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

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FXUS66 KMTR 230555
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco Bay Area
1055 PM PDT Tue May 22 2018

.SYNOPSIS...Cool weather and morning low clouds will continue
through most of the week with inland temperatures remaining below
normal for this time of year as a deep marine layer continues to
influence the region. A late season cold front will approach
California late Thursday into Friday bringing a slight chance of
showers to most of the area. Showers should end by Saturday
morning before a warming trend brings inland temperatures back to
near seasonal normals by Sunday.

&&

.DISCUSSION...as of 9:37 PM PDT Tuesday...Low clouds extend well
inland this evening, under a deep marine layer. Drizzle was also
reported in many locations mainly along the coast today, more
drizzle is in the forecast tonight and Wednesday morning. Expect
extensive low cloud coverage Wednesday morning.

Sea temperatures are chillier than usual for late May and has the
stratus machine cranked up, a steepening onshore pressure gradient
each day responsible for driving chilly westerly winds. Public reports
also noting the strength of the winds many days this month, today
being no exception.

A closed upper low approaches from the west later this week
bringing a slight chance of showers later Thursday into Friday,
best chances will be over the North Bay and along the coastline to
the Santa Cruz Mountains and Monterey Peninsula. A few showers
may linger into Saturday morning over the North Bay otherwise
it`ll be dry, a warming trend is in the cards beginning early next
week. For additional specifics, the previous forecast discussion
highlights more details about upcoming weather changes.

&&

.PREV DISCUSSION...as of 1:34 PM PDT Tuesday...Visible satellite
imagery shows this morning`s low clouds have dissipated for inland
areas while much of the coast remains under broken to overcast
conditions. Late clearing has slowed this afternoon`s warming,
keeping temperatures across the area about 5 degrees cooler than
this time yesterday. An upper low remains near Las Vegas, allowing
for breezy onshore winds to continue this afternoon with onshore
gradients still around 2.5 mb from sfo to sac. Expect low clouds
to redevelop this evening moving inland and down the valleys
overnight.

Despite some brief shortwave ridging over the eastern Pacific
tomorrow, seasonably cool temperatures will continue with many
inland locations around 5 to 10 degrees below normal as we remain
under the influence of a deep marine layer. Expect afternoon highs
along the coast in the low 60s with inland areas reaching the low
70s.

An upper level low with an associated surface cold front will then
approach the area on Thursday. This will bring chances of showers
to the region Thursday night into Friday morning. QPF totals
remain light with most areas seeing a few hundredths to just over
a tenth of an inch. The highest amounts will likely be in the
North Bay coastal hills where up to a quarter of an inch is
possible. For now, the main impact from this system would be for
the commute Friday morning when the bulk of the precipitation is
expected. The forecast was updated this afternoon to increase POPs
and QPF across the region with higher QPF totals in the North Bay
and other terrain favored locations along the coast.

Showers will remain a possibility through Saturday morning as the
core of the upper low slowly moves inland, but any remaining
showers would bring little if any additional accumulations. The
main impact will be continued unseasonably cool weather,
especially inland.

As the low continues to move east on Saturday, a modest warming
trend will occur starting Saturday afternoon through Memorial Day
as a ridge develops over the eastern Pacific. Inland temperatures
will rebound to near seasonal normals by Sunday with more
widespread upper 70s in the afternoon. As warming continues on
Monday, some inland locations may even be slightly above normal
with widespread afternoon highs forecast in the 80s.

&&

.AVIATION...As of 10:55 PM PDT Tuesday for 06Z TAFs...A deep
marine layer and a moderately strong pressure gradient persists
across the region spreading widespread low clouds inland. MVFR to
borderline IFR cigs expected to continue through tonight and
through Tuesday morning. Onshore flow will continue to diminish
overnight.

Vicinity of KSFO...A deep marine layer will maintain MVFR cigs
across area terminals through much of the forecast period.
Temporary clearing possible Tuesday afternoon. Onshore winds
around 10 kt will continue through tonight. Winds will ramp up
again Tuesday afternoon to around 15 kt with occasional higher
gusts possible.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...MVFR/IFR cigs will continue across area
terminals through tonight. Temporary clearing possible Tuesday
afternoon/evening. Light onshore winds will continue through
tonight. Winds will ramp up again Tuesday afternoon to around 10
to 15 kt.

&&

.MARINE...as of 9:02 PM PDT Tuesday...Generally light northwest
winds are expected this evening and overnight, though locally
breezy conditions are possible near the Golden Gate and Angel
Island. Winds will become southerly by Thursday morning as a weak
low pressure system approaches from the west. This low will bring
a chance of showers Thursday through Friday night. A long period
southwest swell will persist with a shorter period northwest swell
through the week.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tngt...None.

$$

PUBLIC FORECAST: Canepa
AVIATION: CW
MARINE: CW/Rowe

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