Scientific Forecaster Discussion
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Area forecast discussion
National Weather Service Sacramento California
320 am PST Mon Dec 9 2019
high pressure builds over the region on today, which will lead to
a period of dry conditions and near average temperatures early
this week. Precipitation chances return to areas north of
Sacramento on Wednesday with more widespread precipitation
expected late in the week.
skies have cleared as the trough continues to south of the area.
Infrared difference imagery shows an extensive area of dense fog along
the eastern edge of the Central Valley extending from about
Oroville southward through the San Joaquin Valley. Light northerly
flow over the western half of the Sacramento Valley has so far
prevented the fog from shifting further to the west. Current
temperatures are considerably cooler across most of the area
compared to 24 hours ago and range from the mid 20s in the colder
mountain valleys to the 40s to around 50 in the Central Valley.
Heights will continue to build today as an offshore ridge moves
through. This ensures a period of dry weather to start the week
with near average temperatures. Valley fog is expected to mix out
by mid to late morning.
The ridge axis crosses the state early Tuesday before a weak
shortwave moves through Tuesday evening into early Wednesday.
Moisture seems to be meager so precipitation will be light,
mainly focused over the northern Sacramento Valley and into the
higher terrain. Any snowfall will lead to little to no
Ridge briefly rebounds Wednesday, then a wide swath of deep
moisture will approach norcal beginning late Wednesday. Overall
lift appears to be rather weak, but increasing warm-advection will
likely result in some light precipitation across the northern half
of the forecast area and northern Sierra Nevada. Snow levels
expected to be over 8k ft, so little to no winter travel impacts
Extended discussion (friday through monday)...
the extended forecast calls for zonal flow over the area. A weak
shortwave disturbance will slide over US on Thursday, dragging a
cold front into the region. The chance for showers remains in the
forecast at this time, keeping the bulk of any precip over the
mountainous regions. A more vigorous trough will dig into the area
on Friday. Ensembles remain in good agreement with pushing a cold
front south through the area Friday night into Saturday morning.
This will be the best chances for widespread precip activity for
interior norcal, with the chance for showers lingering throughout
the day on Saturday. Snow levels start off fairly high, but once
the front passes through we could see accumulating snow at pass
level on Saturday. By Sunday, a shortwave ridge builds over the
area which will bring drier weather through Monday.
a tongue of fog has developed along the eastern side of the
valley, bringing IFR and LIFR conditions to several taf sites.
Farther north and west of this, light north winds are prevalent
which has kept fog development at Bay. The fog is expected to
linger throughout most of the morning, with VFR conditions
forecast by early afternoon.
dense fog advisory until 10 am PST this morning for central
Sacramento Valley-motherlode-northern San Joaquin Valley-
southern Sacramento Valley.