Special Weather Statement, NWS Sacramento, CA

Area Forecast Discussion
National Weather Service Sacramento CA
441 AM PDT Tue Mar 21 2017

.Synopsis...
A series of weather systems will bring cooler and more unsettled
weather to the region this week. Chance of thunderstorms today
with gusty winds and small hail.

&&

.Discussion...
Upper trough centered off the West Coast with surface cold front
approaching the NorCal coast early this morning. Plenty of showers
continue across the region with breezy southerly winds and mild
temperatures. Current temperatures are in the upper 30s and 40s in
the mountains with 50s elsewhere.

Mild airmass lies across the region ahead of the front with radar
profilers indicating the snow level is generally around 7-8K feet.
Precipitation fell as snow earlier in the night over Donner Pass
but has changed back to rain, so little to no travel impacts are
expected until around midday when cooler air will begin to make it
into the northern Sierra.

Primary weather concern for today will be extent and severity of
deep convection expected to develop in the Central Valley during
the midday hours as the short-wave (now inside 130W) moves
onshore. Still lots of questions to whether we'll see a whole lot
of clearing this morning allowing for greater destabilization of
the boundary layer.

High-res models continue to point toward the 18Z-22Z time-frame
as most likely for thunderstorm development from Butte County
southward. They also quickly evolve cells to the north of
Sacramento into more linear orientation while maintaining more
discrete cells across the northern San Joaquin Valley. Primary
concern with stronger storms will be copius amounts of small hail
along with gusty winds though a brief tornado or two cannot be
ruled out, especially over the northern San Joaquin Valley where
it looks like the best combo of instability and low-level shear
will be present. We'll continue to monitor.

Showery precip continues tonight and Wednesday as the upper trough
moves overhead. Snow will continue in the mountains with snow
levels lowering to 4-5K feet. There may be some travel impacts at
times through the passes as around 3-6 inches of snowfall
accumulation is expected for Donner Pass and Echo Summit.

Short-wave ridging briefly builds in for Thursday with a break in
precipitation across most of the area and a bit of sunshine ahead
of the next approaching system for the end of the week!

&&

.EXTENDED DISCUSSION (Saturday THROUGH Tuesday)
Stormy pattern expected to continue next weekend as an upper
trough slides across the region. Temperatures will be about 5 to
10 degrees below normal with Valley rain and snow for elevations
above 3500 feet. An upper level ridge will build on Monday, which
will bring a return of mostly dry weather for the valley and
warming temperatures. Chances for rain are possible Monday for the
higher terrain.

&&

.AVIATION...
More widespread precipitation is expected today with increasing
MVFR/IFR conditions, and southerly winds with gusts 20 to 30 knots
in the valley after 12z. These conditions will continue through
this afternoon with chances for thunderstorms. VFR conditions
expected beyond the late afternoon.

&&

.STO WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from midnight tonight to 6 PM PDT
Wednesday for Western Plumas County/Lassen Park.

Winter Weather Advisory until 6 PM PDT Wednesday for West Slope
Northern Sierra Nevada.

&&

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