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

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FXUS66 KMTR 250559

Area Forecast Discussion
National Weather Service San Francisco Bay Area
958 PM PST Sat Feb 24 2018

.SYNOPSIS...Clearing skies are expected overnight along with cool
temperatures, although not as cold as last night. Dry weather and
slightly warmer temperatures are expected on Sunday. A cold front
is forecast to bring a brief period of light precipitation to the
region late Sunday night and Monday morning, with showers
lingering into Monday afternoon along with locally blustery
conditions. A stronger and wetter storm system is expected to
bring widespread precipitation to the region later next week, most
likely around Thursday.


.DISCUSSION...As of 8:50 PM PST Saturday...A weak upper level
disturbance moving through northwesterly flow aloft resulted in
some clouds and even isolated showers this afternoon. Northwest
winds also increased after this upper level feature passed. Winds
will gradually subside overnight and skies should mostly clear by
midnight. The result will be another cool night tonight. However,
early evening dewpoints are running as much as 20 degrees higher
than 24 hours ago. This increased moisture will help hold temps
up tonight and therefore do not expect as cold a night as last
night when 11 locations set or tied record lows. Only the coldest
valleys will see temperature drop to around freezing late tonight
and early Sunday.

Sunday is expected to be a dry day with slightly warmer
temperatures. Winds will be light for the most part except for
increasing west to northwest winds in the afternoon, especially
near the coast.

Models are in agreement in bringing the next system in from the
north-northwest by late Sunday night. A cold front is forecast to
spread rain across the North Bay between midnight Sunday night and
sunrise Monday morning, and then south across the rest of the
forecast area on Monday morning. Unlike the cold systems that
moved into our area this past week, this Sunday Night/Monday
morning system is forecast to produce widespread precipitation,
with most of our area expected to pick up measurable rain.
However, the front is forecast to move through quickly and the
models generally agree that total rainfall amounts will generally
be a quarter of an inch or less. This system isn`t expected to be
quite as cold as recent systems, but cold enough to drop snow
levels to 3000 feet by early Monday and possibly as low as 2500
feet. Thus, we may see up to an inch of snow on some of the
higher peaks in the Bay Area and perhaps heavier and more
widespread accumulation across the higher portions of the Santa

Showers are expected to linger behind the front on Monday
afternoon and perhaps into Monday evening across portions of
Monterey and San Benito Counties when a cutoff low develops over
the Central Coast. Precipitation chances are expected to end in
all areas by late Monday night as the upper low drops south to
near Point Conception.

Brisk west to northwest winds are forecast to develop behind the
cold front on Monday. By Monday afternoon and evening we could
see gusts up to 35 mph along the coast. Winds will subside near
the coast on Monday night, but will turn to the north and remain
gusty in the hills through Tuesday morning.

Temperatures on Monday night will be quite chilly as skies clear
from north to south. However, there should be enough mixing from
gusty winds in the hills to keep temperatures from dropping below
freezing in most locations. Overnight lows are expected to drop
below freezing once again in the valleys of interior Monterey
County and San Benito County by Tuesday night.

The longer range models agree that a more potent and wetter system
will impact much of California later next week. Rain could begin
in the North Bay as early as Wednesday afternoon, but the bulk of
the precipitation with this system is expected between Wednesday
night and Thursday evening. If this system develops and tracks as
currently forecast by the models, our region will see its first
widespread soaking rains in more than a month.

&& of 9:58 PM PST Saturday...VFR with exception of areas
MVFR cigs over the San Mateo Coast, South Bay, and north Central Coast
tonight and Sunday morning. Winds are gradually diminishing within the
boundary layer and drying will tend to settle back in over the remaining
Bay Area overnight and Sunday morning.

High pressure extends into the Great Basin temporarily reversing the
SFO-WMC pressure gradient to weak offshore and flattening the SFO-SAC
pressure gradient tonight into Sunday morning. A low pressure system
and cold front arrive with wet weather from the north later Sunday
and Monday. MVFR cigs are likely to be widespread late Sunday afternoon
through Sunday night into Monday morning, wet weather will also increase.

Vicinity of KSFO...VFR tonight into Sunday, MVFR cig developing later
Sunday afternoon and persists into Sunday evening. Westerly wind has
decreased to near 10 knots late this evening, wind possibly becoming
light N-NE by early Sunday morning. An amendment to the wind forecast
in the KSFO taf will be issued shortly.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...VFR tonight into Sunday, MVFR cigs developing
later Sunday afternoon and evening. Onshore winds gradually dissipate
and become E-SE 5-10 knots later tonight and Sunday morning.



A few locations may be near record low temperatures Sunday morning
and possibly Tuesday morning next week. Temperatures will be mainly
below late February normals through early next week, but increasing
clouds, showers, and breezy winds with a low pressure system arriving
later Sunday into Monday should help keep lows above records on Monday.

Location          Sunday          Tuesday

SF Bay Area

Healdsburg        29 in 1920      25 in 1962
Santa Rosa        24 in 1915      24 in 1962
Calistoga         29 in 1966      24 in 2012
Kentfield         29 in 1920      26 in 1962
San Rafael        26 in 1904      29 in 1962
Napa              30 in 1962      28 in 2011
San Francisco     38 in 1887      38 in 1962
SFO Airport       35 in 1953      32 in 1951
Half Moon Bay     33 in 1996      31 in 2011
Oakland Airport   33 in 1953      31 in 1962
Richmond          36 in 1962      34 in 1962
Livermore         28 in 1942      25 in 1962
Moffett Field     34 in 1953      30 in 1962
San Jose          28 in 1894      28 in 1893
Gilroy            31 in 1965      24 in 1962

Monterey Bay Area

Santa Cruz        30 in 1911      25 in 1962
Salinas           32 in 1997      25 in 1962
Salinas Airport   25 in 1935      29 in 1962
Monterey          35 in 1956      27 in 1962
King City         23 in 1974      23 in 1962

&& of 9:44 PM PST Saturday...High pressure over the
eastern Pacific will extend into the Great Basin tonight and
Sunday morning. A low pressure system presently over the Gulf of
Alaska and British Columbia will move southward into northern
California by later Sunday into Monday with a cold front moving
southward across the coastal waters and bays Monday. Chilly
weather persists through next week and weekend, more wet weather
returns later Wednesday and mostly continues into Friday.


     .Tngt...SCA...Pigeon Pt to Pt Pinos 0-10 nm
             SCA...Pt Arena to Pigeon Pt 10-60 nm
             SCA...Pt Arena to Pt Reyes 0-10 nm
             SCA...Pt Reyes to Pigeon Pt 0-10 nm
             SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm
             SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm




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