Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Francisco Bay area
1041 PM PDT Monday Sep 22 2014
Synopsis...near seasonal conditions will continue across the San
Francisco and Monterey Bay area early this week. Cooler weather
and chances for rainfall are then expected by midweek as an upper
level system impacts the region.
Discussion...as of 9:00 PM PDT Monday...upper level ridge building
over the area allowed for temperatures to warm up 5-10 degrees
over yesterday. The coast remains free of stratus this evening but
conditions favor stratus reforming late tonight and burning off at
the usual time Tuesday.
The upper ridge will remain through Tuesday before an upper level
low approaching the Pacific northwest pushes the ridge east on
Wednesday. A frontal system will bring a chance of rain from the
North Bay and the San Francisco Bay area with a slight chance as
far south as the Monterey Bay area. Timing of the onset of
precipitation according to latest models will be Wednesday
afternoon along the North Bay coast...Wednesday evening over the
North Bay interior...late Wednesday night into Thursday morning in
the San Francisco Bay area...and Thursday in the Monterey Bay
area. The front is narrow and will only bring a short period of
steady light rain.
Upper level low will deepen off the California coast Thursday
night and Friday. The trough axis moves inland by Friday night. Rain
chances decrease behind the front but there will continue to be a
slight chance for showers Thursday night through and Friday night.
Expected rainfall amounts are about .10 to .25 inches in the North
Bay with up to .50 inches in the coastal hills...and less than .10
inches further south. Dry and cool northerly flow will settle
over the area Saturday on the back side of the trough.
Temperatures will not change much on Tuesday but some cooling will
start to take place in the North Bay on Wednesday due to increasing
clouds. Cooling will hold off until Thursday elsewhere. Cool
temperatures will then continue into Saturday.
Dry conditions are expected Sunday through early next week as
upper level ridge builds off the coast. Temperatures will warm
back up to near normal.
Aviation...as of 10:41 PM PDT Monday...mainly clear skies prevail across
the region. MVFR/IFR ceilings returning late tonight with very little
change in the marine layer as an upper level trough approaches.
Clearing is anticipated around 17z-18z Tuesday morning. Light
onshore flow expected through tonight across most terminals with
locally light and variable winds expected over Monterey Bay area
Vicinity of ksfo...VFR. Borderline MVFR/IFR ceilings returning around
13z tonight. Clearing expected around 17z-18z Tuesday morning.
Light onshore winds of 5 to 10 knots expected overnight.
Ksfo bridge approach...similar to ksfo.
Monterey Bay area terminals...VFR. MVFR ceilings will return after
11z tonight. Clearing expected around 16z-17z Tuesday morning.
Light and variable winds expected overnight.
Climate...autumn officially begins (autumnal equinox) at 7:29 PM
Marine...as of 8:49 PM PDT Monday...light west to northwest
winds will persist across the coastal waters as high pressure
remains over the eastern Pacific. A cold front will move through
the region Wednesday and moderate period northwesterly swell will
Public forecast: west pi
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