Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 171149

Area Forecast Discussion
National Weather Service Sacramento CA
349 AM PST Tue Jan 17 2017

Dry today, then a series of winter storms will begin Wednesday
and continue into early next week. Current timing of storms is
Wednesday night...Friday and Sunday. Each storm will bring gusty
winds and heavy snow over the mountains.

Upper ridge over the west coast bringing fair skies to the CWA
this morning. Exception is the central valley where fog has formed
again. Most locations not showing as much fog as 24 hours ago but
patchy dense fog may still be possible. Upper ridge begins to
break down this afternoon as a Pacific frontal system approaches
the coast. Most areas of the forecast area will see increasing
clouds today ahead of this system and non fog impacted areas will
see cooler temperatures closer to normal. In areas where the fog
clears more quickly today...temperatures may be a little warmer
than yesterday. Pacific front reaches the north coast tonight with
light pre-frontal precipitation spreading over norcal. Under warm
air advection tonight...snow levels will remain moderately high
but will lower slowly on Wednesday as the overall airmass cools.
Light precipitation spreads southward on Wednesday covering most
of the CWA by afternoon. Heavier precipitation then begins moving
into the region late Wednesday afternoon and evening as the main
frontal system pushes inland. This appears to be a moderately
moist system with around .75 to 1.5 inches expected in the valley
from mid day Wednesday to mid day Thursday with up to about 2
inches over the Sierra. Gusty winds will accompany this system as
well but exceptionally strong winds are not expected based on
surface gradient progs. Snow levels will likely start out too high
to be impactful over the northern mountains early in the storm so
heavier snowfall there will be limited to highest elevations. The
higher elevations of the Sierra will see much more snowfall and
winter storm watch of heaviest precipitation period of mid day
Wednesday to mid day Thursday looks good. Should see a transition
to showers Thursday afternoon as the frontal band shifts east of
the state. Next Pacific system moves in quickly on the heals of
the Wednesday night storm pushing onto the coast Thursday night
and into and across the state on Friday. This is about 6 hours
slower than previous model runs with main impact of this storm now
hitting during the day on Friday. This system looks similar to
the Wednesday night system on QPF amounts and winds but this will
be a colder system with snow levels 3000 feet or lower through the
day Friday and into Friday night. This should make for more
significant impacts over the northern mountains and still cooler
daytime temperatures.


Weak upper ridging moves through Saturday with models suggesting
lingering showers possible over the mountains. Precipitation then
spreads across the area Saturday night into Sunday as next Pacific
frontal system impacts interior NorCal. Significant QPF expected
as models showing upwards of 2+ inches in portions of the Central
Valley Sunday through Monday with 3+ inches in the foothills and
mountains. Snow possible down into the foothills with this system
and several feet of new snow expected at pass levels impacting
travel. Strong southerly winds forecast Sunday and wind advisories
may be issued for portions of Interior NorCal. Decreasing showers
Tuesday as weak high pressure returns to the forecast area.


Upr rdg movs thru tda as Pac fntl sys apchs. Areas MVFR/IFR with
isold LIFR poss in ST/BR/FG in Cntrl Vly til arnd 21z otrw VFR
conds for Intr NorCal tda with incrsg mid to high clds. Sfc wnds
mnly lgt thru tngt. Lcl MVFR conds in pcpn acrs Nrn/Cstl mtns aft
03z Wed.


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


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