Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 180542
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1042 PM MST Sat Feb 17 2018

.SHORT TERM...(This evening through Tuesday)
Issued at 235 PM MST Sat Feb 17 2018

Major winter storm is bearing down on the northwest attm and this
system will spread snow across the entire west tonight. The system
will spread east of the divide Sunday morning with arctic front
sagging swd. Snow will rapidly develop behind the front as both
warm upglide overruns it and right entrance region jet streak
support lines up. This upper support (jet) gradually sags swd into
Natrona and sern Fremont during the day and camps out into Monday
morning. Initial frontogenesis Sunday wanes some Sunday night
before redeveloping with potential resurgence of baroclinic band
Monday morning with approach of trough and new jet streak.
Favorable temperatures early on east of the divide combined with
this jet support will have the potential to produce several hours
of heavier snow as it sags swd. The best of all of this is still
the Natrona County area with gradually, but still potential
warning amounts, swwd to about RKS. Still some concern into at
least ern Fremont depending on length of jet support and potential
mid level circulation but opted to go with a solid winter wx
advisory for later Sunday into Monday. Further west, first part of
this multi-day storm already produced 10 inches at Raymer in the
Tetons since yesterday but more is on the way for tonight and
Sunday. Some strong upper jet support and tight baroclinic
boundary sagging swd will get the snow going quite heavy from n-s
tonight. Have upgraded all watches to warnings in the west. Only
Sweetwater County will remain a watch with some uncertainty on
timing and amounts. Lean a warning due to the travel route and at
least high end advisory amounts with more towards warning ern end
but next shift can finalize it. Otherwise, turning bitter cold
with temperatures steady to falling behind the front and then just
downhill from that through Monday night. Continued trend of
lowering temps the next couple days (Sunday night into Tuesday).
Bitter cold wind chills with this system too as the cold air
rushes in and then with a potential clearing sky Monday night, we
could see our last round of very cold temperatures of the season.
General trend today is for a slower trough movement with the
actual axis over us or possibly still over wrn WY. Either way, a
slow moving system producing snow and bitter cold temperatures.


.LONG TERM...(Tuesday night through Saturday)
Issued at 235 PM MST Sat Feb 17 2018

Just some lingering light snow is expected in the far west for
Tuesday night as we get on the back side of the main trough during
which time a couple of more ripples within the main trough track
across the area Tuesday night and into Wednesday. In fact, the
Canadian does not appear to track the main troughpa associated with
the upcoming short term Sunday/Monday snow event until 00Z Thu. Then
a couple of more prominent Pacific shortwaves track across the area
with the next one delivering potentially significant snowfall to the
west Thursday and Thursday night. Then the next such shortwave will
deliver more snowfall to the west next weekend with snowfall
increasing Friday night and continuing on into Saturday night. The
Canadian splits the energy from this trough keeping most of the
energy in the southern stream over the Desert Southwest by Friday
night so for now will go more with the GFS/Euro soln.

Temperatures will gradually moderate closer to seasonal temps by the
end of next week as H7 temps warm from -22C in Northeast Wyoming
12Z Wednesday to -10C by next Saturday. Wednesday morning will start
out frigid with low temps approaching 25 below in some protected
areas (coldest it has been in many areas since late December), with
highs in the teens and 20s, then by Saturday, some areas will break
the freezing mark.

&&

.AVIATION...(For the 06Z TAFS through 06Z Monday)
Issued at 1020 PM MST Sat Feb 17 2018

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

Snow will occur over most of the west through 06Z Monday. MVFR to
IFR conditions will occur with frequent mountain obscuration. A
gusty wind will occur in places. KJAC will see snow and a gusty wind
through 02Z Monday. KRKS will see a gusty wind through 04Z Monday
with VFR conditions, then the wind shifts to the northeast after 04Z
Monday.

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

A gusty wind at most of the terminal sites through 15Z. A cold front
will move into the north around 12Z, then push south into central WY
around 19Z, then along the continental divide by 22Z. Snow will be
developing over the north Sunday morning with snow developing over
the central Sunday afternoon. Snow will occur over most areas
through Sunday night. Expect MVFR to IFR conditions in the snow with
mountains frequently obscured.

&&

.FIRE WEATHER...
Issued AT 235 PM MST Sat Feb 17 2018

Very active weather will continue this weekend into early next
week. Very strong winds will blow in the mountains, foothills, the
Wind Corridor (Jeffrey City to Casper) and along the Cody
Foothills at times through early Sunday morning. The I-80
corridor will also be windy to very windy through Sunday. Snow
over the northwest mountains will increase and spread throughout
the west into the overnight hours. An arctic cold front will drop
south east of the Divide Sunday with falling temperatures, snow
and gusty north wind. Winds will rapidly decrease during the
morning hours Sunday, while snow continues into Monday.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...

Winter Storm Warning from 2 PM Sunday to 11 PM MST Monday for WYZ029-
030.

High Wind Warning until 5 AM MST Sunday for WYZ003-005-011-015-016-
018>020-022.

Winter Storm Warning from 11 AM Sunday to 5 PM MST Monday for WYZ019-
020-022.

Winter Weather Advisory from 2 PM Sunday to 2 PM MST Monday for
WYZ017-018.

Winter Storm Warning until 5 PM MST Sunday for WYZ001-002-012>014-
023>025.

Winter Storm Warning from 8 AM Sunday to 2 PM MST Monday for WYZ011.

Winter Weather Advisory from 5 AM Sunday to 11 AM MST Monday for
WYZ010.

Winter Weather Advisory until 2 PM MST Monday for WYZ016.

Winter Storm Warning from 5 AM Sunday to 2 PM MST Monday for WYZ015.

Winter Weather Advisory until 5 PM MST Sunday for WYZ026.

Winter Storm Warning from 5 AM Sunday to 8 AM MST Monday for WYZ027.

Winter Weather Advisory from 2 PM Sunday to 11 PM MST Monday for
WYZ028.

Winter Weather Advisory from 5 AM Sunday to 2 PM MST Monday for
WYZ008-009.

Winter Weather Advisory from 8 AM Sunday to 11 AM MST Monday for
WYZ003-004.

Winter Weather Advisory from 8 AM Sunday to 2 PM MST Monday for
WYZ005>007.


&&

$$

SHORT TERM...Skrbac
LONG TERM...Lipson
AVIATION...AR
FIRE WEATHER...Skrbac



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