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

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FXUS66 KMTR 231303

Area Forecast Discussion
National Weather Service San Francisco Bay Area
503 AM PST Mon Jan 23 2017

.SYNOPSIS..Scattered to numerous showers will continue to impact
the region through late this evening with a potential for embedded
thunderstorms. Brief heavy rainfall within stronger showers and/or
thunderstorms will pose a threat for flash flooding of area creeks
and urban areas. Showers will then taper off late tonight into
Tuesday morning with dry conditions likely through the upcoming

&& of 03:13 AM PST Monday...The entire region
remains in an unstable, post-frontal environment with showers
moving inland into the San Francisco Bay Area and Central Coast
early this morning. This activity will continue through much of
the day as the main mid/upper level low off of the Pacific
Northwest coast slides southward down the California coast. Cannot
rule out a few thunderstorms through the day as well as the air
mass aloft continues to cool and remains unstable. While
widespread heavy rainfall is not anticipated, any stronger showers
or thunderstorms that produce brief, heavy downpours will pose a
threat for flash flooding of area streams as well as urban areas.
Thus, a Flash Flood Watch remains in effect through late
afternoon/evening given the supersaturated soils and elevated
levels of local creeks, rivers and reservoirs.

By late tonight, the upper level low will weaken off our coast
with the trough axis beginning to shift inland. This will allow
for showers to diminish in coverage from north to south through
early Tuesday morning. With lingering moisture in place and the
proximity of the trough, showers will remain possible over the
souther portion of the Central Coast into Tuesday morning. Tuesday
afternoon will give way to mostly dry conditions region-wide with
breaks in cloud cover also likely as an upper level ridge builds
across the eastern Pacific. By late Wednesday into Thursday
morning, the models show a weak upper level disturbance dropping
into northern California. This system appears to remain weak and
have limited moisture to work with as it pushes inland. However,
cannot rule out light rain over the coastal waters and into the
North Bay from Wednesday night into Thursday morning. Otherwise,
most areas will remain dry as this system pushes inland to our

The models are in good agreement late in the forecast period with
dry weather conditions likely region-wide Thursday through at
least the upcoming weekend. With the ridge over the eastern
Pacific building inland across the state, temperatures will likely
warm to above seasonal averages with low to mid 60s possible
during the afternoon hours Saturday and Sunday. Given clearing
skies Tuesday into Wednesday, cool/chilly overnight temperatures
are expected before moderating a bit late in the week as the ridge
builds aloft.


.AVIATION...As of 5:02 AM PST Monday...VFR/MVFR. Also, very
localized IFR cigs/vsbys reported due to light winds and an air
mass that`s nearly saturated from surface to lower levels from
extensive and recent rain. Off and on moderate to heavy showers
will become re- invigorated through this morning and afternoon
with isolated t-storms developing. Moderate dynamics combine with
even colder air throughout a deeper layer of the atmosphere today
causing greater amounts of instability over the ocean, bays and
land. Small hail is likely with showers and t-storms.

Vicinity of KSFO....VFR with winds possibly becoming gusty to 20-25
knots from the west this morning as newly developing showers /maybe
a thunderstorm?/ move in from the west. Generally wet today with
showers continuing.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...VFR. Showers indicated in the 12z tafs. We
may see a few thunderstorms today with small hail.

&& of 03:13 AM PST Monday...A low pressure system with a
large pool of cold and unstable air over the eastern Pacific will
continue to move southeastward over the coastal waters and bays
through tonight. Unstable air will result in additional heavy
showers and possibly a few thunderstorms. The low will then reach
southern California later Tuesday. Large westerly swell will
persist through Tuesday morning.


 .Tday...Flash Flood Watch...Entire San Francisco Bay Area
and Central Coast
             High Surf Advisory...Entire Coastline from Sonoma
County through Monterey County
             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...Rough Bar Advisory for SF Bar




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