417
FXUS65 KRIW 092206
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
406 PM MDT Sun Mar 9 2025

.KEY MESSAGES...

- Windy over the Wind River, Absaroka, and Big Horn Mountains through
  Monday. Windiest over the Absarokas, with gusts over 50 mph,
  and gusts around 70 mph possible for portions of the eastern
  side of the range. Windy for the Cody foothills Monday morning
  and afternoon.

- Windy over the Wind Corridor through Monday. Gusts 35 to 45
  mph are common, with wind prone areas, like Outer Drive in
  Casper, getting gusts over 50 mph.

- Seasonal temperatures today, with a warming trend through Thursday.
  Colder Friday.

- The next Pacific weather system may impact the area Wednesday night
  through Friday.

&&

.DISCUSSION...
Issued at 112 AM MST Sun Mar 9 2025

As I write this, we are getting very close to the time change. Many
people say this messes with their sleep, but to most shift workers,
we call this Sunday. Anyway, things look somewhat quiet for the next
few days, with one exception.

And that would be the wind. We have two areas of concern, and these
are the usual suspects. Mainly the southwestern Wind Corridor from
Muddy Gap though Natrona County and in the Lee of the Absarokas. We
will focus on the southwestern Wind Corridor first. The ridge over
the area is beginning to flatten and with a weak shortwave
approaching from the northwest, things will become rather windy
here. Wind is already increasing as I write this, and some gusts over
40 mph are fairly likely (around a 4 in 5 chance), especially in the
favored area, like Wyoming Boulevard. The chance of high wind gusts
(greater than 60 mph, 65 mph in the more wind prone areas) remains
rather low, less than 1 out of 7 through today. The strongest wind
would be later tonight through midday tomorrow, when the shortwaves
approaches and there is a bit of jet enhancement. The HREF ensemble
has a 4 out of 5 chance of wind gusts over 50 mph in the wind prone
areas. Mid level winds are decent, rising to around 50 knots at 700
millibars after 06Z tonight through around 18Z Monday when wind
begins to weaken. The NBM ensemble is not quite as bullish though,
with a less than 2 in 5 chance of wind gusts past 55 mph. For now,
we will hold off on any high wind watches. If things look windier,
we can issue something during the day or evening.

It is the same situation in the Lee of the Absarokas. The difference
is this area will be closer to the jet. The models are also keying
in on the maximum impact from around 10Z to 18Z Monday as the trough
axis passes. We do have some 50 knot barbs as well at 700 millibars.
The chances of high wind around Cody, is generally less than 1 out
of 3. Wind looks stronger around Clark but criteria here is 75 mph
gusts and the chance is less than 1 out of 4. So, again, we will
hold off on any wind highlights.

Otherwise, things look fairly quiet through Wednesday. The
aforementioned shortwave may bring isolated showers to the northern
border on Monday, but otherwise it will remain largely dry through
at least Wednesday morning. Temperatures will continue to rise
through the period, most slowly in snow covered areas like the Wind
River Basin but these areas will see highs in the 50s by Tuesday as
the warming temperatures, longer days and strong March sun melt the
snow.

The next question is what will occur with the next Pacific system
that will approach for the latter half of the week. We have two
features that will determine the outcome. One is an upper level low
that will be passing to the south of Wyoming, and the second is some
northern stream energy that will be moving toward the area from
Montana. As of this morning, trends are down for snowfall. The main
deterministic models, the GFS and European, have the upper level
low further south of the area, across southern Colorado and
northern New Mexico. As a result, phasing would occur further
east and reduce the potential for a big snowstorm. This also
looks like a faster moving system than the one earlier this
week, and this will reduce snow amounts as well. In western
Wyoming, at this time it is looking like advisory level amounts.
As for the lower elevations East of the Divide, the NBM
ensemble gives at most a 2 out of 5 chance of 3 inches or more.
One concern I do have is that if the northerly push is faster,
it could lead to a decent period of northerly upslope that could
push snowfall amounts higher. The most likely time for this
would be on Friday morning. So, we have to watch this.
Temperatures will fall behind this system, but only back to
somewhat below normal given the air is Pacific, not Arctic.

&&

.AVIATION /00Z TAFS THROUGH 00Z MONDAY/...
Issued at 402 PM MDT Sun Mar 9 2025

All terminals to be VFR through 00Z/Tuesday. Ridge axis
overhead late Sunday afternoon will flatten over the next 24
hours as shortwave energy rides east along the US/Canada border.
The tail end of this shortwave traverses northern Wyoming
overnight and Monday leading to a period of increased westerly
wind. This will be the primary aviation concern through Monday.
KCOD sees westerly wind steadily increase overnight with 15-30kt
speeds common between 06Z - 18Z/Monday. There is the potential
for LLWS at KCOD given the close proximity to the foothills.
KCPR generally keeps 20 - 35kt southwest wind through the
period. KRIW, KLND, and KRIW may also see gusty westerly wind
mix to the surface Monday afternoon. There is a 30 percent
chance of 15 - 25kt southwesterly surface wind at these
terminals centered around 21Z/Monday. For now, have hinted at
this potential with 10 - 20kt wind in the forecast. KJAC and
KRKS will see sustained west to southwest wind 12 - 24kts
develop between 16Z - 19Z/Monday.

&&

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

&&

$$

DISCUSSION...Hattings
AVIATION...CNJ/VandenBoogart