Area Forecast Discussion
Issued by NWS San Francisco Bay Area, CA
FXUS66 KMTR 270049
Area Forecast Discussion
National Weather Service San Francisco Bay Area
549 PM PDT Wed Apr 26 2017
.SYNOPSIS...Isolated showers across the region will continue to
diminish this afternoon as a weak frontal system pushes further
inland. Dry weather returns for Thursday as high pressure builds
over the eastern Pacific. Further warming of daytime temperatures
will then be likely through the weekend and potentially into early
next week as high pressure strengthens along the California
.DISCUSSION...as of 01:51 PM PDT Wednesday...Very light
precipitation continues to be reported early this afternoon
across portions of the region, mainly in/around San Mateo County.
Rainfall from earlier today generally added up only to a few
hundredths of an inch or so with some higher elevations picking up
around 1/10". Should see chances for light rain showers to
diminish through the remainder of the day as the weak system
pushes further south and inland. Low clouds will likely linger
into tonight with temperatures only falling into the lower 50s for
most locations while upper 40s are possible in the North Bay and
in the hills.
A warming trend will then get underway beginning on Thursday,
especially across the North Bay where cooler conditions exist this
afternoon. With clearing skies by late week, temperatures will
warm a few more degrees on Friday as a ridge builds over the
eastern Pacific. Meanwhile, an upper level low is forecast to
develop and move into the Four Corners region Thursday into Friday
and will result in the tightening of the surface pressure
gradient along the coast. This will result in breezy northerly
winds from Thursday into Friday, especially in the hills with
gusts of 35 to 40 mph possible.
By the upcoming weekend, the ridge of high pressure aloft will
become the dominate feature and allow for additional warming.
Daytime temperatures will likely warm into the 70s to lower 80s
inland while the typically cooler coastal areas approach the 70
degree mark. The latest forecast guidance now suggest the ridge
will continue to build and shift inland into the West Coast by
early next week. The result will be weak offshore flow at times,
especially for inland areas, with more widespread 80s for daytime
.AVIATION...as of 5:49 PM PDT Wednesday...A robust influx of
moisture compared to April climatology will continue to interact
with a surface cool front located off northwestern California.
This front will accelerate to approx 30-40 mph moving southeastward
across the Bay Area and north Central Coast this evening and
tonight; additional pockets of light rain or drizzle are quite
likely up until frontal passage.
Preceding this front nearly saturated air up to approx 7 thousand
feet is causing IFR cigs to develop with spill-over of IFR now
extending eastward across the San Francisco Peninsula. Based on
the WRF model IFR will quite likely continue to spread into the
East Bay and South Bay through this evening with lowering confidence
as to if and when cigs/vsbys may lift later in the forecast period.
This incoming change of air mass following the cold front is very
shallow based, the NAM shows cooling at 925 mb not beginning until
Thursday morning thus the caveat here is it could be slow clearing
tonight into Thursday morning specifically along the immediate
coastline and nearest the bays. KMUX is mostly if not entirely
echo-free at the moment due to the shallow based nature of this
present weather pattern.
Vicinity of KSFO...IFR cig persisting this evening, possibly seeing
a return to MVFR cigs beginning 06z though timing is low to very low
confidence. If W-NW winds happen to increase with gusts up to 20-25
knots as forecast mixing may help lift cigs somewhat. WRF model leans
toward a gradual reduction in humidity, but not until much later tonight
into Thursday morning. Coordinated with CWSU office.
SFO Bridge Approach...San Mateo Bridge reports BKN cig as low as 1,300
feet, similarly plenty of saturated air will continue to reach into
the approach this evening.
Monterey Bay Terminals...MVFR lowering to IFR as similar to the Bay
Area greater amounts of moisture will consolidate this evening prior
to the arrival of a cool front. Off/on showers or drizzle tonight.
Clearing Thursday with MVFR/VFR probably returning mid-late morning.
.MARINE...as of 4:52 PM PDT Wednesday...Northerly flow will
increase across the entire region tonight and Thursday as high
pressure builds. The stronger winds will result in steep wind
waves and fresh swell. These hazardous conditions will persist
into the weekend.
.Tngt...SCA...Pigeon Pt to Pt Pinos 0-10 nm from 3 AM
SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm from 3 AM
SCA...Pt Arena to Pt Reyes 0-10 nm from 9 PM
SCA...Pt Reyes to Pigeon Pt 0-10 nm from 9 PM
SCA...Pt Arena to Pigeon Pt 10-60 nm from 9 PM
SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm
SCA...SF Bay until 3 AM
PUBLIC FORECAST: RGass
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