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

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FXUS66 KMTR 230012

Area Forecast Discussion
National Weather Service San Francisco Bay Area
508 PM PDT Sat Oct 22 2016

.SYNOPSIS...Seasonable weather conditions are forecast through
the remainder of the weekend. An unsettled weather pattern will
develop Monday into Tuesday and bring rain chances to the region,
mainly to the northern portion of the region. Unsettled conditions
are likely again late in the upcoming workweek.

&& of 01:54 PM PDT Saturday...Temperatures region-
wide this afternoon are in the 60s to 70s with passing high level
clouds. This is a result of a weak mid/upper level system pushing
inland across the Pacific North West. As the region remains in a
transition period, little change is expected on Sunday with dry
weather conditions and temperatures near seasonal averages.

A deeper mid/upper level system will then develop off of the Pacific
Northwest coast late Sunday into Monday and will drive a frontal
boundary down into northern California. With this, light rain will
develop across the North Bay early Monday morning and will slowly
spread southward through the remainder of the day. Rainfall will
likely be greatest over the North Bay and coastal ranges north of
San Francisco from this system will much less rainfall south of the
city. This will be a result of the boundary becoming washed out as
it pushes southward into the Santa Cruz Mountains. However, cannot
rule out light rain as far south as the Monterey Bay region late
Monday night into Tuesday. Through Tuesday, rainfall amounts will
range between 1.00"-2.00" for the North Bay Mountains, 0.50"-1.50"
for the remainder of the North Bay and around 0.25" around the
greater San Francisco Bay Area. As mentioned above, lesser rainfall
amounts are forecast down the Central Coast with little to no rain
likely for San Bentio County and interior portions of Monterey

While rain chances may linger over the North Bay Tuesday night, the
rest of the region will see dry conditions develop and likely
persist Wednesday. Forecast models then greatly differ on timing of
and amount of precipitation late in the week as an upper level low
develops off of the California coast. The ECMWF brings in widespread
rainfall as early as Thursday with the GFS and Canadian models
showing rain not returning until late Thursday into Friday with much
lesser rainfall amounts. Will have to continue to monitor the latest
model output in the coming days to see if they begin to converge on
a more similar solution. Regardless, unsettled conditions will be
likely into late next week with temperatures below seasonal

&& of 5:08 PM PDT Saturday...A gradual weakening of
the 500 mb height ridge tonight will speed up a little Sunday. A
surface high pressure ridge currently extends NE across the
northern coastal waters to Humboldt and Del Norte counties and is
forecast to pivot gradually eastward overlapping the CA coastal
counties south through our forecast area Sunday afternoon. Light
onshore winds continue into this evening. SMX-SFO pressure gradient
is neutral then turns southerly tonight and Sunday, a bit ahead of
schedule (a common occurrence) compared to the latest NAM and WRF
model forecasts. Both of these models indicate a southerly surge
developing Sunday with the SMX-SFO gradient forecast to reach 4 mb
by this time Sunday. A southerly flow pattern will be setting up
ahead of the next upper level trough approaching from the NW.

Light winds, compressed marine inversions to 1,000 feet or less
around the area late this afternoon and surface dewpoint temps mid
40s-lower 50s favors a continuation of VFR area-wide tonight then
patchy IFR due to low stratus cigs and/or fog possible along the
Big Sur coastline late tonight/Sunday with a southerly surge. Patchy
MVFR/IFR northern Monterey Bay is likely Sunday afternoon and evening,
low cigs often reach KSNS first during the early evening in this

Vicinity of KSFO...VFR. Westerly winds 10-15 knots subsiding to 10
knots or less later this evening and overnight.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...VFR. Light onshore winds shifting to light
SE winds this evening. VFR looks quite favorable for much of the night,
but low cig coverage will depend upon how quickly the southerly surge
sets up later tonight into Sunday. Some low cigs due to stratus and/or
fog likely by later Sunday morning and afternoon over the northern
Monterey Bay.

&& of 10:43 AM PDT Saturday...Northwest winds will
decrease today as a trough descends into the region. Winds will
shift towards the south tomorrow and strengthen into early next
week. A moderate to large northwest swell train will begin moving
through the coastal waters today then gradually subside through
the coming days.


     .Tngt...SCA...Pigeon Pt to Pt Pinos 0-10 nm until 9 PM
             SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm until 9 PM




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