Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 122014

Area Forecast Discussion
National Weather Service Riverton WY
114 PM MST Thu Jan 12 2017

.SHORT TERM...Tonight through Sunday

Imagery shows split flow developing with a broad longwave trof
across the CONUS and an upstream axis stretching from north central
MT to the southwest over central CA. The southern branch of the jet
crosses southern CA and the desert SW into the UT/wrn CO/srn WY
confluence and then east into central Plains with the northern
branch staying well north across Canada and into the northeast
CONUS. A mesoscale jet streak/baroclinic leaf, which is part of the
jet mentioned above, is currently moving from nrn UT and into sw
WY/nw CO. This feature will keep snow chances around southern WY
through this evening, especially along and south of I80. Wind should
not be an issue with this system and snowfall through the afternoon
and evening should remain below 2 inches for most locations with the
heaviest amounts near the border with Colorado. Otherwise, northwest
WY will also keep some lingering isolated, but decreasing, mildly
convective light snow showers/flurries around today and patchy fog
around tonight.

The rest of the forecast should most remain dry across the FA with
light wind and seasonally cold temperatures. Nothing too extreme

.LONG TERM...Sunday night through Thursday

Beginning of FCST, split flow still in place with a large/broad trof
across the wrn CONUS and a weak close low in the base of the trof
over the srn Rockies/srn Plains and a relatively strong jet diving
down the west coast. WY will start out under weak flow conditions
aloft, little moisture, no precipitation except for an isolated
mountain shower across the far northwest (maybe). Seasonal to
seasonally cold highs/lows throughout the forecast period with
little wind until Tuesday, and even then we are just increasing LL
sw flow a bit...with gusts in the 25 to 35 mph range...nothing
highlight worthy. The next weather system of any note does not look
to arrive until Tuesday night as modest ridging across the wrn CONUS
allows EPAC moisture and warming back into wrn WY along with a ridge
cresting jet. This precip/snow maker will then keep the west wet and
white through the end of the forecast period...and beyond...and
will be highlight worthy for sure. A pattern change back to cold
Arctic looks possible by the next weekend. However, long range
pattern trends look to have a relatively progressive 4/5 wave
pattern in place, so hopefully any cold snaps coming through the
region will be of short duration.



West of the divide...KBPI/KJAC/KPNA/KRKS Terminals

VFR/MVFR conditions will prevail through the forecast period. Now
for the asterisks: A short duration snow event is forecast to
develop over southern Wyoming and last through 09Z. Occasional
MVFR/IFR conditions in lower CIGs and reduced visibility will
occur...especially over/near KRKS. Additionally, vcnty FG (patchy)
is possible at all terminal sites after 09z.

East of the divide...KCOD/KCPR/KLND/KRIW/KWRL Terminals

VFR conditions will prevail through the forecast period. However,
between 04z and 10z there may be a few periods where MVFR in lower
CIGs occur south of a KRIW to KCPR line as an upper level
disturbance passes through southern Wyoming. Will have VCSH at KCPR
and KLND airports from 04Z-10Z Fri. Additionally, vcnty FG (patchy)
is possible at many terminal sites after 10z.



Fire Danger low for all of WY through, at least, the weekend. Cold
seasonal temperatures, good existing snow pack, and relatively light
winds will characterize the next several days. A short period of
light snow will occur across southern Wyoming this afternoon and
evening. Smoke dispersion will also remain poor for all locations
through the weekend.




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