NWS Forecast Area Discussion - San Francisco Area

FXUS66 KMTR 291005

Area Forecast Discussion
National Weather Service San Francisco Bay Area
305 AM PDT Thu Oct 29 2020

.SYNOPSIS...High pressure will bring mostly sunny, mild afternoons
and cool, mainly clear nights through the remainder of the week. A
slight warming trend is then forecast over the upcoming weekend,
along with continued dry weather conditions.

&& of 03:04 AM PDT Thursday...Mainly clear sky
conditions prevail over the region this morning with stratus
nearing the North Bay Coast and Big Sur Coastline. Given the dry
air mass still over the region, expecting low clouds will mainly
stay offshore through the remainder of the morning. The dry air
mass and light winds have allowed temperatures to fall into the
40s and 50s for most urban areas with a few of the coldest valley
locations dropping into the upper 30s. That said, 60s are still
being reported in the hills.

This afternoon will be defined by mostly sunny sky conditions with
temperatures once again warming into the 70s near the coast to lower
80s in the interior valleys. The marine layer looks to deepen
slightly overnight into Friday as the ridge of high pressure aloft.
In response, low clouds will likely return to the coast and linger
into early Friday morning. Coastal temperatures will also cool by a
few degrees in response to the shallow marine layer and increased
onshore flow.

A slight warming trend is then forecast for the upcoming weekend as
the high pressure over the eastern Pacific builds inland. More
widespread 80s will be likely across the interior while coastal
locations warm into the 70s. Overall, this is about 5 to 10 degrees
above seasonal averages while overnight lows will hold in the 40s
and 50s.

The pattern does become more zonal over our region early next week
as a weak mid/upper level trough pushes inland over the Pacific
Northwest. However, dry weather conditions will prevail region-wide
with any precipitation remaining well to the north. In the longer
range, the GFS and ECMWF operational runs continue to show a cold
mid/upper level system dropping southward down the West Coast. If
this solution were to hold true, there would be the potential for
convective precipitation as a much colder air mass advects southward
over the region late next week. At this time, confidence remains low
but will be something worth monitoring in the coming days.

&& of 11:00 PM PDT Wednesday...For 06z tafs. VFR
conditions through most of the period as a predominately dry air
mass remains over the region. Satellite night imagery shows
stratus building offshore but weak E-W gradient should keep clouds
over the water. Winds light to calm overnight through the morning
hours. Onshore flow returning in the afternoon. Models suggest a
return of the marine layer Friday overnight.

Vicinity of KSFO...VFR with clear skies and stratus remaining
well offshore. Onshore winds around 7 kt, becoming light and
variable overnight. Return of onshore flow expected late Thursday
afternoon. Clear skies continuing, aside from some possible haze
if wildfire smoke from the Sierra reaches the area.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...VFR. Stratus along the Big Sur coast but
Monterey Bay is clear and is expected to remain so through the
overnight and morning. Light and variable winds continue
overnight into morning. Onshore flow returns Thursday afternoon.
Return of stratus possible late Thursday night.

&& of 03:04 AM PDT Thursday...Predominately light
northerly winds today. Winds increase gradually Friday and into
Saturday. Mixed seas will persist through the period with a pair
of northwest swell trains in addition to a lighter southerly





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NWS MTR Office Area Forecast Discussion