High Surf in California, August 29, 2021

Area Forecast Discussion
National Weather Service San Francisco Bay Area
853 AM PDT Sun Aug 29 2021

.SYNOPSIS...A southerly surge of marine stratus is bringing patchy
fog conditions to coastal waters and the coast as far north as
Mendocino Co. Today will be hazy with continued above normal
temperatures. Cooling temperatures and increasing humidity will
begin late tonight into midweek as a trough begins impacting
Northern California. A return of onshore flow with this trough
will help push smoke/haze to the east this week.

&&

.DISCUSSION...as of 08:52 AM PDT Sunday...Visible satellite shows
the southerly surge has made its way up the coast to Mendocino
Co. This has deepened the marine layer to around 1200 ft, as per
coastal profilers. Marine stratus has intruded into the Monterey
Bay area, the Salinas Valley, and parts of the Santa Clara Valley
and SF Bay area. Also seeing areas of fog around coastal Monterey
Bay. Stratus should burn off by mid-morning for most areas,
perhaps lingering through the morning along the coast. Another hot
and dry day is in store for interior areas with cooler conditions
around the bays and coast, but still a few to several degrees
above normal. More widespread cooling begins tomorrow through mid-
week, which will provide much needed relief for our interior
areas experiencing wildfires and extremely dry fuels. Forecast
remains on track. See previous discussion for more details.

Also, noting some improvement in smoke concentrations and air
quality around the region, compared to yesterday, but still seeing
lingering smoke/haze on area webcams, more so in interior areas.
Latest HRRR smoke model run shows the smoke sticking around
through the day with significant improvement by late tomorrow,
aided by increasing onshore winds.

&&

.PREV DISCUSSION...as of 03:25 AM PDT Sunday...Nighttime satellite
imagery shows a healthy southerly surge of stratus along our
coastline from SoCal up to Boedga Bay. The stratus is also pushing
through the Golden Gate Bridge and is impacting the East Bay from
about Richmond to El Cerrito to Berkeley. Farther south, the
Monterey Bay and surrounding coastline is also getting a good push
of low clouds. If you have to drive early this morning, take it
slow if you encounter lower visibilities on the road.

With that southerly surge, we're seeing a gradual increase in the
marine layer. Fort Ord Profiler has been around 1000-1300 feet
overnight which is obvious with the increased inland intrusion of
low clouds. The SFO-SAC onshore gradient has doubled in the past
24 hours from 0.9 mb to 1.8 mb. This enhanced marine influence
will help keep conditions cooler for coastal regions today.
However, inland areas will likely remain hot and dry this
afternoon. Expecting highs to generally be in the 70s with a few
80s for coastal regions while inland areas are once again
entrenched in mid 80s to the low 100s.

Smoky and hazy conditions will also linger today across the
region. However, the incoming trough early this week will help in
clearing out our skies. Models continue to show that the upper
level low in Canada will start to deepen it's trough into NorCal
overnight Sunday into Monday then becoming more "troughy" by
midweek as 500 mb heights lower from around 590 dam today down to
580 dam by Wednesday. Thus, our region will be on a cooling trend
for much of this week bringing below normal temperatures by
Wednesday. Continued cooling on Thursday with a slight nudge up on
the thermometers for Friday and Saturday as high pressure over the
desert SW starts ridging into CA and weakening the trough pattern
that will dominate this week.

&&

.AVIATION...as of 04:21 AM PDT Sunday...For the 12z TAFs. Stratus
clouds have reformed over the Pacific. Onshore winds are pushing
them into the North San Francisco Bay and down the East Bay
coastline for near IFR conditions at KOAK. Conditions near the
Monterey Bay are LIFR with isolated patchy fog in areas. HZ/FU
remains in the TAFs as smoke from the wildfires linger reducing
vis and slant range vis at times. However, onshore flow is
forecast to increase through the day helping to increase vis
conditions for at least coastal terminals. Low clouds are forecast
to clear after 16Z for a VFR Sunday afternoon.

Cloud cover is expected to return tonight with more areas in the
North and East Bay terminals with the chance to see ceilings; as
well as terminals near the Monterey Bay once again. How
widespread the cloud cover will be will largely depend on how
deep the marine layer grows on Sunday. So it will be a mix of VFR
conditions for inland terminals, and IFR/LIFR conditions for
coastal/sheltered terminals overnight Sunday into Monday morning.

Vicinity of KSFO...Stratus lingers over the ocean, but VFR currently
and through Sunday. Vis concerns initially for lingering smoke, but
hazy skies should improve a bit through the day as onshore winds
increase. Winds at the terminal expected to top out around 20 kts.
Stratus clouds return Sunday night. Most impacts will be in the
East Bay, but increasing confidence put cigs at the terminal late
in the TAF period.

KSFO Bridge Approach...Similar to KSFO.

Monterey Bay...LIFR with patchy areas of fog. Clearing is
expected after 16Z. VFR forecast for Sunday with locally breezy
onshore winds in the afternoon. Low stratus clouds return to
terminals after 02Z for IFR lowering to LIFR overnight.

&&

.FIRE WEATHER...as of 3:15 AM PDT Sunday...With the marine layer
starting to show signs of deepening and an increase in the onshore
flow, coastal areas should see cooler and wetter conditions today.
However, inland areas, while slightly cooler than yesterday, are
still expected to be hot and dry.

Expecting stronger onshore winds by Monday that will precede
better humidity recovery and a lag in the fine fuels. As September
looms we'll be on the lookout for offshore wind events but for
now warm and dry weather will be the main fire weather element to
watch coupled with the current drought stressed fuels.

&&

.MARINE...as of 08:12 AM PDT Sunday...Patchy fog across the
coastal waters this morning with mainly light to moderate
northwest winds. Locally breezy conditions across the northern
outer waters. Winds to increase tonight into tomorrow with
stronger winds becoming more widespread. Gale force gusts are also
expected over the northern outer waters late tonight into Monday
afternoon. Seas remain predominately driven by shorter period
northwest waves at 8 to 10 seconds along with a light longer
period southerly swell.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tday...SCA...Pt Arena to Pigeon Pt 10-60 nm
             SCA...SF Bay from 3 PM

&&

PUBLIC FORECAST: Lorber/Bingaman
AVIATION: DK
MARINE: AS
FIRE WEATHER: Bingaman

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