NATIONAL WEATHER SERVICE FORECAST DISCUSSION
Area Forecast Discussion
Issued by The National Weather Service
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156
FXUS66 KSTO 180657
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
1055 PM PST Sun Feb 17 2019

.SYNOPSIS...
Cold disturbance will bring showers through the early evening.
Dry Monday and Tuesday. A weak, cold system is possible Wednesday
and Thursday with light mountain and foothill snow.

&&

.DISCUSSION...
Evening Update: Skies have mostly cleared behind the short wave
dropping Swd on the backside of the Wrn States trof this evening.
This will set up a cold nite over Norcal...and the cold temps will
continue for the rest of this month as Nly flow continues along the
W Coast of NOAM.

Issued a Frost Advisory for the east side of the Sac Vly for Mon
morning as winds will be lighter there than on the W side, and good
radiational cooling, clear skies and high RH will be conducive for
frost. Lighter winds, continued clear skies and humidity trending
higher will be even more conducive for widespread frost Tue morning.

Dry, chilly wx over Norcal the next couple of days will remain
chilly and turn unsettled again by mid week as the next short wave
drops into Norcal. This system forms over the Bering Sea and slides
over the Ern Pac ridge and down the W coast of NOAM into Norcal
Wed/Thu. Should one get tired of the cold/wet wx, remember to...
"Endeavor to persevere!"  JHM

.Previous Discussion...
Broad upper trough is positioned over much of the western states
with a disturbance rotating through it over the Sierra foothills.
This will generate snow showers into the early evening. Cold air has
moved over the area with this system, causing low elevation snow
down to many foothill locations. We have received reports of several
inches at foothill locations such as Placerville, Colfax and Sonora.
After a brief break early this afternoon models indicate increased
snow shower coverage and intensity between 3-8pm with instability
rotating behind disturbance. Best snow into the evening will be over
the Sierra from I80 south where 3 to 5 inches will be possible at
pass level...1 to 3 inches is expected for foothill locations
between 1500-3000 feet, locally higher in more intense convective
snow showers.

Upper low will move east Monday into Tuesday with high pressure
providing a return to dry weather. Breezy north winds are expected
to develop on the back side of the low during this period.
Morning lows will be on the cold side with Valley readings in the
low to mid 30`s...foothills mid/upper 20`s. The breezy winds will
act to diminish the freeze threat over the cent/srn Valley.

A cold system will drop south over NorCal Wednesday and Thursday.
This system appears to be quite dry at this time with Valley
rainfall less than 0.10. Due to the cold origin of the system
snow levels could again drop into the foothills around 1500 feet
with 1-3 inches possible. 3-6 inches are currently forecast at
pass level.


.EXTENDED DISCUSSION (Thursday THROUGH Sunday)

Extended period starts out with a cold inside slider type system
dropping into the Great Basin on Thursday bringing a shower threat
to areas mainly east of the central valley. This system which
originated in the Gulf of Alaska will bring low snow levels again
with light snow possible down below 1000 feet. Impacts with this
system should be minor as QPF values with this dry system will be
minimal. At this time, Friday looks dry under northerly upper
flow and high pressure ridging. Temperatures warm on Friday but
cool airmass will keep daytime highs several degrees below normal.
Upper ridge breaks down quickly as next upper low pressure system
drops out of the Gulf of Alaska and approaches the Pacific
northwest coast on Saturday. Models differ on just how far south
precipitation will reach with GFS digging precipitation somewhat
farther south than ECMWF. Current model runs bring precipitation a
bit further south than previous runs. Snow levels with this
system will be more moderate than previous systems but still
relatively low and below 4000 feet. Keep an eye on the forecast
for updated information as confidence is still low at this time.

&&


.AVIATION...

VFR conditions except brief MVFR/IFR conditions in showers through
Sunday evening. Southerly winds northerly winds 10 to 15 mph with
isolated gusts to 20 to 30 mph.

&&

.STO WATCHES/WARNINGS/ADVISORIES...
Frost Advisory from 3 am to 9 am PST Monday for Northern Sacramento
Valley, Central Sacramento Valley, Southern Sacramento Valley.

&&

$$
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