387
FXUS65 KRIW 250942
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
242 AM MST Tue Nov 25 2025

.KEY MESSAGES...

- A mainly dry and cooler day today with diminishing wind.

- The next system moves into the western mountains late Tuesday
  night and Wednesday with light to moderate amounts of snow.

- A complex weather system still looks likely (3 out of 5) to
  impact the area from Friday into Sunday. Details on timing and
  placement of the heaviest snow remains uncertain, especially
  on Saturday and Sunday.

&&

.DISCUSSION...
Issued at 230 AM MST Tue Nov 25 2025

A cold front has moved through Wyoming and most of us are getting a
slap across the face called reality, A.K.A. what the weather usually
is late November in the area. We have been living a charmed life
through most of the eleventh month of the year, with most of our main
climate sites having the warmest first 24 days of the month (8 of
the 9, the only one that isn`t is Buffalo), in many cases more than
10 degrees above normal. This will be the coolest day in a while,
but by late November standards, not too bad. Most locations will
only see temperatures near to slightly below normal, although it may
feel colder given the recent mild temperatures. The other issue will
be a gusty wind, mainly this morning and mainly in the favored cold
advection / northwest flow locations like northern Johnson County.
There have been isolated gusts over 60 mph Monday night. These winds
should decrease through the morning as the pressure gradient
decreases as the front moves away. Any light snow showers should end
by sunrise with mainly dry conditions continuing through this
evening.

The next system, a shortwave will move into northwestern Wyoming
late tonight. This system does not have a ton of moisture to work
with. However, one thing that gives me a bit of concern is that it
will have jet energy in the form of an 120 knot jet streak moving
through Wednesday morning which would maximize the efficiency of the
system. As for potential highlights though, we have decided not to.
The chance of 6 inches of snow or more in the mountains for most
locations is less than 1 out of 4 through Wednesday night. The one
exception is the western Absarokas, where the chance is generally
around 1 out of 3, maxing out at 1 out of 2 in a small area.
However, this area is in an area with no roads and as a result,
basically no impacts. The day shift can monitor in case amounts
increase, but this looks like the only location that would need
highlights. There is good model agreement in timing, in the
steadiest snow falling between 2 am and 2 pm. As for the valleys.
temperatures will be cold enough for snow everywhere. There is a
greater than 3 in 5 chance of an inch of snow in the Jackson and
Star Valleys, but the chance of 3 inches is less than 1 out of 6.
Out there, they need snow badly and it would be welcomed. The lower
elevations East of the Divide would have few impacts, although a few
showers may occur in the northern Bighorn Basin and around Casper on
Wednesday afternoon.

Turkey day looks relatively quiet at this point. There will be some
orographically enhanced snow showers across the western mountains,
but any potential accumulations look to be on the light side. Most
locations will have a fairly nice day with dry conditions and
another day of above normal temperatures with some locations
approaching 50.

Then the interesting stuff moves in starting Friday. The first is in
the form of a cold front dropping southward into the state starting
Friday morning and continuing into early Saturday morning.
Deterministic guidance has come into somewhat better agreement this
morning showing the front dropping into northern Wyoming Friday
afternoon and exiting Saturday morning. Precipitation with this
system looks largely anafrontal, with the highest rates occurring
Friday evening as the moisture encounters a jet couplet moving
across Wyoming. With 700 millibar temperatures initially around minus
4 in eastern portions of the area, precipitation may start as
rain in places like Buffalo, and this could freeze Friday night
as the colder air moves in, bringing slick roads. This still
looks to be the best chance so far of the first accumulating
snow across areas East of the Divide, with many locations having
a greater than 1 in 2 chance of an inch or snow by Saturday.
The chance of 3 inches looks fairly low though, at most 2 out of
5. With north to northwest flow behind the front, the best
chance of this would be the northwest upslope flow locations,
like the southern Bighorns and Thermopolis. There is more
uncertainty on the other factor, a second spoke of energy that
will may move in from the south and combining with another cold
front, this one of Canadian origin, and may bring another round
of snow. The deterministic models are split on this, as are the
ensembles, with some bring a few more inches of snow, mainly to
central and southern Wyoming and others keeping the impacts
mainly south of Wyoming.. This does not look like a huge storm
but given the travel implications over the holiday weekend we
have to watch this closely. Hopefully, this will resolve itself
over the next few days. And, behind this second cold front will
be the coldest air so far this season. The 700 millibar
temperatures will fall as low as minus 18, which could bring
some below zero low temperatures Sunday or Monday night,
especially if there is some snow on the ground. At this point,
it does not look record breaking, but it will fell cold after
all the mild weather through most of November.
&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 950 PM MST Mon Nov 24 2025

VFR conditions expected for the entirety of the period. In wake
of a cold front, winds have turn more northerly and now subsided
as it has pushed to the south and east of LND/RIW/CPR. Some
lingering showers around CPR for the first hour or two, but will
be light in nature if it makes it on station. Otherwise, winds
remain light less than 10kts expect for RKS that will see gusts
up to 25kts between 19-00Z Tuesday afternoon with better daytime
heating and mixing to the surface further south. Increasing
high clouds ahead of the next shortwave overnight into Wednesday
but remaining dry at all TAF sites.

Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for
the latest information on smoke, icing, and turbulence
forecasts.

&&

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

&&

$$

DISCUSSION...Hattings
AVIATION...Lowe