Scientific Forecaster Discussion
fxus66 kmtr 260542
Area forecast discussion
National Weather Service San Francisco Bay area
1042 PM PDT Sat Mar 25 2017
Synopsis...partly cloudy and dry through midday Sunday. The next
weak cold front moves into the North Bay Sunday afternoon with
light rain spreading southward through the remainder of the Bay
area and central coast Sunday evening before ending by sunrise
Monday morning. Cool and breezy Monday afternoon, then high
pressure builds with a warming and drying trend through midweek.
Likely cooler again later in the week with breezy conditions.
Discussion...as of 8:55 PM PDT Saturday...Saturday was a dry day
in between weather systems. Afternoon highs were mostly in the
lower to mid 60s and generally a degree or two cooler than normal.
Evening satellite imagery shows a storm system offshore to the
west of the Pacific northwest and far northern California. This
system currently has a pretty good moisture tap with precipitable
water values up near 1.5 inches. The models agree that most of
the moisture and energy with this system will move inland to our
north on Sunday. However, a shortwave trough currently seen on
water vapor satellite imagery out near 45n/155w is forecast to
track to the east-southeast and drive the tail end of a cold front through
our area Sunday afternoon and evening. There is generally good
model agreement both in terms of precipitation timing and
rainfall amounts with this system. Rain is expected to begin
pushing into northwest Sonoma County by midday Sunday and then
across the rest of the North Bay during the afternoon hours. Rain
will then spread across the rest of the sf Bay area and Monterey
Bay area late Sunday afternoon and evening. Rainfall amounts are
forecast to range form 0.10 to 0.50" in the North Bay, with
amounts of less than a tenth of an inch expected for areas south
and east of the Golden Gate.
Showers will taper off Sunday night with only a few showers
possibly lingering into Monday morning. Otherwise, Monday is
forecast to be a dry day, with brisk northwest winds expected
during the afternoon and evening, particularly near the coast.
Tuesday and Wednesday are forecast to be dry with a warming trend
as an upper level ridge builds over California. By Wednesday high
temperatures are expected to be mostly in the upper 60s and 70s.
Both the GFS and European model (ecmwf) are indicating that an inside slider will
sweep across northeast California late Wednesday night and
Thursday. The 18z GFS, and most 12z GFS ensemble members, track
this system too far to our north and east to generate
precipitation in our area. But the 12z European model (ecmwf) has a more westerly
trajectory and develops light rain across northern and eastern
portions of our area on Thursday. Both model solutions would
result in cooler and blustery conditions by late Thursday with
locally strong north to northwest winds.
Aviation...as of 10:42 PM PDT Saturday...a few locations along
the immediate coastline are reporting MVFR cigs this evening
otherwise it's VFR. Winds remain onshore through tonight the
pressure gradient then becoming near neutral sfo-SAC on Sunday.
Light rain with the next weather system reaches the North Bay
beginning late Sunday morning, light rain spreads southeast over
the remainder of the area through Sunday afternoon and evening.
Vicinity of ksfo...VFR. Tempo MVFR cig 11z-15z Sunday. Light rain is
predicted to begin early Sunday evening.
Sfo bridge approach...same as ksfo.
Monterey Bay terminals...VFR. Onshore winds becoming light and variable
late tonight then southerly on Sunday. Light rain likely beginning
mid-late Sunday evening.
Marine...as of 10:24 PM PDT Saturday...generally light winds and
moderate seas across the waters through tonight. Gusty winds along
the inner waters south of Point Sur will diminish through tonight.
On Sunday, winds over the waters will increase and turn southerly
as a weak cold front approaches.
... Pinos to pt Piedras Blancas 0-10 nm until 2 am
Public forecast: dykema
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