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

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FXUS66 KMTR 271747
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco Bay Area
1047 AM PDT WED JUL 27 2016

.SYNOPSIS...Very warm conditions will persist inland through the
remainder of the week as high pressure remains over the west.
Meanwhile, cooler temperatures will continue near the coast as a
result of weak onshore flow. Slight cooling is expected over the
weekend as an upper level trough develops off of the Pacific
Northwest Coast.

&&

.DISCUSSION...as of 9:40 AM PDT Wednesday...Today will be the
hottest day of the week for many inland locations away from the
coast as a 597DM high pressure ridge centered near Las Vegas
retrogrades westward. A compressed marine layer and weak onshore
flow will provide only limited heat relief along the immediate
coastline and a few miles inland. Elsewhere, Temperature sensors
are running up to 3 degrees warmer than the same time yesterday
morning with the largest degree of warming expected in inland
Monterey and San Benito counties as well as the southern Santa
Clara valley. Triple digit temperatures will be common across
several portions of the inland north, east, and south bay areas. A
few records may be flirted with, but widespread record
temperatures are not expected. Additionally, some of the hottest
air temperatures (104-108F) are forecast across the Big Sur
ridgetops where the Soberanes fire is currently burning
approximately 23500 acres of wild land.

Smoke from the Soberanes fire is evident across the forecast area
with reports of smoke visible in skies from Sonoma and southward.
This smoke is leading to unhealthy air quality for many
communities especially when combined to the warm stagnant air mass
already in place. Be sure to check airnow.gov, the California Air
Resources Board, or your local air quality management district for
more details on your local air quality today.

Todays smoke modeling output suggests that the bulk of new smoke
will be lofted southeast of the fire, along the Big Sur coast.
That said, there is still a smaller fraction of smoke forecast to
push northeastward towards the Salinas area. Furthermore,
lingering smoke from the Soberanes fire`s inception will continue
to linger across the San Francisco and Monterey Bay areas. The
good news is that the latest HRRR-smoke model shows near-surface
smoke dissipating in the Bay Area late this evening/tonight which
should provide for improved air quality by tomorrow morning.

The high pressure ridge is expected to weaken and dissipate late
in the week allowing for a gradual cooling trend. The pattern will
shift to become more of a mean quasizonal flow for the weekend and
into early next week. A weak disturbance passing to the north
after the weekend should help to deepen the marine layer. No
precipitation is expected locally through the next several days,
however, for those travelling to the Sierra Nevada, there could be
some isolated high base thunderstorms as monsoonal moisture
rotates around the ridge Thursday into the weekend.

.PREVIOUS DISCUSSION...as of 3:33 AM PDT Wednesday...The marine
layer depth is very shallow, around 800 feet, and satellite fog
product shows most clear skies except for a shallow fog layer over
the Monterey Bay and extending locally into the Salinas Valley.
The heat signature from the Soberanes Fire is the most notable
thing on the image. Surface observations indicate very mild
temperatures inland and in the hills, with 70s and 80s still being
reported at higher elevation RAWS sites. Meanwhile, near-coastal
locations are cooler than yesterday at this time with readings in
the lower 50s.

Another hot day is anticipated across inland and especially
higher elevation areas today, where highs are expected to be in
the 90s to near 110. There will be a 40-50 degree gradient as you
head to the coast where highs will only be in the 60s. The upper
level ridge responsible for the warm and dry weather will persist
through the remainder of the week, and begin to weaken by the
upcoming weekend when an upper level trough begins to deepen along
the coast. This will bring in slightly cooler temperatures inland.
This upper trough is progged to linger over the western states
through about the middle of next week keeping temperatures more
moderate.

&&

.AVIATION...as of 10:40 AM PDT Wednesday...Low clouds and
visibilities around the Monterey Bay Region this morning have
mostly retreated to the coast with a smoke layer generally above
3500 FT. Further north, the smoke is a bit higher and will
continue to carry mention of clouds around 7KFT as well as some
haze and smoke. Overall, mainly VFR conditions will prevail
through the day with a slight increase in onshore winds.

Vicinity of KSFO...VFR conditions with an increase in onshore
winds through the afternoon and early evening. Low confidence in
ceilings returning early Thursday morning. Thus, will keep
mention of SCT010 in the TAF at this time.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...VFR conditions through the day with haze
and smoke possibly reducing visibilities at times. Also, smoke
has resulted in ceilings between 3KFT-5KFT across regional
terminals. Low ceilings and fog potentially return late tonight
and persist into Thursday morning, however confidence is low at
this time.

&&

.FIRE WEATHER...as of 3:35 AM PDT Wednesday...Warm and dry
conditions will continue today, especially at elevations above
1500 feet as high pressure remains over the region. While weak
onshore flow continues near the coast, light and variable to light
southerly winds remain over the Santa Lucia Mountains and Los
Padres National Forest. In addition, southerly flow aloft has
caused smokey conditions to persist over much of the Monterey Bay
Region and as far north as the South Bay. While surface winds are
forecast to remain light, west to northwest winds are expected to
increase slightly through late week which should help push the
smoke associated with the Soberanes Fire inland and south in the
coming days. Regardless, warm and dry conditions will continue to
impact firefighting efforts through late week.

&&

.MARINE...as of 10:40 AM PDT Wednesday...Moderate to locally
gusty winds will persist over the coastal waters as high pressure
remains over the Eastern Pacific. The strongest winds will be
across the northern outer waters and north of the Bay Bridge.
Winds will then diminish later this week while a mixed swell
moves into the coastal waters. A long period southwest well
arrives later in the week.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tday...SCA...Pt Arena to Pigeon Pt 10-60 nm
             SCA...SF Bay from 2 PM

&&

$$

PUBLIC FORECAST: DRP
AVIATION: RGass
MARINE: RGass
FIRE WEATHER: Sims


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