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

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FXUS66 KMTR 110520

Area Forecast Discussion
National Weather Service San Francisco Bay Area
920 PM PST Sat Dec 10 2016

.SYNOPSIS...Light rain will linger across the Central Coast
tonight with rain expected to end in all areas by Sunday. Sunday
is forecast to be a dry day under partly cloudy skies. Dry
weather will likely continue into Monday as well. Rain is
forecast to return to the northern part of the region by Tuesday
and to all areas by Thursday. Local heavy rain is possible around
the middle of next week along with gusty winds.


.DISCUSSION...As of 8:45 PM PST Saturday...The frontal boundary
that brought widespread rain to our region earlier today has moved
into south-central California. Light rain continues along upslope
portions of the Santa Lucia Mountains at this time, otherwise
precipitation has ended across our region. A forecast update
earlier this evening included a reduction in rain chances tonight.

Rain totals over the past 24 hours in the Bay Area ranged from
only about a tenth of an inch for some locations along the lee
side of the Santa Cruz Mountains to as much as 3 inches in the
North Bay Mountains and Santa Cruz Mountains. South of Monterey
Bay, rain totals were less impressive, ranging from only trace
amounts in the interior valleys to 1.5 inches in the western
Santa Lucias.

Skies are already beginning to clear across the North Bay at this
time. Look for this clearing trend to continue from north to south
overnight. Sunday is expected to be a partly cloudy and dry day
with seasonable highs ranging mostly from the mid 50s to lower

Dry weather is expected to continue through Monday as well,
although high clouds will be on the increase Monday as the next
plume of moist air approaches from the west-southwest. By Tuesday
the incoming moisture plume is forecast to interact with a trough
dropping south out of the Gulf of Alaska. The result will be
widespread precipitation across our region between Tuesday and
Thursday of next week. There is still quite a bit of uncertainty
as to the timing and amounts of precipitation. For the first
couple of days (Tuesday and Wednesday) the models depict a frontal
boundary draped somewhere across the Bay Area, drifting slowly
south and then back to the north as the trough deepens offshore.
Then, sometime around Thursday, the trough is forecast to shift
inland and push the front to the south and east, and also
intensify it. Given latest model guidance, particularly the 00Z
GFS, Thursday looks to be the day with the potential for heaviest
rainfall and hydro issues could develop then. However, we could
also see locally heavy rain rates from late Tuesday into
Wednesday. Strong and gusty winds may be a factor as well,
especially around midweek. Precipitation is expected to taper off
late next week and temperatures will drop as a cooler airmass
sweeps in from the north.

Only other forecast update this evening was a substantial increase
in minimum temperatures on Tuesday and Wednesday nights, as our
area will mostly be on the warm side of the frontal boundary and
widespread clouds will keep temps mild at night.


.AVIATION...As of 9:00 PM PST Saturday...Rain has moved south of
the MRY Bay Area. Current obs indicate rapid clearing has taken
place over the SFO Bay Area. Still some MVFR cigs over the MRY Bay
Area but this should clear out by 08Z. This was indicated by the
previous model runs so forecasts were adjusted to VFR conditions
through Monday except for patchy fog around STS.

Vicinity of KSFO...VFR.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...MVFR cigs becoming VFR after 08Z.

&& of 9:30 PM PST Saturday...Weak high pressure off the
coast will bring light northwest winds to the area. A low
pressure system will move northeast across the the central waters
Tuesday night and Wednesday. This will cause a deformation zone
with northeast winds over the northern outer waters and southerly
winds over the remainder of the coastal areas. Winds will shift
back to the northwest on Thursday.






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