Area Forecast Discussion
Issued by NWS San Francisco Bay Area, CA

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
FXUS66 KMTR 231140

Area Forecast Discussion
National Weather Service San Francisco Bay Area
440 AM PDT Fri Mar 23 2018

.SYNOPSIS...A cold weather system approaching from the north will
bring renewed chances of rain starting in the North Bay today,
and across the remainder of the area tonight and Saturday
morning. Additional shower activity is possible Saturday afternoon
through Sunday morning. Dry weather is expected to return to most
areas by Sunday afternoon and continue well into next week.


.DISCUSSION...As of 3:15 AM PDT Friday...Area radars show shower
activity has ended across the district, and satellite imagery
shows mostly clear skies over much of the area. Skies will
continue to clear by morning as drier air moves in from the
north. Surface dewpoints have already dropped into the 30s, and
ambient temperatures area running from the upper 30s to upper 40s,
10 to 20 degrees cooler than yesterday at this time. Morning low
temperatures are expected to end up tin the mid 30s in the
coldest inland valleys.

Our next rain maker is currently an upper low center off the
Pacific Northwest Coast. This low is progged to move slowly south
along the coast through Saturday morning and then southeast and
eventually across far northern California by Saturday night. Light
rain is forecast to begin in the North Bay on Friday. But rain
won`t move south of the Golden Gate until Friday night and
Saturday morning as a cold front moves in from the northwest.
Expect a short break in rainfall after the cold front moves
through. Shower activity will then likely develop in the North Bay
on Saturday afternoon as the cold upper low draws nearer.
Scattered showers will develop farther south on Saturday night and
then mostly dissipate on Sunday morning.

This upcoming system will be much drier and colder compared to the
Wednesday night/Thursday system. Rainfall amounts from tomorrow
through Saturday night are generally forecast to range form a
tenth to a half inch. The North Bay Mountains may see locally more
than an inch, and some southern interior locations may see little
or no rain over the next few days. Also, there may be sufficient
instability for isolated thunderstorm development late Saturday,
mainly across the North Bay. Snow levels will drop as low as 2500
feet and so we could see light snow accumulation on the higher

Medium to long range models agree that dry weather conditions will
prevail from Sunday afternoon all the way through next week. In
addition, look for a warming trend through at least the first half
of next week as an upper ridge builds near the West Coast.


.AVIATION...As of 4:40 AM PDT Friday for 12Z TAFs. Generally
expect VFR conditions to prevail for most of the day at TAF sites
with cloud decks around 3,000 to 5,000 ft AGL. Will see 1000-950mb
RHs increase after 00Z from north to south prior to the arrival
of another cold front that will arrive in the North Bay around 06Z
Saturday. This will bring a renewed opportunity for light rain
for the tail end of the TAF period.

Vicinity of KSFO...VFR conditions expected today with SCT cloud
decks between 3,000 to 5,000 ft AGL and southwest to west winds.
High resolution models suggest increasing boundary layer RHs
around 03Z Saturday, and continue to stay elevated until a cold
front passes through the terminal around 10Z Saturday. Could see
several hours of MVFR ceilings around this time.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...VFR conditions expected to prevail
through the day at both KSNS and KMRY. KMRY is currently OVC040 as
the mean 950-850 mb winds are providing just enough upslope
along and south of the Monterey Peninsula and into the Santa
Lucias. Expect increasing clouds around/after 03Z Saturday.

&& of 2:48 AM PDT Friday...Winds will gradually
diminish early this morning as yesterday`s storm system continues
to exit the region. Winds will become northwest and increase again
beginning late Friday as another cold front passes through the


     .Tday...SCA...Pt Arena to Pigeon Pt 10-60 nm from 9 AM
             SCA...Pt Arena to Pt Reyes 0-10 nm from 3 PM
             SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm until 3 PM




Visit us at

Follow us on Facebook, Twitter, and YouTube at: is the U.S. government's official web portal to all federal, state and local government web resources and services.