Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 181120

Area Forecast Discussion
National Weather Service Reno NV
320 AM PST Mon Dec 18 2017


Expect seasonal temperatures and moderate temperature inversions
through Tuesday. A fast moving cold front will produce strong
winds Tuesday night into Wednesday, along with very cold
temperatures for late week, and has the potential to bring a
couple inches of accumulating snow to all elevations.



A very strong cold front will move through the region this week with
disruptions to air and ground travel a significant possibility.
Model simulations have been quite consistent for the last 3 days
with the magnitude of cold air expected to drop into the region
this week. What has changed in recent model simulations is the
trajectory of the upper low. The low is digging in a little bit
deeper offshore before it moves into the Sierra, where in previous
simulations it was digging in along the east side of the Sierra,
closer to what we call an inside slider. This change will increase
the amount of available moisture, especially in the Sierra. It is
also intensifying the 700 mb flow, significantly increasing the
wind potential.

Recent wind simulations show the potential for a period of strong
damaging winds mixing to the valleys of western Nevada Tuesday
night. A High Wind Watch has been issued for Sierra and western
Nevada for Tuesday night. Wind gusts at the surface could reach 50
to 60 mph with wind prone areas potentially exceeding 75 mph, and
gusts of gusts of 120 mph or more along the Sierra crest. The
duration of strong winds is expected to be relatively short since
the cold front is moving very quickly through the area, with most
intense winds occurring ahead of the front. The peak winds are
currently projected to be overnight which will make the wind gusts
more erratic, especially in the lower elevations, going from near
calm conditions to very intense wind gusts in a matter of
seconds. This will create very turbulent conditions with strong
wind shear along the cold front.

The intense cold front will very likely bring snow to all
elevations, even `down here` in Reno and Carson City. Current
expectations is for 1 to 2 inches of snow in the lowest valleys.
The westward shift of the low has allowed the system to have a
better over water trajectory and draw more moisture into the
system. This has increased the precipitation potential for the
Sierra with better moisture availability for orographic lift on
the west slopes. Current forecast has been increased to 3 to 6
inches of snow in the mountains. The westward shift has also
lowered confidence some in the amount of snow that may accumulate
in western Nevada, although a brief intense snow squall is still
likely to move through western Nevada with very heavy snowfall
rates for an hour or two.

These slider type storms are always a challenge to forecast. What we
can say with high confidence is that a very strong cold front will
move through the region this week and that temperatures will be
plenty cold for snowfall down to all western Nevada valleys. When
it comes to how much wind vs. how much snowfall we will see,
small changes in the trajectory can affect this balance so there
is still uncertainty in the magnitude of the wind and snowfall.
But, considering the intensity of the cold front, if it was me, I
would be preparing for both a period of high winds and some
accumulation of snow. -Zach

.LONG TERM...Thursday through Christmas Day...

A blocking pattern over the east Pacific will keep storms away from
the Sierra and western NV with dry and cool conditions. Gusty
northeast ridge winds will persist Thursday morning in the wake of
the mid week storm but should ease Thursday night-Friday. A
shortwave will be dropping southward along the backside of a large
North American trough which will usher in another shot of dry cold
air from the northeast Saturday. This will keep temperatures quite
cool, especially at night when readings will drop into single digits
for colder valleys. Hohmann



High pressure will persist through tonight with light winds. A fast
moving upper low pressure system will drop south into the region
Tuesday-Wednesday for a period of strong winds and chance of snow.
Southwest winds will begin to increase across the ridges Tuesday and
continue to increase ahead of a strong cold front Tuesday night.
There will be a period of LLWS Tuesday evening before strong winds
develop late evening into Wednesday morning at lower elevations
along and ahead of the cold front. There will likely be a 2-3 hour
window of very strong surface winds when gusts will exceed 50 kts as
the front works southeast across the area. Once the front passes,
surface winds will decrease to a more steady 15-25 mph although
turbulence will persist as upper level winds remain strong.

A band of snow is still expected along the front with the main
change being a slight increase in snowfall amounts for the northern
Sierra. Snowfall amounts up to 2 inches will be possible for western
NV airports and KMMH Wednesday morning with 2-5 inches from the
Tahoe Basin northward. The snowfall is still expected to fall
quickly in an intense band along the front (lasting from 2-4 hours
in the northern Sierra to 1-2 hours elsewhere). Hohmann


.REV Watches/Warnings/Advisories...
NV...High Wind Watch from Tuesday evening through Wednesday morning

CA...High Wind Watch from Tuesday evening through Wednesday morning



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