Area Forecast Discussion
Issued by NWS San Francisco Bay Area, CA
FXUS66 KMTR 241151
Area Forecast Discussion
National Weather Service San Francisco Bay Area
451 AM PDT Mon Oct 24 2016
.SYNOPSIS...light rain will develop in the north bay today but be
mainly light with the rain band only slowly sagging southward
towards the Golden Gate by late this afternoon or evening. Some
light rain overnight into Tuesday morning for the Peninsula and
East Bay before the front slides back to the north. Dry and
seasonable Tuesday night into Wednesday. Next front arrives
Thursday with a better chance of soaking rains, especially for the
coastal hills. Long range trends remain unsettled with shower
chances next weekend into Halloween.
.DISCUSSION...as of 3:35 AM PDT Monday...Lightning activity
overnight has been confined to the Sierra foothills east of our
district with radar showing rapidly developing cells continuing to
move northeast away from the Bay Area. Our attention is now on the
frontal boundary approaching Cape Mendocino. This feature will
move into northern Sonoma county by mid-morning with some light
rain developing. In general it appears the trends are to slow and
weaken the system as it reaches the north bay and especially
points south of the Golden Gate. The frontal boundary is becoming
occluded with the main upper low and cold advection staying well
north of the Bay Area. So expect periods of rain, mainly light for
the north bay increasing through the afternoon hours. Main commute
impacts should be for the afternoon and evening commute north of
the Golden Gate. Frontal boundary will try and sag south of the
Golden Gate overnight with some light rain for the SF peninsula
and the east bay. However there are weak dynamics and no cold
advection, some favored southwest facing slopes may fair will due
to local orographics but dont believe the deep moisture and
sustained southwest flow will make it as far south as the Santa
Cruz mtns with this system leaving only some light rains for the
Santa Cruz mtns thru Tuesday morning.
Boundary will then shift northward on Tuesday and dissipate in
response to next system and digging offshore trough.
The trends seem to indicate that the heaviest rains with the late
week system will be focused somewhere between the Santa Cruz mtns
and Santa Barbara county putting the central coast (i.e. Big Sur)
potentially in the bullseye for an incoming southwest flow system.
The ecmwf has been pretty consistent with this solution for days
now and the latest 06z gfs is more or less in line. Given the
trajectory of the incoming low would expect the heavier rains with
the late week system for the southern portions of the district
most notably the Santa Cruz mtns and Big Sur hills where 1-4
inches may occur with the late week system Thursday into early
Beyond that the pattern remains unsettled, especially for October
with shower chances continuing but no all day rain events
expected next weekend. Models do portend more storms potentially
lining up by around Halloween into next week.
.AVIATION...as of 5:00 AM PDT Monday...Main concern for the day is
the gusty southerly winds. SFO gusting to 30 kts this morning and
gusts should continue in the 25-30 kt range through the day. Low
to mid cigs settling over the area as a frontal system approaches.
Bases are near 3000 feet. Clouds will lift into VFR range late
this morning except in the North Bay. Deeper moisture arrives
after 22Z in the North Bay spreading into SFO and OAK after 03Z.
Vicinity of KSFO...VFR with cigs at or above 3000 feet. S winds
gusting to 25-30 kt decreasing this evening. Light rain with wet
runways possible after 03Z.
SFO Bridge Approach...Similar to KSFO.
Monterey Bay Terminals...VFR with cigs remaining above 3000 feet.
Southeast winds increasing to 15-20 kt at SNS after 16Z.
.MARINE...as of 02:49 AM PDT Monday...A 985 mb low centered 450
miles west of Crescent City will lift northeast today. Another
low will develop and deepen about 600 miles off the northern
California coast Tuesday and will also track northeast through
Wednesday. Southerly winds will continue to increase today then
persist Tuesday and Wednesday. A weaker low develops off the
central California coast Thursday and Friday so southerly winds
will not be as strong.
SCA...Pt Arena to Pt Reyes 0-10 nm
SCA...Pt Reyes to Pigeon Pt 0-10 nm
SCA...Pigeon Pt to Pt Pinos 0-10 nm
SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm
SCA...Pt Arena to Pigeon Pt 10-60 nm
SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm
SCA...Mry Bay from 12 PM
PUBLIC FORECAST: RWW
AVIATION: W Pi
MARINE: W Pi
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