Area Forecast Discussion
Issued by NWS Riverton, WY

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922
FXUS65 KRIW 222039
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
139 PM MST Mon Jan 22 2018

.SHORT TERM...(This evening through Thursday)
Issued at 118 PM MST Mon Jan 22 2018

A weak Pacific short wave trough with limited Pacific moisture
and a very weak cold front over eastern Idaho and western Montana
will move through western Wyoming this evening with rather widespread
light snowfall. accumulations of 3 to 6 inches are possible mainly
above 9000 feet with 2 to 3 inches below 9000 feet.  Breezy to windy
conditions will prevail along and near the east slopes of the
mountains east of the Continental Divide with areas of light snow
in the north with little accumulation. The windy areas have warmed
some and will continue to warm while the lower areas along the rivers
in the Bighorn and Wind River basins will remain on the cold side but
not as cold by 5 to 8 degrees from last night where some -10 to -20
degree readings were reported.  Limited moisture in west northwest
flow will bring some very light snow to the higher mountains on
Tuesday.  Windy areas will continue along and near the east slopes
of the mountains with warming continuing with decreasing cloud cover.
Tuesday night through Wednesday night will be dry with high pressure
over the west. Windy areas will persist over and near the east slopes
of the mountains.  Another Pacific trough will bring more widespread
light snow to the west on Thursday.  Clouds will increase along with
increasing west to southwest winds east of the Continental Divide.

.LONG TERM...(Thursday night through Monday)
Issued at 118 PM MST Mon Jan 22 2018

Snow will be ongoing in the west Thursday night as a Pacific trough
and cold front continue to move through the area. Models are still
in disagreement on whether or not anything can jump to East of the
Divide. The European is a bit more bullish than the GFS, but even it
does not have a lot. For now, we went with some slight POPS across
the north with mainly dry conditions continuing elsewhere. Breezy to
windy conditions will continue into the night and the first part of
Friday before subsiding somewhat.

The models then diverge a bit as we head into the weekend. On
Saturday the GFS brings another decent surge of moisture into the
west with potential highlights. The European meanwhile builds
ridging across the area with mainly dry conditions through the
weekend with the exception of some snow showers across northwestern
Wyoming as it keeps the best energy well to the north and west. The
GFS also may be too fast in returning moisture as it usually is this
far out in the forecast period. It also has rather vigorous 700
millibar winds ahead of the front, up to 60 knots in some cases so
it could turn quite windy if this verifies. The same holds for
Sunday with the GFS wet and the European dry. For now we played the
middle ground with no POPS higher than the chance category until
things become clearer. At this point Monday looks to be a dry day
before another system may approach for Tuesday or Wednesday,
depending on the all important timing.

&&

.AVIATION...(For the 00Z TAFS through 00Z Wednesday)
Issued at 118 PM MST Mon Jan 22 2018

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

VFR conditions will occur at most of the terminal sites. The
exception will be KJAC airport, where snow and MVFR conditions will
prevail through 09Z Tuesday. Some snow will occur in the western
mountains through tonight with mountains frequently obscured. Other
sites could see nearby showers but should remain largely MVFR. VFR
conditions are expected for all TAF sites after 12Z Tuesday.

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

VFR conditions are expected at the terminal sites through the period.
Isolated snow showers will occur over and near the mountains after
21Z through 09Z Tuesday, especially in vicinity of KCPR where brief
MVFR conditions will be possible between around 03Z and 09Z.

&&

.FIRE WEATHER...
Issued AT 118 PM MST Mon Jan 22 2018

A weak Pacific short wave trough with limited Pacific moisture
and a very weak cold front over eastern Idaho and western Montana
will move through western Wyoming this evening with rather widespread
light snowfall. accumulations of 3 to 6 inches are possible mainly
above 9000 feet with 2 to 3 inches below 9000 feet.  Breezy to windy
conditions will prevail along and near the east slopes of the
mountains east of the Continental Divide with areas of light snow
in the north with little accumulation. The windy areas have warmed
some and will continue to warm while the lower areas along the rivers
in the Bighorn and Wind River basins will remain on the cold side but
not as cold by 5 to 8 degrees from last night where some -10 to -20
degree readings were reported.  Limited moisture in west northwest
flow will bring some very light snow to the higher mountains on
Tuesday.  Windy areas will continue along and near the east slopes
of the mountains with warming continuing with decreasing cloud cover.
Tuesday night through Wednesday night will be dry with high pressure
over the west. Windy areas will persist over and near the east slopes
of the mountains.  Another Pacific trough will bring more widespread
light snow to the west on Thursday.  Clouds will increase along with
increasing west to southwest winds east of the Continental Divide.
The colder areas with less wind will have generally poor smoke
dispersal while the windier areas with better mixing will experience
fair to good smoke dispersal.  These areas will become more widespread
on Thursday.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...Baker
LONG TERM...Hattings
AVIATION...Hattings
FIRE WEATHER...Baker



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