Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 292228
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
328 PM MST Tue Nov 29 2016

.SHORT TERM...Tonight through Friday
Updated to cancel the high wind warning for northern Johnson
County as the high winds earlier have begun to trend down.

Large upper low is slowly relinquishing it`s grip on our forecast
area this afternoon. Even with that said, there is still some
significant effects. High winds continue across Nrn Johnson County
where winds have gusted over 60 mph much of the day. This warning
is out through 5 pm and the timing looks pretty good. Otherwise,
we still have a few mainly higher terrain/mountain snow showers
to deal with. They will gradually decrease to mainly the higher
peaks overnight. On Wednesday a weak ridge moves into the west
with a rather weak moist upglide signature developing as the day
wears on in the far west. Looks like a high pop low qpf type event
with a couple inches of fluff for some of the mountains and a
skiff to an inch possible in the far west valleys. Before that, we
may have to deal with some patchy fog in the far west with brief
clearing tonight. Maybe more stratus for YNP. As our next system
splits with the building upstream ridge, we get a developing upper
low trying to develop near the western Wyo border late Thursday
into Thursday evening. System is fighting the bigger picture of a
ridge so don`t expect this system to have a lot of punch.
Favorable track to bring some brief upslope to the Lander
Foothills but not sure it`ll be much more than a brief shot of
flurries or very light snow Thursday Night/early Friday.
Otherwise, we`ll get some higher elevation flurries/snow showers
with a chance of snow over the I80 corridor. System drops quickly
southward with improving conds as the day wears on Friday.

.LONG TERM...Friday night through Tuesday

Weak high pressure late Friday into Friday night will be short
lived as shortwave energy and moisture approach WY in NW mid
level flow. Mountain snow showers early Saturday morning should
spread to the far western valleys Saturday, with the snow moving
south as the day continues. All model guidance shifts the NW mid
level flow to westerly flow by Sunday afternoon. This looks to be
another good period of mountain snowfall for the western mountains
with the Bighorns perhaps picking up a couple and the basins east
of the divide remaining relatively dry. The western valleys should
pick up a fair bit as well. With the flow more westerly on
Sunday, temperatures should rebound to the 30s and low 40s in the
lower elevations, and wind through the RKS to CPR corridor will
be gusty and strong. The initial shortwave trough from the Pacific
Northwest looks to move through the state and into the northern
plains on Monday, although the model guidance is in disagreement
with the timing and strength. The GFS is currently trending faster
and stronger than the ECMWF. Regardless, the initial cold push
Monday is forecast to be followed by a Canadian push of cold air
on Tuesday. Details on snow potential are still uncertain, but
amounts don`t look too high unless the ECMWF forecast pans out
with the 500 mb low closing in southern WY. The shortwave energy
should still move quickly into the southern plains Wednesday,
with Wednesday morning looking to be the coldest thus far across
the state with subzero low temperatures.

&&

.AVIATION.../00Z ISSUANCE/

Gusty north to northwest surface wind continues over much of the
area as the large scale storm system over the northern plains
slowly moves eastward. Wind will decrease in the early evening,
with some places staying gusty until 06Z/Wed. Precipitation at
terminals has largely ended, although NW to SE areas of banded
showers have developed late this afternoon and will continue into
the early evening hours. Light showers over the western mountains
will continue as well. Higher terrain will be partially obscured
through the night. Patchy fog possible around KJAC as weak ridge
builds overnight, but not expected around KBPI/KPNA with
overnight NW surface wind. Wednesday will see another storm
system approach the state. Clouds will increase across western WY
through the day, with showers possible around KJAC, especially
after 18Z/Wed. Surface pressure gradient will increase Wednesday
to strengthen the west to southwest flow from KRKS to KCPR. VFR
conditions expected for next 24 hours at all TAF sites except
KJAC where MVFR/IFR possible with fog and snow showers.

&&

.FIRE WEATHER...

Winds will gradually decrease tonight but with some gusty wind
continuing in the mountains and east slope foothills. Some light
snow or flurries will develop again in the far west during the day
Wednesday into Wednesday night with a chance of snow in the upslope
favored areas east of the divide by Thursday night, mainly the
Lander Foothills and southward. The mountains, Cody Foothills and
wind corridor from Rock Springs to Casper look breezy to locally
windy on Wednesday.

&&

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

&&

$$

SHORT TERM...Skrbac
LONG TERM...McDonald
AVIATION...McDonald
FIRE WEATHER...Skrbac



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