Scientific Forecaster Discussion
fxus66 kmtr 232032
Area forecast discussion
National Weather Service San Francisco Bay area
132 PM PDT Mon Apr 23 2018
Synopsis...dry and seasonably warm conditions will continue
today. A cooling trend is forecast from Tuesday through the end of
the week as an area of low pressure offshore slowly approaches the
coast. This low pressure may produce scattered showers from late
Friday into Saturday, mainly across the north.
Discussion...as of 01:27 PM PDT Monday...sunny skies prevail
across most of the Bay area this afternoon. The sunshine and light
winds have allowed for well above normal temperatures away from
the coast. Afternoon temps will likely top out in the 70s to mid
80s. Just like during the Summer months, different story at the
coast. Weak pressure gradients north-S and east-west have kept low clouds
along the coast, mainly San Mateo coast southward. Made some late
day adjust to the forecast to lower temps around the Monterey Bay
and keep clouds through the afternoon.
Otherwise, only minor tweaks were made to the forecast. High
pressure will continue to weaken as an upper low currently
spinning off the West Coast slowly tracks eastward. Night and
morning low clouds will continue through Wednesday and possibly
mix out completely by Thursday/Friday. The lower 500mb heights and
cooler 850mb temps will translate to a slight downward trend in
daytime high temperatures. Temps by Wednesday will be closer to
normal (60s coast, 70s to lower 80s inland) and possibly below
normal by Thursday (60s/70s).
The track of upper lows are always difficult to forecast,
especially in the medium to long range. The 12z model run didn't
shed any New Light on the rain potential Friday into Saturday.
Model consensus brings an upper low into far norcal with some
precip possible across the North Bay. Confidence is low and will
maintain the slight chc of showers sf Bay northward. Quantitative precipitation forecast looks to
be minimal at this point.
Aviation...as of 10:32 am PDT Monday...for 18z tafs...stratus
from earlier this morning has cleared away from the Monterey Bay
terminals and VFR conditions are expected to persist through the
forecast period for most sites. Mainly clear skies today with some
high clouds. Light winds through the rest of the morning becoming
onshore this afternoon at 10-15 kt. Stratus is expected to return
again tonight into tomorrow morning around the Monterey Bay with
some low cloud development possible around the sf Bay region.
Vicinity of ksfo...VFR conditions will prevail through the period
with mainly high clouds. Light winds will increase to around 10
to 20 kt after 21z this afternoon. Slight chance of some low cloud
development late tonight.
Sfo bridge approach...similar to ksfo.
Monterey Bay terminals...IFR/LIFR cigs have retreated back to the
Bay and VFR conditions will prevail through tonight. IFR/LIFR cigs
are expected once again tonight into tomorrow morning. Generally
light winds throughout the day with onshore winds this afternoon,
locally higher at ksns.
Marine...as of 08:16 am PDT Monday...expect diminishing
northwesterly winds through most of the week as the gradient
between weakening high pressure to the northwest and a trough over
the eastern Pacific continues to decrease. Light to moderate seas
will prevail through the forecast period.
Public forecast: mm
Visit US at www.Weather.Gov/sanfrancisco