Area Forecast Discussion
Issued by NWS San Francisco Bay Area, CA
FXUS66 KMTR 260056
Area Forecast Discussion
National Weather Service San Francisco Bay Area
556 PM PDT MON JUL 25 2016
.SYNOPSIS...An inland warming trend will get underway on Tuesday
and persist through late week as high pressure aloft builds in
from the Desert Southwest. However, as onshore flow persists,
cooler conditions along with some overnight/morning clouds will be
likely near the coast. Region-wide cooling is then forecast for
the upcoming weekend as the high pressure weakens and an upper
level trough develops off of the Pacific Northwest Coast.
.DISCUSSION...as of 02:19 PM PDT Monday...While most inland cloud
cover has retreated to the coast, a deeper marine influence has
resulted in a general cool down compared to yesterday afternoon
over much of the region. This trend will be short lived as
mid/upper level high pressure builds westward from the Desert
Southwest through the remainder of the week. As a result, the
marine layer is forecast to become more compressed overnight with
less inland penetration of stratus tonight into Tuesday morning.
Also expecting smoke and haze to impact the region through at
least Tuesday, especially the Monterey Bay Region as the Sobranes
Fire continues down the Big Sur Coast. Please see the Fire Weather
section below for additional details.
Temperatures region-wide, especially inland, will rebound back to
above seasonal averages tomorrow afternoon. Expecting widespread 90s
in the inland valleys and hills/mountains while upper 70s to 80s will
be common near the bays. Many of the warmest inland spots will
likely reach into the 100-105 degree range. Along the immediate coast
and across San Francisco, daytime temperatures will remain cooler,
generally in the 60s as onshore flow persists. These warmer
conditions will persist through at least Thursday as the ridge aloft
remains the dominate weather driver across the region. Do expect
some minor day to day fluctuations in the depth of the marine layer
and associated overnight/morning low clouds and cooler coastal
It is also worth noting that both the NAM and GFS do show an
increase in mid-level moisture advection into the region from late
Wednesday into Thursday from our southeast. At this time, any
potential for high based/elevated convection appears to remain over
the interior portion of the state, well east of our region. However,
will continue to monitor the forecast models in the coming days for
any potential for convection. Again, the forecast remains dry
through the forecast period at this time given the strong high
pressure ridge aloft.
By the weekend, the models generally agree in a slight cooling
trend back to near seasonal averages as the high pressure weakens
and another mid/upper level trough develops off of the Pacific
.AVIATION...as of 5:56 PM PDT Monday...Air mass stability will
increase as a strong mid-upper level high builds over the area
into early Tuesday. Marine layer depth is presently 1,100-1,500
feet. A return to lower level warming will reinforce the marine
inversions and gradually compress the depth of the marine layer
tonight and Tuesday. Moderate to high confidence VFR persists this
evening at most of the Bay Area terminals as stratus/fog remain
confined to the immediate coastline, MVFR cigs/vsbys reducing to
IFR this evening over the north Central Coast.
A deeper layered southerly flow aloft develops over the entire
forecast area through Tuesday thus restrictions to visibilities
due to haze and wildfire smoke are quite likely to expand northward
to the Bay Area through Tuesday. This coincides with a gradually
weakening surface high over NorCal through Tuesday night the result
being lighter sea-breezes in general and increasing the probability
that restrictions to visibilities extends through mid-week.
The SMX-SFO gradient is 1.7 mb, and continues to be somewhat under-
forecast by the NAM model; the SMX-SFO gradient is likely to increase
to 2 mb Tuesday possibly causing a decrease in NW winds along the
inner coastal waters and introducing a southerly component to the
surface wind there as well Tuesday. Mid-high level cloudiness on
the southwestern side of the strong mid-upper level high over the
Desert SW may reach the forecast area by Tuesday evening into Wednesday.
Vicinity of KSFO...W-NW winds under 20 knots this evening, moderate
to high confidence VFR continues this evening. Gradual visibility
restrictions are forecast late tonight and Tuesday. Seabreeze redevelops
Tuesday afternoon and evening, but wind speeds will probably be on
the lighter side.
SFO Bridge Approach...Similar to KSFO.
Monterey Bay Terminals...MVFR cigs/vsbys due to combination of smoke
and stratus. Cigs/vsbys gradually decreasing to IFR tonight due to
stratus and fog, then stratus and fog scatter out but hazy and smokey
conditions persist Tuesday.
.MARINE...as of 09:31 AM PDT Monday...Moderate to gusty northerly
winds will prevail over the coastal waters as high pressure
remains off the West Coast. The stronger winds will be mainly
over the outer waters north of Pigeon Point. Winds will gradually
decrease Tuesday, but remain gusty north of Point Reyes.
.FIRE WEATHER...as of 02:19 PM PDT Monday...Smoke from the
Sobranes Fire is impacting heavier populated areas today across
the Monterey Bay Region and points to the north and northeast.
This is a result of winds aloft becoming more southerly, compared
to previous days when the smoke was being blown southward out over
the Pacific. Meanwhile, surface winds remain light and variable
and more terrain driven over the fire. Expecting a warming and
drying trend over the region the next few days as the
aforementioned high pressure builds in from the Desert Southwest.
This will also compress the marine layer down to around (or below)
1000 feet and make for more challenging fire weather conditions in
the coming days. However, strong surface winds are not expected
through at least midweek.
.Tngt...SCA...Pt Arena to Pigeon Pt 10-60 nm
SCA...Pt Arena to Pt Reyes 0-10 nm until 11 PM
SCA...SF Bay until 9 PM
PUBLIC FORECAST: RGass
FIRE WEATHER: RGass
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