Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 092138

Area Forecast Discussion
National Weather Service Riverton WY
238 PM MST Sat Dec 9 2017

.SHORT TERM...(This evening through Sunday)
Issued at 223 PM MST Sat Dec 9 2017

A strong temperature inversion will remain in place for the rest
of the weekend. Currently, temperatures across much of the western
and central basins are in the 30s, with areas that are mixed out
having temperatures well up in the 50s such as Dubois, Buffalo,
and Cody. Some areas like Sweetwater Station near Beaver Rim
remain chilly due to the thick snow cover there. Will go with
persistence and throw in patchy fog for the far west valleys and
northeast Fremont County for late tonight and Sunday morning given
the similar forecast soundings. On Monday, we will see winds pick
up from the northwest as another clipper type system tracks
southeast across the Northern Plains with the shortwave trailing
southeast across our eastern zones. These winds will weaken the
inversion Monday, just to strengthen again Tuesday.

.LONG TERM...(Sunday night through Saturday)
Issued at 223 PM MST Sat Dec 9 2017

The big news in the medium range is the potential breaking down
or at least flattening of the mean ridge along the West Coast
Friday into this weekend. But before that begins, we have strong
inversions in the snow covered areas out west to deal with each
day. We also still have that small compact system trying to ride
up and over the ridge and drop down just east of us Wednesday.
General trend in all the guidance has been for a further east
track (especially with the Euro and GEM). However, the 12z Euro is
still brushing our nern zones so this will still need to be
watched. Gusty north wind for sure but any closer and we`ll have
to worry about a quick shot of snow as it drops south. Forecast
remains dry but it still warrants watching closely since it`s
still 4 days out. The ridge begins to flatten Thursday night
leading to a potential wind event in the Cody Foothills with
strong cross barrier flow, good thermal gradient and falling
pressures to the northeast. Will add some wind for this period as
the forecast builder is way too light. First shortwave to impact
the area as the ridge flattens occurs Friday into Friday night
with a shot of out west first and then areas of snow east of the
divide by Friday night. After a brief respite Saturday, the flow
starts to flatten again late Sat/Sat night with strong jet passing
to the north. Very strong wly flow starts to develop with windy
to very windy conds developing in many areas Saturday night.
Possible high wind event for the lee of the mountains in Central
Wyoming and possibly the wind corridor.


.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 223 PM MST Sat Dec 9 2017

VFR conditions will prevail through the weekend. The one
exception will be the development of patchy fog once again in the
far west valleys and Yellowstone National Park area late tonight
through Sunday morning.


Issued AT 223 PM MST Sat Dec 9 2017

Apart from patchy freezing fog in the far west valleys and in the
vicinity of Boysen Reservoir in Northeast Fremont County late
tonight and Sunday morning, expect mostly clear skies and dry
conditions through Sunday. A temperature inversion will remain in
place. Winds are expected to remain light through Sunday. Then on
Monday, a cold front could cause gusty winds over the Bighorns and
Johnson County during the morning hours Monday.




LONG TERM...Skrbac
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