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

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FXUS66 KMTR 250458

Area Forecast Discussion
National Weather Service San Francisco Bay Area
858 PM PST Fri Feb 24 2017

.SYNOPSIS...Tonight will be another cool night, but not quite as
cool as last night. A weather system dropping from north to south
off the West Coast will bring rain chances to our area from
Saturday through Saturday night, primarily to coastal areas.
Another system will produce shower chances form late Sunday into
Monday. Dry weather is expected to return by Tuesday. An extended
period of dry weather, along with a warming trend, is then
forecast through the remainder of next week and into the following


.DISCUSSION...As of 8:55 PM PST Friday...By 8 pm Friday evening
temperatures had dropped into the mid to upper 40s across the
region and it`s shaping up to be another chilly night. However,
most model guidance indicates overnight lows will be a few degrees
warmer than last night.

Evening IR satellite imagery shows a cold weather system off the
coast of Oregon, dropping slowly to the south, with another nearly
stationary system offshore along 140W. The system to the north is
relatively dry, while the one to our west contains significant
moisture with precipitable water values as high as 1.7 inches.
The GFS, NAM and ECMWF all forecast the northern system to tap
into the moisture of the system offshore to some extent. However,
all three of these models track the northern system almost due
south, parallel to the coast, over the next 24 hours. This track
would result in most precipitation remaining offshore Saturday
and Saturday night. Only coastal areas have a good chance of
seeing rain through Saturday night, and even in coastal areas
rainfall amounts are mostly forecast to be a quarter of an inch or
less, except locally around a half inch in the Santa Cruz and
Santa Lucia Mountains according to the 00Z GFS. The Canadian model
is still the outlier, forecasting the two systems to more fully
merge and then move inland across California on Sunday, producing
widespread moderate rainfall and gusty winds late Saturday night
and Sunday. Cannot completely rule out the Canadian solution, but
given the agreement and recent consistency displayed by the other
models, have elected to base the forecast on the solution put
forth by the drier models.

A second system dropping south along the coast of the Pacific NW
on Sunday is forecast to dig into the Great Basin by Monday. This
system will be quite dry and is forecast to produce only widely
scattered light showers across our area from Sunday night into
Monday. Very little rainfall accumulation is expected.

Dry weather is forecast to return to all areas by Tuesday, and cool
conditions will persist through then. An extended period of dry
weather will then ensue and continue through the remainder of
next week and into the following weekend as an upper level ridge
builds over California. Expect a warming trend during the second
half of next week with high temperatures climbing up to near 70
by weeks end.


.AVIATION...As of 4:30 PM PST Friday...VFR conditions this
afternoon with just a few cumulus clouds over the hills.
Models show increasing low level moisture after 06Z which may lead
to MVFR cigs in some places after midnight.

Vicinity of KSFO...VFR through the airport evening rush. MVFR
possible by 08z-10z. West winds to 15 kt decreasing after 04Z.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Increasing clouds after 06Z with marginal
VFR/MVFR cigs after 10Z.

&& of 4:30 PM PST Friday...A low pressure system will
drop southward along the coast this weekend replacing today`s
weakening high pressure. Winds will turn southerly on saturday
before returning to a northwest flow by Sunday as the low
dissipates. Generally mild winds and seas are expected through the
forecast period. Light showers will move in Saturday morning from
the north and progress southward along the coast throughout the
day ending by Monday.





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