Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 161243

Area Forecast Discussion
National Weather Service Sacramento CA
443 AM PST Thu Nov 16 2017

Pacific storm brings rain, wind and mountain snow today
with showers ending by Friday morning. Dry Friday and Saturday
with morning valley fog. Another weather system moves through
Sunday night through the middle of next week.


Pacific frontal band continues to drop very slowly southward and
currently located roughly along the interstate 80 corridor from
Blue canyon to the Bay Area. Snow levels with the front remain
relatively high and appear to be around 7000 feet over the
northern Sierra. Radar precipitation estimates indicate the
precipitation intensity so far has been light to moderate except
over the Sierra crest where orographics is bringing a little
higher intensity. Breezy winds are accompanying the front but so
far have not been excessively strong. Snow levels will drop
slightly this afternoon as the cold front continues to move slowly
southward. Models fairly consistent in placing the front along a
line from the Monterey Bay to Tuolumne county by 00z this
afternoon. Main upper trough digs southward into the Pacific
Northwest while a shortwave pivots around the base of the low
tracking through Norcal this afternoon bringing showers to most
of the northern CWA. Isolated thunderstorms may be possible this
afternoon as this shortwave pivots through but instability is
fairly limited so any thunderstorms will likely be quite isolated.
Shower threat continues into Friday morning before upper trough
axis shifts east of the state. If clouds clear enough by Friday
morning, central valley could see some morning fog. Upper ridge
builds over the west coast by Friday afternoon bringing an end to
any shower threat. Upper ridging remains over the west coast over
the weekend bringing dry conditions and a slight warming trend
with daytime highs climbing to near normal by Sunday. Fair skies
will bring a continued morning valley fog threat.



The next Pacific storm will move across interior NorCal late
Sunday into Monday. Forecast models still disagree regarding storm
strength and track. The ECMWF shows a quick moving system that
brings widespread precipitation across the area. Meanwhile, the
GFS pushes the moisture plume into the Pacific Northwest, keeping
precipitation generally north of I-80. Regardless, confidence has
improved and there should be at least some precipitation across
the area.

Confidence in the forecast rapidly degrades after that system.
The GFS has another system right on the heels of the Monday
system, whereas the ECMWF holds it off until mid-to-late next
week. Thus, our forecast remains relatively unchanged. Additional
waves of precipitation could be possible through the extended.



Storm system will continue to bring widespread precipitation
activity from KOVE southward this morning, then showers expected
the rest of the day. Areas of MVFR with local IFR conditions
expected across the Valley, then improving conditions as the
frontal system pushes southward; IFR/ local LIFR continuing over
the mountains. Winds 5-15 kt at TAF sites; higher gusts over the
high Sierra.


Winter Storm Warning until midnight PST tonight for West Slope
Northern Sierra Nevada-Western Plumas County/Lassen Park.


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