Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Sacramento California
300 PM PDT Thursday Sep 29 2016
significant cooling trend through the weekend with daytime highs
15 to 25 degrees below normal Sunday. Chance of showers and
isolated thunderstorms Sunday into Monday. Drier Tuesday into
Thursday with a warming trend.
afternoon temperatures running upwards of 12 degrees cooler than
24 hours ago as large upper low west of b.C. Digs and approaches
the West Coast. Lav MOS guidance has trended a little weaker with
the Delta breeze tonight but still expecting a moderately strong
flow overnight with the potential for some patchy stratus in the
Sacramento area Friday morning.
Moisture starved surface front pushes into northwest California tonight
into Friday with main impact being some breezy to windy conditions
ahead of boundary over interior norcal. Additional cooling will
result, with Max temps tomorrow forecast mostly in the upper 70s
to around 80 with upper 50s to mid 70s for the mountains and
Frontolysis occurs along baroclinic zone as it slides south Friday
night, while associated upper low weakens to trough and swings
inland Saturday. Cooling trend continues Saturday with some breezy
conditions. Secondary colder, more dynamic, low is progged to drop
down the base of long wave and track into norcal Sunday. Models
continue to show widespread precip with this feature over interior
norcal. GFS maintains some increased afternoon cape over the County Warning Area
to support deep moist convection. Best instability currently
depicted over the northern and central Sacramento Valley and along
the eastern foothills and motherlode. 700 mb temps cool to around
-5 to -6 deg c Sunday afternoon with 1000-500 mb thicknesses from
around 541-544 dm over the Shasta and coastal mountains to 545-550
dm over the Sierra Nevada. This suggest snow levels could lower to
around 5500 feet in the north to 6500 feet over the Sierra later
Sunday. Although precipitation is expected to be scattered and highly
variable amounts given the showery pattern, potential exists for
several inches of accumulation at pass levels. Sunday's high
temperatures forecast to be 15 to 25 degrees below normal with mid
60s to lower 70s for the Central Valley. Potential exists for some
new record lowest maximum temperatures to be set Sunday.
Extended discussion (monday through thursday)
the upper level low quickly shifts east into the Great Basin by
Monday. Cool northerly flow aloft takes hold across the region on
Monday, but there still may be enough residual moisture for a few
showers. Overnight temperatures will likely be on the cool side
for a few nights, with 40s across the Central Valley and 20s
possible over higher terrain.
Drier weather is expected by the middle of next week as the
eastern Pacific Ridge rebuilds into California. High temperatures
are expected to warm back to near normal levels, though overnight
lows may remain on the cooler side.
VFR conditions across valley terminals the next 24 hours.
Southerly onshore wind continue across the valley through Friday,
with local gusts up to 25 kt during the afternoon. Near the Delta
and over higher terrain...higher gusts are possible.