Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 180228
AFDREV

Area Forecast Discussion
National Weather Service Reno NV
628 PM PST Sun Feb 17 2019

.UPDATE...

Radar imagery shows lake enhanced snow starting to increase off
Pyramid Lake and moving into areas like Palomino Valley...Spanish
Springs...and Hungry Valley in northern Washoe County. There are
also indications that minor lake enhancement is developing off
Lake Tahoe on the southwest side of the lake into the Desolation
Wilderness. This is in response to the low level flow shifting to
the northeast as the upper low that brought all of snow to the
area today shifts farther south and southeast.

While the areas with moderate to heavy snow tonight will be
isolated...there is enough concern that bands of snow could develop
along the I-80 corridor in Washoe County to extend the Winter
Weather Advisory for the Sierra Front of western Nevada until 10
pm. We will also extend the Winter Storm Warning for the Tahoe
area until 10 pm.

After the 10 pm to midnight time frame...the extent of lake
enhancement should begin to wane. That does not mean that all of
the snow will end...just that the better chances for accumulation
will end.

&&

.PREVIOUS DISCUSSION... /Issued 323 PM PST Sun Feb 17 2019/

SYNOPSIS...

Snow continues across the region this afternoon with long travel
delays in the Sierra. Some lake effect snows are possible near
Tahoe and Pyramid. Frigid overnight lows are expected early next
week with subzero temperatures possible for some Sierra valleys.
The next round of snowfall looks to arrive midweek as a slider
type system is possible across the Sierra and western Nevada.

SHORT TERM...

Snow continues to fall this afternoon throughout the Sierra and
portions of western Nevada as a cold area of low pressure keeps a
stronghold over the region. The low is beginning to pivot and flow
is transitioning from westerly to northeasterly. This will cut the
upslope enhancement into the western Sierra and also begin to
dissipate the lake enhanced snow showers that are stretching into
south Carson City and Minden at the time of writing.

The wrap-around bands of moisture, however, will continue, with snow
activity this afternoon and between the I-80 and US-50 corridor,
sagging south and weakening across Mono/Mineral/Lyon counties
this evening. With the northeasterly flow, we could see some lake
effect snow forming off of Pyramid Lake heading toward Spanish
Springs. In fact, some high resolution models indicate this may
linger into Monday morning. South Lake Tahoe, the southwest shores
of Tahoe, and portions of US-50 heading out of the Tahoe Basin
could also possibly see locally higher totals if bands form off of
the lake this evening.

Travel continues to be a mess in the Sierra with travel times likely
to be at least 2-3x longer than usual. In fact, road crews have been
reporting traffic at a standstill in many locations along I-80
and US-50 going toward Tahoe. Check with CalTrans and NDOT for
the latest information. If you are looking for a clear travel
window and want to avoid some serious travel headaches, just wait
until Monday. We are continuing the Winter Storm Warning for the
Tahoe area and the Winter Weather Advisory through the Greater
Reno/Carson metro areas through this evening. For northeast
California and Mono County, we are dropping the warnings as
additional snow amounts will be minimal.

The upper trough which has brought loads of snow and rain to the
region this past week slowly slides east Monday into Tuesday, with
the flow remaining northerly. This will keep temperatures cold with
upslope snow showers possible for the eastern Sierra on Monday.
Chances for snow are only around 20%, and if snow does occur, totals
will be light. We should begin to stabilize late Monday into Tuesday
with no additional precipitation.

Temperatures will remain cold, with highs about 10-18 degrees below
normal for this time of the year. Lows will be quite cold the next
two mornings, especially Tuesday morning when temperatures will
plunge as skies clear and winds remain light. Widespread teens to
and single digits are likely for western Nevada with single digit to
below zero temperatures in the Sierra.

Our break in the active weather is short-lived as another system
drops into the area from the north Wednesday. The timing on this has
been speeding up, with the system likely to bring additional snow
(is that starting to become a bad word after this month?) to all
elevations. -Dawn

LONG TERM...Wednesday night through next weekend...

Not much change to the long term forecast. Cold, continental air
sourced from Canada will bring a continuation of much below average
temperatures Thursday and Friday before a potential change to
westerly flow aloft finally brings a milder airmass into northeast
CA and western NV. The main impactful weather system (slider-type)
is still centered around Wednesday and Thursday.

Wednesday night into Thursday, many simulations still support an
upper disturbance dropping south somewhere between the high Sierra
and west-central Nevada, with a band of snow pushing quickly through
the region in that time frame. As simulations remain solidly against
the system passing much west of the crest, expect that whatever snow
we get will be similar or even less in the northern Sierra/Tahoe
area than in western and west-central NV (as is typical with
sliders). Farther south, into Mono County, tends to do better
than Tahoe as upslope northeast flow can aid snow production
there. As this is the always tricky "inside slider" track, more
details are still very fluid as snowfall with sliders is very
sensitive to the exact track of the system. In fact, often it can
be within 12-24 hours before the details really start to congeal.
Sorry...that is all I can tell you at this time!

Thursday night and Friday, the region returns to dry weather
although it will stay quite chilly given how late it is in winter.
By next weekend, flow aloft turns more westerly in many simulations
with milder air returning to the region. There are a few outliers
showing another cold system dropping down the West Coast next
weekend, namely the 06Z/18Z GFS. That model often flops around in
its non 12/00Z runs and it is not supported strongly in its
ensembles so will call that a much less likely solution for now.
-Snyder

AVIATION...

Low pressure is moving directly over the Reno-Tahoe and Carson City-
Minden areas this afternoon. This has been responsible for the
widespread light to moderate snow today west of a KLOL-KHTH line,
with the heaviest snowfall amounts from the low west of the Virginia
and Pah Rah Ranges of western NV. Widespread IFR conditions in snow
currently should shift mainly south of Interstate 80 late this
afternoon and into early evening, with -SN/SN and IFR/LIFR
conditions likely to linger another 2-3 hours near/south of Hwy 50
(KMEV/KCXP/KTVL) before snow showers shift off into Mono, Mineral,
and southern Lyon Counties overnight.

Drier northerly flow develops Monday for mainly VFR conditions,
although lingering MVFR conditions are possible in Mono and western
Mineral Counties in the morning with upslope northeast flow.
-Snyder

&&

.REV Watches/Warnings/Advisories...
NV...Winter Storm Warning until 10 PM PST this evening NVZ002.

     Winter Weather Advisory until 10 PM PST this evening NVZ003.

CA...Winter Storm Warning until 10 PM PST this evening CAZ072.

&&

$$

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


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