000
FXUS66 KMTR 151527
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco Bay Area
827 AM PDT Tue May 15 2018

.SYNOPSIS...Typical "May Gray" weather conditions with seasonably
cool temperatures will persist over the region today in advance of
an approaching upper level system. A few showers will be possible
over the interior portions of the region Wednesday morning as the
weather system pushes inland. A drying and slight warming trend
is then forecast late in the week under a weak ridge of high
pressure.

&&

.DISCUSSION...as of 08:27 AM PDT Tuesday...Satellite imagery
continues to show low clouds over most of the region with bases of
1,500 to 2,500 feet. Persistent overnight cloud cover has kept
low temperatures across the region in the 50s this morning with
higher elevation areas reporting in the 40s. Afternoon high
temperatures today are expected to remain relatively cool as
clouds only partially mix out ahead of an approaching mid/upper
low. Some inland areas may experience clearing this afternoon
while most coastal locations and parts of the North Bay remain
under cloudy skies throughout the day. Expect highs this afternoon
in the 50s to 60s along the coast with mid to upper 60s for most
inland areas. No changes to the forecast are needed at this time.
For additional details refer to the previous discussion below.

&&

.PREV DISCUSSION...as of 03:00 AM PDT Tuesday...Low clouds with a
base of 1,500 to 2,500 feet continue to impact much of the region
this morning in response to a deep marine layer and moist,
onshore flow from the Pacific. This has helped to keep
temperatures in the 50s for much of the region with a few 40s
reported in the higher elevations. Temperatures will be slow to
warm this afternoon as clouds only mix out partially in advance of
an approaching mid/upper level low.

As the upper level low pushes onshore over the San Francisco Bay
Area late tonight into Wednesday morning, low clouds will once again
spread over much of the region. However, a well defined marine layer
will not be as likely tonight into Wednesday morning in response to
slightly cooler air moving in overhead. A few rain showers cannot be
ruled out over the interior portions of the region as the upper
level low pushes inland. However, the latest forecast models show
the best chances to remain over Northern California and into the
interior portion of the state. Seasonably cool conditions are likely
again on Wednesday in response to cold air advection associated with
the low. Look for daytime temperatures to only warm into the 60s for
most locations.

Dry weather conditions return to the entire region late Wednesday
into Thursday as the mid/upper level low shifts inland to our east.
With the marine layer likely to be mixed out, temperatures will be
on a warming trend with weak high pressure building over the eastern
Pacific. This will allow for temperatures to warm back to near
seasonal averages by Saturday.

Medium range guidance suggests another mid/upper level trough will
drop southward out of the Pacific Northwest late Sunday which would
result in some cooling early next week.

&&

.AVIATION...As of 4:47 AM PDT Tuesday...For 12z TAFs. Satellite
imagery reveals widespread low clouds across all area terminals
this morning. The Fort Ord Profiler depicts a deep 3000 ft marine
layer. MVFR cigs will persist through the morning with low level cigs
scattering out around noon over most terminals. Light onshore
flow will strengthen this afternoon.

High confidence.

Vicinity of KSFO...MVFR cigs will persist through the morning
with low level cigs scattering out around noon. Moderate onshore
flow around 10 mph will continue through the morning hours then
increase once again this afternoon.

SFO Bridge Approach...Similar to KSFO. MVFR cigs will impact the
approach until around 18z-19z this morning.

Monterey Bay Terminals...MVFR cigs will persist through the morning
with low level cigs scattering out around noon. Light winds will
continue through the morning hours then increase this afternoon.
KSNS wind sensor is down for maintenance therefore no amendments
are scheduled.

&&

.MARINE...as of 2:37 AM PDT Tuesday...Relatively light winds will
prevail through midweek as a weak disturbance gradually makes its
way across the region over the next few days. Winds will
strengthen during the later half of the week as the surface
gradient tightens on the backside of this system. A small mixed
swell will persist through the forecast period.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tday...None.

$$

PUBLIC FORECAST: AS/RGass
AVIATION: CW
MARINE: CW

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