130
FXUS66 KSTO 190941
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
241 AM PDT Sun May 19 2019


.SYNOPSIS...

Rain and mountain snow continue today with Sierra Cascade travel
impacts expected through early Monday morning. Thunderstorms are
possible this afternoon. Another system will impact northern
California Monday night into Tuesday bringing more rain and
mountain snow. Cool temperatures continue through most of the
week.

&&

.DISCUSSION...

An upper low resides just west of the northern California coast
early this morning, with widespread precipitation seen ahead of this
feature. Conditions are beginning to deteriorate in the Sierra with
snow levels expected to drop near 5kft by early this morning. This
low will continue to track southeast, moving over central California
by late afternoon. Accumulations of 6 to 12 inches can still be
expected through early Monday morning, with the heaviest snow this
morning and rates decreasing as this system moves out of the area.

For the Valley, convective models indicate shower and thunderstorm
initiation by late morning with ensemble probabilities signaling the
best chances along and south of I-80 where the strongest
instability resides. Shear will be weak as the low moves overhead
and the main hazards with any scattered or clustered storms will
be heavy localized rain, small hail, and lightning. There is some
indication rate rates may be near or exceed a half an inch an
hour, especially in the late morning and early afternoon with
storms.

This system will move out of the area by early Monday, but only a
brief dry period will be seen before another system tracks over
NorCal Monday night through Tuesday night. Snow levels, once again,
look to be near pass level with snow accumulations around 5-10
inches. Travel impacts should be anticipated, especially Tuesday
morning into the evening hours when the heaviest precipitation is
expected over the Sierra. Thunderstorms may also be possible again
Tuesday in the Valley.


.EXTENDED DISCUSSION (Thursday THROUGH Sunday)

Ensemble guidance continues to feature a broad upper level trough
across the region later in the week, continuing the threat for
mainly mountain showers and below average temperatures. Models
still vary in the details, so have continued to lean on the NBM
and ensembles for precipitation chances and amounts.

&&

.AVIATION...

Widespread MVFR conditions, locally IFR, next 24 hours as a
weather system continues to move across interior NorCal. Areas of
southerly wind gusts 20-25 kts about 18Z. Scattered thunderstorms
possible 15Z-00Z Monday.

&&

.STO WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning until 5 AM PDT Monday for West Slope
Northern Sierra Nevada-Western Plumas County/Lassen Park.

&&

$$