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Area Forecast Discussion (AFD)

Issued by San Francisco Bay Area, CA (MTR)

FXUS66 KMTR 191103

Area Forecast Discussion
National Weather Service San Francisco Bay Area
303 AM PST Tue Feb 19 2019

.SYNOPSIS... Cool, dry weather conditions are forecast to persist
along with cold overnight temperatures through Wednesday morning.
Another cold weather system is forecast to bring light rain 
showers to the region Wednesday into Thursday morning with snow 
likely in the higher elevations. Dry conditions return late 
Thursday and persist into at least Friday. 

&& of 3:00 AM PST Tuesday...Overnight satellite 
imagery reveals mostly clear skies across the entire state of 
California thanks to high pressure. A quick look at many automated
sensors around the Bay Area also indicated rather light winds 
overnight. The exception are the hills where some gusts of 25-35 
mph remain. The combination of light winds and clear skies set the
stage for excellent radiational cooling. Temperatures early this 
morning will be rather cold with lows in the 20s (interior 
valleys) to 30s and 40s (urban areas and coast). The cold 
temperatures will likely lead to frost and some window scraping 
for morning commuters. It should also be noted that if any 
continued water runoff from the recent rains occurs on some roads 
black ice would be possible in the hills/coldest valleys. 

After a cold start, today will feature another sunny day with
highs in the 50s for most locations and colder in the hills/mts

The next weather item of note is currently dropping south along 
the British Columbia Coast. High pressure currently over the 
region will weaken as this disturbance moves in from the north
Wednesday and Wednesday. Latest forecast models indicate it will
be another cold system with 1000-500mb thickness levels/700mb 
temps puts snow levels back to 2500-3000 feet. Unlike some of the
previous systems from the past few weeks this system appears to be
more moisture starved leading to scattered showers. Nonetheless,
forecast will bring scattered showers down the coast early Wednesday
and spreading more inland Wednesday afternoon. Rainfall amounts
will be on the order of a few hundredths to a few tenths at best 
or a dusting in the hills. 

Drier northwest flow returns Thursday as any lingering precip ends
from N-S. Dry weather returns completely Thursday night and Friday
as shortwave ridging develops overhead. Next weekend looks to
start off dry then another round of precip will be possible by
Sunday. A very broad upper level trough sweeps through the region
Sunday into Monday with scattered showers. Additional rain chances
will be possible next week, but details vary from model to model.

Simply put, the storm door remains open. 


.AVIATION...As of 09:29 PM PST Monday...For 06Z TAFs. VFR 
conditions through the period with mainly clear skies for the SF 
Bay Area and Monterey Bay Area terminals. Patchy fog possible in 
the North and East Bay tomorrow morning, although any fog that may
develop is not expected to be widespread. Confidence on patchy 
fog is low, so backed off a bit on fog in KSTS. Winds should 
remain light overnight and through the morning generally less than
10 kt. Winds to turn onshore tomorrow afternoon. Expect 
increasing high clouds towards the end of the taf period.

Vicinity of KSFO...VFR conditions with mainly clear skies. 
Guidance show increasing high clouds towards the end of the taf 
period with latest run of the WRF hinting at maybe some low cloud
development tomorrow night ahead of the next system. Light winds 
overnight generally less than 10 kt before winds turn onshore in 
the afternoon.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals....VFR conditions are forecast to prevail
with light winds. Some southeast drainage winds may to develop 
overnight and early tomorrow at SNS. Increasing high clouds 
tomorrow evening with latest models showing some patchy low clouds
developing late tomorrow night.

&& of 08:45 PM PST Monday...Gusty northerly winds will 
gradually diminish overnight before increasing again during the 
day tomorrow. Northerly winds will then remain elevated through 
mid week as an upper trough moves southward into the Great Basin 
and a ridge of high pressure sets up over the eastern Pacific. A 
series of northwest swells will impact the region through the rest
of the week.


     .Tday...SCA...Pt Arena to Pt Reyes 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...Pt Reyes to Pigeon Pt 0-10 nm from 3 PM




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