Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Francisco Bay area
832 am PDT Wednesday Sep 2 2015
Synopsis...dry weather will continue through next week.
Temperatures will continue to cool through Saturday as an upper
level trough digs southward into the Pacific northwest. Warmer and
drier conditions return over the weekend and early next week.
Discussion...as of 8:30 am PDT Wednesday...thanks to a much
deeper marine layer (now over 2000 feet) plus an onshore flow at
the surface...cloud cover is much more substantial today compared
to recent mornings.
Current forecast appears to be on track. No substantial updates
Previous discussion...generally quiet weather will continue for
the Bay area with seasonably cool weather through Saturday
followed by a gradual warm up over the Holiday weekend into early
Overnight satellite imagery continues to show a diffuse marine
layer trying to develop with patchy stratus along the coast and
locally inland. Sodars and the feet Ord profiler put the marine
inversion 1500-2000 feet this morning. Therefore...will keep the
low clouds and patchy fog this morning. Model guidance also
suggests patchy drizzle will also be possible. This maybe the
result of a passing shortwave trough currently visible on water
vapor to the SW of Point Conception.
The more notable weather item today will be the cooling
trend and slightly below normal temperatures...especially inland. The
aforementioned shortwave trough and a longwave trough over the
Pacific northwest will aid in dropping 850mb temperatures (by 3c) and lowering 500mb
heights over the region. The end result will be a cool down of 5
to 8 degrees over Tuesday/S maximum temperatures...especially away from the
coast. After the shortwave exits to the east later today...the
broad longwave trough will keep cool conditions in place as we
head into the Holiday weekend. Patchy night and morning clouds
will still be possible the next few days. Temperatures will
generally be in the 60s to near 70 along the coast and 70s to near
90 inland. Overnight lows will remain somewhat mild and mostly in
the 50s...a few pockets in the 40s is not out of the question.
By this weekend...a Pacific northwest low is forecast to swing through the
northern part of the state bringing a slight chance of rain well
north of the state. As the system exits high pressure will
develop inland with a thermal trough along the coast. Weak to
moderate offshore flow is forecast to develop Sunday into Labor
Day. The offshore flow will bring warmer temperatures with little
to no marine layer.
Still no sign of precipitation. The latest CPC 6-10 day calls for near
normal precipitation with above normal temperatures.
Aviation...as of 6:45 am PDT Wednesday...stratus continues to
fill in over the sfo Bay area and will take a while to clear out.
Forecast is for MVFR ceilings at sfo through 18z possibly as late as
Vicinity of ksfo...MVFR through 18-19z. West winds gusting to
25-27 knots through 06z.
Ksfo bridge approach...similar to ksfo.
Monterey Bay area terminals...stratus not as extensive this
morning due to some airmass mixing earlier this morning. As a
result ceilings should clear earlier. MVFR ceilings through 18z.
Marine...as of 4:50 am PDT Wednesday...an upper level trough off
the Pacific northwest will deepen and move inland on Saturday.
This will bring increasing northwest winds over the northern
waters beginning this afternoon and continuing through Sunday.
... Arena to pt Reyes 0-10 nm from 2 PM
Small Craft Advisory...pt Reyes to Pigeon pt 0-10 nm from 2 PM
Small Craft Advisory...pt Arena to Pigeon pt 10-60 nm from 2 PM
Small Craft Advisory...sf Bay from 2 PM
Public forecast: Bell/mm
aviation: west pi
marine: west pi
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