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

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FXUS66 KMTR 220635
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco Bay Area
1035 PM PST Wed Feb 21 2018

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

&&

.DISCUSSION...As of 9:00 PM PST Wednesday...A weak weather system
brought isolated showers to our region today, but for the most
part today was a dry and cool day under mostly sunny skies.
Afternoon highs were a few degrees warmer than yesterday.

Evening satellite imagery shows the next cold weather system over
the Pacific Northwest, dropping to the south. Because this system
originated over western Canada, it does not have a whole lot of
moisture to work with. Therefore, by the time this system sweeps
into our area tomorrow afternoon, it`s expected to produce only
widely scattered showers. Models also indicate there may be
sufficient instability for isolated thunderstorms in the
afternoon, mainly over the North and East Bay. Isolated showers
and thunderstorms may produce small hail and snow levels are
expected to drop as low as 1800 feet by late afternoon.
Precipitation is expected to taper off early Thursday evening and
end by late evening. Rainfall totals are forecast to be less than
a tenth of an inch, except perhaps a bit more in the Santa Lucias.
Only a dusting of snow is likely at higher elevations.

Tomorrow`s system is also expected to produce blustery conditions
by afternoon. 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 incoming system will bring a reinforcing shot of cold air into
our region with 850 mb temps forecast to drop as low as minus 5
deg C by late tomorrow. Once winds decrease and skies clear later
tomorrow night, look for temperatures to drop to freezing, or
slightly below, across inland areas. Temperatures on Thursday
night aren`t forecast to be quite as cold as they were on Monday
night, but close. The airmass will begin to moderate by Friday
night. However, winds will be lighter and the airmass will be
drier by then. So, overnight lows on Friday night could be just as
cold as Thursday night.

Dry conditions are forecast over the weekend, along with gradual
warming. Even with the expected warming, temperatures will be
about five degrees cooler than normal this weekend as a cool
northwest flow persists across California.

The medium range models maintain a cool and unsettled weather
pattern going into next week. A system arriving from the north
late Sunday night and Monday is forecast to track slightly farther
to the west compared to systems this week, and thus have greater
over water trajectory and moisture. Thus, on Monday we could see
more widespread precipitation as well as greater precipitation
amounts. Snow levels are currently projected at around 2500 feet.

In the longer range, the models agree that more wet and cool
weather is likely again later next week.

&&

.AVIATION...as of 10:30 PM PST Wednesday...VFR conditions are
expected this evening before another upper level shortwave
approaches the area late tonight. Models indicate lower level
moisture after 09Z but only lasting a few hours as strong
northerly winds help to clear out the clouds after 14-15Z.

Vicinity of KSFO...VFR except for a period of lower clouds between
10Z-13Z possibly lowering into MVFR range. West to northwest winds
increasing to 10 kt in the morning then ramping up to 25-28 kt
gusting 32-34 kt after 23Z.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...VFR. Scattered clouds developing Thursday
morning.

&&

&&

.MARINE...as of 10:23 PM PST Wednesday...Winds will increase to
gale force over the outer waters Thursday afternoon and evening
after an upper level shortwave passes through. The strong winds
will bring steep fresh swell.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tngt...SCA...Mry Bay from 3 AM
             SCA...Pt Reyes to Pigeon Pt 0-10 nm from 3 AM
             SCA...Pigeon Pt to Pt Pinos 0-10 nm from 3 AM
             SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm from 3 AM
             SCA...Pt Arena to Pigeon Pt 10-60 nm
             SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm
             SCA...Pt Arena to Pt Reyes 0-10 nm
             SCA...SF Bay from 3 AM

&&

$$

PUBLIC FORECAST: Dykema
AVIATION: W Pi
MARINE: W Pi

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