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

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FXUS66 KMTR 261553

Area Forecast Discussion
National Weather Service San Francisco Bay Area
853 AM PDT Thu Apr 26 2018

.SYNOPSIS...Upper low off the coast will keep temperatures below
normal through the end of the work week and into the weekend. Some
coastal drizzle or very light showers possible later tonight
through early Saturday as the upper low moves onshore, however
most areas will remain dry with below normal temperatures being
the main impact. Cool and dry pattern continues into early next

&& of 8:53 AM PDT Thursday...Yet another cloudy
morning for much of the area as the central California coast
remains under the influence of a deep marine layer in excess of
2,000 ft. Visible satellite imagery shows the cloud deck pushing
well into the Salinas Valley, some of the East Bay Valleys
including the Livermore area, as well as the North Bay Valleys.
Expect the clouds to mix-out through the morning with many areas
away from the immediate coastline clearing out before lunch. An
upper level low largely responsible for deepening the marine layer
is currently near 35N/135W, or about 700 miles west of San
Francisco. Temperatures with afternoon will be a few to several
degrees cooler for most locations with coastal areas in the 50s
and 60s and interior areas in the 60s and 70s. No major changes
planned for the morning update with the short-term remaining on
track. For additional details, please refer to the previous
discussion section.


.PREV of 3:27 AM PDT Thursday...Marine layer now in
excess of 2000 feet with fog product showing another good push of
stratus into most inland valleys. Upper low well off the coast is
responsible for the deep marine layer and below normal temperature
pattern. Unseasonably cool highs today with 60s near the
coast/bays and only some low to mid 70s inland. The low will
slowly approach the coast tonight into Friday. As this occurs some
coastal drizzle may occur as the marine layer continues to deepen
overnight into Friday as initial vorticity lobs passes over the

Core of upper low looks to move onshore near Cape Mendocino on
Friday with continued slight chance of some coastal drizzle in
deepening marine layer environment. Light showers associated with
the instability aloft will be confined to the far North Bay,
mainly later Friday night Saturday morning. Daytime highs Friday
and Saturday continue to be unseasonably cool with deep marine
layer, substantial clouds and a cool airmass aloft leading to lots
of daytime highs only in the 60s throughout the Bay Area.

The main low finally ejects eastward late Saturday night into
Sunday. So for the weekend Sunday looks to have more sunshine and
slightly warmer temperatures.

Longwave trough stays over the West Coast with a cold but dry
shortwave dropping towards the Central Coast by Monday and
Tuesday. This will continue to keep temperatures on the cool side
of normal through the end of the month but no precip expected with
this upper level shortwave. Modest warming and drying trend by the
middle of next week but no hot weather nor storms of note in


.AVIATION...As of 4:45 AM PDT Thursday...Southwest flow enabling
another marine stratus intrusion this morning. Advancing low
interacting with stratus deck has resulted in higher bases
(500-800 feet higher than yesterday morning) and will likely
result in slightly earlier mix outs versus yesterday morning. In
addition, southwest flow with higher decks has allowed for a hole
in the deck to form over KSFO and most of the northern San
Francisco Bay. Otherwise, a few passing high clouds this morning,
stratus returns tonight, generally light onshore winds with
locally breezy/gusty conditions this afternoon/early evening.

Vicinity of KSFO...Southwest flow and higher bases working against
cigs at KSFO this morning, however, not uncommon to see these
types of holes in the deck fill in at or around sunrise. Watch
satellite and see what happens approach in full effect. Otherwise,
a few passing high clouds this morning, sustained winds up to
around 15k this afternoon, with an odd gust or two to around 20kt
possible. Lower cigs potentially return late tonight into sunrise

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...MVFR through mid to late morning. Some
model data suggests OVC- BKN/MVFR cigs all day but currently not
look that pessimistic given southwest to west flow unfavorable
for lingering stratus over terminals.

&& of 8:37 AM PDT Thursday...Generally light west to
northwest winds will prevail with locally breezy conditions near
the coastal gaps and prominent points this afternoon and into
Friday. Light to moderate seas will continue through the forecast
period with a mixed south and northwest swell developing late in
the week.





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