor and amend as necessary, particularly as gusts
approach Airport Weather Warning criteria.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...VFR. Scattered clouds developing Thursday
morning with brief showers possible, particularly at KMRY. Strong
onshore winds will develop in the afternoon with sustained winds
around 20 kt at KMRY and 25 kt at KSNS, and gusts approaching 30
kt.

&&

.MARINE...as of 03:38 AM PST Thursday...Northerly winds will
continue to increase over the coastal waters through the day as an
upper-level disturbance passes over the  region. This will result
in gale-force winds in the outer waters.  The strong winds will
bring steep fresh swell and hazardous seas.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tday...SCA...Pigeon Pt to Pt Pinos 0-10 nm
             SCA...Pt Arena to Pigeon Pt 10-60 nm until 1 PM
             GLW...Pt Arena to Pigeon Pt 10-60 nm from 1 PM
             SCA...Mry Bay from 9 AM
             SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm from 9 AM
             SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm
             SCA...Pt Arena to Pt Reyes 0-10 nm
             SCA...Pt Reyes to Pigeon Pt 0-10 nm
             SCA...SF Bay

&&

$$

PUBLIC FORECAST: DRP
AVIATION: Rowe
MARINE: Rowe

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