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

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FXUS66 KMTR 300059
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco Bay Area
559 PM PDT Wed Mar 29 2017

.SYNOPSIS...Cooler and breezy conditions return to the region
on Thursday as a cold front sweeps through overnight. This system
will result in a chance of very light precipitation from late
tonight into early Thursday morning, however most locations will
not receive measurable rainfall. Breezy to gusty winds will be
possible from late Thursday into Friday. A warming trend is then
expected for the upcoming weekend as high pressure rebuilds over
the region.

&&

.DISCUSSION...as of 01:56 PM PDT Wednesday...High pressure aloft
has resulted in mainly clear skies and seasonably mild
temperatures across the region this afternoon. Meanwhile,
unsettled conditions continue to impact the Pacific Northwest and
northern California as a system approaches from the north. This
system will dive southward overnight as the main mid/upper level
trough pushes inland well to our north. This system will bring a
slight chance of light precipitation to portions of the region
beginning late tonight over the North Bay and then through the San
Francisco Bay Area and Central coast early Thursday morning. Most
of the short-rage models show this system producing only very
light rainfall amounts, generally a few hundredths of an inch or
so for locations that do experience precipitation. However, this
may result in wet roadways for the Thursday morning commute across
much of the greater San Francisco Bay Area.

In wake of this frontal passage, daytime temperatures on Thursday
will be at least 5 to 10 degrees cooler compared to today.
Conditions will likely feel even cooler as breezy northerly winds
develop region-wide. Wind speeds are forecast to increase further
Thursday night into Friday as the main upper level system drops
southward into the Desert Southwest and surface pressure gradients
tighten along the coast. With this, the strongest winds are
likely in the higher elevations across the region with wind gusts
in excess of 45 MPH likely. Thus, a wind advisory will likely be
posted overnight in the hills/mountains for the Thursday
Night/Friday time frame.

While winds are forecast to diminish some late Friday into
Saturday, cannot rule out breezy conditions in some of the higher
elevations. However, a warming trend is expected for the weekend
as high pressure rebuilds back over the region as the mid/upper
level trough exits to the east. Temperatures fall back to near
seasonal averages for early next week as northwesterly flow aloft
returns and another weather system pushes inland to our north.
With that said, dry weather conditions are likely to persist for
our region through the middle of next week.

The longer range guidance continues to show a return to wet
weather conditions by late next week. The models generally agree
that a more potent weather system will drop southward into
northern California by Thursday or Friday of next week with a
moderate moisture tap. Both the GFS and ECMWF show widespread
rainfall across the region by next Friday. However, being more
than a week out, confidence remains low at this time and changes
to the forecast are likely.

&&

.AVIATION...as of 5:59 PM PDT Wednesday...Fragments of coastal
stratus /MVFR cigs/ are developing from Sonoma county to San Mateo
county. A more solid band of low clouds is advancing southeastward
across the northern coastal waters per visible imagery. 925 mb
level warming is cresting late this afternoon and early evening
which may initially help suppress incoming coastal stratus and fog
under compressed marine inversions. However, fairly rapid and
significant cooling follows later tonight and Thursday morning,
e.g. NAM output is consistent with forecasting upwards of 10
Celsius cooling at 925 mb. Advertised surface cold front accelerates
southeastward across the Bay Area tonight and north Central Coast
early Thursday morning accompanied by pockets of light rain or
drizzle.

Vicinity of KSFO...VFR with westerly winds gusts to 25-30 knots.
Based on late afternoon visible imagery and area observations
decided to forecast onset of MVFR cig a little earlier, coordinated
with CWSU office. 00z taf indicates tempo MVFR cig as early as
05z (not in taf, but cig development may be 1-2 hours earlier than
forecast based on low clouds rapidly advancing over the coastal
waters plus there`s additional stratus development on the San Mateo
coast at the moment). Drizzle or light rain forecast by 07z accompanied
by a period of IFR cig until greater cooling arrives later tonight/Monday
which should lift cigs back to MVFR. VFR returns by 17z Thursday,
expect strong and gusty W-NW winds Thursday afternoon and evening.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...VFR with westerly winds 10-15 knots this
evening. Stratus developing to the NW will likely focus on the
Monterey Peninsula this evening, moderate to high confidence IFR
cigs developing between 04z-07z IFR then prevailing with light
drizzle or rain developing late tonight into Thursday morning.

&&

.MARINE...as of 4:49 PM PDT Wednesday...High pressure off the
California coast will keep moderate northwest winds through this
evening. Winds will briefly decrease tonight as the high weakens
but will increase again Thursday through Friday as strong low
pressure develops over the Intermountain Region. Long period
swells will continue through this evening. A larger long-period
swell is expected to arrive Sunday night and Monday.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .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 from 3 AM
             SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm from 3 AM
             SCA...Rough Bar Advisory for SF Bar until 6 PM
             SCA...Mry Bay until 3 AM
             SCA...SF Bay until 9 PM

&&

$$

PUBLIC FORECAST: RGass
AVIATION: Canepa
MARINE: W Pi


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