802
FXUS65 KRIW 111647
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1047 AM MDT Tue Mar 11 2025

.KEY MESSAGES...

- Remaining dry and mild through Wednesday with gusty breezes in
  the favored locations.

- The next weather system will bring light to moderate snow and
  strong wind from Thursday through Friday.

- Another, potentially more potent system may arrive early next
  week.

&&

.DISCUSSION...
Issued at 157 AM MDT Tue Mar 11 2025

We are now entering the middle of March, the so called "Ides of
March." The Ides Of March are usually related to the soothsayer in
the play Julius Caesar, the foreshadowing of Julius` stabbing by
Brutus. Others relate the Ides of March to a classic Rock Band that
is concerned a one hit wonder with the song "Vehicle" back in 1970,
it will take you anywhere you want to go. But, meteorologists often
fear the Ides of March, as it tends to be an active period of
weather. As increasing warmth clashes with the winter that doesn`t
want to go away yet. And these contrasts in air masses are what
bring the active weather.

And there will be a period of active weather across western and
central Wyoming, but not quite yet. Flat ridging will bring largely
quiet weather for around the next 36 to 48 hours. With the flat
ridging, we will still see some gusty wind in the favored areas,
especially from Muddy Gap through Casper. Mid level wind does not
look sufficient for high wind though. We also raised temperatures
somewhat. The past gradually warming temperatures have really eroded
the snowpack, and this will continue through Thursday.

The active weather will return following this as a Pacific system
approaches the area. A few showers will be possible in the west
later Wednesday night, but vast majority of any precipitation would
hold off until after 6 am Thursday. Moisture amounts with this
system look largely moderate. There will be a period of snow in the
west, with the heaviest period of snow looking to be later in the
afternoon or evening as the trough axis and cold front swing
through. Amounts in the mountains look to be in the advisory range,
with at least a 3 out of 4 chance of 6 inches or more.  Chances of
12 inches or more are small, at most 2 out of 5 and that is mainly
southwestern Yellowstone and the highest elevation of the Wind River
Range where impacts would be minimal at best. The valleys may only
see limited accumulation since 700 millibar temperatures rising to
minus 4 to minus 3 may raise snow levels to 6500 to 7000 feet until
toward sunset and the cold front swings through. And, another sign
spring is approaching, is that we have a bit of CAPE and negative
lifted indices. The result is there could be some thunder and
lightning Thursday afternoon. The steadiest snow here should end by
midnight Thursday night, but westerly flow will keep some snow
showers going into Friday.

As for East of the Divide, Thursday will be another dry and mild day
as downsloping west to southwest flow will dominate. The concern
here will be wind. The tightening pressure gradient will increasing
southwest flow. The 700 millibar winds rise to 50 to 55 knots
starting late Wednesday night and continuing into Thursday in the
favored Muddy Gap to Casper areas. The NBM ensemble is showing a 1
in 2 chance of wind gusts past 55 mph across the south side of
Casper with a 3 in 5 chance of gusts past 40 mph across most of the
area. The most likely time period looks to be similar to Sunday
night, from around 3 am through early afternoon. We may need high
wind watches but still time to decide. The other wind concern is the
northwest flow / post frontal variety, with this occurring later
Thursday night and into Friday. This would be in areas favored by
northwest flow, mainly the northern Bighorn Basin, Johnson County,
the Wind River Basin and Sweetwater/ Southern Lincoln Counties. MOS
guidance has sustained winds over 40 mph at both Buffalo and Rock
Springs. The probabilistic guidance gives at least a 1 in 2 chance
of wind gusts past 50 mph at these locations as well. Again, wind
highlights may have to be considered later Thursday night into
Friday.

And the next question is for snowfall. This does not look like a big
storm East of the Divide since the system is a progressive one, with
most areas only seeing a 6 to 12 hour period of snow. There could
also be some lost accumulation as the snow may begin as rain before
the cold air arrives. There is still some uncertainty as for
amounts. The highest amounts look to be in the northerly flow,
upslope areas, since there will be a period of that post frontal.
The most impacted time will be from around 4 am Friday morning until
early afternoon. The X factor will be a weak jet streak moving into
the area that may give a bit more lift to enhance the dynamics a
bit. This does not look like a warning level storm. However, some
advisories may be needed for impacts. A rapidly developing Colorado
low will tighten the pressure gradient again and bring some gusty to
strong wind as the snow arrives. So, impacts to travel may be
enhanced somewhat even though amounts would not be that great, The
main area for accumulation would be from Lander to Casper, but even
here there is at most a 2 out of 5 chance of 3 inches of snow from
this system. There are also some indicates of convective snowbands
that may develop in the afternoon, but these are hard to nail down
this far out. All snow should end after midnight as the system moves
away.

Things remain active into the weekend. Another system will approach
the west for Saturday. Guidance has trended a little weaker though,
so it may end up just being a nuisance storm. A more potent system
may arrive for early next week with a more widespread chance of
snow, but details are nearly impossible to hash out this far
out.

&&

.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 1045 AM MDT Tue Mar 11 2025

VFR conditions for all TAF sites for the entirety of the period.
Gusty southwest winds at CPR/RKS up to 25-30kts through 01Z
towards sunset with radiational cooling overnight. All other
sites look to remain below 10 to 15kts with winds increasing
once again Wednesday around the end of this TAF cycle. A few to
scattered high clouds with dry conditions continuing. No other
weather elements are expected at this time.

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