Area Forecast Discussion
Issued by NWS San Francisco Bay Area, CA
FXUS66 KMTR 231742
Area Forecast Discussion
National Weather Service San Francisco Bay Area
1042 AM PDT Thu Mar 23 2017
.SYNOPSIS...Mild and dry conditions are anticipated today as high
pressure briefly builds in over the state. Rain and moderately
south winds return to the North Bay area late tonight as a
frontal system approaches. Rain and winds will spread southward
Friday as the front moves across the region. A break in the rain
is expected Saturday with rain anticipated to return to the
district as early as Sunday afternoon and persist into Monday
as a low pressure system moves through the region.
.DISCUSSION...as of 8:35 AM PDT Thursday...Main forecast issue for
the shift remains the system that will push through tonight and
Friday across our entire region. 12Z guidance now coming in is
very close to the previous 0Z and 06Z runs, so not anticipating
any major changes. Will continue to highlight the potential for
moderate to heavy rain tomorrow along with gusty winds as the
front goes through. CNRFC forecast continues to keep gauges well
below flood stage for the Russian, Salinas, and Napa rivers along
with Coyote Creek. Overall current forecast appears to be on
.PREVIOUS DISCUSSION...Doppler radar continues to pick up a
couple stray showers here and there but showers have wound down
considerably overnight. Mild and dry conditions await the region
today as the area transitions between storms. High pressure will
briefly build in over the state this morning resulting in mostly
sunny/clear skies and seasonable highs in the lower to mid 60s.
Temperatures along the coast will likely only see a degree or two
of warming while inland temperatures warm anywhere from 3 to 5
degrees with southernmost inland valley seeing the most warming.
The forecast remains on course with models solutions remaining
fairly consistent with regard to storm track and intensity for
the next storm system heading our way. Rain chances will begin
tonight over the North Bay then will slide south overnight into
Friday as the frontal system moves across the region. The bulk of
the rain will move through the Bay Area during the day Friday
making for a wet morning and afternoon commute. Precipitable water
values are forecast around 1" to 1.25" with this system. This
will translate into rain totals around 1.5" to 3" in the North
Bay and 2/3" to 1.5" across the Bay Area. Areas from the Monterey
Bay south will see a slight delay in the rain with the main band
of rain moving through Friday afternoon/evening. Accumulations of
less than 2/3" are expected. Coastal mountain will see the
highest rain totals as orographic coupled with a perturbation
along the front enhances the rainfall amounts as the system slides
south. Coastal mountains as well as the mountain of the North Bay
may see rainfall totals in anywhere from 3" to 4+".
Gusty southerly winds are also anticipated to accompany this
system with speeds of 25 to 35 mph anticipated. High gusts
possible over elevated terrain. A wind advisories is not expected
at this time but will be monitored closely.
As the system slides south Friday evening the North Bay region
will begin to see drier conditions with clearing expected
overnight. Cool and drier weather is forecast for Saturday as high
pressure over the Eastern Pacific ridges north and east across
the state. This drying trend will be short-lived as the next
system approaches from the west on Sunday spreading rain across
the district Sunday afternoon into Monday. Precipitable water
values for this system are forecast around 1"...slightly less than
Friday`s system. Therefore accumulations totals will not be as
high with this storm.
Long range models remain in agreement with bringing in a large
ridge of high pressure over the Eastern Pacific that will drive
the storm track to the north. If this solution holds the region
may be in for an extended period of dry weather.
.AVIATION...As of 10:35 AM PDT Thursday...For 18z Tafs. Patchy
MVFR cigs possible through late this morning. Otherwise VFR
conditions prevail through this evening. Expecting winds to
increase this afternoon to 10-15 kt. Showers expected to move
in from North to South beginning with KSTS at around 04z Friday.
Steady rain expected across all terminals by tomorrow morning.
MVFR cigs possible early Friday morning for Bay Area terminals.
Low confidence on timing of rain.
Vicinity of KSFO...Mainly VFR with periods of MVFR cigs. SE/SW
winds 10-15 kt beginning late this afternoon. Rain and lower CIGs
return early Friday morning.
SFO Bridge Approach...Same as KSFO.
Monterey Bay Terminals...Patchy MVFR possible this morning with
VFR prevailing. W/WSW winds 10-12 kt this afternoon. Rain not
likely until after 12z Friday, but a shower or two before is still
.MARINE...as of 08:25 AM PDT Thursday...Winds will become
southerly and increase this afternoon ahead of another storm
system. Wind gusts may reach gale force at times late tonight and
into Friday...especially for the northern coastal waters. Seas
may be rough ahead of and just behind the storm system on
Friday...but should decrease by saturday morning. winds will
switch back to the northwest by saturday morning. another weak
storm system is expected sunday and may briefly switch winds out
of the south. However...winds will quickly turn back to the
northwest by monday morning.
.Tday...SCA...Pt Arena to Pigeon Pt 10-60 nm from 11 AM
SCA...Pt Arena to Pt Reyes 0-10 nm from 3 PM
PUBLIC FORECAST: Bell/CW
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