Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 182123

Area Forecast Discussion
National Weather Service Sacramento CA
223 PM PDT Sun Mar 18 2018

Dry weather today into Monday with warming temperatures. Wet
weather returns Tuesday into Friday, and possibly into next


Clouds have been on the increase this afternoon as the cirrus
shield associated with a storm system near 36N 145W moves
overhead. A cold airmass remains in place, and temperatures have
been slow to warm up this afternoon. Temperatures at this hour are
in the mid 50s across the Valley, with 20s to 40s over the
mountains. Highs this afternoon are on track to be roughly 5 to 10
degrees cooler than normal. Isolated showers may develop over the
mountains this afternoon into early evening as a very weak trough
passes through.

Most of the region will remain dry Monday and Monday night. The
next weather system will then begin to move into the region on
Tuesday. This upcoming system has the look of an atmospheric
river, with Integrated Vapor Transport (IVT) values of 250-500
kg/ms being projected. The first surge of moisture will likely
make landfall to our south...either toward central or southern
CA on Tuesday. NorCal should still receive light precipitation
during this timeframe.

Heavier precipitation will begin on Wednesday across Northern CA
as the upper trough pushes inland. Snow levels should initially be
rather high: on the order of 6500-7500 feet. Periods of moderate
to heavy precipitation will be possible, particularly over the
mountains. Our snowpack will likely be able to absorb much of
this rainfall across the higher elevations: snowmelt will only
occur in the lower elevations, along the periphery of the current
snowpack. Gusty winds are also possible on Wednesday across the



We will see a wet start to the extended period as a Gulf of
Alaska trough merges with subtropical moisture. This will bring
widespread Valley rain and Mountain snow heavy at times. Snow
levels Thursday morning will start out 5000 to 6000 feet but will
fall to 3000 to 4000 feet Thursday night. Things will dry out a
bit on Friday as some of the energy pushes off to the east but
Mountain snow showers will continue. The latest EC run has trended
towards the GFS in keeping shower activity into the weekend. We
will see pieces of energy spin off of an upper level low set up
over the PacNW. The greatest shower chances will be in the higher
elevations and snow levels throughout the weekend will remain in
the 3000 to 4000 range. Hazardous Mountain travel will be likely
Thursday into Friday and will be hazardous at times over the
weekend. The trough associated with the upper level low should
swing through on Sunday and that will bring quieter weather for
next week. High temperatures will be running 5-10 below average
throughout the period.




VFR conditions are expected the next 24 hours at TAF sites. SCT to
BKN high clouds can be expected. Winds remain under 10 knots.




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