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Area forecast discussion 
National Weather Service San Francisco Bay area
216 am PDT Tuesday Sep 30 2014

Synopsis...patchy low clouds along the coast this morning will
lead to one more day of seasonable temperatures across the Bay
area. By tonight offshore winds will develop across the north and
East Bay hills which will usher in some drier air and wipe out the
marine layer. A sharp warming trend will start Wednesday and then
continue right through the weekend with widespread readings in the
80s and 90s throughout the Bay area and central coast. No significant
cool down is forecast until Monday or Tuesday of next week.

&&

Discussion...as of 2:16 am PDT Tuesday...a poorly defined 1000 foot
marine layer persists along the coast this morning with patchy
marine clouds developing around the Bay and valleys once again
this morning. Onshore gradients remain around 2 mb from sfo-SAC
with a very weak front moving into far northern California. This
boundary will wash out by midday and in its wake a strong surface
pressure gradient will set-up across the region. North winds will
develop in the SAC valley this evening and then overspread the
Napa hills by later tonight. NAM 925 mb winds are forecast around
25-35 miles per hour over the ridges late tonight through early Wednesday morning.
In general the winds are expected to only impact some of the
higher peaks above 2500 feet...as we usually need a cold advection
pattern to mix the air down. Therefore wont issue any wind
advisories and just expect the usual windy spots like Montana Diablo
and the County line along Napa/Yolo and northern Sonoma to see
some of the stronger winds.

Expect temperatures to warm from 5-10 degrees on Wednesday under the
ideal adiabatic/donwslope warming pattern. Ridge-top winds will ease
by middle-morning but then a much drier airmass will settle over the
region where even subtle downslope winds will allow valleys temperatures
to quickly soar into the 80s and lower 90s for much of the Bay area.

By Thursday high pressure will be centered over much of California
with light but persistent offshore flow continuing. 850 mb temperatures
will warm to around 20 celsius by Thursday and then stay between
20-22 celsius through the weekend. Although not exceedingly warm
aloft the surface and low level pattern will promote warm to hot
weather across the district Thursday through Sunday. Most of the
MOS guidance hints at Friday as a possibly exceedingly warm day
with widespread 90s and some near triple digit heat.

Heat impacts will be a concern for sensitive populations (elderly
and young) as well as a prolonged period of fire weather concerns.
Will still have to mull over possible fire weather headlines but
let day shift coordinate that with land management agencies. One
subtle mitigating factor is the rain from last week that has
raised some of the fuel stick readings. Nonetheless it wasn't enough
rain to have lasting impacts given the long term drought and the
forecast of several days of hot weather and low humidity.

No real change in the pattern until at least Monday when some
onshore winds return to the coast. Long range models keep the
ridge over the West Coast at least through the middle of next
week.

&&

Aviation...as of 10:55 PM PDT Monday...patchy clouds across the
area this evening with some terminals dropping down to MVFR
levels. Difficult forecast with the guidance suggesting low ceilings
almost all night at all spots which the satellite (and stronger
northerly gradient) suggesting that we could see frequent breaks
overnight. Will go mostly with model guidance but changes may need
to be made by the middle of the next shift if it is not working
on. Only fair confidence for tonight into the morning hours.

Vicinity of ksfo...1 minute ob have gone back to scattered after a
period of bkn018. Satellite shows just patchy clouds around and
upstream so a big hesitant to completely believe the model
guidance which brings in MVFR for much of the night. Do feel
confident that tonight will be the final potential for low clouds
as the flow GOES more offshore. Only fair confidence.

Ksfo bridge approach...so far clouds have stayed out of the
approach and appears it may end up filling in after the terminal.

Monterey Bay area terminals...clouds confined to the coast so far
just impacting kmry. Should see an increase with low clouds to
ksns by 08z. Generally west winds under 10 knots. Moderate
confidence.

&&

Marine...as of 10:55 PM PDT Monday...northwest winds will continue
to increase tonight through Tuesday morning in wake of a weak
frontal passage. High pressure will then build into the coastal
waters through middle week...maintaining moderate to occasionally
strong wind speeds and building seas. Winds will then diminish by
late week as surface high pressure weakens.

&&

Climate...record high temperatures for Wednesday through Friday
(10/1 to 10/3) along with the most recent date it occurred.

Sf Bay area
location.................10/1...........10/2............10/3...
Kentfield................97/2012.......100/2012.........99/2012
San Rafael..............104/1980.......106/1980........105/1980
Napa....................106/1980.......102/1980........103/1917
San Francisco............97/1980........96/1980.........97/1985
sfo Airport..............97/1980........96/1980.........94/1985
Oakland (downtown)......103/1980.......103/1980........100/1985
Oakland Airport..........94/1952........98/1980.........95/1985
Richmond.................99/1980.......100/1980.........97/2012
Livermore...............102/1952.......106/1980........106/1980
Moffett field............93/1980........95/2012.........97/1985
San Jose.................97/1980........96/2012.........97/1985
Gilroy..................104/2001.......107/1980........106/1980

Monterey Bay area
location.................10/1...........10/2............10/3...
Monterey................103/1980.......101/1980.........96/1985
Santa Cruz..............102/1965.......102/1980........102/1980
Salinas.................104/1980.......100/1980.........97/1985
Salinas Airport.........105/1980.......103/1980.........99/1985
King City...............109/1980.......107/1980........102/1980

&&

Mtr watches/warnings/advisories...
... Arena to pt Reyes 0-10 nm
Small Craft Advisory...pt Arena to pt Reyes 10-60 nm
Small Craft Advisory...pt Reyes to Pigeon pt 10-60 nm
Small Craft Advisory...pt pinos to pt Piedras Blancas 0-10 nm
Small Craft Advisory...Pigeon pt to pt pinos 10-60 nm
Small Craft Advisory...pt pinos to pt Piedras Blancas 10-60 nm
Small Craft Advisory...pt Reyes to Pigeon pt 0-10 nm

&&

$$

Public forecast: rww
aviation/marine: Bell
climate: Bell

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