Area Forecast Discussion
Issued by NWS San Francisco Bay Area, CA
FXUS66 KMTR 100010
Area Forecast Discussion
National Weather Service San Francisco Bay Area
410 PM PST Fri Dec 9 2016
.SYNOPSIS...Moist onshore flow will persist over the region through
tonight ahead of our next approaching system. Rain will increase in
coverage along the coastal ranges overnight ahead of a frontal
boundary that will spread from north to south across the region late
tonight through Saturday afternoon/evening. More widespread rainfall
will accompany this boundary as it moves through the region Saturday
during the day. Clearing conditions are forecast from late Saturday
through Sunday with the potential for unsettled conditions to return
for a good portion of next week.
.DISCUSSION...as of 01:45 PM PST Friday...Mostly dry conditions
persist over the region this afternoon with only a few reports of
light rain under the moist onshore flow. This too has resulted in
a mix of sun and clouds region-wide with temperatures warming into
the upper 50s to 60s for most locations. Meanwhile, our next
weather system can be seen pushing into northern California on the
latest satellite imagery.
The latest forecast models, including short-range high resolution
models, show this system dropping southward into the North Bay late
this evening and into the San Francisco Bay Area overnight. Ahead of
the main frontal boundary, rain will develop along the coastal
ranges and persist through Saturday morning as the main band of
precipitation spreads southward across the Central Coast through
Saturday afternoon. Rainfall is forecast to range from 1" to 3"
along the coastal slopes with 1/4" to 1" for much of the remainder
of the region. However, cannot rule out lesser amounts in the
typical inland valley locations due to the rain shadow effect. There
is the potential for higher rainfall rates compared to those during
the past 24 to 48 hours as this system has better mid/upper level
support and deeper moisture advection. At this time, we do not
anticipate widespread issues across our burn scars, yet will closely
monitor should hourly rates exceed 3/4 to 1 in/hr.
Drying conditions are forecast from north to south Saturday
afternoon and evening. This may also allow for additional breaks in
the cloud cover with less cloud cover likely on Sunday when dry
conditions are expected region-wide. In wake of the frontal passage,
temperatures will also cool both during the daytime and overnight
hours from Sunday into Monday.
The weather pattern appears to remain active through a good portion
of next week. However, the forecast models condition to differ from
one another and from run-to-run on the timing, location and amount
of precipitation. Thus, have kept a slight chance to chance of
precipitation through a good portion of next week. In the coming
days, the hope is that the models will converge on a more similar
solution and will allow us to have a better handle on next week`s
weather conditions. Until then, stay tuned and enjoy the upcoming
.AVIATION...As of 4:00 PM PST Friday...Pretty quiet this afternoon
with some borderline MVFR cigs around the area. More MVFR cigs
will form tonight due to nighttime cooling. Models indicate some
moisture possibly bringing light rain to the area as early as 06Z.
By Saturday morning rain should become more widespread around the
SFO Bay Area with cigs lowering to near IFR. Unsettled weather
then continues through Saturday afternoon.
Vicinity of KSFO...MVFR cigs through the night with cigs lowering
to around 1500 feet by 06Z and close to 1000 feet by morning.
Light rain could begin as early as 06Z. South winds increasing
after 08Z with gusts to 20 kt.
SFO Bridge Approach...Similar to KSFO.
Monterey Bay Terminals...MVFR cigs after 03Z. Light rain is
possible but more likely it will hold off until Saturday.
Winds generally light S-SE.
.MARINE...as of 8:18 AM PST Friday...Light to occasionally
moderate southerly winds will prevail today then increase tonight
and into early tomorrow as a frontal boundary approaches the area.
Winds will weaken and veer towards the northwest behind this front
for the remainder of the upcoming weekend. A dominate westerly
swell train will move across the waters through the remainder of
the work week.
.Tngt...SCA...Pt Arena to Pigeon Pt 10-60 nm from 9 PM
SCA...Pt Arena to Pt Reyes 0-10 nm from 3 AM
SCA...Pt Reyes to Pigeon Pt 0-10 nm from 9 PM
SCA...SF Bay from 3 AM
PUBLIC FORECAST: RGass
AVIATION: W Pi
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