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Area Forecast Discussion (AFD)

Issued by San Francisco Bay Area, CA (MTR)

FXUS66 KMTR 191537

Area Forecast Discussion
National Weather Service San Francisco Bay Area
837 AM PDT Thu Sep 19 2019

.SYNOPSIS...Seasonably cool conditions will persist on Thursday
followed by a warming trend forecast through the upcoming weekend.
A low pressure system moving southward to our east early next week
may create the potential for warming temperatures, dry offshore
flow and increased fire concerns. 

&& of 08:37 AM PDT Thursday...Mostly clear skies 
overnight allowed temperatures to drop into the mid to upper 40s 
in the inland valleys, while lows along the coast were in the mid 
to upper 50s. An upper trough centered to our north will continue 
to track east, keeping us in a cool northwesterly flow pattern for
today. Temps at 850 mb were measured around 9C on the 12z Oakland
sounding, and are forecast to warm to about 11C this afternoon. 
Cool temperatures aloft will prevent a well-defined marine layer 
today and will keep high temperatures seasonably cool. Highs are 
expected to range from the upper 60s to lower 70s along the coast 
with mid 70s to around 80 in the inland valleys. A warming trend 
will begin on Friday and continue through the weekend as the 
upper trough shifts east and a ridge in the eastern Pacific 
expands towards the West Coast. Made a minor adjustment to sky 
cover this morning, otherwise forecast is on track. For additional
details, see the previous discussion.


.PREV of 03:00 AM PDT Thursday...Seasonably cool 
conditions are forecast over the region today as a mid/upper 
trough persists over the region. Afternoon temperatures will be 
cooler at the coast today compared to yesterday, generally ranging
from the upper 60s to lower 70s while inland areas warm into the 
middle 60s to upper 70s. In addition, mostly sunny conditions are 
likely region-wide. 

High pressure building over the eastern Pacific will then begin to 
build toward the West Coast through the upcoming weekend. This will 
result in a warming trend through the weekend with more widespread 
80s across the interior by Friday and even lower 90s by Saturday 
afternoon. With the lack of a marine layer and persistent onshore 
flow, coastal areas will also warm into the 70s to even lower 80s 
through Saturday. 

Conditions trend slightly cooler on Sunday and Monday as a mid/upper 
level trough drops southward into the Pacific Northwest and 
Intermountain West. Mainly dry weather conditions are likely as this 
system will lack sufficient moisture and the best mid/upper level 
support stays inland to the east of the region. With the upper level 
low lingering over the Desert Southwest into early next week and a 
ridge of high pressure building inland to our north, weak offshore 
flow will potentially develop over the region. As a result, warming 
temperatures and much drier conditions are likely to develop by 
Tuesday and Wednesday of next week. Thus, the forecast will need to 
be closely monitored in the coming days as this pattern will create 
the potential for increased fire concerns. 


.AVIATION...As of 04:35 AM PDT Thursday...Well mixed out marine
layer and less observed vs model low level moisture keeping
predominately clear skies/VFR regionwide. Fog satellite imagery
does shows a few pockets of low clouds around the broader region
this morning which may spread and manifest into few clouds into
the sunrise hours. NW winds pick up across the coastal waters
today meaning locally breezy to gusty conditions by this afternoon
through coastal gaps including near KSFO where peak winds of 18kt
sust and gusts to 24kt are possible. For tonight, models keep
boundary layer relatively dry with mostly clear skies. 

Vicinity of KSFO...VFR. A few clouds may develop into sunrise
hours before mixing out by mid morning. Afternoon onshore winds
sustained 15-18kt with gusts 22-24kt possible. 

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...Generally VFR. Sat imagery does show some
low cloud development near KWVI and meandering southward towards
KSNS. Winds mainly light except locally breezy with isolated weak
gusts in the Salinas valley this afternoon. 

&& of 08:20 AM PDT Thursday...Northwest winds will 
increase through the day over the waters, with the strongest winds
in the outer waters north of Point Reyes and locally south of 
Point Sur along the Big Sur coast. An 11 second northwest swell 
will be the predominate wave in the waters today, bringing the 
potential of hazardous conditions from squared seas to portion of 
the waters. A much lighter southerly swell will also be mixed in.


     .Tday...SCA...Mry Bay from 3 PM
             SCA...Pt Arena to Pt Reyes 0-10 nm from 3 PM
             SCA...Pigeon Pt to Pt Pinos 0-10 nm from 3 PM
             SCA...Pt Arena to Pigeon Pt 10-60 nm from 9 AM
             SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm
             SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm from 3 PM




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