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

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FXUS66 KMTR 220011

Area Forecast Discussion
National Weather Service San Francisco Bay Area
411 PM PST Tue Jan 21 2020

.SYNOPSIS...Rain is forecast to spread from north to south across
our area today as a weak weather system moves into northern
California. Rainfall amounts will be light to locally moderate,
with no significant weather impacts expected. Mostly dry and
warmer conditions are then expected for the remainder of the work
week, with rain likely to return over the upcoming weekend.

&& of 2:33 PM PST Tuesday...Doppler radar continues
to pick up light rain impacting parts of the San Francisco Bay
Area this afternoon. Rainfall amounts through 2 pm range anywhere
from a few one-hundredths to several tenths of an inch in the
North Bay Valleys, a few tenths to just north of an inch in the
North Bay mountains, and zero to 0.05" elsewhere. We`ll see more
light rain come onshore associated with a cold front and spread
south as the afternoon and evening hours progress; though, the
rain band is expected to weaken and fall apart in the process.
Total rain amounts will generally be between 0.25 to 0.50" for
most populated areas in the North Bay, SF Peninsula, and East Bay,
and less than a quarter inch for the Santa Clara Valley and
Monterey Area. In fact, some locations in Monterey and San Benito
Counties will likely remain completely dry. The North Bay
Mountains and Santa Cruz Mountains could see up to an inch of rain
with isolated higher amounts (e.g., Venado). Overall - beneficial
rainfall expected with the main impact being the wet roadways
from the evening commute.

Rain chances will decrease from north to south overnight with
perhaps a few lingering showers around sunrise in parts of
Monterey County. An upper level ridge will build over the the West
Coast on Wednesday and Thursday, allowing for dry and warming
conditions region-wide. There will likely be some overnight valley
fog development, so there is some uncertainty in regard to maximum
temperatures if, for example, low clouds/fog linger through the
day in the North and East Bay Valleys. Locations with mostly clear
skies in the afternoon will likely warm into the 60s with
potential for middle and even upper 60s in parts of southern
Monterey County.

Forecast guidance indicates another round of wet weather to return
over the weekend to parts of northern and central California. At
this point in time it appears to be a bit wetter than today`s
system, but the heaviest precipitation will be focused north and
of our area. Looking ahead to next week, high pressure over the
eastern Pacific will keep the storm track directed at the Pacific
Northwest with northern California on the southern edge of these
systems. The latest precipitation outlooks from the Climate
Prediction Center gives much of the Bay Area and central
California coast slightly favored odds of experiencing drier than
normal conditions for both the 6-10 day and 8-14 day periods.

&& of 3:45 PM PST Tuesday...For 00z TAFs. A weak
frontal boundary continues to slide south across the forecast
area bringing lower cigs, lower vsbys, and light rain to area
terminals. Latest satellite imagery shows the frontal boundary
moving just south of Point Reyes along with broken to overcast
high clouds across the region. lingering low level moisture will
result in patchy fog mainly over the North Bay terminals. Moderate
southerly winds are expected ahead of the front. Winds will not
see they typical switch to the west or northwest behind the front
but rather turn variable or stay southerly. Winds will return to a
more westerly direction Wednesday afternoon.

Vicinity of KSFO...MVFR/VFR cigs will prevail tonight with rain
showers continuing through this evening then tapering through
tonight. Moderate and locally gusty southerly winds will ease this
evening becoming light and variable overnight.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...MVFR/VFR cigs will prevail tonight with
rain showers expected by this evening then tapering overnight.
Moderate and locally gusty south to southwesterly winds will ease
this evening becoming light southeasterly overnight.

&& of 2:30 PM PST Tuesday...Moderate to locally gusty
southerly winds will persist ahead of a cold front that will
continue to move through the region this evening. Winds will
generally be light in wake of the frontal passage. A longer period
northwest swell will peak midweek generating hazardous seas
conditions for smaller vessels. Another long period northwest
swell will then arrive later this week.


     .Tngt...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




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