Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 231130
AFDREV

Area Forecast Discussion
National Weather Service Reno NV
330 AM PST Thu Nov 23 2017

.SYNOPSIS...

Very mild conditions will prevail through Saturday with a few record
highs threatened. Most areas will remain dry although very light
rain is possible Thursday in northeast California and far northwest
Nevada. Saturday is expected to be very windy ahead of a strong
cold front which will bring snow to the Sierra and northeast
California Sunday and Sunday night. Expect travel delays
transiting the Sierra due to slick driving conditions and higher
post holiday traffic volume. It will be much colder early next
week.

&&

.SHORT TERM...

The forecast remains on track with very few model differences from
previous runs. Currently, some light rain is falling over northern
Lassen County through northern Washoe County as a weak boundary
remains draped in that vicinity. This boundary is projected to
shift southward through the morning hours bringing a hundredth or
two of rain as far south as the Tahoe Basin by late morning.
Otherwise, precipitation washes out as the boundary loses support.
Additionally, cloud cover associated with the boundary will
limit fog formation in Sierra Valley and around Truckee this
morning. Still, some pockets of freezing fog will be possible
where cloud cover remains minimal in Sierra valleys.

After a relatively benign Thanksgiving Day and Black Friday, winds
begin to increase Saturday as a potent Pacific storm moves
towards the region. Upper level jet wind projections show a
larger area of 100+ knots with a maximum around 150 knots
superimposed over the Sierra. This will translate to strong gusty
surface winds for the region, especially for downslope areas
along and west of Highway 395. The current wind forecast continues
to have strong gusts to 60 mph along the Sierra Front with ridge
winds topping 100 mph. Expect some travel restrictions for high
profile vehicles especially through wind prone locations like
Highway 395 in Washoe Valley and from Doyle to Susanville. A High
Wind Watch remains in effect for much of the region. Winds will
drop, especially for Sierra valleys, as precipitation moves into
the region Saturday night. However, shadowed locations like the
Sierra Front will likely see gusty conditions continuing through
the night into Sunday. Boyd

.LONG TERM...Sunday through Tuesday...

The focus remains on the strong cold front to move through Sunday
night and potential late holiday weekend travel impacts as a result.
It still looks windy for Sunday as more moisture moves into the
region. How strong the winds are Sunday is up for debate. A faster
solution like the GFS has more moisture into the Sierra and
therefore dampening the mountain wave a bit. This would result in
breezy winds, but nothing excessive and lighter than Saturday
evening, at least north of highway 50. Slower like the EC keeps high
winds into Sunday afternoon.

Despite the timing differences, the overall impact for snowfall in
the Sierra looks the same. Snow levels will start 8-9000 feet, then
gradually fall about 1-2000 feet into Sunday evening before crashing
with the cold front. Most of the moisture remains ahead of the
front, which will keep the heaviest accumulations above about 7000
feet or so. Still, several inches of snow over the major Sierra
passes of Donner and Echo is likely. Lighter amounts down to 5000-
5500 feet.

Spillover into Western Nevada is not ideal, but there will likely be
some at least for the Sierra Front and 395 corridor. Strong SW winds
aloft with good speed shear and strong frontal forcing are
favorable. However, the instability and moisture is not that deep,
only up to 600 mb or so which is unfavorable. Will keep amounts
light beyond the east slopes of the Sierra.

Behind the front Monday it will be much colder, but nothing abnormal
for late November. Winds will also diminish behind the front and
showers look to rapidly diminish as well as much warmer temps aloft
stabilize the atmosphere. The cooler temps will continue into
midweek with temperatures near seasonal averages overall as a low to
moderate amplitude ridge moves overhead. It does appear overnight
lows may be a little cooler than average while highs are a little
above.

&&

.AVIATION...

MVFR visibility restrictions have occurred early this morning at
TRK. Expect variable fog thickness through the night as mid/high
clouds intermittently pass over the terminal. Overall, the depth
of fog and duration is not expected to be as thick/long as
yesterday, but periods of IFR remain possible through the morning.
Cloud cover should thicken by late morning as a weak boundary
drops southward along the Sierra. This boundary could produce a
hundredth or two of rain for Sierra terminals.

Otherwise, ridge winds continue to gust around 50kts creating some
light to moderate mechanical turbulence. These winds will continue
today through Friday before increasing substantially as a potent
Pacific storm nears the region. Strong mountain waves are expected
Saturday and Sunday with severe turbulence likely. Surface gusts
are forecast to meet and exceed 50 kts at times. Anticipate LLWS
as well.

Precipitation will begin as rain through Flight Level
14000ft MSL Saturday night. Expect periods of IFR rain and
ultimately snow Sunday and Sunday night; periods of MVFR Cigs will
be possible for western Nevada terminals. Snow levels will fall
gradually through Sunday reaching ridge level. A strong cold front
is projected to bring snow levels down to near western Nevada
valley floors by Monday morning. Boyd

&&

.REV Watches/Warnings/Advisories...
NV...High Wind Watch from Saturday morning through Sunday afternoon
     NVZ003-005.

     High Wind Watch from Saturday morning through Saturday evening
     NVZ002.

CA...High Wind Watch from Saturday morning through Sunday afternoon
     CAZ070-071-073.

     High Wind Watch from Saturday morning through Saturday evening
     CAZ072.

&&

$$

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


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