Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 142248

Area Forecast Discussion
National Weather Service Reno NV
248 PM PST Sun Jan 14 2018


Dry conditions and above average temperatures will continue through
Monday with high pressure over northeast California and western
Nevada. Ridgetop winds increase Monday ahead of a modest, fast-
moving system for Monday night and Tuesday. A stronger and colder
storm system will bring gusty winds with snow and rain Thursday
into Friday.



Current water vapor satellite imagery shows a trough approaching
the west coast. This trough will not carry a lot of moisture
into CA/NV but precipitation will reach the west coast Monday and
then quickly move across the Sierra and the western Great Basin
Monday evening through Tuesday morning. The quick eastward
movement of this system will limit precipitation amounts. 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.

This not a cold system for a January storm, but winter driving
conditions are likely in the Sierra Monday night/Tuesday morning,
mainly above 7,000 feet. Up to 4 inches of snow are possible above
7,000 feet. This storm won`t produce very strong winds either,
with Sierra ridges gusting 40-55 mph beginning Monday afternoon,
and valleys generally 20-30 mph Tuesday afternoon/evening (30-40
mph at wind prone locations).

Wednesday looks to be a break between storms, but Sierra ridge gusts
will increase Wednesday as the next, stronger storm approaches.
Gusts across Sierra ridges will likely increase to around 100 mph
Wednesday afternoon, creating moderate-severe turbulence and wind
shear in the lee of the Sierra. JCM

.LONG TERM...Wednesday night and beyond...

Bottom line up front...forecaster confidence is increasing for
Thursday-Friday winter impacts to the region, including lower
elevations. If you have travel plans Thursday-Friday, you should
be paying close attention to the forecast, as cold temperatures
with snow and gusty winds are likely.

After an unusually warm January so far, winter will finally arrive
to the region by the end of the week and even into next week as
well. A much needed Sierra snow will be on tap as a colder, stronger
storm accompanied by a weak to moderate Atmospheric River (AR) and
potent Pacific jet stream is set to move into the region, which
should be a solid January storm by Sierra standards. Snowfall
amounts of over 1 foot are possible above 7000 feet, and from
several inches to around 1 foot down to 5500 feet. Colder air will
allow for higher snow to liquid ratios (and slightly greater snow
amounts) Thursday evening into Friday behind the front. There is
some variance among the medium range guidance as to when the colder
air arrives, but with the expected strong upper level jet we
continue to favor the faster scenarios where snow levels could fall
to near 5000-5500 feet by early Thursday evening, then down to all
valley floors Thursday night. Light snow amounts and slick roads are
possible for Reno-Sparks-Carson City and even for parts of west
central NV for the Friday morning commute.

Ridge winds will remain strong Thursday into Friday, associated with
the strong jet/cold front. Peak wind gusts over 50 mph are possible
during this time with ridge winds in the Sierra near 100 mph.
Powdery snow and gusty winds will likely produce blowing snow and
poor visibility for the Sierra passes.

As the main upper low moves overhead Friday, brisk and chilly
conditions are expected, although high temperatures will not be
that far from average for this time of year. Scattered clouds and
bands of snow showers will continue around the region due to
instability under the low. There could also be lake effect snow
bands downwind from Tahoe and Pyramid Friday, so we will need to
keep an eye on that as well. While additional snow amounts will
be lighter and more spotty, the Friday evening commute could still
be hindered in some locations due to temperatures quickly falling
to near/below freezing after sunset.

For next weekend, cool temperatures are likely to continue. A
shortwave ridge on Saturday will limit snow chances, then on Sunday
the medium range guidance begins to diverge with another storm
approaching the west coast. Some scenarios bring precip (mainly
snow) as soon as late Saturday night, while others hold off the
precip until the following Monday or Tuesday. With a continued
active Pacific jet stream, for now we will again favor the more
progressive outcome and include a chance for snow again Sunday,
mainly near the Sierra and in northeast CA/northwest NV. As with the
Thursday system, gusty winds are again likely to accompany this
storm. Beyond next weekend, additional storm systems with relatively
cool air could follow through the open door into the western US,
which should help the Sierra catch up on narrowing the seasonal
snowpack deficit. MJD



High cloud coverage will continue to increase throughout the rest
of the day into Monday as a shortwave trough from the northwest
begins to break down the ridge of high pressure which is currently
overhead. Expect VFR conditions to continue into Monday along
with light winds. The only exception will be for KTRK where light
winds and high cloud coverage will still be unable to inhibit the
development of early morning fog between 10-14Z on Monday.

By 06Z Tuesday, overcast conditions with increasing southwesterly
flow ahead of the trough will be the result as the weak system from
the northwest begins to move in. Winds will be gusty at times in the
15-20 kt range with even higher gusts on the Sierra ridge tops.
Turbulence is expected, especially as the associated cold front
sweeps across the Sierra and western NV mid-day Tuesday.

A second, but stronger system is on tap for Thurs-Fri which will
bring strong winds along with snow eventually dropping down to
valley floors. For more information, see the long term discussion
above. -LaGuardia


.REV Watches/Warnings/Advisories...


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