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FXUS66 KMTR 180537

Area Forecast Discussion
National Weather Service San Francisco Bay Area
937 PM PST Sat Feb 17 2018

.SYNOPSIS...Blustery and much colder weather conditions will
develop on Sunday as a strong cold front sweeps through the 
region. There is also a chance of showers from late Sunday into
Monday, mainly near the coast and in the Santa Cruz and Santa
Lucia Mountains. Snow levels are forecast to drop as low as 1,000
feet and locally lower by Monday. Widespread freezing 
temperatures are expected for inland areas once winds subside on 
Monday night. Cool and unsettled weather is expected to persist
through the end of next week.


.DISCUSSION...As of 9:10 PM PST Saturday...Warming that began 
yesterday continued today. Afternoon highs today ranged from the 
mid 60s to mid 70s and were anywhere from 5 to 10 degrees warmer 
than normal. Today will be the last warm day our region will 
likely see for quite some time as a major pattern change gets 
underway tomorrow.

Evening satellite imagery shows a cold weather system over the
Pacific Northwest with the leading edge of the cold air just
beginning to pass south of the CA/OR border at this time. This 
system is forecast to continue plunging south overnight and a cold
front will sweep from north to south across our region on Sunday 
morning. Much cooler and blustery conditions will develop behind 
the front on Sunday. High temperatures on Sunday are generally 
forecast to be from 10 to 20 degrees cooler than today. By late 
afternoon northwest winds will likely gust as high as 40 mph along
the coast. The cold front is expected to be dry for the most 
part, with only isolated light showers possible in the coastal 
hills on Sunday. 

As the cold upper trough continues to dig south on Sunday night,
the models indicate shower chances will increase, primarily in 
coastal areas and in the Santa Cruz and Santa Lucia Mountains. 
Precipitation amounts are forecast to be light and rather 
insignificant, but only if considering liquid precipitation. Snow 
levels are forecast to fall as low as 1500 feet by late Sunday 
night and then down to 1000 feet, or locally lower, by Monday as 
one of the coldest air masses our region has seen in years sweeps
over our area. The NAM continues to forecast more precipitation 
compared to the GFS or ECMWF. The 00Z NAM forecasts precipitation 
totals as high as 0.40" in the northern Santa Lucia Mountains of 
Monterey County from Sunday night through Monday. This 0.40" of 
liquid precip would translate into as much as 5 inches of snow 
above 1500 feet in the Santa Lucias. In the Santa Cruz Mountains 
most models, even the NAM, forecast only about a tenth of an inch 
of precip or less. The exception is the 12Z local WRF model which 
forecasts as much as 0.80" of precipitation in the Santa Cruz 
Mountains on Sunday night and Monday. This much precip would 
translate into several inches of snow at higher elevations and 
with the projected snow levels we could easily see accumulating 
snow at the summit of highway 17 and along skyline boulevard 
(highway 35). Because the WRF is an outlier with much more precip 
compared to other models, forecast confidence is too low to issue 
a Winter Weather Advisory for the Santa Cruz Mountains at this 
time. But this is something we will need to watch closely. We will
also need to consider Winter Weather Advisories for the Santa 
Lucia Mountains. All other mountain zones are expected to see 
little or no accumulating snowfall with this system. Rain and snow
showers are expected to end in all areas by Monday evening.

Northwest winds are forecast to remain locally strong and gusty
through Sunday night and Monday, especially near the coast. At
this time it appears winds will mostly remain below advisory
levels except for a few of the windier locations such as Point
Reyes. A wind advisory is not anticipated at this time.

Besides snow potential and winds, the other primary impact from
this system will be freezing temperatures. Overnight lows on
Sunday night are expected to remain above freezing in most areas 
due to brisk winds and good mixing. By Monday night winds are 
forecast to subside and skies will clear. This will set the stage 
for the coldest night of this winter season, and widespread 
freezing temperatures are expected across inland areas late Monday
night and Tuesday morning. Overnight lows on Monday night are 
forecast to range from the mid 20s to lower 30s inland, and from 
the mid 30s to lower 40s at the coast. A Freeze Watch has been 
issued for all inland areas of our forecast area from late Monday 
night into Tuesday morning. Several hours of subfreezing 
temperatures are possible. Once the Freeze Watch is transitioned 
to a Freeze Warning, we may also need to issue Frost Advisories 
for some of our coastal zones. 

Earlier it had appeared that Tuesday night could be as cold as 
Monday night. However, recent models now show a system dropping in
from the north by late Tuesday night. Widespread cloud cover 
associated with this system will help keep minimum temperatures up
above freezing in most areas on Tuesday night, except perhaps in 
the far southern portion of our area.

Longer range models maintain a cool and unsettled pattern through
the rest of the week and into next weekend. 


.AVIATION...As of 9:30 PM PST Saturday...Low clouds are developing
along the coast ahead of an upper trough. MVFR cigs will spread
over the SFO and MRY Bay Area overnight with possible IFR for
cigs and vsby at STS. Increasing northwest winds will help to 
scatter out the clouds by midmorning.

Vicinity of KSFO...MVFR after 08Z. West winds to 15 kt through 

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...MVFR spreading into SNS after 09Z.  



Here are record low temperatures and the years they occurred for 
Monday through Wednesday next week.

Location          Monday          Tuesday          Wednesday

SF Bay Area

Healdsburg        28 in 1932      22 in 1922       28 in 1929
Santa Rosa        26 in 1932      26 in 1913       26 in 1913
Calistoga         25 in 1918      25 in 2006       25 in 2006
Kentfield         27 in 1932      27 in 1913       29 in 1953
San Rafael        32 in 1990      32 in 2006       33 in 1955
Napa              29 in 1990      28 in 1920       29 in 1955
San Francisco     38 in 1897      38 in 1897       36 in 1890
SFO Airport       36 in 1990      37 in 2011       34 in 1955
Half Moon Bay     34 in 1954      32 in 2013       31 in 2006
Oakland Airport   35 in 1955      34 in 2006       33 in 1955
Richmond          35 in 1990      35 in 1990       35 in 1981
Livermore         27 in 1956      28 in 1942       27 in 1955
Moffett Field     35 in 1949      34 in 2006       32 in 1955
San Jose          32 in 1990      30 in 1897       25 in 1897
Gilroy            27 in 1964      30 in 1990       31 in 1976

Monterey Bay Area

Santa Cruz        30 in 1990      29 in 1913       30 in 1955
Salinas           29 in 1990      31 in 2006       31 in 1970
Salinas Airport   29 in 1933      28 in 1953       30 in 1953
Monterey          35 in 1990      35 in 2006       36 in 1952
King City         25 in 1955      22 in 1953       23 in 1953

&& of 09:27 PM PST Saturday...Low pressure dropping
south along the west coast will result in  increasing north to
northwest winds. Small craft advisories will  transition into gale
warnings Monday night after a cold front pushes through. Winds
will slowly decrease Tuesday and Wednesday.


     .Tday...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 Pinos to Pt Piedras Blancas 0-10 nm
             SCA...Pt Arena to Pigeon Pt 10-60 nm
             SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm
             SCA...SF Bay from 9 AM




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