Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 062311

Area Forecast Discussion
National Weather Service Riverton WY
411 PM MST Fri Dec 6 2019

.SHORT TERM...This afternoon through Saturday night

Mostly clear skies and light winds in place this afternoon across
much of the area east of the Divide. Overcast skies remain in
place over southern and western portions, minus Sublette County.
Gusty winds are now in place near Cody and Casper. Winds near Cody
are expected to subside briefly by this evening, before increasing
again late tonight. This will be due to a tight temperature
gradient that will be in place between the Absarokas/Yellowstone
Plateau and the Bighorn Basin. The leeside trough will remain in
place through Saturday, which will keep winds gusty over Natrona
County. 700mb winds will increase to 50kt over southern portions
of the county after 12Z Saturday. Thus, have issued a High Wind
Warning for much of Natrona County for much of the day Saturday.

Low clouds are expected to continue into this evening, filling in
over Sublette County. Areas of fog will be possible once again
tonight over portions of Sublette and southern Lincoln counties.
Visibilities of 1/2 to 1/4mi are also possible again. Fog will
also be possible again tonight in the Wind River Basin. Apart from
a slight chance for flurries over portions of Yellowstone,
conditions will be dry across the area this afternoon through
Saturday morning.

Chances for snow will increase over far western portions after
12pm Saturday, as Pacific moisture increases over the area.
Ejecting shortwaves from a filling storm system moving over the
PACNW will bring the first chances of snow to these areas by
Saturday afternoon. Snow levels will range between 7000 and 8000
feet, before falling after sunset. A steady stream of moisture
will move over the area, from Yellowstone southward to the Star
Valley and the Salt/Wyoming Ranges, Saturday night and through the
day on Sunday. Moderate to heavy snow will be possible late
Saturday night through Sunday morning, with snow continuing
through the day. Snowfall totals up to 6 inches expected in the
lower elevations and up to 12 inches in the mountains, especially
the Tetons. Thus, Winter Storm Watches are in effect for portions
of the far west.

.LONG TERM...Sunday through Friday

Snow will continue across the west Sunday. Some light snow is likely
to spill east of the Divide Sunday night, but accumulations should
stay in the trace to 2 inch range, with most locations on the
lower end. Snow should be out of the area by sunrise Monday.
Meanwhile, a stronger cold front will beckon in colder air across
the area, with Monday high temperatures generally 10 to 15 degrees
cooler than on Sunday. Gusty winds on Sunday ahead of this front
will continue from Rock Springs to Casper.

Northwest flow will prevail over the area through Thursday. While
most areas will stay dry through the period, the western mountains
could see occasional snow showers. The next shot for a more
significant system will be towards the end of the period; models are
hinting at another weekend snow event across the northwest.


.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 355 PM MST Fri Dec 6 2019

Most sites will be at VFR conditions overnight and Saturday morning.
The exception will again be at KBPI and KPNA which will likely see
fog develop overnight. Gusty winds will continue at KCOD and KCPR
through the period. Gusts of 20 to 30 knots are expected at KCPR
before 12z Saturday, with gusts after 12z approaching 50 knots. Snow
will move into the far west after 18z, mainly impacting KJAC in this



Southwest winds 20 to 25 mph with gusts up to 35 mph will continue
over zones 280 and 289 through tonight. These winds will increase
to 30 to 35 mph with gusts up to 60 mph by sunrise Saturday
morning. These winds will continue through the day, before
subsiding back down to gusts of 35 mph Saturday evening. These
gusty winds will continue Saturday night. Gusty winds will occur
over the mountains during this time. Otherwise, winds will
generally be light across the area.

Clouds and light snow will increase by Saturday afternoon over far
western portions, with generally mostly sunny conditions expected
east of the Divide. Moderate to heavy snow will occur over the far
west Saturday night into Sunday.


High Wind Warning from 8 AM to 6 PM MST Saturday for WYZ020-022.

Winter Storm Watch from Saturday evening through Sunday evening
for WYZ023-025.

Winter Storm Watch from Saturday afternoon through Sunday
evening for WYZ012-013.



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