Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 192039

Area Forecast Discussion
National Weather Service Reno NV
139 PM PDT Mon Mar 19 2018


Dry weather is expected through early Tuesday with light winds.
A period of light valley rain and higher elevation snow is expected
Tuesday evening and Tuesday night. A much stronger system pushes
into the region Wednesday night through early Friday morning. This
will bring periods of valley rain and heavy Sierra snow along
with gusty winds. The weekend will be colder with snow showers
possible down to all valley floors.



The only significant changes during the short term part of the
forecast cycle were made to Wednesday. The model guidance is
pointing toward a drier period east of the Sierra Wednesday before
spill over begins in earnest Thursday.

Ahead of the main system...the first period of precipitation
develops Tuesday afternoon/overnight. There are really two processes
going on at this time.

North of I-80 there is an area of warm air advection that brings
light precipitation to northeast California down to about the
Tahoe area and into far western Nevada. The uplift is stronger and
persists longer near the Oregon border. There is some question
about snow levels...but at this time it appears there is enough
warm air near the surface...with limited evaporational cooling due
to increased limit snow accumulations to areas
above 5000 feet from Highway 70 north. There will likely be some
light accumulations above 6500 feet in the Tahoe basin. The
forcing decreases enough by early Wednesday to remove POPs from
western Nevada.

Farther south into Mono County Tuesday night...the initial push
of moisture associated with a deep moisture plume begins to affect
the area. The forcing is not overwhelming and much of the
precipitation is due to upslope flow and confined near the crest.

A definite break develops Wednesday east of the Sierra but
upslope in the Sierra and weak forcing in far northeast California
should keep precipitation going through the day in those
locations...albeit not very heavy. Breezy winds are likely in
western Nevada with strong gusts over the ridges.

A more significant deep moisture plume begins to push into the
area Wednesday night into Thursday. This is subtropical air so
snow levels climb above 7000 feet in northeast California...above
7500 feet around Tahoe...and above 8000 feet in Mono County. This
will confine snow to the highest elevations into Thursday

QPF was increased a bit with this storm as the moisture plume is
spread a bit farther north now and there is a period of jet
coupling in the Sierra and northeast California that could lead to
increased precipitation rates Thursday morning/afternoon. Snow
levels begin to fall late Thursday night...but by then the
moisture plume is sliding south. The biggest snowfall totals
should be above 7000 feet for Tahoe and 7500 feet for Mono County.
We will issue watches for these areas. Moderate to heavy rain is
possible below these levels until Thursday evening. That could
cause minor flooding in urban areas where snow has not been
removed to allow for drainage. There could also be rises on small
streams below 7000 feet that drain into the Tahoe basin and on
the east side of the Sierra.

In the lower valleys this event will be all rain with totals
approaching 0.50-0.75 inches in the valleys and foothills of
western Nevada, and for areas of northeast California east of
Susanville. Much of the snow in the valleys should melt or sublimate
Tuesday and Wednesday...but there remains a slim possibility that
minor flooding of poor drainage areas could occur in some urban

.LONG TERM...Friday through Monday...

The cold front which finally drives snow levels down to all valley
floors is still not due to move through until Friday (northeast CA,
Tahoe area, western Nevada) or Friday night (Mono, Mineral, eastern
Churchill Counties). The best shot for lower elevation snowfall and
road impacts will be Friday night into Saturday morning as an upper
low off the Pacific Northwest coast comes inland. At this time, the
Sierra from Alpine County northward and western NV north of
Interstate 80 stand the best chance at picking up a light snowfall
from the final upper disturbance. For the Basin south of I-80, the
forcing is currently simulated to remain too far north with snow
showers dissipating before reaching those areas.

Chances for showers diminish Sunday and Monday, with temperatures
beginning to rebound towards normal in the GFS with temperatures
holding below average in the EC with a weak residual trough
hanging around. -Snyder



VFR with light winds below ridges for most of northeast California,
the Sierra, and western Nevada through the day Tuesday. The
exception is at/near KTRK where there is a 30-40% chance for FZFG
from about 3-9 AM Tuesday, much higher if skies become clear;
however, high clouds are expected tonight and a 045-060 AGL deck is
possible by around sunrise Tuesday.

A weak system will bring light rain and snow Tuesday evening into
early Wednesday morning for the Sierra, northeast CA, and far
northwestern NV...with substantially lowered ceilings and terrain
obscuration likely. For western NV, some higher terrain obscuration
is possible Tuesday evening with light rain.

A much stronger storm for Wednesday evening through Thursday night
will bring periods of gusty winds, moderate to heavy mountain snow,
and valley rain. Terminals should all just see rain, but expect
widespread mountain obscuration and periods of MVFR (30% chance IFR)
ceilings and visibility. Winds will bring turbulence and areas of
wind shear, with local studies indicating LLWS possible for KRNO
with southerly winds Wednesday into Thursday. Snow showers are
possible for all airports Friday afternoon into Saturday, with the
potential for minor accumulations overnight and in the morning.


.REV Watches/Warnings/Advisories...
NV...Winter Storm Watch from Wednesday afternoon through late
     Thursday night above 7000 feet in NVZ002.

CA...Winter Storm Watch from Wednesday afternoon through late
     Thursday night above 7500 feet in CAZ073.

     Winter Storm Watch from Wednesday afternoon through late
     Thursday night above 7000 feet in CAZ072.



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