Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 172206
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
306 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 00Z TAFS through 00Z Sunday evening)
Issued at 235 PM MST Sat Feb 17 2018

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

Continued MVFR, with occasional IFR in ceilings and visibility in
areas of light snow over the western/northwestern mountains in Park,
Teton, Lincoln and Sublette counties. Western mountains will be
frequently obscured through 00Z Monday. MVFR ceilings and
visibilities reduced in snow will be most probable at KJAC, and
secondly at KPNA and KBPI. Increasing winds aloft will result in
areas of LLWS. Surface winds west at 20-25kts with gusts of 30-35
kts will prevail across the I80 corridor.

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

Lower elevations will have prevailing VFR conditions tonight. The
exception will be in vicinity of KCOD, where lower ceilings and
vicinity showers may bring local MVFR conditions after 08Z Sunday.
Increasing winds aloft will also result in areas of LLWS. Southwest
surface winds between South Pass and Casper will continue to
increase this afternoon and continue through the 12Z Sunday. The
winds will blow 20-35kts with gusts of 40-65 kts are expected from
late this afternoon today through 12Z Sunday. Additionally, any snow
from the incoming Arctic Front will likely hold off until after 08Z
Sunday before spreading south along with associated MVFR/IFR/mtn
obscn. Then the arctic front with it`s snowfall will continue to
track south, reaching KCPR by 18Z Sunday and then KLND/KRIW by 21Z
Sunday along with the asct MVFR/IFR mtns obscn.

&&

.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 Watch from Sunday afternoon through Monday
afternoon for WYZ028>030.

High Wind Warning until 5 AM MST Sunday for WYZ015-016-018>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-
013.

High Wind Warning until 5 AM MST Sunday for WYZ003-005-011.

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

Winter Storm Warning until 5 PM MST Sunday for WYZ014-023>025.

Winter Weather Advisory from 8 PM this evening to 5 PM MST
Sunday for WYZ026.

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

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...Lipson
FIRE WEATHER...Skrbac



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