Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 272210
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
310 PM MST Mon Feb 27 2017

.Short Term...Tonight Through Thursday

A series of short wave low pressure troughs in west southwest flow
aloft will bring periods of rather light snowfall to the west
through Thursday. The highest accumulations will be in the Tetons
and southern Yellowstone National Park where 3 to 6 inches each
day can be expected. The other areas of the west will be in the 2
to 4 inch range with 1 to 2 inches in the valleys. East of the
divide strong west to southwest winds will blow over and near the
east slopes of the mountains and across the wind corridor fro Rock
Springs to Casper. Warming in the windy areas is expected but so
far the warming has been unimpressive considering the wind speeds.
Some areas near the foothills may experience some blow over
snowfall but amounts will be insignificant.

.Long Term...Thursday Night Through Monday

Thursday night: Modest PAC NW moisture continues to flow into the
region over a ridge and through NW flow into WY. Along with one or
two embedded waves, this will keep the northwest/northern portion of
the FA slightly unstable. Together with a little extra mountain
lift, the mountains across northwest/northern WY will remain under
conditions that will produce light (snow) showers. Temperatures at
all locations through Friday morning will continue to remain largely
below seasonal with little to no significant snow-melt.

Friday through Sunday: Weak ridging/upper level NW flow will flatten
in response to an approaching embedded upper level SW trough/jet
streak that will arrive near western WY Friday night. The transition
to nearly zonal flow on Friday will allow for increased lee side
troughing and gusty strong wind potential. Some of these winds will
border on `High` periodically across the usual suspect areas (lee
side foothills east of the Continental Divide and across the Wind
Corridor) from Friday through much of the day Monday. Will nail down
more specifics as the forecast moves closer to the end of the week.
Temperatures will respond positively to the lee side troughing/wind
set-up east of the Divide from Friday through Monday...reaching near
normal seasonal temperatures and starting another period of melt-
off. Additionally, relatively light snowfall will continue in some
fashion over northwestern WY until Saturday morning and the arrival
of the jet when precipitation will increase both spatially and in
intensity across the western mountains...and especially the
northwestern mountains where the moisture will be. If position and
timing of this system remain on track, highlights will surely be
needed from Saturday night onward for at least Teton and Park
counties.

&&

.Aviation.../00Z Issuance/

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

An upper level trough is currently approaching WY with modest
moisture and a few embedded disturbances ahead of the trough causing
some areas of snow showers to continue across the forecast area.
Widespread VFR/MVFR with areas of localized IFR conditions in light
snow and mountain obscurations will characterize much of the
forecast period. Scattered snow showers will also continue to drift
east and south of a boundary along and south of the Interstate 80
corridor into early this evening. Drier air will then move into the
southern portion of the area later this evening with isolated to
scattered light snow showers remaining primarily over the west
central and northwest mountains after 06z before then next upper
level disturbance arrives across the western forecast area late in
the morning, lowering CIGS and increasing snow chances once again
through the end of the period, particularly at KJAC and KPNA.

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

An upper level trough is currently approaching WY with modest
moisture and a few embedded disturbances ahead of the trough causing
a few areas of snow showers to move across the southern and central
portion of the forecast area. VFR conditions will prevail through
the forecast period for most terminal sites. KWRL, however, will see
MVFR, to possible brief IFR, with lower CIGS and reduced visibility
in -SHSN between 03Z and 06Z as one of the disturbances moves over
the terminal. Otherwise, isolated to scattered MVFR snow showers
will continue to drift near and south of a vcnty KLND-KCPR line,
along a boundary, early into this evening period.

&&

.Fire Weather...

A series of short wave low pressure troughs in west southwest flow
aloft will bring periods of rather light snowfall to the west
through Thursday. The highest accumulations will be in the Tetons
and southern Yellowstone National Park where 3 to 6 inches each
day can be expected. The other areas of the west will be in the 2
to 4 inch range with 1 to 2 inches in the valleys. East of the
divide strong west to southwest winds will blow over and near the
east slopes of the mountains and across the wind corridor fro Rock
Springs to Casper. Warming in the windy areas is expected but so
far the warming has been unimpressive considering the wind speeds.
Some areas near the foothills may experience some blow over
snowfall but amounts will be insignificant.  Poor smoke dispersal
is expected through Thursday in the valleys. The windy areas over
and near the mountains and through the wind corridor may
experience fair to good smoke dispersal in the afternoons through
Thursday.


&&

.RIW WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

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


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