Area Forecast Discussion
Issued by The National Weather Service
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FXUS66 KSTO 201204

Area Forecast Discussion
National Weather Service Sacramento CA
404 AM PST Wed Feb 20 2019

A weak, cold system moves through today into early Thursday with
light mountain and foothill snow. Breezy winds Thursday with dry
weather Friday. Light precipitation possible once again over the
weekend and early next week.


Mid level clouds cover most of the forecast area this morning
ahead of a weak upper shortwave trough now over the northwest
corner of the state. Cloud cover bringing warmer temperatures
this morning with early morning temperatures anywhere from 4 to
10 degrees above 24 hours ago. Radar is showing some light
precipitation just west of Shasta county and models spread light
precipitation southward across the forecast area today. Snow
levels with this cold system will be quite low at around 2000
feet. As a result, snow ratios will be relatively high at 15:1 or
more. Therefore, even fairly light precipitation will translate to
several inches of snowfall over the Sierra so will leave up
winter weather advisory currently in place. Cooler airmass and
cloud cover will bring cooler Max temperatures this afternoon.
Precipitation will drop off late tonight as a secondary trough
moves into Socal. Main upper low forecast to move into the
southern Great Basin on Thursday. The Sierra Cascade crest may see
a few light showers under cyclonic flow but the remainder of the
forecast area should remain dry on Thursday with a little warming.
Northerly flow between upper low over southern Great Basin and
high pressure ridge over the eastern Pacific will bring breezy
north winds Thursday afternoon and evening.

High pressure pushing in over the state will bring fair skies and
warmer temperatures on Friday. Mainly clear skies and lessoning
wind will allow morning lows Friday to cool again with near
freezing temperatures returning to the central valley. Still
should be enough wind around, however, to keep temperatures from
dropping to much below freezing. Mainly fair skies will continue
into Friday night but warming airmass should keep morning lows
Saturday elevated above Friday morning lows.

An upper trough digging out of the Gulf of Alaska and down the
west coast is forecast by models to start bringing precipitation
to the northern forecast area by Saturday afternoon. Forecast
models show fairly light precipitation dropping southward over
the region as the upper low shifts slowly southward. Forecast
models keep this trough of low pressure stretched out over the
Pacific northwest going into early next week for a continued
threat of light precipitation with relatively low snow levels
remaining over the region.


A weak system moves through Sunday, bringing light Valley
rainfall and a few inches of mountain snow. Snow levels should be
around 2000-3000 feet.

Models trending towards nearly stationary frontal boundary with
precipitation continuing into early next week and potentially
beyond. Confidence in details remains low for now. Will keep
unsettled pattern continuing through next week.



General VFR conditions with local MVFR cigs through 18z, then -ra
spreading through the Valley with areas of MVFR. Snow levels
around 015-025 ft amsl with IFR over mountains.

Winter Weather Advisory until 10 PM PST this evening for West
Slope Northern Sierra Nevada-Western Plumas County/Lassen Park.


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