Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 060630
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1130 PM MST Tue Dec 5 2017

.UPDATE...
Issued at 937 PM MST Tue Dec 5 2017

BYG airport has gusted to 52 kts. The HiRes W-NMM and soundings
show the high wind continuing for the rest of the night across
northern Johnson County especially north of Buffalo. The winds
look to remain near high wind through much of the day tomorrow.
Thus have issued a high wind warning through 3 PM with the most
confidence in the next few hours.

NPW and updated grids are out.

Also increased PoPs significantly across the northern Bighorn MTS
where some light snow should develop overnight. The lower
elevations look to remain dry through at least sunrise.

&&

.SHORT TERM...(This evening through Friday)
Issued at 1230 PM MST Tue Dec 5 2017

A very large high pressure ridge along the west coast extending
north well above the Arctic Circle will produce cool dry northerly
flow over western and central Wyoming through the week with gradual
warming.  Some moisture over northern and eastern Wyoming will
support some light snow showers at times over the northern Bighorn
and Absaroka mountains.  Cold air advection will battle areas of down
slope winds producing lee side warming making the temperature forecast
the forecast challenge through Friday.

.LONG TERM...(Friday night through Tuesday)
Issued at 1230 PM MST Tue Dec 5 2017

The extended will feature warming temps at the higher elevations and
mixed areas along with colder air remaining in the basins and
valleys underneath temperature inversions, given the long nights and
short days for this time of year as high pressure amplifies to our
west and attempts to build in from the west. Models struggle with
this pattern, warming up the basins and valleys too quickly. As we
remain on the front side of the ridge at the beginning of next week,
another backdoor cold front will push south across the area next
Monday, enabling the cold inversions to mix out before cooling off
again along with cooling temps elsewhere. This next front will come
through dry early next week with any moisture sliding off to the
northeast of our area.

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1126 PM MST Tue Dec 5 2017

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

The persistent stratus over the far western valleys impacting KJAC
terminal is expected to scatter out by mid-Wednesday morning.

Otherwise VFR conditions with little cloud cover is expected
today. Variable to considerable mid-high level cloudiness is then
expected tonight. Breezy northwest to north winds will impact the
Upper Green River Basin today. Winds at KJAC should remain
northerly all day, and could be breezy at times.

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

The worst conditions Wednesday are expected over the Bighorn
Mountains, and northern Johnson County where strong northwest
wind, low ceilings, light snow along with some blowing snow will
occur. KBYG terminal could see a prolonged period of MVFR ceilings
with flurries at times with strong northwest wind.

The KCPR terminal will see ceilings lower to near MVFR by midday to
early afternoon with even outside chance of a snow shower this
afternoon into the evening. However kept ceilings in the low VFR
range for now.

Elsewhere considerable mid-level cloudiness at times with breezy to
windy north to northwest wind today. Improving conditions are
expected tonight as the moisture and any light snow shifts away from
the area.

Note: The Riverton ASOS is currently down, but parts have been
ordered, and the hope is to have it restored by midday Wednesday.

&&

.FIRE WEATHER...
Issued AT 1230 PM MST Tue Dec 5 2017

A very large high pressure ridge along the west coast extending
north well above the Arctic Circle will produce cool dry northerly
flow over western and central Wyoming through the week with gradual
warming.  Some moisture over northern and eastern Wyoming will
support some light snow showers at times over the northern Bighorn
and Absaroka mountains.  Cold air advection will battle areas of down
slope winds producing lee side warming making the temperature forecast
the forecast challenge through Friday.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
High Wind Warning until 3 PM MST Wednesday for WYZ010.

&&

$$

UPDATE...Murrell
SHORT TERM...Baker
LONG TERM...Lipson
AVIATION...Murrell
FIRE WEATHER...Baker


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