Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 081037

Area Forecast Discussion
National Weather Service Riverton WY
337 AM MST Fri Dec 8 2017

.SHORT TERM...Today through Sunday night

Conditions across the entire forecast area finally settle down
today. Gusty NW winds will continue this morning over the
Bighorns and northern Johnson County, before finally subsiding
this afternoon. Mid to high clouds will also continue to stream
over the area from the north, but these are also expected to exit
the area by this afternoon. Otherwise, expect mainly light winds
and clear skies through the forecast period. Temperatures are
expected to rise, despite the warmer H7 temperatures, based off of
the trend Thursday afternoon. The light to non-existent snow
cover was not enough to keep the temperature inversions from
weakening in the basins and valleys Thursday. The exception to
this was the Star Valley and northern portions of the Upper Green
River Basin. Have kept daytime temperatures suppressed somewhat in
these areas today and Saturday. However, temperatures for most
lower elevation locations should rise into the lower 40s by
Sunday. Also bumped temperatures in the higher elevations several
degrees to account for the H7 temps continuing to range between -2
and +2C.

.LONG TERM...Monday through Friday

Overview...A persistent ridge over the western U.S. will continue
to bring dry and mild weather to most areas through the extended
period. The exception will be across western valleys and lower
central basins where inversions will keep temperatures several
degrees cooler with occasional patchy morning fog.

Discussion...Upper air pattern Monday morning features high-
amplitude ridge over the Intermountain West with the next in a
series of clippers diving down the front side of the ridge into
the Northern Plains. Precipitation with this system will remain
east of the area with the main effect of bringing some gusty NW
winds across eastern Johnson County Monday morning, along with
slightly cooler temperatures where inversions do not factor in
over the weekend. Upper ridge to retrograde slightly to along the
west coast by Wednesday. Both GFS and ECMWF show a Pacific system
splitting into the ridge with a clipper diving SSE across Wyoming
Wednesday morning. This system will be moisture-starved, bringing
possibly some localized very light snow or flurries. The systems
passage will bring an overall cooling trend to the area Wednesday,
and also act to erode inversions somewhat over the western valleys
and lower central basins. Medium-range models advertise some
breaking down of the western ridge late in the extended period or
just beyond, next weekend. Prefer to go slow here with any
significant changes to this persistent pattern, per GFS; so upper
ridge and generally dry and mild weather will continue to prevail
through at least the end of the workweek.


.AVIATION...For the 12Z TAFS through 12Z Saturday

VFR conditions are expected through the forecast period. The only
exception could be patchy morning fog across the extreme far western
valleys, but KJAC has remained fog free over the past couple of
nights, and this trend of no fog should continue. Breezy west to
northwest wind along with marginal LLWS will be found in a few



Temperature inversions will remain in place through the rest of
the week, mainly over the central basins and western valleys.
Expect poor mixing in these areas. Considerable warming will occur
in the higher elevations through the weekend. Gusty winds will
continue this morning over the Bighorns and northern Johnson
County, before finally subsiding this afternoon.




LONG TERM...Meunier
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