Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 282035
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
135 PM MST Mon Nov 28 2016

.Short Term...Tonight Through Tuesday

Organized snowfall quickly coming to an end in the western
mountains and not much yet east of the Continental divide outside
of the mountain areas.  As the closed upper level low pressure
center moving into Minnesota ejects east northeast through the
evening, strong northwest flow aloft will line up with the Bighorn
mountains significantly increasing the flow over northern Johnson
county. Have upgraded High wind watch to a high wind warning for
tonight and Tuesday. Some light snow showers will linger over and
near the mountains in the northwest flow with colder temperatures
moving in.

.Long Term...Tuesday Night Through Monday

Cold northwest flow will gradually shift to the east as a high
pressure ridge aloft shifts east into western Wyoming.  General
clearing will occur while some low stratus may linger over and
near the mountains. Overall wind will decrease. A Pacific low
pressure trough will approach the western mountains Wednesday
afternoon increasing through the night with some warming east of
the Continental Divide as clouds increase.  A cold front will
move south from Montana on Thursday with light snow spreading
across the central and east as cold air moves in. Snowfall
amounts in the cold air look very limited but some places along
the north and east facing mountain slopes may see 1c to 3 inches
of light fluffy snow. This will start a rather prolonged cold
spell which will be hard for the valleys and basins to recover
from as temperature inversions will develop and the cold dense air
will be hard to scour out of the lower elevations. Will likely
need to add areas of fog to the forecast but am more concerned
with snow amounts at this time. Friday looks rather benign with
Wyoming between troughs and high pressure in place. Temperatures
will likely be the biggest forecast challenge. Friday night and
saturday a Pacific low pressure trough will move towards northwest
Wyoming from Northern Idaho and Western Montana with light
snowfall spreading across the west and north. This will keep some
light snow over the mountains through Saturday night but moisture
looks very limited and cold air will remain trapped in the
valleys and basins. The flow aloft is expected to shift from the
northwest to west with a flat ridge. Moisture will increase into
the west ern mountains Sunday afternoon and Sunday night with a
warmer source region. Moisture content should increase with more
productive snowfall resulting. Windy areas will increase across
the south and east. Snowfall amounts could be significant Sunday
night and Monday as a trough deepens to the west of Wyoming with a
continued favorable moisture plume. Winds across the south and
east could get quite strong ahead of a cold front moving south
from Montana.

&&

.Aviation.../00Z Issuance/

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

The coverage of snow over the west will continue to decrease in
coverage this afternoon and evening, but occasional MVFR/IFR
conditions will continue in snow shower activity through the
evening. After midnight and through the day Tuesday, lower
elevations should be mainly dry, with a continued chance of snow
showers/flurries over the mountains. A cold front is likely push
south southwest across much of eastern Sweetwater County between 04Z
and 07Z...shifting winds from the west northwest to north northeast
including at KRKS. However this should be brief with winds shifting
back to the west northwest between 10Z and 14Z. Breezy northwest
winds will impact KBPI and KPNA tonight and Tuesday. Mountains will
be obscured much of the time.

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

Windy to strong northwest wind is expected in many areas tonight and
Tuesday. The strongest wind will be across northern Johnson, and the
northern Big Horn Basin. Models showed LLWS impacting the WRL
terminal late tonight into the day Tuesday. Scattered snow showers
developing over the mountains pushing southeast into the lower
elevations will be possible through tonight with the best chance
between 00Z and 07Z Tuesday. Although MVFR/IFR conditions will be
possible with this snow shower activity, confidence is not high
enough to prevail any terminal with those conditions. On Tuesday,
snow showers will be mainly confined to the northern mountains
especially over the Big Horn Range. Northern Mountains will
frequently be obscured in low ceilings and snowfall.

&&

.Fire Weather...

Organized snowfall quickly coming to an end in the western
mountains and not much yet east of the Continental divide outside
of the mountain areas.  As the closed upper level low pressure
center moving into Minnesota ejects east northeast through the
evening, strong northwest flow aloft will line up with the Bighorn
mountains significantly increasing the flow over northern Johnson
county. Have upgraded High wind watch to a high wind warning for
tonight and Tuesday. Some light snow showers will linger over and
near the mountains in the northwest flow with colder temperatures
moving in. The basins and valleys will have inversions in place
with poor smoke dispersal. The windy areas of the east will have
good smoke dispersal on Tuesday.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 5 PM MST this afternoon for WYZ012-
023-024-027.

High Wind Warning from 11 PM this evening to 5 PM MST Tuesday
for WYZ010.

&&

$$

SHORT TERM...C.Baker
LONG TERM...C.Baker
AVIATION...WM
FIRE WEATHER...C.Baker


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