Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 201046

Area Forecast Discussion
National Weather Service Reno NV
246 AM PST Sun Jan 20 2019


A strong, fast-moving storm pushes into the region today and
tonight, bringing gusty winds, valley rain and high elevation
snow. Snow levels will drop quickly late today, bringing
widespread snow impacts to the region. Brisk and cooler conditions
will follow Monday with a generally quiet pattern developing for
the remainder of next week.



A strong storm moving off the Pacific will bring another round of
heavy snow to the Sierra today and tonight. Fortuitously, it`s
also World Snow Day. Periods of heavy rain and gusty winds can be
expected in the lower elevations today with rain likely changing
to snow late tonight in the western Nevada foothills, even down
here in Reno/Sparks area overnight. Only significant changes to
the forecast made overnight were to add a slight chance of
thunder today due to the strong instability aloft today.

The overall character of this storm is defined by a very strong
cold front with the bulk of the moisture, though not all of it,
ahead of the front in many areas. This will lead to heavy rain at
elevations below around 6500-7500 feet until the front arrives
when rain will rapidly change to snow.


Winds are currently gusting to around 70 mph along the Sierra
ridges with gusts of 100+ mph expected this afternoon. The incoming
band of heavy precipitation is just making landfall in far
northwest California. Ahead of the main band of precipitation,
increasing warm air advection should begin to squeeze out
precipitation in the central Sierra, with rain this morning and
relatively high snow levels of 7500-8000 feet possible.

Snow levels should fall slowly this morning ahead of the front as
heavy precipitation begins to drag the snow levels down through
the day. Best estimate is for rain to change to snow at Donner
Summit around noon with the change-over potentially taking until
late afternoon in the Truckee/Tahoe area until the cold front
arrives around 5 pm. In the Mammoth area precipitation won`t
arrive until around mid afternoon, but will likely all be in the
from of snow. Current QPF forecast is for around 2.5 inches along
the Sierra crest around Tahoe and Alpine County with 1-1.5 inches
in the Tahoe Basin and the eastern Sierra.

The main boom-bust zone for snow continues to be the 5500-6500
range. The current forecast for Truckee/Tahoe is for 4-8 inches of
snow in general, but could be significantly more or less
depending on how quickly the cold front arrives.

Monday night, behind the cold front, a period of strong easterly
winds are possible along the Sierra crest with the main focus in
Alpine and Mono counties, when winds could again gust to 80-100


Gusty winds with a period of heavy rain, eventually changing to
snow, is expected at the lower elevations of northeast California
and western Nevada. Most of the precipitation below 5000-5500
feet should fall as rain with snow accumulations of 2-4 inches
possible in the foothills and Virginia Highlands. In the lowest
valleys, snow showers are likely overnight but accumulations are
currently expected to be less then an inch. The best estimate for
rain changing to snow in the foothills is around 7 pm with snow
levels falling to the valley floors around 10 pm.

Total precipitation amounts of 0.35-0.5 inches are possible in
the lower elevations of western Nevada with up to 0.75 inches
possible in the foothills. Gusty winds are expected this afternoon
with gusts of 30-40 mph, but stronger winds should be dampened by
heavy rain spilling into the region. Cold temperatures and
clearing skies can be expected Monday night into Tuesday behind
the cold front. -Zach

.LONG TERM...Wednesday through Saturday...

No significant changes were made to the inherited extended forecast
this cycle.

A ridge axis to the west keeps the region under northwest flow aloft
through early Friday. The models do indicate periodic sheared out
cyclonic vorticity advection in the northwest flow moving over the
area. This should just provide intermittent increased cloud cover.
Otherwise...we should remain dry through the forecast period. Low
level easterly flow Wednesday and Thursday may keep high temperatures
near to slightly below normal.

The ridge axis drifts east Friday with warming aloft. That should
promote increased valley inversions for early Friday; mixing
increases later in the day and into Saturday. The ridge axis moves
east on Saturday. This is likely to be the warmest day of the
extended period.



Surface winds and winds aloft increase through the day as a moderate
to strong area of low pressure approaches the forecast area today.
This should lead to increased turbulence aloft and the potential for
low level wind shear. Surface gusts may exceed 35 kts for terminals
east of the Sierra by this afternoon. The better chance for low
level wind shear exists a along cold front late tonight as surface
winds shift rapidly to the west-northwest at the surface while
remaining west-southwest aloft.

Lowering clouds heights and increasing precipitation coverage will
drive conditions to IFR/MVFR in northeast California and the
northern Sierra this afternoon. Precipitation spreads east and south
through the evening and overnight hours bringing periods of lowered
cigs/vsbys to the eastern Sierra and western Nevada. Mountain
obscurations will accompany the lowered ceilings.

Snow levels fall to the Sierra valleys in the evening leading to
accumulating snows at KTRK/KTVL this evening and overnight. Snow
accumulation at KMMH starts later tonight. Slushy accumulations of 4
to 8 inches are possible.

Snow levels fall later in the lower valleys. There is the potential
for accumulating snows at the western Nevada and northeast
California terminals...but amounts should be less than 1 inch.

Low pressure hangs around Monday with snow showers over much of the
area. The better chances for widespread showers will be east of
Highway 95 Monday.

Building high pressure will mean a return to dry conditions for
Tuesday through much of the rest of the week. Gusty northeast winds
over the Sierra ridges are likely early Tuesday.


.REV Watches/Warnings/Advisories...
NV...Winter Storm Warning from 10 AM Sunday to 4 AM PST Monday NVZ002.

     Lake Wind Advisory from 8 AM to 7 PM PST Sunday for Pyramid Lake
     in NVZ004.

CA...Winter Weather Advisory from 4 PM Sunday to 4 AM PST Monday
     above 5000 feet in CAZ071.

     Winter Weather Advisory from 4 PM Sunday to 4 AM PST Monday

     Winter Storm Warning from 10 AM Sunday to 4 AM PST Monday CAZ072.



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