109
FXUS66 KSTO 251032
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
332 AM PDT Mon Mar 25 2019

.SYNOPSIS...
A slow moving storm system arrives today. A stronger storm is
possible Tuesday night and Wednesday. Afternoon thunderstorms
will be possible Tuesday and Wednesday. Unsettled weather will
continue on Thursday with showers and possible thunderstorms
before the return to dry weather.

&&

.DISCUSSION...
Radar indicates just a few light pre-frontal showers across the
northern half of the forecast area early this morning. Otherwise,
mid and high clouds cover much of the region. Current temperatures
are mild and range from the 20s and 30s in the mountains to the
mid 40s to mid 50s across the Central Valley.

Satellite imagery shows the large closed low off the coast,
centered along 140W just north of 40N, and moving only very
slowly. Heavier precipitation along the front offshore is mainly
moving northward as the eastward progression has nearly stalled.
Have continued the previous trend and slowed the onset of
precipitation spreading inland later today, especially across the
southern half of the forecast area. It will likely be this evening
before any meaningful precipitation spreads into the northern
Sierra, and have downgraded the warning for that area to an
advisory.

Some residual light precipitation expected to linger Tuesday as
warm-advection increases ahead of the next system. An isolated
thunderstorm or two may develop across the northern Sacramento
Valley in the afternoon.

The next system moves in Tuesday night into early Wednesday and is
expected to bring heavier snowfall to the mountains along with
lower snow levels. The system will be more convective with steeper
mid-level lapse rates enhancing snowfall rates over the mountains.
Sufficient shear and instability appears possible for stronger
thunderstorms across the area Wednesday afternoon.

Cyclonic flow with embedded short-waves will keep a threat of
showers across the area on Thursday.

&&

.EXTENDED DISCUSSION (Friday THROUGH Monday)
Lingering showers possible Friday, mainly over the mountains of
Shasta and Western Plumas counties. Drier weather expected
Saturday as upper level ridging moves through Interior NorCal. By
Sunday, GFS, GEFS, NAEFS, suggest probability for some light
precip on the increase as short wave trough approaches. POP looks
to be more widespread Monday over CWA with additional waves,
however overall precip amounts continue to look light attm.

&&

.AVIATION...
Dtrtg conds ovr Intr NorCal this mrng as Pac fnt sprds precip
inld. In Cntrl Vly, areas MVFR/IFR conds sprdg fm NW to SE aft 15z
tda with fnt bcmg lcl MVFR/IFR aft 06z Tue. Shasta/Cstl mtns
wdsprd MVFR with lcl IFR/LIFR aft 12z til arnd 03z Tue. Ern fthls
and Wrn Plumas mtns/Nrn Siernev wdsprd MVFR/IFR with lcl LIFR aft
18z bcmg areas MVFR/IFR with lcl LIFR aft 13z Tue. Sn lvls arnd
040 amsl in Shasta mtns, 040-050 amsl ovr Cstl rng, and 050-060
amsl in Wrn Plumas/Nrn Siernev. Lcl Sly sfc wnd gsts to 25 kts in
Cntrl Vly btwn 18z-03z with fropa. Areas S-SW sfc wnd gsts up to
45 kts or gtr poss ovr hyr mtn trrn nxt 24 hrs.

&&

.STO WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning from 9 AM this morning to 11 AM PDT Tuesday
for Western Plumas County/Lassen Park.

Winter Weather Advisory from 7 PM this evening to 11 AM PDT
Tuesday for West Slope Northern Sierra Nevada.

&&

$$