Scientific Forecaster Discussion
fxus66 kmtr 210517
Area forecast discussion
National Weather Service San Francisco Bay area
1017 PM PDT sun Aug 20 2017
Synopsis...cooling will continue early this week as an upper
trough of low pressure becomes nearly stationary over the eastern
Pacific. Coastal areas will see little in the way of change with
continued night and morning low clouds and patchy fog.
Discussion...as of 08:23 PM PDT Sunday...the forecast remains on
track. The evening update only included some minor tweaks to temps
and sky. The most significant of the minor tweaks were to the sky
cover over the East Bay this evening and tonight. Instead of
clear, they have been made partly cloudy. This is a result of the
easterly flow aloft and the storms over the sierras today. Some of
the blow off is heading toward East Bay which necessitated an
increase in cloud cover for the night. Looking at the convective
parameters, it looks like all the energy has been used up and
should not pose any threat of rain or lightning for the area. That
said, we are 24/7/365 and watch the radar when anything is
happening in our neighboring areas. If what is forecast changes,
we will be on it. Have a great night and enjoy our partial eclipse
tomorrow. Be eye safe, don't stare at the sun.
Previous discussion...as of 2:00 PM PDT Sunday...clouds have burned-off
from most of our County Warning Area although still have a few patches near and
along the coast. Temperatures have been running close to
yeterday's numbers with most locations in the 60s and 70s at the
coast with 70s and 80s inland. Satellite shows widspread clouds
off the coast, and with the marine layer still over 2000 feet plus
the onshore gradient still around 2 mb west-to-east clouds will
return back to most of the same locations overnight.
For those planning on watching the eclipse (remember to get the
correct lenses) tomorrow morning, still looks like the farther
inland you are the better shot at seeing it starting at 9 am. The
big question remains how quickly the clouds will dissipate through
the morning hours. Feeling right now is the South Bay through
Santa Clara Valley will see mostly clear conditions around the
start while farther to the north stretching from San Francisco to
Oakland there will likely be clouds at first. However, the hope if
they will dissipate during the hour with good viewing before the
peak time. Most of our coastal locations will likely remain cloudy
Outside of the eclipse, not much to talk about as we are going to
continue to see overnight clouds, clearing during the day, and
temperatures remaining cool the first part of the week followed by
a modest warming trend going into the weekend as a ridge of high
pressure rebuilds into our region. No chance of rain.
Aviation...as of 10:17 PM PDT Sunday...a weak surface low is 100
miles SW of the Monterey peninsula and its mid level counterpart
is over The Channel islands; a drying south wind cleared away a
fair amount of stratus and fog along the immediate coast during
the afternoon. Stratus and fog is expected to redevelop tonight.
Wildfire smoke may present slant range visibility reductions at
sunrise Monday morning, mainly inland where there are the best
chances for no stratus or fog. Residual mid-upper level moisture
from convection earlier today over the Sierra Nevada has reached
the Bay area. Stratus and fog redevelops tonight reaching into the
North Bay more quickly and extensively than it does over to the
East Bay and South Bay areas including the Bay Side of the sf
peninsula. Stratus should also fill in slowly along the north
Warming 925 mb level temperatures results in reinforcement and possibly
some compression of the marine layer depth tonight, thus IFR cigs and
vsbys becoming increasingly likely tonight into Monday morning. VFR
should return by mid-late Monday morning with the last places to clear
out being the North Bay and along the immediate coast of Santa Cruz
and San Mateo counties.
Vicinity of ksfo...west wind near 10 knots this evening. VFR likely
holding much of the night, tempo IFR forecast 12z-16z Monday morning.
VFR returns Monday. Hazy due to wildfire smoke affecting slant range
visibilities Monday morning sunrise.
Sfo bridge approach...similar to ksfo.
Monterey Bay terminals...MVFR/IFR cigs redevelop this evening. Hazy
conditions due to wildfire smoke possibly affecting slant range
visibilities Monday morning sunrise. IFR cigs tonight and Monday
morning til approx 17z.
Eclipse...here are the times for the start, peak, and end of the
eclipse for Monday morning. The percent of obscuration for each
location is also listed.
... Rosa...San Francisco...Oakland...San Jose...Monterey
Marine...as of 9:35 PM PDT Sunday...northwest winds over the
outer coastal waters will continue to subside this evening and
overnight. Breezy from the Golden Gate bridge to Angel Island
will dissipate later this evening. Winds are forecast to remain
generally light for both Monday and Tuesday.
Public forecast: Bell/bfg
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