Frost Advisory 1, NWS Sacramento, CA

Area Forecast Discussion
National Weather Service Sacramento CA
156 PM PST Sat Nov 7 2020

.SYNOPSIS...
Scattered showers and moderate to locally heavy mountain snow
expected tonight and Sunday. Breezy north to east winds possible
Sunday into Monday with lowering humidity. Below average
temperatures expected to continue through the week, with near
freezing Valley temperatures expected Monday morning.

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.DISCUSSION...
Early this afternoon, radar indicates only some light returns over
the Sierra Nevada with dry weather seen elsewhere. These drier
conditions will only briefly hold before another round of
mountain/foothill precipitation is expected to begin this evening as
the main low continues to rotate across California and Nevada.
Periods of moderate to locally heavy snow will begin to fall over
the mountains beginning this evening, with the heaviest snowfall
expected overnight into Sunday morning. Snow levels remain generally
around 4.5 kft tonight but decrease into Sunday morning down to
roughly 2.5-3.5kft. Hazardous mountain travel is expected during
this time and a Winter Storm Warning remains in place for elevations
above 4kft through tomorrow afternoon. Total snow accumulation
during this time is generally from 5-8 inches, with locally higher
amounts at higher mountain elevations. The weather system begins to
push out of the area Sunday afternoon with some breezy north to east
winds developing behind it. Gusts up to 30 mph are expected, with
relative humidity values about 20 percent or higher.

Cold air remains in place after this system exits and high pressure
moves back across Northern California. Monday morning looks to see
some of the coldest low temperatures of the week with Valley lows
near freezing and mountain temperatures down into the single digits
or teens. With some winds continuing into the overnight hours,
conditions may stay mixed enough to stop a widespread freeze. Any
localized areas that do reach freezing may see sensitive plants
damaged. Dry weather remains in place through mid-week.

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.EXTENDED DISCUSSION (Wednesday THROUGH Saturday)...
Cluster ensemble analysis is in good agreement long wave
troughing over the Western US will continue into mid-week and into
the weekend before a more zonal pattern starts to emerge. This
will likely bring rounds of cloudy and possibly unsettled weather
to Northern California.

The next best chance for unsettle weather is a low pressure system
projected to dig south out of the Gulf of Alaska and impact
Northern California by next weekend. This system is forecast to have
some marine influence as well. Integrated water vapor transport
analysis indicates moisture levels hitting the criteria for at
least a weak atmospheric river associated with this disturbance.

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.AVIATION...
VFR conditions expected at the TAF sites the next 24 hours.
Increasing clouds this evening becoming BKN around 050 overnight.
Widespread IFR conditions expected over the northern Sierra by 06Z
Sunday. Snow levels 040-050, lowering to 025-035 by 12Z Sunday.
Surface wind gusts under 12 kts.

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.STO WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning until 4 PM PST Sunday for West Slope
Northern Sierra Nevada.

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