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

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FXUS66 KMTR 260559

Area Forecast Discussion
National Weather Service San Francisco Bay Area
959 PM PST Sat Jan 25 2020

.SYNOPSIS...Light rain will continue across the North Bay this
evening and develop farther to the south by late tonight and early
Sunday. Precipitation is expected to end in all areas by midday
Sunday. Dry conditions are forecast from Sunday afternoon through
Monday evening before the next weak weather system brings rain
chances to primarily the North Bay late Monday night into Tuesday.
Dry weather, along with a warming trend, is forecast from
Wednesday through next Saturday.


.DISCUSSION...As of 8:35 PM PST Saturday...Light warm advection
rain began to fall across Sonoma County late this afternoon and
current KMUX radar shows light rain remains confined to the North
Bay this evening. Anywhere from a quarter to a half inch of rain
has fallen across northwest Sonoma County thus far, with amounts
of less than a tenth of an inch south and east of Santa Rosa.
Satellite shows that the incoming cold front is still a ways
offshore and the 00Z NAM indicates rainfall will not spread south
of the Golden Gate until the cold front approaches later tonight
and early Sunday morning. Additional rainfall overnight and Sunday
morning is expected to be a quarter inch or less in most areas,
except locally more in Sonoma County. The cold front is forecast
to move through our area by mid morning Sunday, but widely
scattered light showers will likely linger until midday. Isolated
showers may continue into the afternoon hours across the southern
portion of our area, but otherwise tomorrow afternoon should
feature dry conditions, mild temperatures, and partly cloudy
skies. Dry weather will continue through Monday.

The next system is forecast to move through the Pacific Northwest
and far northern California Monday night into Tuesday. Rain is
possible across the northern portion of our area, mainly late
Monday night into Tuesday morning, but amounts are expected to be

For the remainder of next week, the models agree that an upper
ridge over the Eastern Pacific will build eastward over California
and strengthen. H5 heights are forecast to climb as high as 588 dm
by the end of the week, while 850 mb temperatures warm to a balmy
17 deg C across the southern portion of our area. Expect these
developments to result in a warming trend from Wednesday through
next Saturday. Widespread highs in the mid to upper 60s are
forecast by Thursday and some lower 70s are likely across the
southern portion of our area by Friday and Saturday.

In the longer range, both the GFS and ECMWF ensemble mean indicate
cooler weather during the first full week of February. And while
the ensembles show some potential for precipitation that week,
amounts are projected to be light.

&& of 9:59 PM PST Saturday...For 06Z TAFs. A weak cool
frontal boundary is moving in from the west. VFR-MVFR this evening
with areas LIFR-IFR ceilings and visibilities tonight and Sunday

Vicinity of KSFO...VFR-MVFR then IFR by 09z tonight with light rain
showers. VFR returns on Sunday.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...VFR-MVFR, lowering ceilings to IFR tonight
with light wet weather tonight into Sunday morning. VFR returns on

&& of 9:12 PM PST Saturday...Winds will shift to become
south to southwest across the waters by this evening ahead of a
weak surface frontal boundary before shifting to become northerly
by Sunday morning. A long period west to northwest swell will this
evening. Additional long period northwest swells will arrive by
early next week.






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