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Area Forecast Discussion (AFD)

Issued by San Francisco Bay Area, CA (MTR)

FXUS66 KMTR 190954

Area Forecast Discussion
National Weather Service San Francisco Bay Area
254 AM PDT Tue Sep 19 2017

.SYNOPSIS...An upper level low will dominate the western US 
through this week. There is a slight chance of rain in the far 
North Bay Wednesday morning as a frontal system moves through 
otherwise look for dry and breezy conditions with cooler than 
average temperatures. A slow warming trend is expected by the 


.DISCUSSION...as of 3:00 AM PDT Tuesday...An upper level low is
over the Pacific Northwest. The marine layer is mixed out and only
patchy low clouds are being reported this morning. 850 mb temps
have dropped a few degrees C since yesterday so highs today will
be about 3-5 degrees cooler.

A strong shortwave trough rotating around the low will move into 
the district tonight and Wednesday morning bringing a slight 
chance of rain to far northern Sonoma county. The shortwave will 
help to deepen the low over the California interior Wednesday and 
Thursday bringing a dry and cool northwesterly flow to the area. 
Temperatures Wednesday and Thursday will only be in the 70s inland
while coastal areas will benefit from the lack of clouds and be 
in the 60s. Breezy conditions are expected through the week. 925
mb winds get as high as 35 kt tonight through Thursday night with
the strongest winds in the afternoon and evenings. This will 
mainly impact the higher elevations but a few gusts to 30-35 kt 
could occasionally mix to the surface.

The trough moves into the Great Basin Friday and will result in a
slight warming on Friday with decreasing winds. A more noticable
warming trend is expected this weekend as the trough moves 
further east and upper level ridging builds off the west coast 
into the Pacific Northwest coast. This could bring offshore flow 
to the area. If this verifies coastal areas could see temperatures
into the 70s while inland highs should warm back into the 80s.


.AVIATION...As of 10:38 PM PDT Monday...For 06z Tafs. High clouds
streaming across the region will continue through the night. This
will keep any low clouds development patchy in nature. VFR 
conditions are expected to prevail through the forecast period. 
Moderate west winds will continue to ease becoming light and 
locally variable overnight.

Vicinity of KSFO...VFR conditions will prevail through the 
forecast period. West winds will continue to ease overnight. 

SFO Bridge Approach...similar to KSFO. 

Monterey Bay Terminals...VFR conditions will prevail through the 
night. Patchy MVFR/IFR cigs possible around sunrise Tuesday 
morning however confidence remains very low. Light west winds will
continue to ease becoming light and locally variable overnight.


.MARINE...as of 9:00 PM PDT Monday...A cold front moving across 
the coastal waters will bring moderate to locally gusty northwest 
winds. Northwest winds will continue to increase through the 
forecast period as ridge builds in from the west. A moderate 
sized, longer period northwest swell is anticipated to arrive 
tonight into early Tuesday.


     .Tday...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
             SCA...SF Bay from 1 PM




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