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Area Forecast Discussion (AFD)

Issued by San Francisco Bay Area, CA (MTR)

FXUS66 KMTR 190529

Area Forecast Discussion
National Weather Service San Francisco Bay Area
929 PM PST Mon Feb 18 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 9:00 PM PST Monday...A dry and cool 
northerly flow has settled over the area. Humidities are running
20 percent lower than 24 hours ago. The airmass has warmed
slightly today but the drier air will allow for more radiational
cooling tonight so the overnight lows will be close to what they
were this morning. Could see some patchy frost in the interior

Current forecast looks good. No updates.

Previous discussion...With light winds and clear sky conditions 
again tonight, temperatures will cool into the 30s for most to 
around 40 in San Francisco and along the immediate coast by 
Tuesday morning. Cannot rule out areas of frost for inland 
locations and even patchy fog in portions of the East Bay Valleys 
as well as in the southern Santa Clara Valley around sunrise. 
Daytime temperatures on Tuesday look to be similar to today as 
well, generally in the 50s. 

From previous discussion...A reinforcing shot of colder air will 
advect southward down the coast Wednesday into Wednesday night 
with an associated short-wave disturbance. This system will likely
produce isolated to scattered (at best) showers over the region 
with snow likely in elevations above 2,500 feet. Moisture will be 
limited with this system which will prevent more widespread 
showers. This system may bring overnight temperatures up by a few 
degrees given the increase in cloud cover. However, look for 
cooler than normal values to persist through midweek. 

A short-wave ridge will build over the region Thursday night into 
Friday which will result in the return of dry weather. Temperatures 
again change little as broad troughing remains in place over much of 
the western portion of the country. The forecast models differ from 
one another heading into the upcoming weekend with the GFS being 
most promising of additional light rainfall on Sunday. Meanwhile, the 
ECMWF keeps precipitation to our north. Either way, widespread 
precipitation in the extended does not appear likely and 
temperatures look to stay below seasonal averages. 


.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.


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




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