Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 161813

Area Forecast Discussion
National Weather Service Sacramento CA
1013 AM PST Tue Jan 16 2018

Active weather pattern continues, with a stronger and colder
storm system ariving Thursday-Friday. A similarly cold and wet
storm system is expected Sunday-Monday.


Our weak frontal system has largely moved east of the region, with
precipitation tapering off across interior Northern CA.
Precipitation totals were light for the most part, with readings
generally below a third of an inch. With these scant totals, and
particularly from about Sacramento southward, not enough mixing
occurred to break up the fog and low clouds. A shower or two will
continue to be possible across the region today, but most of the
area should remain dry.

A shortwave ridge of high pressure will build over the area
tonight into Wednesday, ending the shower threat. With increasing
subsidence, fog and low clouds are likely to return to much of
the Central Valley late tonight and Wednesday morning.

The next Pacific storm system will begin to move inland Wednesday
evening, with the front passing through the interior during the
day Thursday. Showery precipitation should continue into Friday.
This system will be stronger than the current one, but rain
shadowing may occur across portions of the Valley, limiting lower
elevation precipitation. Orographics should be quite strong for
the Shasta drainage and Sierra however. This system will be a fair
bit colder than recent storms, with snow levels starting at or
below major Sierra pass levels, and lowering to 2500-3500 feet on
Friday. Our current forecast calls for 12-18 inches of snow above
6000 feet along the Sierra, and a dusting possible down to around
3000 feet. Light snow accumulations will also be possible above
2000 ft along Interstate 5 in Shasta County.

As the trough axis passes overhead, a bit of instability is
projected across portions of the Central Valley Friday afternoon.
We`ll take a look at putting thunderstorms into the forecast, with
the primary impact being the potential for accumulating small hail
/ graupel.




Short-lived upper level ridge will build across the area on
Saturday, resulting in generally dry conditions. The ridge of high
pressure will be displaced as an upper trough deepens along the
West Coast. Forecast models similar in bringing widespread
precipitation across interior NorCal Sunday into Monday as
associated Pacific frontal boundary pushes through. There are
still some minor differences in timing as well as precipitation
amounts this far out. Regardless, mountain travel impacts could
be possible given the cold nature of this system. Breezy to gusty
winds could be possible as the system moves through.

Lingering showers will continue early Tuesday as the system exits
the area. Guidance indicates a brief period of dry weather before
the next system moves in around the middle of next week, but
models solutions diverge significantly. Nevertheless, it appears
that active weather could continue through the extended period.
Temperatures will gradually warm up by the end of the forecast
period, but should remain near or slightly below normal.



MVFR/IFR conditions, locally LIFR, continue across interior NorCal
as frontal system pushes through. Precipitation can be expected
generally through 14z across TAF sites. Conditions improve by 20
Tuesday but areas of MVFR/IFR are expected to continue with the
potential for Valley fog Wednesday morning. Winds will remain
under 10 knots.


Winter Storm Watch from Thursday afternoon through Friday
afternoon for West Slope Northern Sierra Nevada-Western Plumas
County/Lassen Park.


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