Mills, Wyoming 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

962
FXUS65 KRIW 290434
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1034 PM MDT Sun Jun 28 2026

.KEY MESSAGES...

- Scattered light rain showers will spread from south central to
  central Wyoming this evening and into the overnight hours.
  Rain will have a hard time reaching the ground, but those in
  Sweetwater, Fremont, and Natrona Counties could see a few
  brief rain showers (30% chance).

- Temperatures will approach freezing for western valleys and
  basins around sunrise Monday, with frost likely (70% chance)
  and a freeze possible (40% chance). Typical cold spots and
  high elevation valleys like Bondurant have a higher chance of
  a freeze.

- On Monday morning, light accumulating snow is forecast across
  northwestern Wyoming for the high mountains above 10,000 ft.

- East of the Divide, windy conditions will develop Monday with
  a 50% chance of wind gusts in excess of 50 mph in central
  Wyoming.

- Tuesday morning is forecast to be chilly again, with frost
  possible in western Wyoming valleys and basins.

&&

.UPDATE...
Issued at 1234 PM MDT Sun Jun 28 2026

Main considerations for this update were related to wind and cold
products. Starting with wind, models are still borderline on the
high wind potential Monday. 700mb winds continue to show 40 to 45
knots, just too low for greater confidence. Wind prone places like
Outer Drive in Casper, South Pass, and the slopes of the Green
Mountains/Rattlesnake Hills could easily see gusts around 60 mph,
but widespread high winds do not seem likely at this time.
Nevertheless, gusts around 50 mph will be common across the Wind
Corridor of South Pass to Casper Monday morning and afternoon.
An isolated gust to 60 mph is not out of the question.

For frost, temperatures in the upper-20s to mid-30s occur tonight
and Monday night for western valleys and basins. Climatologically,
end of June is where these locations typically see their last
"spring" freeze. So, although this is not too out of the ordinary, a
warm winter and spring has led to an earlier growing season for much
of the area. Places of greatest impacts are for the Green River
Basin, which should be a bit warmer this time of year, so places
like Big Piney and Farson should be aware of frost the next couple
nights.

&&

.DISCUSSION...
Issued at 230 AM MDT Sun Jun 28 2026

Well, the day has finally arrived. On a day I am working, we
are not in the outlook for severe weather across western and
central Wyoming. In nine days I have worked, there has been at
least a Marginal risk on seven of those days. And kudos to the
SPC, they were right on yesterday. Thankfully, things are more
tranquil right now, with just some areas of light to
occasionally moderate rain. And, something else in the
mountains, we will talk about that in the discussion.

All in all, today looks not as active. It will feel more like May
across areas east of the Divide, and more like April west of
the Divide. The bowling ball of an upper level low is now moving
from Oregon and into Idaho. Most guidance shows much drier air
spreading across much of the area, and as a result any shower
activity will be limited. The main area of showers will be
across far northwestern Wyoming, with another across
southwestern areas. Amounts today should remain on the light
side though, generally a tenth of an inch or less. There is also
a less than 1 in 5 chance that a shower or storm could develop
in eastern Natrona and Johnson Counties as just enough moisture
may return. Elsewhere, the chance is less than 1 out of 10.
Instability is rather limited, with at most 200 J/kg of CAPE, so
any lightning would be limited. The main concern today looks to
be fire weather. With the 100 knot jet still over the area,
many areas have a greater than 1 out of 2 chance of wind gusts
over 25 mph. However, humidity is rather borderline, largely
remaining above 15 percent. Cooler temperatures today will help
with this as well. So, no Red Flag Warnings today, although
Elevated Fire Weather will be likely.

Concerns ramp up tomorrow, and there will be a contrast west
and east of the Divide. The upper level low will lift northward
into Montana, and drag a trough which will become negatively
tilted as it moves across the Cowboy State. This will be the
main factor with the weather. In areas east of the Divide, the
concern will be wind. I did give thought to a High Wind Watch
for the Green Mountains and Natrona County. There will be a
decent setup, with a trough mixing across the state. This area
will be in the left front quadrant of the jet to enhance
downward momentum as well. The 700 millibar winds are still
borderline though, generally only peaking out at around 45
knots when I would like the see several 50 knot barbs. The NBM
ensemble also only gives at most a 1 in 3 chance of gusts over
55 mph except in the mountains and in areas where criteria is
higher. So, we will hold off on any High Wind Watches for now.
The strongest wind would not be until Monday afternoon, so we
will let the day crew take another look at it. Nevertheless, it
will be a windy day across much of the area. As for fire
weather, there will be many areas of elevated fire weather.
With temperatures still on the cool side, humidity should stay
above critical levels. Wind should decrease during the evening
as the trough moves away to the east. With the strong
downsloping flow, very few places would see a shower or
thunderstorm on this day east of the Divide.

