Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 071131

Area Forecast Discussion
National Weather Service Reno NV
331 AM PST Wed Dec 7 2016


An active weather pattern will push multiple storms across the
region over the next several days. The next system will impact the
region tonight into Thursday morning and will bring snow
accumulations to the Sierra and western Nevada, along with potential
for freezing rain in the valleys. More rain and high elevation snow
is likely Thursday through Saturday with additional systems possible
into early next week.



Post-frontal low clouds have been clearing through the early morning
hours which combined with light winds have allowed most locations to
drop into the teens and 20s. Colder valleys in Lassen County have
already dropped into the single digits with negative values at
Bogard. High temperatures this afternoon will struggle to reach
above the freezing mark across the Sierra and western Nevada. This
cold air mass will come into play as moisture pushes across the
Sierra and western Nevada and will provide chances for snowfall as
early as late afternoon today across the Sierra and far western
Nevada. Precipitation will begin as snow across all valley floors
with the cold air in place and will then begin a transition to
rainfall with a potentially impactful period of freezing
rain/drizzle early Thursday morning.

A Winter Weather Advisory goes into effect later this afternoon and
continues into Thursday morning. Current timing looks to have snow
development occurring around 4-7pm and then persist into Thursday
morning. Travel impacts will be possible by this afternoon in the
Sierra and western Nevada with very slick and icy roads through
Thursday. The main window to see a threat of freezing rain/drizzle
looks to occur about 1am-6am across the Sierra with western Nevada
seeing the best potential during the early morning commute roughly 4-
8am Thursday morning. Motorists should prepare for slow travel,
possible chain restrictions and should allow for extra time to reach
their destinations. This freezing rain potential is a result of
warmer air aloft pushing across colder surface air. As the warm air
aloft thickens, we will see transition to rainfall during the day on
Thursday with snow levels rising 7,500-8,000 feet. Mountain
shadowing should be lessened as forcing is isentropically driven.
Overall, roughly looking for ranges in the 1-4" range across western
Nevada and Mono County before the transition to rainfall and 2-5"
for the Tahoe Basin with near a foot possible right along the crest.

The other accompanying impact will be winds. As strong flow aloft
crosses the northern Sierra we will see to gusty periods of winds
mainly across the Tahoe Basin and Sierra Front Thursday afternoon
with gusts in the 35-45mph range possible and a stronger round of
winds on Friday afternoon with gusts up to 50 mph possible. This
will lead to dangerous boating conditions, travel restrictions for
high profile vehicles, and possible turbulence/shear for aviation
operations. Fuentes

.LONG TERM...Saturday through Tuesday...

Not a whole lot of change in the long term as it still looks
unsettled, but the details remain low confidence. The models
continue to show an active pattern into the middle of next week with
an active Pacific jet stream and strong polar front draped across
the Pacific Northwest.

For the weekend, the GFS is showing the last of the incoming system
out by Saturday afternoon while the EC has another rather strong
impulse moving through and is quite wet. Sunday, the roles are
reversed with the GFS bringing in the next system during the
afternoon while the EC shows a break. At this point, kept the going
forecast relatively unchanged with a better chance on Saturday and
lower chance on Sunday. However, did increase the precip chances on
Sunday due to the GFS and its ensemble in decent agreement. There
will likely be a 12-24 hour precip in the chances of precip, but
timing it is low confidence with the models in such disparity. Snow
levels at least look somewhat consistent between the models and are
6-7000 feet, a little lower than Friday. Winds also will be gusty on
the ridges, but less so in the valleys.

Early next week, the GFS/EC and ensembles all show another moderate
AR system to affect the region Monday and Tuesday, at least north of
highway 50. The models are in a bit better agreement with the main
jet remaining near or north of the Oregon border. The system is not
looking that well organized, but it does look quite mild with snow
levels back up to 7-8000 feet. With the organization not being great
with modest forcing, the precip rates will fortunately be low to
moderate, although bouts of precip could continue through midweek.
Winds could also be gusty at times in the valleys with temps mild
for mid December.


VFR into this afternoon before -SN arrives around 00Z near the 395
corridor and points east by 06Z. MVFR CIGS/VIS in the snow with OCNL
IFR conds in any heavier bursts. Then after 09Z, the precip type
will begin to change over. There will be a warm nose from 6-8000
feet MSL moving in which will likely change the precip type to -RA
in the Sierra by 18Z below about 7-8000 feet. However, in the lower
valleys to the east a period of -FZRA is possible from 09-18Z. High
confidence that some valleys will see FZRA, but picking out any one
valley is difficult. Each valley and associated terminal has about a
40-50% chance of seeing FZRA for 2-3 hours including KRNO and KCXP.

The overall precip will be light with about 1-3" of snow
accumulation on runways, and in the valleys that see -FZRA, ice
accumulation up to a tenth of an inch. Improving conditions after
18Z as the trapped cold air mixes out with some MVFR CIGS in -RA,
mostly in the Sierra. Winds will also increase after 18Z for the
terminals with peak gusts to 25-30 kts from the SW. There will be
mtn wave turbulence, but at this time the threat of LLWS looks to be
about 30% or less. However, t he threat of MVFR CIGS will continue
into Friday in the Sierra due to continuing -RA.

.REV Watches/Warnings/Advisories...
NV...Winter Weather Advisory from 4 PM this afternoon to 10 AM PST
     Thursday NVZ005.

     Winter Weather Advisory from 4 PM this afternoon to 10 AM PST
     Thursday NVZ002.

     Winter Weather Advisory from 4 PM this afternoon to 10 AM PST
     Thursday NVZ001-003-004.

CA...Winter Weather Advisory from 4 PM this afternoon to 10 AM PST
     Thursday CAZ070-071.

     Winter Weather Advisory from 10 PM this evening to 10 AM PST
     Thursday CAZ073.

     Winter Weather Advisory from 4 PM this afternoon to 10 AM PST
     Thursday CAZ072.



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