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Area Forecast Discussion (AFD)

Issued by San Francisco Bay Area, CA (MTR)

FXUS66 KMTR 181143

Area Forecast Discussion
National Weather Service San Francisco Bay Area
343 AM PST Mon Feb 18 2019

.SYNOPSIS...Clearing skies and light winds will allow for cold
overnight low temperatures the next couple of nights. Mostly sunny
skies and slightly warmer temperatures are expected during the
daytime on Monday and Tuesday. Another cold trough will bring a 
chance of light scattered showers on Wednesday and Thursday. 
Temperatures will remain below normal through the week ahead.

&& of 03:25 AM PST Monday...The upper low has 
shifted east and is now centered over far eastern Nevada, leaving 
a cold airmass in place under northerly flow. Only a few isolated 
showers remain in the southern coastal waters with clearing skies 
elsewhere. Northerly flow has advected a drier air mass into the 
area with dew points generally in the upper 20s to the 30s. These 
drier conditions have prevented fog from forming thus far, but a 
few isolated patches may be possible in portions of the North Bay 
Valleys towards sunrise. Winds have decreased from this afternoon 
with generally light northwesterly flow at the surface. 

Clearing skies and light winds allowed temperatures to cool 
quickly late this evening and overnight, with most locations in 
the 30s to lower 40s. Temperatures by sunrise will bottom out in 
the upper 20s to lower 30s in the inland valleys, mid to upper 30s
near SF and Monterey Bays, and the lower 40s along the immediate 
coast. Areas of frost will be possible in the colder locations 
after 4 AM this morning.

Monday will be mostly sunny and a couple degrees warmer, with 
highs mainly in the mid 50s. Plenty of sunshine and light winds
will also help Monday feel quite a bit warmer than Sunday.
Conditions Monday night will be similar to the current night, and
low temperatures will be quite cool once again. Temperatures in
the 30s will be common across the area with lower 40s limited to 
locations on the immediate coast. Northerly flow will continue on 
Tuesday as the upper low slowly drifts east and the upper ridge 
remains anchored off the coast. This will translate into another 
day of mostly sunny skies and highs in the mid 50s. 

The pattern starts to change on Wednesday as a cold trough drops 
down the east side of the ridge. The trough has a northerly 
trajectory over the continent, and will not contain a lot of 
moisture. Additionally, the low center and best dynamics will 
remain to our east. Scattered showers will develop on Wednesday 
afternoon and continue through Thursday. Rainfall amounts are 
expected to be very light, and due to the scattered nature of the 
showers, some areas may not see any measurable precipitation. This
system will bring a reinforcing shot of cold air aloft, and snow 
levels will remain low. Therefore, some of the peaks above 3000 
feet could see a dusting to a couple inches of snow Wednesday 
through Thursday. Increasing cloud cover during this time should
keep low temperatures several degrees milder. 

A shortwave ridge will move overhead on Friday, bringing a return
to dry conditions. On Saturday, another cold trough will dive down
the east side of the ridge into the Pacific Northwest. Models vary
somewhat on how far south the trough digs before it turns
southeast. The ECMWF keeps precipitation to our north, while the 
past several runs of the deterministic GFS have varied between dry
and light precipitation. Confidence remains low in the pattern 
the following week as model solutions diverge. 


.AVIATION...As of 3:40 AM PST Monday...For 12Z TAFs. VFR
conditions under mostly clear skies are expected through the
forecast period except for patchy fog in the North and East Bay
Valleys through 16Z. Generally light winds.

Vicinity of KSFO...VFR through the forecast period. High
confidence. Light WNW winds increasing to about 12 knots in the

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...VFR through the forecast period. Light


.MARINE...As of 03:08 AM PST Monday...Gusty north to northwest 
winds will persist across most of the coastal waters through the 
week. Lighter winds are expected in the bays. Northwest swell will
gradually subside through tonight. A longer period moderate 
northwest swell will become the predominant swell by Tuesday.


     .Tday...SCA...Pigeon Pt to Pt Pinos 0-10 nm
             SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm
             SCA...Pt Arena to Pt Reyes 0-10 nm
             SCA...Pt Arena to Pigeon Pt 10-60 nm
             SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm



MARINE: Dykema

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