Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 132003
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
103 PM MST Thu Dec 13 2018

.SHORT TERM...This evening through Friday night
Issued at 1235 PM MST Thu Dec 13 2018

Lee enhanced high clouds will continue propagating south from
Montana as a sfc lee side trough extends south. High pressure will
build in from the west resulting in dry weather tonight and Friday.
Temperatures will warm aloft which will strengthen temperature
inversions in the valleys and basins through Friday night. H7 temps
will demonstrate a marginal temp gradient between YNP and the Cody
Foothills that will initiate elevated west winds in the Cody
Foothills today through Friday morning, especially around Clark. The
temp gradient will strengthen somewhat in this area Friday night for
marginally strong winds in the Cody Foothills Friday night into
Saturday. A northern stream shortwave will help increase the
gradient Friday night. This same shortwave will produce some snow in
Northwest Wyoming with light accumulations starting late Friday
night continuing through Saturday.


.LONG TERM...Saturday through Thursday
Issued at 1235 PM MST Thu Dec 13 2018

A fast-moving trough/cold front will move over northern portions of
the forecast area Saturday morning. The main impacts from this
system will be light snow across northwest portions and windy
conditions along the leeside of the Absaroka and Wind River
Mountains. 700mb winds of 50-60 knots are progged in these areas by
12Z Saturday, lasting through 18Z. The cold front associated with
this system will clip Johnson County, but is expected to move over
eastern portions of the state, outside of the forecast area. The
system will quickly exit over the High Plains by Saturday afternoon,
with winds subsiding during this time.

A ridge of high pressure will build over the region Saturday night,
remaining in place through Monday. This will likely bring strong
inversions back over western valleys and lower central basins Sunday
and Monday, keeping these areas trapped under shallow cold air.
Otherwise, conditions will be unseasonably mild and dry. A weak
shortwave will move across northern portions Monday, which could
bring another quick shot of snow to the northwest.

Model guidance continues to be split, but now starts that split by
Wednesday. The main diverging point is whether or not the strong
northern branch of the jet will maintain its strength over the
region, as it rides over a building ridge. Will continue to lean
toward the potential for high winds in the Absaroka Mountains and
Cody Foothills Tuesday night into Wednesday. In addition, chances of
snow were maintained across the west. The ridge axis becomes more
centered over the state by Thursday, with a possible system
impacting northern portions with wind and snow early Friday
morning.

&&

.AVIATION...For the 00Z TAFS through 00Z Friday afternoon
Issued at 1235 PM MST Thu Dec 13 2018

East of the Divide...KCOD/KCPR/KLND/KRIW/KWRL Routes

VFR conditions will prevail through the period. A gusty wind will
occur at KCPR for most of the period, and at KCOD through 16Z Friday
morning.

West of the Divide...KBPI/KJAC/KPNA/KRKS Routes

VFR conditions will prevail at the terminal sites through the period.
Gusty winds will continue at KRKS for a bit longer this afternoon,
decreasing after 01Z.

&&

.FIRE WEATHER...
Issued AT 1235 PM MST Thu Dec 13 2018

A ridge of high pressure will move back over the area this afternoon
through Friday with warming mountain temperatures and returning
valley/basin temperature inversions. Areas of increased winds will
also blow at times through the period in the Cody Foothills,
especially on Saturday morning. All areas will see windy to very
windy conditions into this evening. Southwest winds will also blow
from the Red Desert to Casper through the period.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...Hulme
LONG TERM...LaVoie
AVIATION...Hulme
FIRE WEATHER...Hulme


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