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

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FXUS66 KMTR 261829
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco Bay Area
1129 AM PDT Mon Jun 26 2017

.SYNOPSIS...Onshore wind flow today will lead to cooler
conditions through Tuesday. Modest warming is expected during the
second half of the week, however highs will fall well short of
the recent heatwave.

&&

.DISCUSSION...as of 8:37 AM PDT Monday...Completed a minor
forecast/grid update to account for current sky cover which is
showing mostly clear conditions for Santa Cruz/Monterey and San
Benito while a deep marine layer over the Bay Area allowed low
clouds to push into the far East Bay valleys early this morning.
Onshore gradients are around 2 mb at this hour but winds out in
the Delta are howling with Travis AFB currently sustained at 23 kt
from the southwest and gusting to 29 kt. This will keep a cool
onshore wind flow in place today into Tuesday as a weak shortwave
moves onshore near the Oregon border. Still expect morning clouds
to slowly mix out and burn back to the coast.

Forecast for the upcoming work week looks benign and seasonable
with a zonal flow aloft in place. Expect seasonable daytime highs
through midweek then perhaps slight warming later in the week
before the next trough arrives Friday/Saturday with a cooling
trend.

&&

.PREV DISCUSSION...as of 3:00 AM PDT Monday...Clouds mostly
cleared from our CWA later yesterday but satellite shows that they
have returned to San Mateo County northward. Clouds are
continuing to stream to the southeast and will be down into
Monterey County by sunrise. Patchy fog and drizzle can be expected
into the morning.

Synoptically the ridge of high pressure that had been overhead is
now well to the east while the onshore flow combined with a
moderate marine layer will lead to cooler conditions compared to
yesterday especially for spots away from the coast. Highs will
range from 60s near the water with mostly 70s to mid 80s inland.
In general, temperatures will be 3 to 6 degrees cooler compared to
Sunday. Similar conditions can be expected tonight into Tuesday.

By Wednesday a ridge of high pressure will rebuild into the
Pacific and toward our region. This will lead to slight warming
into Thursday. Inland highs will return to the upper 70s to lower
90s with coastal spots in the 60s to the mid 70s. Those
temperatures will hold into early next week and possibly into the
following week.

&&

.AVIATION...As of 11:27 AM PDT Monday...It`s been extra challenging
to forecast stratus cigs in the last 12-18 hours; a classic example
as to the sensitivities of marine based clouds interacting with area
topography and other finer scale waves propagating through the
atmosphere. This complexity, of course, greatly reduces forecast
confidence.

Similarly complex weather even at this late morning hour there is
an ongoing stratus feed into the Bay Area while a sharp stratus/no
stratus line extends south from San Mateo county. Area-wide dewpoint
temperatures are a couple degrees lower than sea surface temps which
should generate more coastal stratus and add to the stratus feed
entering the Bay Area today and tonight, and while the set-up is
similarly true along the north Central Coast, other influences by
local terrain, etc. are causing the leading edge of the stratus
field to dissipate.

18z tafs for the Bay Area are geared toward ongoing MVFR cigs with
occasional mixing causing cigs to mix out to few-sct this afternoon
during maximum diurnal warming. All the while the marine layer is
deep near 3,000 feet and undergoing a mix of cooling/warming at 925
mb; btw, this is a different solution as compared to yesterday`s NAM
run when it was showing cooling of 1C-2C at 925 mb level today.
Tonight`s 925 mb temp change is more consistent with previous runs
indicating 2C-4C cooling South Bay and north Central Coast.

Vicinity of KSFO...Thought is that stratus will continue to reach
the terminal with tempo sct 20z-24z today. Early return possible
this evening if stratus along the coast remains intact, onshore
winds and deep marine layer otherwise favorable for more stratus.
West wind gusts up to 20-25 knots most likely during maximum
afternoon warming.

SFO Bridge Approach...Coordinated with CWSU, better chances for VFR
in the approach today and similarly this evening. Low confidence
regarding tonight`s stratus coverage.

Monterey Bay Terminals...VFR. MVFR cigs probable this evening then
MVFR prevailing through 18z Tuesday with a deep marine layer.

&&

.MARINE...as of 10:40 AM PDT Monday...High pressure remains located
over the Eastern Pacific. Locally gusty winds are forecast along
the immediate coast and in San Francisco Bay today. A dominant
southerly swell will persist into Wednesday morning.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tngt...SCA...SF Bay until 9 PM
             SCA...Mry Bay until 9 PM
             SCA...Pigeon Pt to Pt Pinos 0-10 nm until 9 PM
             SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm

&&

$$

PUBLIC FORECAST: RWW
AVIATION/MARINE: Canepa


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