Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 201141

Area Forecast Discussion
National Weather Service Reno NV
341 AM PST Sat Jan 20 2018


Dry and cool conditions will prevail this weekend as weak high
pressure moves over the region. A weak disturbance may bring very
light snow for parts of eastern California Sunday night and
Monday, but this system is trending drier. A stronger cold storm
is expected late Wednesday into Thursday, bringing more snow to
the Sierra and possibly to lower elevations.



The small area of heavy snow (producing isolated amounts near 1
foot) over parts of Douglas, Alpine, northern Mono and southwest
Lyon counties from Friday evening has diminished, as compact area
of enhanced forcing weakens with upper low exiting to the
southeast. A small lake effect snow band has recently formed near
the south shore of Lake Tahoe, but it does not look very intense
or persistent.

Otherwise, a shortwave ridge moving across CA-NV will limit
precipitation potential through most of this weekend, with
more typical mid-late January daytime highs in the lower-mid 40s
in lower elevations and 30s near the Sierra. Lows tonight will
drop off to the teens to lower 20s for most areas.

For Sunday night and Monday, a weak disturbance accompanied by a
small band of Pacific moisture reaches northern CA. This system
continues to trend toward shallower moisture depth, leading to
lighter precip amounts east of the Sierra crest. Even the warm
advection aloft is not very impressive, with very little in the
way of forcing. Due to these less favorable precip signals, we
have trended lower for snowfall potential--generally less than 2
inches across northeast CA, the Tahoe basin and northern Mono
County and maybe up to 4 inches near the Sierra crest west of
Tahoe and northward into far western Lassen County. Lower
elevations of western NV and far eastern CA are less likely to
receive any meaningful amounts of snowfall, as strong shadowing
is evident on the latest guidance data. By Monday evening, any
leftover shower activity should diminish as the moisture feed
shuts down and the disturbance exits to the east. MJD


.LONG TERM...Tuesday and beyond...

No significant changes this morning as our next decent storm is
set for midweek. On Tuesday, warm advection has trended a bit
north and so precipitation will be light and mainly from the Tahoe
Basin and I-80 northward to the Oregon border, if we see any at
all. We maintained some low chance pops for these areas, otherwise
there will continue to be considerable high clouds.

By Wednesday, the next progressive trough will move into the west
coast. Precipitation may reach northeast CA during the afternoon
but latest model data has slowed the timing a bit with the main
cold front and precipitation band reaching the area Wednesday
night. Winds aloft and surface gradients tighten Wednesday with
700 mb flow increasing to 50 kts or more. Conditions are starting
a bit colder than the last system with lower overall heights while
sounding profiles show a moistening atmosphere. So winds closer to
the surface do not look overly strong but we could still see a
period of wind gusts 40-50 mph, locally stronger in wind prone
areas Wednesday afternoon/evening.

There is initially a narrow moisture tap feeding the cold frontal
band as it approaches Lassen County late Wednesday, but it then
weakens as the trough amplifies and progresses rather quickly
inland. So this will be a limiting factor for precipitation
amounts. Still looks like a decent storm, with another foot or
more in the Sierra from western Lassen County all the way down
into Mono County. Since this storm is starting out colder, impacts
will likely be felt along this entire stretch of the Sierra. Snow
levels will begin above the lower valley floors Wednesday evening
before crashing behind the cold front. So even some light snow
accumulations are possible lower down although confidence in the
impacts is low due to uncertainty with post frontal QPF. Snow will
taper from north to south on Thursday as the front works
southeast across NV. Isolated snow showers will persist Thursday
night into early Friday mainly north of Highway 50 as the trough
exits. After a mild day Wednesday, temperatures will drop to below
normal for the balance of the week. Hohmann


Low clouds and some light snow are possible at KTVL early this
morning as some lake enhanced snow bands continue. Otherwise,
drier conditions overspreading the region will keep generally VFR
conditions through the weekend. The exception will be KTRK where
some FZFG will continue through about 17Z this morning. Hohmann


.REV Watches/Warnings/Advisories...


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