Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 121046

Area Forecast Discussion
National Weather Service Reno NV
346 AM PDT Mon Mar 12 2018


Drier conditions continue today as significant winter weather
approaches. A stronger system will bring gusty winds, rain, and
snow Tuesday and Wednesday. Unsettled conditions will continue
into the weekend. Additional periods of heavy snow are expected
to occur in the Sierra with the potential for light accumulations
in western Nevada late this week. Temperatures will be near
average through the early portion of this week before falling
below average later in the week.



Today`s conditions will be rather benign with increasing cloud
cover and breezes as low pressure continues to drop down the
Pacific Coast. Wind gusts north of a Susanville to Gerlach line
increase to around 30 mph with gusts around 20 mph elsewhere this

Focus for the short term continues to be on the onset of a period
of significant winter weather that will start on Tuesday. The
trend has been for increasing QPF amounts and precipitation
chances in the Sierra and western Nevada each successive model
run. The first wave is expected to move into the Sierra early
Tuesday afternoon with snow levels generally starting around
7500-8000 feet. These levels will drop below 7000 feet by Tuesday
evening as the strongest forcing associated with this wave moves
over the Sierra. Cold air catches up Tuesday night with snow
levels dropping much more rapidly to around 4000 feet by Wednesday
morning. Higher resolution models project a slight "break" by
Wednesday evening with precipitation rates falling somewhat.

A Winter Weather Advisory has replaced the Winter Storm Watch for
now. Snow will begin to accumulate in the Sierra Tuesday
afternoon as the first wave in a series moves into the region.
The heaviest period of snow from Tuesday through Wednesday will
occur Tuesday evening. Expect travel conditions to degrade in the
Sierra with more widespread chain controls and slick roads
becoming likely. Current estimates for accumulations are generally
2 to 6 inches below 7000 feet. Favored areas mainly west of
Highway 89 around the Tahoe Basin and west of Highway 395 in Mono
County could see higher accumulations. Up to 18 inches will be
possible along the Sierra Crest. Snow will continue to accumulate
Wednesday afternoon and evening during the "break" between waves,
but will accumulate at a much slower rate.

Snow accumulations in western Nevada are expected to be light, but
could impact the Wednesday morning commute. Preceding light rainfall
will likely limit accumulations, but up to an inch or so may
accumulate creating slick conditions for area roadways -
especially for roads above 5000 feet along the Sierra Front and
around Virginia City.

Winds will also cause potential impacts. Winds increase further
Tuesday with widespread gusts around 40 mph from the Oregon border
through western Nevada and Mono County.

Finally, Instability increases Tuesday afternoon, and some isolated
thunderstorms will be possible mainly north of a Reno to Lovelock
line. Instability parameters are even more unstable Wednesday
afternoon with another round of isolated thunderstorm possible.

.LONG TERM...Wednesday Night through Sunday...

The good news this forecast cycle is the operational models...and
most of the GEFS ensemble members...are coming into better agreement
through Friday. The solutions do start to diverge Saturday.

The GFS is trending a bit more toward the ECMWF from late Wednesday
night through much of Friday. This means we have increased POPs and
QPF more during this time frame with the heaviest precipitation now
zeroing in on the Thursday night/Friday time frame. With the upper
low from the GFS slated to edge closer into the region...we expect
snow levels to fall a bit more than previously forecast and are
likely to get accumulations in the lower valleys by the Thursday
night/Friday time frame...especially as a surface based trough
slides through increasing instability and aiding spill over late
Thursday night. Breezy conditions still look likely for late
Wednesday and again Thursday...especially across western Nevada
where there will be breaks in the precipitation through early

Overall...confidence has increased in the early part of the extended
forecast due to the models coming into better alignment. It is
likely we will need watches for the Sierra and far western Nevada
starting Thursday...but for now we will hold off issuing any watches
so as to keep confusion with the first part of this overall storm
Tuesday and Wednesday to a minimum.

As stated the time we get to Saturday the model
solution agreement begins to break down. The GFS is reverting to a
split flow regime with the main part of the low sliding down the
coast while the ECMWF swings the upper trough over our region. This
puts the southern third of the forecast in a better position for
precipitation if the GFS verifies. If the ECMWF proves out the
entire forecast area would likely see snow showers. By Sunday the
ECMWF has pushed the trough east and largely dried out the region.
Meanwhile the GFS slowly moves the low east across the desert
southwest and keeps a chance for showers over the southern portions
of the forecast area.

Since the models are not in very good agreement for Saturday and
Sunday...we will not make any significant changes to that time
period and leave a broad brushed slight chance to chance POPs in
each day.



Mid and high level clouds have kept fog and stratus at bay this
morning. KTRK may still see some fog this morning, but it will not
be nearly as dense as yesterday. Conditions are generally
expected to be VFR with light breezes around 20 kts today. Ridge
winds increase tonight with gusts 50-60 kts resulting in mountain
waves over and downstream of the Sierra.

Southerly valley winds increase further Tuesday with gusts around
35 kts. Primary concerns will be for the potential of LLWS at KRNO
due to erratic gust spread. This would be a larger concern,
however, if gusts were expected to be in excess of 50 kts. Winds
drop off Tuesday night with frontal passage.

Instability increases Tuesday afternoon, and some isolated
thunderstorms will be possible mainly north of a Reno to Lovelock
line. Instability parameters are even more unstable Wednesday
afternoon with another round of isolated thunderstorm possible.

Other concerns will be for accumulation snow for Sierra terminals.
A Winter Weather Advisory has been issued from Tuesday afternoon
through Wednesday afternoon. Light accumulations for Sierra Front
terminals will also be possible by Wednesday morning.

Significant weather is expected to continue through the rest of
the week into the weekend. Heavy snow accumulations will be
possible for Sierra terminals with lighter accumulations for the
Sierra Front. Winds will also be problematic as several waves of
activity are expected. Boyd


.REV Watches/Warnings/Advisories...
NV...Winter Weather Advisory from 1 PM Tuesday to 5 PM PDT Wednesday

CA...Winter Weather Advisory from 1 PM Tuesday to 5 PM PDT Wednesday

     Winter Weather Advisory from 1 PM Tuesday to 5 PM PDT Wednesday

     Winter Weather Advisory from 1 PM Tuesday to 5 PM PDT Wednesday



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