Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Francisco Bay area
1020 PM PDT Friday may 22 2015
Synopsis...low pressure will gradually exit the area to the east
over the next few days...resulting in a slight warming trend this
weekend. Patchy drizzle is possible in coastal areas late tonight
and Sunday morning...especially south of San Francisco.
Otherwise...dry weather is forecast through the weekend and well
into next week.
Discussion...as of 8:50 PM PDT Friday...an upper trough moving to
the east of California produced considerable thunderstorm
activity over Nevada and eastern California today. The low was too
far east to generate anything more than a few afternoon cumulus
build-ups over our area.
The longwave trough position will continue to shift eastward over
the next few days. However...a shortwave trough is forecast to
traverse California from northwest to southeast on Saturday...triggering another round
of convection over the Sierra Nevada...and perhaps as close to our
forecast area as Lake County. Considerable low level moisture
remains across our area...and as the shortwave approaches from the
northwest later tonight...it may enhance onshore flow enough to
produce areas of drizzle in coastal areas late tonight and
Saturday morning...particularly in coastal areas south of the
The general trend over the weekend will be for gradual warming and
more widespread clearing as the longwave trough continues to move
to the east and an upper ridge over the eastern Pacific edges closer
to the West Coast. Temperatures should climb to near normal by Sunday.
The warming trend will probably stall on Monday and Tuesday as an
upper low settles into the Pacific northwest and temporarily weakens the
ridge. Warming is then likely to resume during the second half of
next week when the models agree that the upper ridge will re-build
along the West Coast. But temperatures are not expected to warm
more than a few degrees above normal...and relatively cool
conditions will persist near the coast due to continued onshore
Aviation...as of 10:07 PM PDT Friday...not much change from the
previous discussion. VFR/MVFR ceilings continue this evening with a
mix of cloud layers around the region. Low level moisture will
linger into tonight with a few patches of drizzle becoming
possible very late at night. An upper level high over the epac
will slowly edge in from the west during the period. Subsidence
associated with the high will result in a gradual warming within
the lower levels causing the marine layer inversion to become re-
established over the Holiday weekend. By late Sunday night into
Monday 850 mb level temperatures are predicted to reach near 15c.
Vicinity of ksfo...MVFR ceilings. Gusty westerly winds are likely to
return on Saturday.
Ksfo bridge approach...similar to ksfo.
Monterey Bay area terminals...VFR/MVFR gradually decreasing to IFR
very late. Patchy drizzle possible late. Clearing returns by late
Marine...as of 10:02 PM PDT Friday...high pressure is strengthening
over the coastal waters in the wake of a sluggish upper low. This
pattern is leading to generally deteriorating conditions from
increasing northwest winds and building seas. Unfavorable winds
and seas are forecast persist through the weekend before beginning
to taper off early next week.
Overall forecast looks good. Minor adjustments made to the forecast
winds for the San Francisco Bay waters north of the Bay Bridge
Saturday afternoon and evening....decided to add a Small Craft
Advisory. Bumped up forecast winds a little for Sunday...but may
not be enough. Later shifts may need to consider adding a Small
Craft Advisory in for later Sunday.
... Arena to pt Reyes 10-60 nm
Small Craft Advisory...pt Reyes to Pigeon pt 10-60 nm
Small Craft Advisory...pt Arena to pt Reyes 0-10 nm
Small Craft Advisory...pt Reyes to Pigeon pt 0-10 nm
Public forecast: dykema
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