Scientific Forecaster Discussion
fxus66 kmtr 252045
Area forecast discussion
National Weather Service San Francisco Bay area
145 PM PDT Wed Apr 25 2018
Synopsis...cool, Summer likely conditions will persist over the
region through Thursday with additional cooling expected Friday
into the upcoming weekend. There will be a slight chance of
showers Friday night into Saturday for the far northern portions
of the North Bay as the upper level system responsible for the
cool down pushes inland to our north. Dry conditions along with a
slight warming trend appears likely early next week.
Discussion...as of 01:45 PM PDT Wednesday...the marine layer
again impacted the region this morning with low clouds slow to
burn-off through the late morning. Temperatures range from the
upper 50s at the coast to lower 70s in our warmer inland locations
as well as higher elevations above the 1,800 foot marine layer.
Looking for similar conditions tonight into Thursday ahead of an
approaching mid/upper level trough.
Temperatures will trend a few degrees cooler on Friday and continue
to be below seasonal averages into the upcoming weekend in response
to the mid/upper level trough pushing inland. The core of the upper
level low will then push into the Pacific northwest and northern
California late Friday into Saturday and bring a slight chance of
showers. Rain showers may develop as far south as the northern
portions of the North Bay during this time frame. However,
widespread rainfall is unlikely and most locations will remain dry,
especially south of the Golden Gate bridge.
A slight warming trend is then likely early next week as the trough
axis shifts inland and a ridge of high pressure develops over the
eastern Pacific. However, the ridge is forecast to stay far enough
offshore to prevent significant warming. Ongoing dry weather
conditions are also expected in the extended forecast period.
Aviation...as of 10:37 am PDT Wednesday for 18z tafs. Low
ceilings impacted all taf terminals this morning with widespread
LIFR/IFR/MVFR conditions. Visible satellite shows the gradual
eroding/mixing-out of the stratus as of the 18z taf publication
and think most terminals will transition to VFR conditions in the
next hour or so. The Fort Ord profiler indicates the marine layer
as gradually increased over the past 12 hours from about 1,500 ft
to 2,000 ft deep, likely in response to the approaching upper
level low. More of the same is expected this tonight with low
clouds again for Thursday morning.
Vicinity of ksfo...transitioning from MVFR to VFR conditions at
the taf publication time as this morning's stratus mixes out.
West to northwest winds are expected this afternoon around 15 kt.
The main concern turns to what is going to happen this
evening/overnight with the stratus return. At this point think
we'll see broken conditions return sometime after 6-7z Thursday, or
several hours earlier than this morning. Will continue to monitor
and update the taf accordingly.
Sfo bridge approach...similar to ksfo.
Monterey Bay terminals...MVFR/IFR conditions at kmry until late
morning as stratus lingers over the terminal. There is a non-zero
chance we could see the low clouds persist into the afternoon, but
confidence is too low to adjust the taf as so. Expect low clouds
to return sometime in the late afternoon/evening hours with
overcast conditions again for tomorrow morning.
Marine...as of 10:21 am PDT Wednesday...generally light to
locally moderate west to northwest winds will continue through
the week. Light to moderate seas will also persist through the
forecast period with a mixed south and northwest swell developing
late in the week.
Public forecast: rgass
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