676
FXUS65 KRIW 162301
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
401 PM MST Thu Jan 16 2025

.KEY MESSAGES...

- Mild and breezy for many today. Southwest winds gusting 30 to
  40 mph along the Muddy Gap to Casper corridor will continue
  through tonight.

- A strong Arctic cold front will move north to south across the
  region Friday, brining snow and blowing snow concerns to much
  of central WY, with impacts to travel likely Friday.

- Frigid air follows the cold front, with the coldest
  temperatures occurring Sunday night through Tuesday morning.
  High temperatures Monday may not climb above zero for
  central WY basin locations, with a 40% chance of low
  temperatures below -20F.

- Cold weather and the active pattern look to stick around
  through the rest of next week.

&&

.DISCUSSION...
Issued at 257 PM MST Thu Jan 16 2025

Temperatures have climbed into the 50s across some locations this
afternoon, with most east of the Divide basins seeing temperatures
at least above freezing with the exception of the Wind River Basin.
Strong southwest winds along the Muddy Gap to Casper corridor also
persist this afternoon with gusts 30 to 40 up to 50 mph. And except
for some fog that persists in the Jackson Hole valley, mostly clear
skies will persist across much of the region through the evening.
This afternoon would be a perfect time to get outside and enjoy the
warmer and sunny weather, because it will quickly come to an end.

By midday tomorrow, most of us will be experiencing gusty north
winds and snow along with temperatures that are in some cases as
much as 20 to 25 degrees colder than today. An Arctic cold front
will begin to push into the region by sunrise Friday morning,
reaching the Owl Creek/Bridger Mountains by around 9 AM and reaching
the Continental Divide by Noon. Gusty north winds gusting 20 to 30
mph will occur with and behind the cold front, with locally stronger
winds where upsloping occurs along the Owl Creek/Bridger Mountains
(including through Wind River Canyon) and the southern Bighorns.

Along with the north wind, snow will also filter in quickly behind
the front. Snow showers will be heavy at times, particularly across
the Wind River Basin and across south and western portions of the
Bighorn Basin from Meeteetse Rim to Thermopolis and east towards
Tensleep. Snowfall amounts will generally be in the 1 to 3 inch
range for most lower elevations east of the Divide. With yet another
set of model runs producing amounts in that range, have a high
confidence level (80%) in those amounts for most locations. Where
confidence is lower is across foothills and upslope favored
locations such as Lander and Thermopolis. Have added an Advisory for
Thermopolis and adjacent Owl Creek/Bridger mountains to account for
that uncertainty regarding potential for higher end amounts in those
locations. Highest amounts look to be in the upslope favored Lander
Foothills, with 4 to 6 likely (70% chance) up to 7 inches (20%
chance).

Another source of uncertainty will be snow banding behind the front
and the potential for snow squalls. Snow banding looks to be most
likely across the Wind River Basin, particularly around Riverton and
along the Hwy 20/26 corridor in the central part of the Basin. Snow
squalls still look to be possible (20 to 30% chance) with this event
as well. Greatest concern for snow squalls will be along the
northern I-25 corridor from I-25 Divide to Buffalo.

Snow will end overnight, with localized lingering snow showers across
the foothills and east of the Divide mountains possible (20% chance)
through Saturday morning. Otherwise, Saturday will be cold, with
highs in the teens. By Sunday morning, as skies clear, the coldest
air will move in and temperatures will drop into the double-digits
below zero for most locations. Confidence is 80-90% regarding these
cold temperatures. Cold temperatures will stick around through
Tuesday, as models suggest a reinforcing blast of cold air early
week. With a building ridge early to mid next week, southwest winds
will increase and temperatures will slowly moderate for most
locations through the week. For cold basins that have existing and
new snowpack such as the central Wind River Basin, temperatures will
remain cold through much of next week.

&&

.AVIATION /00Z TAFS THROUGH 00Z FRIDAY/...
Issued at 401 PM MST Thu Jan 16 2025

VFR flight conditions at all terminals will prevail overnight ahead
of an arctic cold front makes its move into Wyoming around sunrise
on Friday. This cold front will bring snow, north winds with blowing
snow potential and MVFR to IFR ceilings and visibilities. The first
impacted terminals are forecast to be KWRL and KCOD around 14/15Z
and KCPR around 16Z. As the front treks south, KRIW and KLND can
expect MVFR to IFR ceilings and visibilities due to snow after 18Z.
KPNA has a greater chance at snow Friday afternoon compared to KBPI,
but chances remain around 30% so went with a PROB30 only at KPNA. At
KRKS, snow chances increase just outside of this TAF period but
added a PROB30 in case the front treks south a bit faster than
anticipated. Overall, the greatest impacts from this cold front will
be along and east of the Divide.

Ahead of the front at KJAC, KBPI and KPNA, overnight fog with the
clear skies cannot be completely ruled out. Because confidence in
fog is low at these locations, opted in low FEW/SCT ceilings. Windy
conditions ahead of the front are anticipated at KRKS with gusts
around 25kts beginning Friday morning.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 9 AM to 11 PM MST Friday for
WYZ005-007>009-017>020.

&&

$$

DISCUSSION...Hensley
AVIATION...Gerhardt