Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 092139

Area Forecast Discussion
National Weather Service Reno NV
139 PM PST Tue Jan 9 2018


Low pressure over southern California is tracking east. This low
may produce light rain or snow for areas south of Highway 50
tonight. Another weak area of low pressure moves into the Great
basin from the northwest tonight and brings showers. Still a third
weak area of low pressure may bring light precipitation to areas
near the Oregon Border Thursday. High pressure develops for the
weekend with dry and mild weather. Model simulations show the
potential for wetter weather next week.



The short term forecast remains rather chaotic as the upper level
closed low over southern California continues pressing east while
a secondary wave tries to move southeast this evening with
moderate jet support on the back side of the main long wave

Precipitation on the north side of the upper low...including that
associated with a deformation area that develops in the model data
overnight near central likely to affect Mono County...
Mineral County...southern Lyon County...and far eastern portions
of Churchill County this evening and overnight. Snow levels remain
rather high. The lack of significant forecast liquid precipitation
and the high snow levels should preclude much in the way of
accumulations below 8500 feet.

A secondary short wave is shown in the model guidance trying to
drop southeast across the northern half of the forecast area this
evening. There is a small amount of cooling behind the wave; snow
levels should drop a little. Forcing is also less than overwhelming...
but showers along the front in northeast California and western
Nevada along with terrain induced precipitation in the northern
Sierra are possible. We will handle this possibility with higher
pops early in the evening...then let the pops drop back to the
chance range.

Much of Wednesday afternoon through Thursday morning should be dry
as a ridge starts to develop. Valleys in the Sierra and western
Nevada with light winds and some clearing are likely to experience
fog Thursday morning; the most susceptible are the Martis Valley
and the Sierra Valley.

Lastly...a weak wave tries to move over the ridge Thursday
afternoon/evening. This wave effectively flattens the northern
portion of the ridge briefly. Warm air advection precipitation is
possible north of a line from Susanville to Gerlach with the best
chances...albeit small...near the Oregon border.


Upper level ridging remains in place for the weekend resulting in
dry weather, light winds, and above average temperatures. High
temperatures look to climb 10+ degrees above season averages with
highs in the mid to upper 50s across western Nevada. The ridging
will set up valley inversions as well so highs in the Sierra will
also be similar to western Nevada valleys with mid and upper 50s
over the weekend.

Models then show signs for a period of wetter weather as the ridge
axis shifts east and a strong zonally oriented jet stream makes
its way towards the west coast. A couple of waves of moisture show
potential to move through in the late Monday to Tuesday timeframe
followed by a potentially wetter and longer duration system by
Thursday. The upper level flow remains quiet amplified downstream
so could see delayed timing and perhaps more of a glancing blow
with the first system on Tuesday. At this time, the GFS holds on
to more of a dry glancing blow solution on Tuesday while the EC is
much wetter. The forecast is not quite as aggressive as the EC
but still has chances for precipitation across the Sierra and
western Nevada which is more in line with the FV3. Fuentes



Periods of light rain and high elevation snow along with copious
clouds will produce MVFR and IFR conditions in the mountains this
evening and overnight. Mountain obscurations will be common.
Outside of the mountains mostly VFR will prevail with occasional
MVFR in showers. Winds remain light at the terminals and even the
winds near the ridge tops will be less than 40 kt. Turbulence is
a possibility...but should be light to moderate at best...and
somewhat discontinuous. We are not expecting any accumulations on
the runways tonight or early Wednesday...even in the Sierra.

Clouds break up and ceilings lift Wednesday afternoon and evening.
Fog is likely in the valleys of the Sierra and possibly those in
western Nevada where light winds develop Thursday morning. This
would result in MVFR to IFR conditions.

Another weak wave of low pressure may bring lowered ceilings to
areas near the Oregon border Thursday afternoon/evening...but
confidence in this occurrence is low right now.


.REV Watches/Warnings/Advisories...



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