Area Forecast Discussion
Issued by NWS Reno, NV

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995
FXUS65 KREV 051320
AFDREV

Area Forecast Discussion
National Weather Service Reno NV
520 AM PST Mon Dec 5 2016

.SYNOPSIS...
A couple of weak systems will bring much colder temperatures today
through Wednesday along with low end chances for snow showers. A
wetter atmospheric river pattern sets up at the end of this week
with a wintry mix of precipitation expected Thursday into Saturday.
Additional storms are possible the early part of next week.

&&

.SHORT TERM...
No major changes made to the forecast with high confidence in an
active weather pattern this week.

Bottom Line: Travel impacts possible starting late Wednesday through
the weekend with chances of rain and snow for the Sierra and western
Nevada. There is also a very small chance that freezing rain could
impact some western Nevada valleys.

Highlights:
- Quiet today with light valley winds but windy conditions continue
for the mid slopes and ridges.
- Real cold front drops south into area Tuesday with another round
of snow showers mainly north of Interstate 80 and breezy, cold
northwest winds.
-Wintry mix of precipitation possible late Wednesday night into
Thursday as a moderate atmospheric river makes landfall into N. CA
and NV.

Inversions will redevelop across the valleys tonight, especially for
Nevada, which will result in light winds for those locations. Any
inversions that develop in Sierra valleys will likely mix out
allowing more breezy conditions. Winds along the mid slopes and
ridges will remain gusty through today.

For Tuesday, the more significant cold front with its cold upper
trough will drop into Nevada. Light snow showers are expected
across the region on Tuesday, with the best chances north of
Highway 50. This system lacks a decent moisture tap, so snow
totals will only be a dusting up to an inch with locally a couple
inches possible if more organized bands form. This system will
bring a major cooldown to the region with high temperatures on
Wednesday likely to only reach the 30s even in the warmest valley
locations.

Warm air advection and moisture begin to spread into the region late
Wednesday night into Thursday. Simulations vary with the onset of
precipitation with one showing it starting as early as Wednesday
afternoon while the others are later Wednesday night. Models are
showing that precipitation will begin as either light snow or even
freezing rain. Model soundings show the atmospheric profile is
entirely below zero, which would lean against the possibility of
freezing rain, but we think it is still worth mentioning. The more
likely scenario will be light snow showers then slowly
transitioning to a mix of rain/snow through Thursday.

Regardless of the type of precipitation (rain, snow, freezing rain),
we are expecting travel impacts for Thursday morning, so be sure to
keep an eye on the forecast. This is just the first of multiple
waves of precipitation that will affect the Sierra and western
Nevada through the weekend.
-Weishahn

.LONG TERM...Thursday through Sunday...
Confidence continues to increase this morning in a moderate AR event
across the Sierra and Western NV. That said, the system isn`t the
most organized, and looks to come across in a couple parts. In
addition, the models diverge as to how cold. The first will be
the warm air advection along the warm front Thursday morning. Snow
levels will begin a rapid ascent behind the warm front with a
warm nose possible off the surface. Current soundings indicate a
change from snow to rain sometime Thursday morning for locations
below 7000- 7500 feet. However, there is the possibility of FZRA
mixing in during the transition and added it to the forecast. By
afternoon, as the precip wanes, snow levels should jump to near
7-8000 feet and limit the threat for any freezing rain.

Then, the main band of precip will move in Thursday night into
Friday with snow levels of 7-8000 feet continuing before coming down
Friday afternoon to near 6000 feet (lower north/higher south). Snow
could continue to affect the higher passes depending on the location
of the jet which the models don`t agree on. The GFS is further north
and warmer while the EC is cooler and further south. Right now the
forecast leans a little more to the GFS, but that could change. The
models are in better agreement with the amount of QPF (at least in
the Sierra), and the focus is more on the Tahoe Basin. Amounts
still look to be 1-3" in the Sierra with around 1/4-1/2" along the
Sierra Front into Eastern Lassen County and less than 1/4"
elsewhere. Snow amounts will be limited below 7000 feet, but a
foot or more at pass level is possible depending on the snow
level.

As far as wind, it all depends on the amount of spillover. 700 mb
winds do hit 50-60 kts at times, and with an AR spillover could
be good. However, the models differ with the EC showing more
favorable thermodynamic and kinematic profiles than the GFS. At
this point, expect some gusts to 45 mph along the Sierra Front and
other wind prone areas of NE California and Western NV Thursday
evening into Friday evening.

After this system goes through a general moist, west flow will
continue with embedded short waves. All the models and ensembles
show this idea, but none of these waves looks big. Still, periods of
rain and snow will continue through the weekend with moderate
confidence. Low confidence on snow levels as the models show a sharp
front and differ on jet position. The GFS is warmer with snow levels
6500 feet or higher while the EC is colder with snow down to the
valley floors at times. Of note, the GEFS is colder than the GFS
with the EC in much better agreement with its ensemble. For this
reason, the forecast trends more toward the EC.

&&

.AVIATION...
VFR conditions through this evening with some W-NW wind gusts to 20
kts in valleys and 45 kts over the ridges. Some mtn wave turbulence
will occur but no significant LLWS is expected. The winds will
continue overnight with the threat of -SHSN gradually increasing
from north to south after 06Z. Local areas of MVFR CIGS/VIS in the
SHSN with the best threat north of the KSVE-KLOL terminals.
Improving conditions after 00Z Wed with lighter winds.

The next storm is set for late Wed night through Friday with periods
of MVFR and IFR conds, especially in the Sierra. Winds will also be
an issue with mtn wave turbulence, but the amount of LLWS and speeds
at the terminals is still to be determined.

&&


.REV Watches/Warnings/Advisories...
NV...None.
CA...None.
&&

$$

For more information from the National Weather Service visit...
http://weather.gov/reno



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