Area Forecast Discussion
Issued by NWS Sacramento, CA
FXUS66 KSTO 220433
Area Forecast Discussion
National Weather Service Sacramento CA
933 PM PDT Tue Mar 21 2017
A series of weather systems will bring cooler and more unsettled
weather to the region this week. Chance of thunderstorms
Scattered showers continue this evening mainly north of about
I-80 in the valley and over the mountains. The trough of low
pressure remains off the west coast but will move closer to coast
overnight. This should enhance shower activity over the area
after around midnight and during the day on Wednesday.
Thunderstorm activity does not look as great as it did for today
but some isolated thunderstorms look possible especially over the
San Joaquin Valley and into the adjacent foothills. A wet morning
commute looks likely in the central valley with brief heavy
downpours possible during the day
I pushed back the timing for snow issues traveling over the crest
until midnight for the western slopes. Some models may delay the
onset of snow until morning. Colder air filtering in this evening
means that when it does arrive expect snow below pass levels with
possible chain controls. The bulk of the snow does look like it
will fall during the day before tapering Wednesday evening.
Enough clearing occurred this morning to allow for the development
of thunderstorms across the Valley late this morning-early
afternoon. As of noon, main orientation was linear from about
Oroville south to Lodi. This line was causing torrential rainfall
with localized flooding on roadways. Several reports of over a
half inch of rain falling in less than 30 minutes in Sac metro
area. As indicated by hi- res guidance over the past few days,
more discrete cells are popping up across the northern San Joaquin
Valley. Primary concern is hail with gusty winds, though still
cannot rule out a brief tornado or two where best instability and
low-level shear lie.
Precipitation becomes more showery late this evening and tonight.
Another line of moderate precipitation looks to move through
early Wednesday morning as upper level trough moves overhead.
Timing again looks favorable for some thunderstorms in the Valley
during the afternoon hours. At present indications, this activity
looks like it won`t be as strong as today`s. Snow levels will fall
to around 5000 feet with several inches of accumulation likely
near pass levels. This is bound to cause a few travel headaches so
travelers should carry chains and be prepared for delays.
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)
Friday into early next week shows another stormy pattern setting
up for interior NorCal. The most significant storm wave will be
Friday into Saturday which will have similar rain and snow amounts
to our current Monday-Tuesday system...around half an inch to over
an inch of rain in the valley with a few inches up to a foot of
snow over the Sierra, Lassen Peak, and Shasta County mountains.
Snow levels around 5000 feet. Winds could be breezy to locally
gusty on Friday as the front passes. Temperatures will be about 5
to 10 degrees below normal. Showers diminish on Saturday into
early Sunday. Then another weak storm wave could move inland
Sunday evening into Monday morning. An upper level ridge will
build on Monday, which will bring a return of mostly dry weather
for the valley and warming temperatures.
Scattered showers with areas MVFR/IFR over the Mtns and in the
Vly overnight. Mtns conditions deteriorating overnight down to
IFR/LIFR. Snow level lowering to near 6000 feet.
Winter Weather Advisory until 6 PM PDT Wednesday for Western
Plumas County/Lassen Park.
Winter Weather Advisory until 6 PM PDT Wednesday for West Slope
Northern Sierra Nevada.