Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 121822

Area Forecast Discussion
National Weather Service Riverton WY
1122 AM MST Mon Feb 12 2018

.SHORT TERM...Monday through Wednesday night
Issued at 300 AM MST Mon Feb 12 2018

As expected, the front has slid across the area. And behind the
front, some light snow has broken out across portions of northern
and central Wyoming. This occasional snow should continue through
much of the day, although with little moisture to work with, amounts
should remain relatively light. As a result, we will issue no
highlights as amounts will remain below criteria. I am a bit
concerned with the area possibly coming under the influence of the
left front quadrant of a jet streak passing to the south of the
area. It is weaker and further south than the one on Friday though.
However, it could lead to the development of some of those pain in
the neck snow bands that can screw up a forecast quicker than you
can say bust. And like Friday, with the cold temperatures and high
snow ratios it could pile up quick. As I have previously stated,
these are hard to pinpoint until they occur. Otherwise, it will be
a cold February day, although the wind should decrease through
the day. The snow should end by around midnight as high pressure
builds into the area from the north.

High pressure will then build into the area and bring dry weather
from late tonight through Tuesday. The concern here switches to
temperatures. There will still be a decent southwest breeze across
the usual locations and like Rock Springs and Casper and this should
mix the atmosphere enough to raise temperatures. In the Basins, with
light winds and snow cover, inversions will likely hold; so we
have lowered continuity several degrees and well below guidance.

The next system then moves in for Wednesday with the next chance of
snow. The models are probably rushing the snow in too quickly so we
removed the POPS in the morning and confined them to the western
mountains during the day. Snow will then spread East of the Divide
Wednesday night. The other concern will be for wind, potentially
strong. The GFS shows some 50 to 60 knot winds at 700 millibars from
late Tuesday night through Wednesday across the southwestern Wind
Corridor and the Lee of the Absarokas. Still a little early for any
wind highlights, but something to consider. It should help mix out
the basins however, and allow for milder temperatures that could
bring some snow melt.

.LONG TERM...Thursday through Monday
Issued at 300 AM MST Mon Feb 12 2018

A weather system moves through the area Thursday bringing a
chance of snow and colder temperatures. Hard to pinpoint where the
best snowfall will occur at this time. The snow decreases
Thursday night with some lingering snow showers in the mountains.
Friday looks dry for most places. The GFS model has some light
snow in NW WY while the ECMWF model is dry. Will keep snow in NW
WY. High temps will moderate a little on Friday. Saturday will be
dry for most places. The GFS continues with some light precip in
NW WY Saturday while the ECMWF is dry. Once again will have some
snow in NW WY. High temps Saturday will be milder for all areas.
The next storm system brings a good chance of snow to the west
Saturday night, Sunday, and Sunday night. East of the continental
divide, snow is forecast to develop Sunday morning or afternoon
and continue through Sunday night. Snow is likely to occur next
Monday as well in many locations. Both models are bringing a shot
of arctic air into the area Sunday into Monday. Thus much colder
highs can be expected. Plenty of time to watch how this potential
significant storm evolves this coming weekend.


.AVIATION...For the 18Z TAFS through 18Z Tuesday
Issued at 1122 AM MST Mon Feb 12 2018

West of the Continental Divide...KJAC, KBPI, KPNA, and KRKS

An upper level disturbance moving up from the Great Basin will fill
in points further south with areas of MVFR, local IFR conditions in
light snow from around 18z through 21z, affecting KRKS, KBPI and
KPNA.  Clearing will occur behind this system late Monday afternoon
and Monday evening, leaving some snow showers lingering near
Wyoming`s southern border after 06z Tuesday.

East of the Continental Divide...KCPR, KCOD, KRIW, KLND, and KWRL

Areas of MVFR, local IFR ceilings with occasional MVFR visibilities
in light snow will persist across the area through Monday afternoon.
Surface winds will be primarily out of the E-NE through 00Z Tuesday.
Mountains will remain mostly obscured. An upper level disturbance
moving up from the Great Basin will likely bring a shot of more
widespread MVFR/IFR conditions in -SN vicinity and south of a KLND-
KRIW-KCPR line 18z-22z Monday.  Clearing, prevailing VFR conditions
are expected 02z-12z Tuesday.


Issued at 300 AM MST Mon Feb 12 2018

Occasional snow will fall today, although large amounts are not
expected. A gusty wind will occur this morning but will slowly
subside through the day. Temperatures will be well below normal with
relative humidity remaining rather high. Mixing and smoke dispersal
will be generally fair to poor.





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