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

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FXUS66 KMTR 261501

Area Forecast Discussion
National Weather Service San Francisco Bay Area
801 AM PDT Sun Mar 26 2017

.SYNOPSIS...A weak weather system will spread light rain across
the North Bay this afternoon and across most of the remainder of
the forecast area this evening and overnight. Showers will mostly
end by Monday morning. Expect decreasing clouds on Monday with
brisk afternoon and evening northwest winds. High pressure will
then produce dry weather through midweek, along with a warming
trend. Shower chances will return to northern and eastern portions
of our region Wednesday night and Thursday as a weather system
drops inland to our east. Temporary cooling and blustery
conditions are also expected with this system.


.DISCUSSION...As of 8:00 AM PDT Sunday...Rain will return to our
region later today as a weak system moves from the north. Ahead of
it light rain is possible. Based off of KMUX radar data, did a
minor update to the forecast to bring a chance of rain farther
south into the afternoon. Otherwise, everything looks on track.

Latest QPF from CNRFC still in line with the previous forecast -- 1/4"
to 1/2" for the North Bay Mountains with generally less than
0.15" for the rest of the CWA.

No major updates planned.

.PREVIOUS DISCUSSION...High clouds have been increasing overnight
as a weak weather system approaches from the west-northwest. The
models have slowed the arrival of precipitation with this system,
with rain now expected to develop only in the North Bay between
midday and late afternoon. Most areas south and east of San
Francisco will probably remain dry through late afternoon. Light
rain is then expected to develop over most of the remainder of our
forecast area during the evening hours. Rainfall totals through
tonight are forecast to range from 0.10-0.40" in the North Bay,
with totals mostly under a tenth of an inch for all other areas.

A few showers may linger into Monday morning, but for the most
part Monday should be a dry day as the system departs quickly to
the southeast and a high pressure ridge builds just offshore.
Brisk northwest winds are likely by Monday afternoon with
strongest winds expected near the coast where local gusts up to 35
mph are possible late Monday afternoon and early evening.

The upper ridge offshore is forecast to build inland over
California on Tuesday and Wednesday, bringing dry weather along
with a warming trend. High temperatures by Wednesday are forecast
to be mostly in the upper 60s and 70s.

The GFS and ECMWF have come into better agreement regarding a
system that will impact our area shortly after midweek. Both
models show a system dropping in from the northwest and across far
northern California on Wednesday night, and then proceeding into
the Great Basin by Thursday. This system will be an `inside
slider` which will mean that most, if not all, precipitation will
be confined to areas to our north and east - which is what the
GFS is forecasting. However, the past two runs of the ECMWF have
forecast precipitation farther to the south and east and into our
area. Have therefore added shower chances across the northern and
eastern portions of our area for Wednesday Night and Thursday. A
cooler airmass will arrive with this system on Thursday and high
temperatures may cool by as much as 10 degrees from Wednesday to
Thursday. In addition, potentially quite strong and gusty north to
northwest winds will develop on Thursday and continue into
Thursday Night. Locally blustery conditions may then continue in
the hills into Friday night as well. If conditions develop as
currently forecast by the models, wind advisories may be needed
for portions of our forecast area later in the week.

Warming and drying will occur late in the week and into next
weekend as an upper ridge once again builds across California.


.AVIATION...As of 4:32 AM PDT Sunday...aside from a few locations
along the immediate coastline reporting MVFR cigs...VFR
conditions are generally the rule. Expect VFR conditions through
most of the day. Late this evening light rain will develop across
the North Bay and spread south overnight. CIGS will be at times
MVFR by early morning tomorrow.

Vicinity of KSFO...VFR. Light rain is predicted to begin early
Sunday evening with MVFR cigs overnight..

SFO Bridge Approach...Same as KSFO.

Monterey Bay Terminals...VFR. Light rain likely beginning mid-
late Sunday evening with CIGS lowering to MVFR by early Monday

&& of 2:43 AM PDT Sunday...Generally light winds and
moderate seas expected across the waters through most of today.
Northwest winds will increase over the waters by Monday as high
pressure builds over the Eastern Pacific.






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