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. 


Discussion...as 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 low level wind shear 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. 


Marine...as 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. 


Mtr watches/warnings/advisories... 
... Arena to Pigeon pt 10-60 nm 



Public forecast: rww 
aviation: west pi 
marine: west pi 
fire weather: rww 

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