Local Area Forecast Discussion

FXUS66 KSTO 201117

Area Forecast Discussion
National Weather Service Sacramento CA
317 AM PST Sat Jan 20 2018

Sunny and Dry Saturday followed by an active weather pattern. The
first storm will arrive Sunday through Monday, followed by
another mid week.



Main forecast concerns for the short term period are a series of
storms that will bring widespread rain and mountain snow to
northern California.

Water vapor imagery shows the trough base associated with the last
system passing over California with a more stable shortwave ridge
of high pressure sliding into the forecast area. This dry and
stable feature will bring clearing skies and cool temperatures
this morning, with a nice seasonable day ahead for today with high
temperatures near normal. Breezy winds are expected this afternoon
as pressure gradient exists through Sunday.

The next weather making system arrives Sunday afternoon/evening
and will bring more rounds of precipitation to northern
California. 850-700 MB thickness charts indicate a good amount of
cold air in place from the last passing trough, which will lead to
lower snow levels for the impending system. Snow can be expected
to as low as between 2000 and 3000 feet, but the main
accumulations will be above 4000 feet with snow amounts ranging
between 3 to 12 inches for the mountains from Sunday night into
Monday afternoon.

Light precipitation will continue Tuesday before the next system
arrives into Wednesday. Early projections are that this system
will bring heavy mountain snow and moderate rainfall to the



Mid range models in fairly good agreement in bringing a Pacific
frontal system into northwest California Wednesday morning then
through the north state during the day on Wednesday. 00z runs
slowed this system down about 6 hours but 06z run sped it back up
again. This system looks to be of moderate strength with
moderate snow levels between about 4500 and 5500 feet. Main
frontal band moves into the Sierra Thursday night with several
inches of snowfall expected for likely travel impacts. Main upper
trough pushes through the region on Thursday with cold air behind
the front bringing snow levels down to 2500 to 3500 feet.
Instability will keep showers going through the day with daytime
highs remaining a little below normal. Upper ridge begins to build
over the eastern Pacific and west coast on Friday pushing the
shower threat northward to north of about Red Bluff. Upper ridge
continues to amplify on Saturday bringing daytime temperatures up
to a few degrees above normal. Most of the CWA should remain dry
next Saturday if current models hold but a shortwave slipping over
the ridge could bring a few showers over the mountains of
northern Shasta county.



Areas IFR/MVFR visibility and ceilings southern Sacramento valley
and northern San Joaquin valleys through 18z. Otherwise VFR.
Northwest to northeast winds up to about 15 mph.


Winter Storm Watch from Sunday morning through Monday morning
for Mountains Southwestern Shasta County to Northern Lake County-
Shasta Lake Area / Northern Shasta County-Western Plumas
County/Lassen Park.



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