FXUS66 KMTR 190603
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco Bay Area
1003 PM PST Sat Jan 18 2020

.SYNOPSIS... High pressure building over the West Coast will
result in dry and seasonably cool weather conditions through the 
weekend. Light rain is possible starting Monday, with higher 
chances of precipitation developing by Tuesday. Mostly dry 
conditions are then expected for the remainder of next week, with 
rain possibly returning next weekend.

&&

.DISCUSSION...As of 8:50 PM PST Saturday...Although an upper 
ridge began to build over California today, considerable high 
cloud cover kept temperatures near or slightly cooler than normal.
The upper ridge is forecast to strengthen further tonight and 
early Sunday, resulting in about 2-3 deg C warming at 850 mb. This
should translate into at least slight warming at the surface, 
although moist westerly flow aloft off the Pacific will maintain 
high cloud cover and prevent temperatures from warming more than a
few degrees in most areas. Surface dewpoints are slightly lower 
this evening compared to last evening, so it's unlikely there will
more than patchy fog development late tonight and early on 
Sunday.

An upper trough is currently centered over the Eastern Pacific 
along 145W. Models generally agree that this system will bring
light rain to much of our forecast area from late Monday night
through Tuesday. At the southern periphery of this trough, and 
slightly in advance of the trough axis, is a weak disturbance that
has tapped into subtropical moisture. This weak feature is 
generally forecast to dissipate prior to reaching the California 
coast on Monday. However, the ECMWF has been consistent in brining
light precipitation into our area on Monday in advance of the 
primary upper trough. Our current forecast includes only a slight
chance of rain on Monday afternoon and evening which seems 
appropriate given that only the ECMWF forecasts light 
precipitation then. Rain chances will then increase from north to 
south late Monday night and Tuesday morning as the primary frontal
system arrives. Rain intensity is forecast to be mostly light 
with this system, but may be moderate in the North Bay. Most rain
should end by late Tuesday, although a few showers may linger 
into Tuesday night. As much as three-quarters of an inch or rain 
is forecast in the North Bay through late Tuesday, with generally 
a third of an inch of less expected elsewhere in our forecast 
area.

Although the pattern remains progressive through the rest of next
week, most of the moisture and energy will be focused to our north
and so dry and mild conditions will likely prevail in our area
through at least the end of the work week. The exception is
in the North Bay on Friday where the 12Z ECMWF brings in some 
rain. The forecast becomes more uncertain by next weekend when the
ECMWF indicates a higher potential for significant precipitation 
in our area compared to the GFS. 

&&

.AVIATION...as of 10:03 PM PST Saturday...For 06z TAFs, VFR except
for possible patchy fog and/or low clouds late tonight and early 
Sunday in the North Bay valleys. Winds generally light offshore 
with high pressure over the Great Basin. 

Vicinity of KSFO...VFR, offshore wind for most of the 06z taf.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...VFR, offshore winds.

&&

.MARINE...as of 9:59 PM PST Saturday...High pressure over the 
Great Basin will maintain generally light to moderate offshore 
winds across the coastal waters through Sunday. Winds will turn 
southerly and increase by Monday morning ahead of an approaching 
frontal system. A moderate northwest swell will arrive late 
Saturday and Sunday while a larger northwest swell arrives the 
middle of next week.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tngt...SCA...Pt Arena to Pt Reyes 0-10 nm
             SCA...Pt Arena to Pigeon Pt 10-60 nm
             SCA...Pt Reyes to Pigeon Pt 0-10 nm from 3 AM
             SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm from 3 AM

&&

$$

PUBLIC FORECAST: Dykema
AVIATION: Canepa
MARINE: RGass

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