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FXUS66 KMTR 260527

Area Forecast Discussion
National Weather Service San Francisco Bay Area
1027 PM PDT Mon Sep 25 2017

.SYNOPSIS...A warm offshore flow will continue through at least 
Wednesday with above average daytime temperatures, mild overnight 
conditions and breezy winds in the hills. Conditions cool slightly 
near the coast on Thursday before spreading inland Friday as onshore 
flow returns. 

&& of 9:00 PM PDT Monday...High pressure at the
surface and aloft over the Eastern Pacific coupled with a thermal
trough along the coast lead to a beautifully warm fall day across
the region today. High pressure at the surface ridging across the
Pacific Northwest and into the Great Basin result in a drying and
locally breezy offshore winds that lead to further warming across
the region. Temperatures rose an average of 3 to 5 degrees over 
yesterday highs under clear and sunny skies this afternoon. Mid 
60s to the lower 70s were observed along the coast while 
widespread 80s were observed inland. Offshore flow contributed to 
a few low to mid 90s across the North Bay. Temperatures were on 
average 10 degrees warmer than seasonal norms. 

As high pressure continue to build in over the district through 
midweek temperatures are forecast to continue warming. 
Temperatures are anticipated to warm another 3 to 5 degrees 
Tuesday with highs forecast to reach into the 70s along the coast 
with a few 80s possible as winds turn increasingly offshore. Mid 
to upper 80s are expected farther inland with low to mid 90s in 
the warmest inland areas. While Tuesday's highs will likely be an
average of 10 to 15 degrees above seasonal norms they are not 
expected to reach record territory. No heat advisories are
expected as this pattern of dry offshore flow poses a low heat
risk for those sensitive to the heat. However remember to always stay
cool and well hydrated.

Temperatures are expected to plateau by Thursday as an 
approaching upper level trough begins to break down the ridge of 
high pressure and onshore flow returns to the region. This will 
initially result in cooler conditions at the coast. As an upper 
level trough nears the West Coast the onshore gradient will 
tighten resulting in a stronger onshore push and likely widespread
cooling across the region as the cooler marine air infiltrates 
farther inland. Nonetheless, models indicate mostly sunny and dry 
weather will persist through the end of the work week.

From previous discussion...While above average temperatures have 
been forecast to continue into the upcoming weekend, the latest 
forecast models are showing more of a troughing pattern across the
West Coast from this weekend into early next week. Until we see a
bit more consistency in the model solutions in the day 5-8 time 
frame, will not make any significant changes to the extended 
forecast. With that said, if the latest trends hold true, 
temperatures will have to be lowed back to below seasonal 
averages. The 12Z operational run of the ECMWF also brings a 
slight chance of precipitation to the region Sunday night into 
Monday. Again, will hold of on major changes until we gain better 
confidence in the forecast models.


.AVIATION...As of 10:27 PM PDT Monday...Offshore winds and dry 
conditions support VFR tonight and Tuesday. Light winds except 
gusty in the North Bay and East Bay mountains/hills. Easterly 
winds may also become locally gusty along the San Mateo coast late
tonight and Tuesday morning.

Vicinity of KSFO...VFR.

SFO Bridge Approach...Similar to KSFO. 
Monterey Bay Terminals...VFR. Light E-SE winds tonight. Westerly 
winds return Tuesday afternoon and evening.


.FIRE WEATHER...As of 2:57 PM PDT Monday...No real change from
previous forecast. Red Flag Warnings remain in effect through 
Weds afternoon for the North and East Bay hills. Latest hi-res
models showing winds increasing overnight with decreasing RH.
Typically the window to watch for is late overnight and shortly
after sunrise. Winds will decrease Tuesday afternoon, but temps 
will be hot and RH will be low. Hi-res models show another burst 
of gusty northeast winds in the north and east bay hills Tuesday 
night into early Weds. Winds will finally ease by Weds afternoon 
but by then the fuels will be very dry with low humidity and 
likely the hottest day of the week with widespread readings into 
the upper 80s and 90s. We are near the peak of Bay Area fire 
season and this is a classic critical fire weather pattern.

&& of 10:07 PM PDT Monday...Moderate northwest winds
will persist over the northern outer waters tonight and tomorrow
as high pressure resides over the  eastern Pacific and a thermal
trough sits over California. The thermal trough over the
California interior will shift slightly westward reaching the
coast by Tuesday morning and again early  Wednesday morning. Winds
over the northernmost and southernmost waters will decrease by
late in the day tomorrow.


     .Tngt...SCA...Pt Arena to Pt Reyes 0-10 nm until 2 AM
             SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm until 2 AM
             SCA...Pt Arena to Pigeon Pt 10-60 nm




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