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Area Forecast Discussion (AFD)

Issued by San Francisco Bay Area, CA (MTR)

FXUS66 KMTR 182113

Area Forecast Discussion
National Weather Service San Francisco Bay Area
213 PM PDT Wed Sep 18 2019

.SYNOPSIS...Showers will linger early this afternoon across
portions of the Central Coast before ending later this afternoon. 
Seasonably cool temperatures are expected today and Thursday. A 
warming and drying trend is then forecast for late this week and 
into the upcoming weekend as high pressure builds in from the 
eastern Pacific. Another system moving to our east early next week
may create the potential for dry offshore winds and increased fire

&& of 02:13 PM PDT Wednesday...The cold front 
continues to progress through the forecast area and has now 
reached Santa Cruz/Santa Clara Counties. Scattered showers persist
along the front with light rainfall accumulations continuing in 
these areas. Rainfall totals so far today have been light, with 
most places north of Monterey/San Benito Counties picking up a few
hundredths of an inch of rainfall and locally higher amounts of 
0.1 to 0.2 inches in the higher terrain and around Oakland. The 
front will continue to weaken as it shifts south, with little to 
no measurable precipitation anticipated for much of the Central 
Coast. Behind the front, skies remain mostly cloudy with KMUX 
radar detecting a few scattered returns across the North Bay. Any 
showers north of the front are not likely to produce more than a 
few drops at the surface. 

Clearing has also been observed over the coastal waters as drier
air filters in. This area of clearing will eventually move onshore
this afternoon with decreasing clouds. Temperatures this 
afternoon will be seasonably cool, with highs in the upper 60s to 
70s in most locations, with parts of interior Monterey and San 
Benito reaching the 80s under mostly sunny skies.

As skies clear tonight, cool overnight lows are expected in the 
valleys with upper 40s to lower 50s with mid to upper 50s near the
coast and bays. The base of the upper trough responsible for 
bringing us scattered showers and cooler temperatures will shift 
through our forecast area on Thursday. Highs are expected to be 
similar to today, ranging from the upper 60s at the coast to the 
70s and lower 80s inland, which are near to slightly below normal 
for the date. 

High pressure over the eastern Pacific will then begin to build
towards the West Coast on Friday and Saturday, resulting in a 
warming trend for the region. The strongest warming will be felt
inland, with highs on Friday reaching the mid to upper 80s and
upper 80s to mid 90s on Saturday. Light offshore flow and a lack 
of a strong marine layer will also allow temperatures to warm at 
the coast, where temperatures in the 70s to low 80s are

Temperatures trend slightly lower Sunday into Monday as another 
upper level trough drops southward into the Pacific Northwest and
into the Intermountain West. There remains some uncertainty with 
the track, but at this time, dry conditions look most likely with 
temperatures near to slightly above seasonal averages. Depending 
on the exact track of the aforementioned system, the development 
of offshore flow looks possible early next week which may result 
in an increase in temperatures and much drier conditions. This 
pattern will be closely monitored in the coming days as it may 
create the potential for increased fire concerns.


.AVIATION...As of 10:42 AM PDT Wednesday...For 18Z TAFs. A weak 
cold front continues to pass through the San Francisco Bay Area 
this morning, resulting in a a mixture of MVFR to VFR ceilings at 
the terminals. As the afternoon progresses, skies will go from 
BKN/OVC to more FEW/SCT at or above 3,000 ft AGL in the post- 
frontal environment with stratocumulus/cumulus development. 
Challenging forecast with overnight regarding the potential for 
low clouds. Think there will be enough mixing to prevent 
widespread low clouds, but still possible to see MVFR and even IFR
ceilings at some terminals.

Vicinity of KSFO...Ceilings are beginning to lift at SFO as of the
18Z TAF publication time with VFR conditions. After the front
passes through, winds will transition from a light south/southwest 
direction to the west around 15 kt with FEW-SCT stratocumulus/cumulus

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...MVFR/VFR conditions this morning,
becoming VFR later in the day. Light S/SE winds will become
onshore as the day progresses.

&& of 08:17 AM PDT Wednesday...Generally light and 
variable to locally moderate northwest winds will prevail today. 
The strongest northwest winds will be focused along and south of 
Point Sur. Northwest winds strengthen across the waters by 
Thursday afternoon becoming moderate for most of the waters. Mixed
seas will continue with a moderate period northwest swell and a 
light southerly swell.


     .Tngt...SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm from 9 PM




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