Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 170920

Area Forecast Discussion
National Weather Service Reno NV
220 AM PDT Sat Mar 17 2018


A winter storm will continue to impact the region into early
Saturday morning with dangerous travel conditions in the Sierra.
Snow showers and well below normal temperatures Saturday will
give way to a drying and warming trend for early next week. The
next storm system is forecast to bring rain and heavy mountain
snow for Wednesday and Thursday.



Most mountain roads continue to have chain controls, and at lower
elevations there is clear ice this morning along some stretches
of roadways and sidewalks, so be prepared for transitions from dry
to icy surfaces if you travel.

The main cold front has moved out and an upper low has moved
over the eastern Sierra and western NV. The upper low has created
an unstable airmass which will become more unstable this
afternoon. Probably not unstable enough for lightning (though we
can`t rule out a few strikes) but enough for convective snow
showers to continue through this afternoon. Some of the stronger
showers could be capable of creating a quick inch of snow, especially
in the Sierra.

One forecast challenge is the threat for freezing fog tonight as
skies begin to clear with abundant surface moisture due to the
recent snow. North of I-80 there may be just enough high cloud
cover to limit fog development, but in the Martis Valley and along
I-80 from the Truckee exits to Donner Lake freezing fog is likely
late tonight. Across western NV, can`t completely rule fog
development out, but model sounding don`t look favorable for other
than isolated patches.

Sunday looks dry and partly cloudy due to weak ridging aloft,
outside of perhaps some snow flurries in the Sierra. Sunday night
clouds should increase with westerly flow, which limits the
potential for freezing fog going into Monday morning. JCM

.LONG TERM...Monday onward...

Greatest concern in the long term period continues to be the system
for the late Tuesday through Thursday time frame. There are two
features of note, the first being an atmospheric river (AR) moisture
tap late Tuesday into Wednesday and the second being a colder trough
Thursday. AR detection tools continue to indicate the deepest
moisture heading into central and southern California, bringing the
greatest impacts to Mono County south. However, much of the Sierra
and northern California are within the ensemble plume for the
northern edge of the AR moisture. The trend for this AR has been
southward, and how far north the moisture makes it will likely be
dependent on the timing and location of the upstream trough and how
the subtropical jet and polar jet interact.

At this point, feel we will get into the warmer wetter portion of
the storm for a short period Wednesday, followed by the colder
trough and moisture from that storm Thursday. The warmer portion of
the storm could bring snow levels up to 6500-7000 feet for the
central and northern Sierra and 7000-8000 feet for the southern and
eastern Sierra. The period of higher snow levels is only likely to
last 12-18 hours before the trough and associated cold front shift
into the region Thursday morning. Snow levels have the potential to
reach valley floors by Thursday night, however it is still
questionable how much moisture will be around at this point.

While there are still uncertainties on how the two parts will
interact, what can be said is periods of heavy mountain snow look
likely along with valley rain late Tuesday through Friday. How much
travel will be impacted will be dependent on exact snow levels and
how long of a duration there may be accumulating snow along Sierra
passes. A period of stronger winds also looks probable Wednesday and
especially Thursday which may bring travel restrictions for high
profile vehicles, choppy conditions on area lakes, and turbulence
for aviation interests.

Beyond this system, operational forecast models begin to diverge and
are nearly 180 degrees out of phase. Ensembles support anything from
a secondary wave bringing additional cold air and snow to the region
to a ridge beginning to build along the west coast with warming and
drying conditions. Obviously, this means a very low confidence
forecast for next weekend, so check back for updates. -Dawn



Convective showers could create brief bursts of snow or snow
pellets this morning through this afternoon, especially in the
Sierra. Expect terrain obscuration and periods of MVFR conditions
in the Sierra, with a 30% chance for these conditions in western

As skies begin to clear, freezing fog is likely at KTRK by late

The next storm system is forecast to bring rain and heavy
mountain snow for Wednesday and Thursday. JCM


.REV Watches/Warnings/Advisories...


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