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Area forecast discussion 
National Weather Service San Francisco Bay area
1016 PM PDT Wednesday may 27 2015

Synopsis...high pressure building along the West Coast will
result in a modest warming trend through Saturday...most apparent
inland. Temperatures will then cool Sunday into early next week
as a weak upper level trough approaches the coast. There is a slight
chance of showers across the North Bay from late Sunday into
Monday...but most locations are expected to remain dry through the
forecast period.

&&

Discussion...as of 8:55 PM PDT Wednesday...although the marine
layer compressed slightly today as the upper ridge offshore edged
closer to the coast...it has held relatively deep at 2000
feet. And...onshore surface pressure gradients have remained
relatively robust. Consequently...temperatures today were below
normal yet again...a trend that has continued unabated for nearly
the entire month of may.

Evening water vapor satellite imagery shows the upper ridge just
offshore...centered along 128w...moving slowly to the east. The
models continue to show the ridge shifting eastward over California over the
next two days and also amplifying a bit. Inland areas should see
temperatures finally climb to near normal tomorrow and then above
normal by Friday and Saturday. Meanwhile...a stubborn onshore flow
will prevent coastal areas from warming much. The marine layer
will likely compress to about 1000 feet by week's end...which will
limit the amount of night and morning low clouds across inland
areas...and also allow for more afternoon clearing near the ocean.
But some coastal spots will likely remain mired in low clouds and
fog through the end of the week and into the weekend. With a
compressed marine layer...fog will become more of an issue in
coastal areas and we will likely see some patchy dense fog near
the ocean by week's end.

The ridge is forecast to gradually move off to our east over the
weekend. Saturday will be the final warm day for inland areas before
an approaching upper trough triggers a rapid deepening in the
marine layer by Saturday night and a strong inland push of marine
air and associated cooling by Sunday. In addition...most models
indicate this weather system may produce some light rain across
the northern part of our forecast area from late Sunday afternoon
through Sunday night. The 12z European model (ecmwf) is the most bullish with
precipitation...and also fastest...dropping measurable rain as far south
as San Mateo County by late Sunday afternoon. Depending on what
the 00z models show...we may need to increase probability of precipitation across the
North Bay on Sunday afternoon and Sunday night...and also extend
probability of precipitation a bit farther south. The incoming trough will also likely
generate coastal drizzle along our entire coast on Saturday night
and Sunday. Inland temperatures are expected to cool by as much
as ten degrees from Saturday into Sunday and then another 5-10
degrees by Monday.

&&

Aviation...as of 9:57 PM PDT Wednesday...coastal low clouds will
continue to move inland tonight. The marine layer has compressed
more and is roughly 1500-1700 feet deep. IFR coverage may be a bit
more extensive tonight because of the compressed marine layer. The
upper level ridge over the area will gradually strengthen during
the period.

Vicinity of ksfo...westerly winds will continue to usher in additional
stratus overnight.

Ksfo bridge approach...similar to ksfo.

Monterey Bay area terminals...IFR ceilings tonight. Clearing is likely
by late morning Thursday.

&&

Marine...as of 9:51 PM PDT Wednesday...high pressure will reside
over the eastern Pacific during the period. Coastal low clouds and
patchy fog will continue to move inland overnight on onshore
winds. Expect locally gusty west winds over the San Francisco Bay
waters otherwise light to occasionally moderate northwest winds
over the coastal waters.

&&

Mtr watches/warnings/advisories...
...

$$

Public forecast: dykema
aviation/marine: canepa

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