Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 160450 AAA

Area Forecast Discussion...UPDATED
National Weather Service Reno NV
850 PM PST Mon Jan 15 2018

Quick update to fine tune the "storm" tonight and Tuesday.
Satellite imagery showed shortwave trough moving into northern CA
with radar showing band of showers across far northwest CA. Trough
is looking weaker as it continues to move inland with higher
resolution models bringing some light QPF to the northern Sierra
to northern NV late tonight and Tuesday morning. The main
deterministic model runs (00Z NAM/GFS) don`t even bring more than
isolated showers to the Tahoe Basin between about 12Z-18Z. We
tapered pops a bit for southern areas and indicated a faster
drying trend Tuesday afternoon as most of the showers will be
exiting. In addition, gradients relax Tuesday afternoon and
evening and winds become lighter. Hohmann



Ridgetop winds are increasing ahead of a fast moving storm for
late tonight and Tuesday. A stronger and colder storm system will
bring gusty winds with snow and rain Thursday and Friday.


.PREVIOUS DISCUSSION... /Issued 317 PM PST Mon Jan 15 2018/


Ridgetop winds are increasing this afternoon ahead of a fast-
moving storm for late tonight and Tuesday. A stronger and colder
storm system will bring gusty winds with snow and rain Thursday
and Friday.


A ridge of high pressure will be replaced by a relatively weak
storm tonight into Tuesday morning. Sierra ridge gusts should be
in the 40-55 mph range this afternoon through Tuesday, and valley
wind gusts should increase to around 20-30 mph by Tuesday
afternoon/evening. For storm total precipitation, we expect
0.50-0.75" near the Sierra crest, and 0.25-0.50" in the Tahoe
Basin and across NE California. Amounts across western NV could
vary from a few hundredths in Mineral County to 0.10-0.25" north
of I-80, especially as the storm is weak and may not spillover
efficiently into western Nevada. Snow levels will be around 7,000
feet tonight and Tuesday morning, with up to 4 inches of snow
possible for areas above 7,000 feet. Precipitation with this
storm should be over by Tuesday evening with no showers expected
on Wednesday.

Wednesday will be a brief break between storms, but Sierra ridge
gusts will be on the increase ahead of the next stronger storm.
Increasing gusty winds across Sierra ridges to around 100 mph by
late Wednesday will result in the increased probability for
moderate-severe turbulence and wind shear in the lee of the
Sierra. JCM

LONG TERM...Thursday through Monday...

Thursday and Thursday night, a strong front will move through
northeast California and western Nevada. The front will bring
strong, gusty winds followed by a period of moderate to heavy
mountain snow, with valley rain changing to snow behind the front.
After a break later in the day Friday through Saturday night, a
colder system arrives for Sunday into Monday, bringing the threat
for breezy conditions and notable snow for most elevations. The main
features of the long term have been broken out by element below.

* WINDS THURSDAY: Bumped up winds substantially Thursday afternoon
  and evening, especially for ridges and wind-prone areas along the
  Highway 395 corridor. Simulated cross-sections and soundings from
  the GFS and NAM are showing a possible downslope event in the
  immediate lee of the Sierra within about 6 hours of the strong
  cold frontal passage (FROPA). Widespread gusts to 50 mph are
  expected near and west of Highway 95 Thursday afternoon and
  evening, with gusts 65-75 mph possible in wind-prone areas along
  Interstate 580 and Highway 395 between Janesville and the Mammoth
  airport. Areas of blowing dust could be a minor-moderate concern
  to the north and east of dry sinks. Winds should decrease
  substantially for most areas with FROPA as strong flow aloft
  allows for good spillover.

* PRECIPITATION THURSDAY-FRIDAY: For northeast California and the
  eastern Sierra, potential QPF/snowfall amounts are similar to
  previous forecasts; basically, the Thursday-Friday system looks to
  be a moderate winter storm with a brief moisture tap. With this in
  mind, a winter storm watch has been issued for Lassen County south
  through the Lake Tahoe area with 1-2 feet of snowfall possible
  above 6500 feet and 3-6 inches possible down to 4500 feet. Given
  the strong front and significant winds aloft to push precipitation
  east of the Sierra, spillover potential into western and west-
  central Nevada looks good by Thursday evening and overnight into
  Friday morning, at least for the several hour period along and
  behind the FROPA (when the moisture tap is pointed directly at the
  area). A quarter to 0.50" of precipitation looks reasonable for
  far western Nevada, with 0.10" to 0.25" farther out in the Basin
  and Range.

* SNOW LEVELS/LOWER ELEVATION SNOWFALL: Crashing behind cold front.
  With decent flow aloft, moisture up to around 500 mb, and some
  instability post-frontal snowfall into western NV looks pretty
  good at this time. Several inches of snowfall is certainly
  possible west of Interstate 580/Highway 395 Friday morning, with
  some accumulation possible down to valley floors. FRIDAY MORNING`S

* SUNDAY-MONDAY: Definitely bears watching but details still to be
  hashed out. The system should start out colder than Thursday`s so
  more substantial snowfall possible down to lower valley floors.
  Late Sunday into Monday morning could bring travel headaches. Stay



The shortwave trough from the west is on track to impact the region
for late tonight into Tuesday. High to mid-level clouds will
continue to increase throughout the day with a pick up in the winds
of up to 15 kts with gusts of up to 20 kts. VFR conditions will
stand for all terminals through late this evening.

As the weak system makes its way through the Sierra, a period of
MVFR conditions can be expected between 09-18Z Tuesday for
KTRK/KTVL. Light rain and mountain snow is forecast leading to
mountain obscuration and icing possibilities. Winds will also be a
slight issue as the associated cold front moves through gusting up
to 25 kts at area terminals with ridge gusts of up to 50 kts. Due to
the gusty southwest flow, mountain turbulence is expected along and
downwind of the Sierra Crest.

By Thursday, a more potent winter system is projected to arrive with
strong winds and heavy mountain snow. Turbulence and wind shear is
expected for Thursday into Friday along with varying snow
accumulations at all area terminals. -LaGuardia


.REV Watches/Warnings/Advisories...
NV...Winter Storm Watch from Thursday afternoon through Friday
     afternoon NVZ002.

CA...Winter Storm Watch from Thursday afternoon through Friday
     afternoon CAZ071-072.



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