The concern in the west shifts to a wintery one, as heavier
precipitation develops as flow turns westerly behind the trough
passage and still somewhat moist upslope kicks in. New guidance has
also trended a bit cooler Sunday night and Monday, with 700 millibar
temperatures falling as low as minus 3C when best orographics
move in behind the trough. This could drop snow levels down to
7000 feet at times, and I would not rule out even see some wet
snowflakes in the Jackson Valley Monday morning. Most locations
above 8000 feet have at least a 1 in 2 chance of at least an
inch of snow, with a greater than 1 in 2 chance of over 3 inches
above 9000 feet in the Tetons and Yellowstone Park. The highest
locations of these locations (above 11000 feet) even have a 1
in 2 chance of 6 inches or more. As for travel problems, they
shouldn`t be too bad as most of the snow should fall during the
day and being only a week past the solstice, the snow would have
trouble sticking on most roads. However, we are at the peak of
tourist season. Anyone visiting from out of state should be
aware it can snow during any month of the year in Yellowstone
and the Tetons, so be prepared for wet and cold weather if you
are venturing there on Sunday or Monday.

I was watching the 70s detective series Columbo yesterday, and as he
would say there is "Just One More Thing." And that concerns the
potential for frost. Recent model trends have shown more
clearing today and tonight, especially in the southern zones.
With the chilly air mass still in place, this will be the night
to watch. The NBM ensemble gives a greater than 1 in 2 chance
of temperatures below 32 degrees in much of the Green River
Basin as well as southern Lincoln County and even in the Star
and Jackson Valleys. Sky cover will be the X factor though. We
may need some highlights for tonight or Monday night.

For Tuesday through much of next week, the reasoning remains the
same as yesterday. Wyoming will be stuck between a trough over the
western United States and strong ridge to the east, which should
bring record heat to the eastern half of the country. That
means we will be along the path of shortwaves that will bring
chances of convection each day. We are still in low confidence
in exact timing of the waves and placement of the heaviest
precipitation though. With flow turning more southwesterly,
temperatures will recover to near to somewhat above normal but
no extreme heat is expected. It will also remain rather breezy
and with low dewpoints expected, fire weather may also be a
concern for much of next week.

&&

.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 1030 PM MDT Sun Jun 28 2026

VFR conditions are expected to prevail across nearly all terminals
through the TAF period. Winds will remain light (12kt or less)
for all terminals through 12Z. The line of weak/virga showers
will continue from western Sweetwater County to Sheridan County
through the rest of the night and dissipate by 13Z. This line
may move over KRIW/KLND, but is not expected to have any impact
other than lowered VFR ceilings. A PROB30 group continues at
KRKS through 08Z. Other terminals such as KJAC, KPNA, KCOD, and
KWRL see precipitation chances develop between 15Z and 20Z and
primarily end around 00Z. Weak rain showers will be possible
across the Bighorn Basin after 00Z, but are not expected to
directly impact KCOD or KWRL. Winds will begin to increase
across the forecast area after sunrise with gusts of 25 to 35kt
beginning by 14Z. However, terminals such as KCOD and KCPR will
see stronger winds with gusts of 40 to 45 knots. These gusty
winds are expected to prevail through 00Z and begin to subside
after sunset. The exception will be KCOD and the east slopes of
the Bighorn, Absaroka and Wind River Mountains, where gusts of
35 to 45kt will continue. Mountain obscuration is expected to
persist across the western mountains tonight and Monday,
shrinking back over far northwestern portions after 00Z. Expect
turbulent winds over the mountains. LLWS is not expected at any
terminal, however areas north of KCOD could be impacted.

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

&&

.FIRE WEATHER...
Issued at 230 AM MDT Sun Jun 28 2026

A combination of a gusty wind and low humidity will bring
elevated fire weather to many locations east of the Continental
Divide this afternoon. Relative humidity may fall into the
teens at times, but remain above critical levels. On Monday,
wind gusts to around 50 mph are possible in Fremont and Natrona
Counties with a gusty wind in most locations along with humidity
dropping to around 20 percent in many locations east of the
Continental Divide.

&&

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

&&

$$

UPDATE...Wittmann
DISCUSSION...Hattings
AVIATION...LaVoie/Dziewaltowski
FIRE WEATHER...Hattings