Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 190512 AAA
AFDREV

Area Forecast Discussion...UPDATED
National Weather Service Reno NV
912 PM PST Wed Jan 18 2017

.UPDATE...

After a lull in the precipitation over the last few hours, we will
see an increase in snowfall over the Sierra passes over the next
few hours, roughly between now through midnight. Snow levels look
to still be around 6000-6300 feet as of 9PM, with a mix of
rain/snow around South Lake Tahoe and Truckee.

The heaviest band of precipitation can be seen over the CA
Central Valley and starting to make the climb up the western
slopes of the Sierra. We should see snow levels lowering overnight
and into Thursday morning as well, bringing light snow down to
the foothills of western NV, especially west of Highway 395 where
up to 1-2 inches can be expected down to around 5000 feet. For the
valley floors, expect to see a dusting of snow overnight, but
generally less a half inch. Could have some slick conditions by
Thursday morning for western NV, especially in the foothills,
North Valleys, and Virginia City Highlands.

Heavy snow will push south into Mono County overnight tonight,
with snow amounts up to 6-12 inches along and west of US-395,
including Mammoth Lakes. The Sierra Crest of Mono County and up
through Tahoe will be pushing nearly two feet of snow by tomorrow
morning. Hoon


&&

.PREVIOUS DISCUSSION... /Issued 331 PM PST Wed Jan 18 2017/

SYNOPSIS...

A more active storm pattern will bring three systems to the
Sierra and western Nevada through the weekend, with the heaviest
precipitation coming from tonight`s system and Sunday`s system.
The systems will bring snow for the Sierra, with rain and snow
for the lower valleys through Friday, and mostly snow with
Sunday`s storm. Much drier weather is possible by the middle of
next week.

SHORT TERM...

Low pressure nearing the West Coast is pushing a modest moisture
tap (PWAT up to 1-1.25" into northern CA) into northern CA this
afternoon. With heavier precipitation pushing into the Tahoe Basin,
snow levels have come down to all valleys (~5800 feet) a few
hours earlier than expected...with CALTRANS cameras indicating
slush sticking to some roads already. Chain controls are already
in place for much of the northern Sierra and higher areas of
northeast CA. Out into the western Great Basin, some colder air is
still stubbornly trapped in valleys east of a Dayton to Fernley
line with temperatures in the mid to upper 30s. Still, roads have
warmed well above freezing and there are no NDOT restrictions at
this time.

Tonight into Thursday morning, snow continues in the Sierra with
snow amounts generally on track for the northern Sierra. For Mono
County, I have bumped up snowfall expectations for the Mammoth Lakes
area perhaps 3-6 inches through tomorrow. Out into western NV from
about Gerlach south, snowfall amounts have generally been
decreased to less than a half-inch below 5000 feet. Above 5000
feet, a couple slushy inches is still possible late tonight. The
light snow into western NV could make for some slick conditions
Thursday morning for the commute, mainly off the lower valley
floors (North Valleys, foothills west of town, Virginia
Highlands).

There will be a general lull in snow showers Thursday afternoon
through early Friday morning as the next system loads up over the
eastern Pacific. That system does not appear to have a solid
moisture feed like today`s system. However, the system looks
colder for higher snow ratios and Sierra snowfall possibly only
slightly less than with the current system. Also, a period of warm
air advection (WAA) Friday morning could bring a more widespread
snowfall (~1-4 inches) to western NV valleys as the WAA negates
lee side drying more efficiently. This could easily bring more
widespread commute issues to western NV Friday morning...although
given uncertainties it is still too early to issue winter weather
products. -Snyder

LONG TERM...Saturday night through Wednesday...

Computer simulations continue to show the potential for a strong
winter storm to impact the region Sunday into Monday. This storm has
the potential to bring significant snowfall to the Sierra as well as
western Nevada, but forecaster confidence remains low to medium with
the track of the storm.

The latest ECMWF and GFS solutions show a strong upper level jet
paired with a small segment of an atmospheric moisture tap that
would result in a period of strong winds and heavy snow from the
Sierra and down to potentially all valley floors Sunday into Monday.
Precipitation would begin early Sunday morning and readily spillover
into western Nevada valleys as well. Heaviest precipitation would
midday Sunday through Sunday night. Both models keep snow showers in
across the Sierra and western Nevada through Monday, with some
solutions even showing a mesoscale band developing early Monday
morning and dropping across the I-80 corridor. Any banding that
would develop behind the main trough axis would result in
localized higher amounts. This is one of those low frequency,
relatively low confidence, but high impacts scenarios. So this
storm will bear some watching through the upcoming week.

For those of you who grow weary of the active weather, confidence is
increasing for a period of quiet weather (i.e. no atmospheric rivers)
by midweek. Tuesday there may be some residual showers, but then
ridging builds in Wednesday which would allow the region to focus
on recovery efforts and drying out (or digging out) from this active
first half of January. -Edan

AVIATION...

First system of the week has pushed into the Sierra and western
Nevada with widespread lowered cigs and localized visibility
reductions where rain or snow is occurring. Precipitation intensity
should increase in the evening hours in the Sierra with localized
heavier snow bands possible tonight. Sierra terminals can expect
snow accumulations between 4 to 8 inches in the Tahoe Basin with 3
to 5 inches for KMMH. Rain should change over to snow for KCXP and
KRNO after midnight. For KRNO and KCXP we may see up to a half-inch
or so of snowfall by Thursday morning, but up to 2 inches will be
possible above 5000 feet.

Winds have stayed across the higher terrain today due to cold air
damming along the Sierra front. Winds may pick up later this
evening, but should remain much lower than the Sierra gusts (80-100
mph)

Conditions are forecast to improve marginally late Thursday for
western Nevada terminals. MVFR conditions may persist in the Sierra
as snow showers continue. Another system moves in Friday with snow
expected for most areas. Then a stronger system starts to affect the
area late Saturday into Sunday with gusty winds and snow. -Edan

&&

.REV Watches/Warnings/Advisories...
NV...Winter Weather Advisory until 4 AM PST Thursday NVZ005.

     Winter Weather Advisory until 4 AM PST Thursday NVZ002.

CA...Winter Weather Advisory until 4 AM PST Thursday CAZ070-071.

     Winter Weather Advisory until 7 AM PST Thursday above 6000 feet
     in CAZ073.

     Winter Weather Advisory until 4 AM PST Thursday CAZ072.

&&

$$

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


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