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

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788
FXUS66 KMTR 301521
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco Bay Area
821 AM PDT Sun Apr 30 2017

.SYNOPSIS...Sunny and seasonably warm weather will continue across
our region today with temperatures similar to those of yesterday.
Warming is then forecast from Monday through Wednesday as
offshore flow develops and high pressure strengthens over
California. Widespread 80s are forecast by Tuesday and Wednesday,
with some lower to mid 90s in the warmest inland areas. A cooling
trend is then forecast Thursday and Friday as the upper ridge over
California is replaced by a trough. Rain showers are possible
next weekend when an upper low is forecast to develop over
California.

&&

.DISCUSSION...As of 8:10 AM PDT Sunday...Sunny skies across our
entire region with the exception of a small patch of clouds
around Monterey Bay. A ridge of high pressure building into our
CWA along with an offshore flow at the surface will lead to
several warm days for both the coast and inland spots. Highs today
will be in the 60s to mid 70s at the coast with mid 70s to mid
80s inland. Additional warming is likely for Monday through
Wednesday as the ridge strengthens and moves to California.
Offshore winds will also be on the increase tonight and Monday
night especially for higher elevation spots.

Current forecast appears to be on track. No major updates planned.

.PREVIOUS DISCUSSION...The light offshore flow that was in place
across our region early yesterday morning has been replaced by
light onshore flow. As a result, current surface dewpoints are as
much as 15 degrees F above what they were at the same time early
yesterday morning, and patchy light fog is currently being
reported at Half Moon Bay and Watsonville. However, the boundary
layer has probably not moistened enough for widespread development
of coastal low clouds/fog. Thus, sunny conditions are expected
across our forecast area once again today. However, our warming
trend will be suspended for today as increased moisture in the low
levels will offset continued airmass warming aloft. The net
effect will probably be slightly cooler high temperatures near the
coast today, and temperatures near persistence inland.

Offshore flow is forecast to redevelop tonight as surface high
pressure builds inland to our north and east. In fact, locally
gusty north winds are expected to develop in the hills by late
tonight and Monday morning, and then again late Monday night and
Tuesday morning. Wind gusts in the hills may reach 30-35 mph in
isolated locations during the night and morning hours. This
offshore flow will result in renewed drying of the airmass across
our region. At the same time, the upper ridge that is currently
centered offshore is forecast to shift eastward and over
California, resulting in and increase of 850 mb temperatures
from about 12 degrees C currently to about 19 or even 20 deg C by
Wednesday. These developments will result in a resumption of the
warming trend on Monday, with warming continuing regionwide into
Tuesday and on into Wednesday in many areas. The warmest days of
the week are expected to be Tuesday and Wednesday when widespread
80s are forecast, with low to mid 90s likely in the warmer inland
areas. Even coastal areas will probably see highs up around 80
due to offshore flow. High temperatures will be as much as 15
degrees warmer than normal on Tuesday and Wednesday, and these
two days are likely to be the warmest days our region has seen
since last October.

Significant cooling is forecast for Thursday and Friday as the
upper ridge moves off to our east and an upper trough develops
near the West Coast. Expect temperatures to cool by at least 10
degrees on Thursday and drop back down to around seasonal averages
by Thursday. Low clouds and fog will likely develop in coastal
areas by Thursday.

The longer range models indicate an upper low will drop south
along or near the West Coast next weekend, producing a chance of
showers across our forecast area. The 00Z ECMWF is especially
bullish with precip chances showing widespread rainfall across our
area by next Sunday.

&&

.AVIATION...As of 04:22 AM PDT Sunday...For 12z Tafs. Another day
of VFR in store at all terminals. High pressure will continue to
dominate over the region, with perhaps only a few high clouds
through the day. Winds should remain light-moderate, occasionally
gusty, from the west/northwest this afternoon. By late tonight,
guidance suggests some low level moisture returning, especially
for Monterey Bay terminals. The extend and coverage is still
unknown at this time. With high pressure in control, did not see
enough reason to include cigs in the 12z taf update. Moderate to
high confidence.

Vicinity of KSFO...VFR. Light to moderate onshore winds this
afternoon and evening, gusty at times.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...VFR. Mainly light to moderate onshore winds
this afternoon, should stay below 15 kt. Did include FEW-SCT low
clouds by 08z, with the possibility of MVFR/IFR cigs before
sunrise Monday. However, confidence is low at this time.

&&

.MARINE...as of 04:05 AM PDT Sunday...High pressure will continue
to generate strong northwest winds today and through the majority
of the forecast period for the coastal waters. Winds may subside
slightly by Thursday. In addition, the strong winds will also
continue to cause very rough seas due to fresh swells with short
periods.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tday...SCA...Pigeon Pt to Pt Pinos 0-10 nm from 3 PM
             SCA...Pt Arena to Pt Reyes 0-10 nm
             SCA...Pt Reyes to Pigeon Pt 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
             SCA...Mry Bay from 3 PM

&&

$$

PUBLIC FORECAST: Bell/Dykema
AVIATION: BAM
MARINE: BAM


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