Area Forecast Discussion
Issued by NWS Riverton, WY

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516
FXUS65 KRIW 162134
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
234 PM MST Thu Feb 16 2017

.SHORT TERM...Tonight through Friday

The Pocatello radar shows some precipitation moving toward the area
this afternoon in association with a weak system moving in from the
west. The models have actually backed off on the QPF from this
system from previous runs. Just about all areas should remain sub
advisory so we will keep things to an special weather statement. The
heaviest snow still looks to fall from later this evening until
after midnight when a bit of jet energy and the front swing through
the area. Meanwhile, dry conditions should persist east of the
Divide. The GFS does show a weak area of precipitation over western
Natrona County. However, the NAM has nothing so we will keep the
forecast dry. Gusty winds will continue around Casper into tonight
but should remain sub warning for the most part. These should end
later tonight after the frontal passage.

Friday for the most part looks relatively quiet under a weak and
flat transitory ridge. The latest NAM has some light precipitation
across the south so we added some POPS but kept them in the slight
category. The cold front is rather weak so at this point we kept the
high temperatures for tomorrow fairly similar to today`s. Another
system may spread more precipitation into the west tomorrow from the
southwest but should hold off until Friday evening.

.LONG TERM...Friday night through Thursday

An active medium range period is expected initially across the
western portion of the forecast area. The models remain consistent
with a mean longwave trough developing off the west coast and
then moves inland the middle of next week. Period begins with
splitting trough moving through with mainly the nrn piece
affecting Western Wyoming with light snow mixed with rain in the
wrn valleys. There remains uncertainty at this time involving how
significant snow amounts will be west of the divide on
Monday/Tuesday. The GFS/GEM have again come in colder with
lowering heights with the developing trough, compared to the
ECMWF, which has lesser amounts of precipitation and higher
heights/thickness values.

Will continue with consistency with likely pops in western
counties based upon model runs with significant pcpn potential in
the far west early next week. Areas east of the divide will
continue to bask in the warmer temps with gradient winds
increasing by Monday/Tuesday. Strong to high winds in the wind
corridor Monday through Tuesday are quite possible with high winds
along the Cody Foothills and possibly Lander Foothills still
looking possible later Monday into early Tuesday. Temps will
remain an issue with warm advection ahead of the next system
between Monday and Tuesday across central/eastern sections. The
models remain in consistency involving shifting the mean trough
eastward across the forecast area between Wednesday and Thursday.
This will need to be watched as potential remains for a
significant snowstorm for areas east of the divide by Thursday,
with cold advection occurring.
&&

.AVIATION.../00Z ISSUANCE/

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

A weak system will move into the area tonight and bring lowering
ceilings in the western mountains with mainly light snow breaking
out between 00Z and 04Z Friday. The best chance for MVFR and brief
IFR conditions in snow and low ceilings will be KJAC. Model
soundings showed the possibility of some LLWS redeveloping at KJAC
in the late afternoon/early evening hours. Mountains will become
obscured in most areas this evening with the least impact over South
Pass. Ceilings and visibility should improve after 12Z Friday after
the system moves away to the east. Another system will bring the
chance of snow and lowering ceilings for Friday evening but effects
should hold off until after 00Z Saturday.

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

Into the evening, considerable  mid-high level cloudiness will
overspread the area associated with a weak system. Considerable mid-
high cloudiness and persist into tonight with mountain tops being
obscured at times. Precipitation associated with this system is
expected to remain along and west of the Divide. The gusty winds
near KCOD and KCPR should subside later tonight and remain generally
light to moderate on Friday.

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

&&

.FIRE WEATHER...

Fire Danger low for all of Wyoming through the weekend as a good
existing snow pack will combine with seasonal to below seasonal
temperatures. A system will move into the west tonight with mainly
light snow. Gusty winds across the wind prone areas east of the
Divide will diminish tonight after the passage of a cold front. Most
areas will have dry weather on Friday before another system moves in
from the west on Friday night.
&&

.RIW WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

SHORT TERM...Hattings
LONG TERM...Troutman
AVIATION...Hattings
FIRE WEATHER...Hattings



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