Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 221724

Area Forecast Discussion
National Weather Service Riverton WY
1124 AM MDT Sun Oct 22 2017

.SHORT TERM...Today through Tuesday night
Issued at 240 AM MDT Sun Oct 22 2017

Synopsis...The shortwave ridge will be in place from SW to NE WY
today, as the flow remains zonal over the US/Canadian border today.
This will change late this afternoon/early evening, as a ridge
builds over the EPAC and into Northern Canada and the Yukon
Territory. At the same time, the PFJ will be over northern and
eastern WY and remain in place through the day Monday. A cold front
embedded within the zonal flow will make its way over northern
portions by 06Z Monday. This front will mainly impact areas east of
the Divide Monday, with strong winds developing over NE WY. As the
ridge continues to build, this will cause a longwave trough to dig
and move over the Great Lakes. This, in turn, will cause the PFJ to
shift eastward over the Plains and NW flow over the region Monday
night through Tuesday night.

Discussion...Light snow over eastern ID continues moving eastward
toward the WY border this morning. The heaviest snow is expected
through sunrise Sunday, but if current radar trends continue it may
not pan out. Otherwise, steady light snow is expected across the
west this morning. Snow is expected to change over to rain in the
lower elevations this afternoon, as mid-level temps and snow levels
rise due to the building ridge. Rain could mix with snow over
Yellowstone, while snow continues above 8500 feet. Additional
accumulations of 2 to 4 inches, with local amounts up to 6 inches,
will occur through tonight. Snow will quickly end early Monday
morning behind the cold front.

Strong winds will remain in play today, as winds of 65 mph have
increased at Clark at 1056pm (a bit early, but as expected ~06Z).
This trend will continue toward sunrise over the Cody Foothills,
Absarokas and the Upper Wind River Basin. Strong winds will also
continue to increase southward over the Wind River Mountains and
have upgraded the High Wind Watch to a Warning for this area. Have
extended the time to match with the other aforementioned warnings,
as the southern portions will subside last. Soundings and some of
the local models show strengthening winds ~50kt 1-2kft AGL in the
Lander Foothills by 12Z this morning. However, none of these models
show these winds impacting Lander proper. Although there will be a
strengthening inversion over the leeside of the Absarokas and Wind
River Mountains, do not trust winds these strong to not impact
Lander at some point today. Thus, have also upgraded the watch to
warning for this area through 00Z Monday. Winds will also continue
to increase over the Wind Corridor this morning, with criteria
expected to be met by sunrise. These winds will continue through the
day, although they will remain gusty 40 to 50 mph through midnight

As the cold front quickly passes through (mainly eastern portions)
Monday morning, strong winds will develop ahead of the front over
northern Johnson County. This could occur as early as midnight
Monday and continue through noon and gradually subside during the

The rest of the period should finally be quiet with warming
temperatures on Tuesday.

.LONG TERM...Wednesday through Sunday
Issued at 240 AM MDT Sun Oct 22 2017

Wednesday will be mild with breezy to windy areas. Will hold off on
any precipitation in the NW through the afternoon. Big changes start
Wed night through Thursday as a blast of cold air from Canada surges
south through WY. Rain will change to snow in the north Wednesday
evening. This rain to snow scenario spreads into the central zones
after midnight Wed night and into the south Thursday morning. At
this point, snow accumulations of 1 to 3 inches could occur with
this system with higher amounts in the mountains and along the
upslope favored foothills. Other big change will be the cold as
highs Thursday will only be in the 30s to lower 40s east of the
continental divide with mainly 40s in the west. A brisk north wind
will also occur with the system and wind chill values in the 20s
will be common. The snow will decrease from north to south Thursday
afternoon and evening. Partial clearing Thursday night and cold low
temps Friday morning. The 00Z ECMWF model is colder and snowier with
this system than the 00Z GFS model at this time. Raised the chance
of precip well above the values produced by the blended procedure.
Lowered the high temps on Thursday based on local forecast
expertise. Friday looks dry and cold. Saturday will be dry for most
places. Scattered snow showers may occur in the Northern Bighorn
mountains Saturday as some moisture is shown in a north flow aloft.
Next Sunday appears to be dry at this time. High temps will be a
little milder Saturday and next Sunday.


.AVIATION...18Z Issuance

Occasional light snow and lower elevation rain will continue through
00Z in the northwestern mountains, mainly in vicinity of KJAC. A
cold front dropping southward will bring a few showers further south
in areas West of the Divide, mainly around KBPI and KPNA tonight.
Strong winds will continue across many areas East of the Divide
through the day today. Areas of wind shear will be found around the
mountains, mainly in vicinity of KCOD and KLND. MVFR conditions will
be found at times around KJAC, otherwise expect VFR conditions around
all TAF sites. Wind shear should end at TAF sites following the
frontal passage this evening. Winds should be lighter at all TAF
sites after 06Z Monday with the exception of KRKS where a gusty west
to southwest wind will continue. VFR conditions are expected at all
TAF sites after 06Z Monday.

Please see the Aviation Weather Center for the latest information on
icing and turbulence forecasts.


Issued AT 240 AM MDT Sun Oct 22 2017

Strong winds will occur today from the Absarokas and Cody
Foothills southward along the east side of the Wind River
Mountains and the Lander Foothills and eastward over the Wind
Corridor from the Red Desert to Casper. This winds will begin to
subside after sunset this evening and slowly diminish through the
overnight hours, as a cold front begins to enter from the north.
At this time, winds will increase over the Bighorns and northern
Johnson County. Strong winds will occur in this area late Sunday
night into Monday.

Light snow will also continue across the northwest this morning,
with most of the snow remaining confined in the higher
elevations. Some snow will be possible in Jackson Valley this
morning, before changing over to rain by the noon hour. This
precipitation will end later tonight, as the cold front moves
through the area.


High Wind Warning until midnight MDT tonight for WYZ002-003-016.

High Wind Warning from 6 AM this morning to 6 PM MDT this
evening for WYZ018>020.

High Wind Watch from late tonight through Monday morning for

High Wind Warning from 6 AM this morning to midnight MDT tonight
for WYZ015.

Winter Weather Advisory until 9 PM MDT this evening for WYZ001-



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