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FXUS66 KMTR 220123

Area Forecast Discussion
National Weather Service San Francisco Bay Area
523 PM PST Thu Nov 21 2019

.SYNOPSIS...Seasonable temperatures with dry weather conditions
will persist through the upcoming weekend. Colder conditions and
unsettled weather develop over the region as early as Tuesday of
next week and continue through Thanksgiving likely impacting
holiday travel. 

&& of 02:09 PM PST Thursday...Under mostly clear 
sky conditions (aside from low clouds over Santa Cruz County in 
response to moist, southerly flow), temperatures have warmed into 
the lower/middle 60s with 40s to 50s in the region's higher 
elevations. A ridge of high pressure will nose into the northern 
portion of the state and result in a very gradual warming trend 
into this upcoming weekend. This will translate to daytime highs 
in the 60s to lower 70s across the warmest interior locations. 
Overnight/morning temperatures will cool into the 40s for most 
while middle/upper 30s will be common in the region's colder 
locations (interior valleys and higher elevations). 

A shift in the weather pattern is forecast to occur Monday into 
Tuesday of next week with the potential for northerly winds and 
drying conditions, especially in the ridges and peaks across the 
region. Previously, the forecast models were in good agreement 
with a pattern that would have resulted in a widespread, moderate 
offshore wind event and associated critically dry air mass. 
However, the models have trended away from this solution during 
the past 24 hours or so. Regardless, fuels over the region remain 
unseasonably dry given the lack of widespread rainfall so far this
season. Thus, while the potential for critical fire weather 
conditions appears to be diminishing, we will closely monitor in 
the coming days. 

On the other hand, confidence has been increasing with respect to
the development of an unsettled weather pattern mid/late next
week. While details remain difficult to nail down at this point,
the forecast models indicate a weather system dropping southward
across the region as early as Tuesday of next week with the
potential for another passing system in the Wednesday to Thursday
timeframe. This colder air mass will also cause daytime
temperatures to cool into the 50s for most urban areas through
much of the week with overnight lows in the 30s and 40s.
Regardless of the details at this time, this pattern will likely
result in adverse travel conditions for those traveling around and
outside of the San Francisco Bay Area and Central Coast during the
holiday week. 

&& of 5:23 PM PST Thursday...The atmosphere is well 
mixed and absent of a marine layer inversion. Hazy conditions due
to evaporated salt particles (salt nuclei) from recent wind swept
seas and an increase in water vapor is continuing to form patches
of low clouds from the San Mateo Coast south to the Big Sur Coast.
With onset of night-time radiational cooling off cloud tops likely 
enhancing low cloud development as well. The 00 tafs continue with
idea of MVFR-VFR with patchy low clouds tonight and Friday morning.
VLIFR-IFR in fog patches are also possible over inland valleys 
tonight and Friday morning. VFR prevailing by Friday afternoon 
under diurnal mixing.

Vicinity of KSFO...VFR though hazy surface visibility, SW wind near
10 knots shifting to light S wind by late evening. Light NE wind 
Friday morning shifting to W near 10 knots Friday afternoon.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...VFR, though it could be borderline MVFR 
visibility at times due to haze. Recent satellite imagery and
surface observations leaning toward MVFR cloud development a
little sooner than advertised, may need to amend for sooner
development of low clouds. MVFR tonight, IFR ceilings/vsbys possible
later tonight mainly due to preexisting hazy conditions conducive
to low cloud development. VFR likely returning by late Friday 
morning and afternoon.

&& of 4:07 PM PST Thursday...Surface low pressure off 
the coast will bring light east to southeast winds through Friday.
Winds will switch to north to northwest late on Friday. A long-
period northwest swell will build on Friday and continue through 
the weekend. Swell heights will increase to become hazardous for 
small crafts over the outer waters. Periods of gusty winds, 
increased seas, and rain are likely next week.






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