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

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FXUS66 KMTR 182052
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco Bay Area
152 PM PDT Wed Jul 18 2018

.SYNOPSIS...Seasonably warm temperatures will persist region-wide
through the forecast period with marine air keeping conditions
cooler at the coast. Monsoon moisture will spread over the region
and provide a slight chance of high-based convection on Thursday and
Friday along with an increase in cloud cover. Drier conditions then
return by the upcoming weekend.

&&

.DISCUSSION...as of 01:51 PM PDT Wednesday...Temperatures are
once again very warm to hot across the interior and in the higher
elevations across the region this afternoon. This is a result of
500 MB heights of 598 DAM centered over the region as high clouds
increase from the south/southeast. Meanwhile, cooler conditions
persist closer to the coast with weak onshore flow and the
presence of a 1,200-1,500 foot marine layer.

While the ridge aloft will maintain seasonably warm conditions
through the forecast period, all attention turns to the increase of
monsoon moisture from the south/southeast in the coming days. The
latest thinking is that moisture advection will continue in the 700-
500 MB layer and even above from late tonight into Friday. The NAM
is most bullish with MUCAPE increasing as well into the 200-600
J/kg range over the Central Coast on Thursday and then spreading
northward into Thursday night. Another surge of moisture and
instability will be possible on Friday as a vort max rotates around
the east side of a mid/upper level low well offshore. In addition,
PWAT values are forecast to exceed 1.25" over much of our region
Thursday into Friday which is 2-4 standard deviations above
climatology. While this is not a slam dunk, do feel the potential
remains for high-based convection Thursday into Thursday night with
even a sprinkle or light shower reaching the surface on Friday as
moisture depth increases aloft. Thus, have added a slight chance of
thunderstorms back into the forecast from Thursday afternoon over
the southern portions of the region shifting northward Thursday
night into Friday afternoon.

The increase mid/high level cloud cover associated with the
aforementioned moisture will also help to cool temperatures inland
by a bit through late week. However, still looking for 60s to 70s at
the coast with widespread 80s to 90s inland. In addition, conditions
will feel more humid/muggy Thursday into Friday. Upper level cloud
cover typically disrupts the marine layer some as well, yet do
expect low clouds to persist near the coast in the coming days.

Drier southwest flow aloft is then forecast to develop by the
upcoming weekend which should end chances for high-based
convection over the region. Higher pressure will also continue to
dominate the pattern with temperatures at or above seasonal
averages (warmest across the interior) heading into early next
week. Do expect marine air to keep conditions cooler at the coast
with night/morning low clouds in the extended as well.

&&

.AVIATION...As of 10:29 AM PDT Wednesday...For 18Z
TAFS...Earlier burn off this morning with terminals VFR. Tonight
do expect some cigs to roll back in, but coverage will likely be
less than this morning. Will also see an increase in mid/high
level clouds as monsoon moisture streams in from the SE.

Overall conf is medium to high.

Vicinity of KSFO...VFR this afternoon. Similar to yesterday winds
will ramp up this afternoon with gusts over 20kt possible. Lower
conf on cigs tonight impacting SFO. Some models actually show a
hole around SFO with cigs on the edges. Will keep cigs in for now,
but may be removed in later updates.

SFO Bridge Approach...Similar to SFO this afternoon. Better chance
for cigs to impact approach later tonight.

Monterey Bay Terminals...VFR this afternoon. Cigs will return this
evening with patchy fog possible late tonight.

&&

.MARINE...as of 08:54 AM PDT Wednesday...Light to moderate winds
will persist for much of the coastal waters as high pressure
remains anchored off the Pacific Northwest Coast. Winds will be
locally stronger north of Point Reyes. Gusty seabreezes will
develop north of the Bay Bridge to the Delta this afternoon and
evening and likely again Thursday afternoon and evening.
Southwesterly swell is forecast to mix with northwesterly swell
this weekend.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tngt...SCA...Pt Arena to Pigeon Pt 10-60 nm
             SCA...SF Bay until 9 PM

&&

$$

PUBLIC FORECAST: RGass
AVIATION: MM
MARINE: MM

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