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

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FXUS66 KMTR 231204

Area Forecast Discussion
National Weather Service San Francisco Bay Area
504 AM PDT Mon Oct 23 2017

.SYNOPSIS...Rapid warming trend will occur today with record or
near record highs this afternoon and then again Tuesday afternoon.
Long October nights will allow for sufficient night time cooling
to avoid any heat headlines. Offshore flow may weaken slightly by
midweek but temperatures look to remain above normal through the
end of the week and perhaps even into the weekend. Long range
models keep dry weather in place through Halloween.

&& of 2:50 AM PDT Monday...Skies are completely
clear across the Bay Area early this morning as offshore flow gets
firmly established. Northerly gradient down the coast is now 6 mb
with 8 mb offshore from the Nevada deserts towards the coast.
This has kicked up some winds in the hills with Mt Diablo gusting
to around 59 mph out of the north. The 00z Oakland sounding last
night showed the subsidence inversion around 3000 feet and it
appears that the strongest winds are staying at this level or
higher. The Rose Peak RAWS just above 3000 feet gusted to 43 mph
last hour. The Hawkeye RAWS, which we often monitor closely during
offshore/fire weather events has had temperatures warm into the
mid 70s with humidity down to 35% so far tonight as dry northeast
winds start to kick into place. So the stage is set for a sunny
and warm late Oct day. Record highs for today are generally in the
upper 80s to mid 90s so a few records may fall today into
Tuesday. Right now Tuesday looks like it may be the hottest day
but offshore winds may be slightly weaker, reducing adiabatic
compression, however an overall warmer airmass may negate that
impact. Either way expect sunny and warm to hot afternoons the
next few days. As always we are concerned about our more heat
sensitive populations such as the elderly, young and homeless
populations. The long October nights and dry airmass will allow
for sufficient overnight cooling with lows generally in the 50s
for populated areas. Hilly locations where the winds wont subside
will stay closer to 70 at night.

Any midweek cooling looks minor as dry east winds stay in place.
We may not have to worry about record highs Weds-Thursday but
there should still be plenty of highs in the 80s.

Latest long range ecmwf brings some stronger onshore flow by late
next weekend or early next week but temps should still be on the
warm side of normal with no rain in the forecast through the end
of the month.


.AVIATION...As of 5:00 AM PDT Monday...Offshore flow continues to
increase this morning as the WMC-SFO pressure gradient is now at
8.7 mb and forecast to be over 10 mb later today. Strong e-ne
winds reported in the hills with winds gusting to 25-30 kt above
1200 feet and gusts to 55 kt at Mt Diablo. Therefore aircraft
could experience LLWS through this morning. Wind shear should
diminish this afternoon as afternoon heating allows more mixing to
the surface.

Vicinity of KSFO...VFR. Low level wind shear through 17z.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...VFR. Possible gusty southeast winds to 24
kt in the morning in the Salinas Valley.


.FIRE WEATHER...As of 2:50 AM PDT Monday...Light to moderate
offshore wind event seems to be unfolding about as expected.
Humidity values staying moist through 3 am with just a few of the
north bay hill sites showing signs of drying. More rapid drying
will occur through the afternoon with poor humidity recovery
forecast tonight. The strongest winds are currently remaining over
the highest hills and not see much evidence or trend for mixing
those down early this morning. None the less we still have warm,
dry and breezy conditions on tap today. Probability of new
ignitions will remain high the next few afternoons with near
record warmth and drying of the fine fuels. At this time just plan
to run generic headlines in the fire weather forecast to raise
awareness without issuing any specific watches or warnings.

&& of 2:50 AM PDT Monday...Strong surface high pressure
is building over the Pacific Northwest. This will push the
thermal trough to the coast resulting in lighter winds through
Friday. Northwest swell will decrease the next few days but
another long-period swell is forecast by the end of the week.


     .Tday...SCA...Pt Arena to Pigeon Pt 10-60 nm




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