Powell, Wyoming 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

751
FXUS65 KRIW 250349
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
949 PM MDT Thu Jul 24 2025

.KEY MESSAGES...

- A few isolated showers and storms slowly fade by midnight.

- Very warm to hot and drier conditions expected Friday through
  Sunday with only isolated showers and thunderstorms across
  far northern WY each afternoon. South-southwest winds will be
  breezy and gusty Saturday and Sunday.

- Elevated to critical fire weather is likely from Friday
  through Monday, with Saturday looking like the day of most
  concern.

- A pattern change Wednesday through Friday next week will bring
  cooler temperatures and very good chances of showers and
  thunderstorms each afternoon and evening.

&&

.UPDATE...
Issued at 105 PM MDT Thu Jul 24 2025

Showers and thunderstorms have commenced from southwest WY into
central WY, and even in northern Johnson County east of Buffalo.
Have increased probability of precipitation and thunder to
several areas where the previous forecast was lacking, including
northern Johnson County and eastern Sweetwater County toward
Casper. Had increasing chances later in the afternoon, but
earlier convection has developed. Was honestly expecting more
development early from the northern Uintas and eastern Wyoming
Range, but those areas are more slow to develop. With the SPC
marginal risk for severe storms line just east of
Johnson/Natrona Counties, expecting stronger storms in eastern
Johnson/Natrona Counties where they should develop and then move
eastward into a more favorable environment.

Another modification to the forecast today and overnight is the
increase in smoke moving over western and central WY from the
south-southwest. The atmosphere should become more hazy and
smokey late this afternoon over southwest WY and then spreading
north and east during the overnight hours. Friday morning should
be noticeably more hazy, but then conditions should improve
through the day as the smoke moves eastward. Another surge
though will move into south-central WY (from the Grand Canyon
fire) Friday evening.

Friday should be back into the "very warm to hot" range with
afternoon temperatures under mostly clear skies and warmer
southwest wind. Conditions will bring elevated fire weather to
parts of southwestern and southern WY, but marginal critical
conditions are not expected until Saturday.

&&

.DISCUSSION...
Issued at 316 AM MDT Thu Jul 24 2025

Meteorology is commonly known as one of the Physical and Mathematical
Sciences. And one of the most common things with meteorology and
mathematics is the sine wave, since these are often associated
with weather patterns, like Rossby Waves. And, it is often how
weather progresses with peaks and troughs, like the sine wave.
And this forecast is no exception.

The variable is thunderstorm coverage and precipitation chances. On
Tuesday and Wednesday, we were on the peak of the wave, with a
decent coverage of showers and thunderstorms. And over the next
several days, we will descend into the trough, with chances decreases
significantly. Not stopping completely, but rather limited. And then
possibly rising back toward the peak next week. And the other
variable is fire weather, where concerns were at the trough
yesterday, but will start rising back toward a peak this weekend.

As for today, we still have decent moisture around mainly east
of the Divide. However, the best upper level forcing has shifted
east of the area today. So, thunderstorm coverage should be
more restricted. Drier air will also start punching in from the
west, reducing chances in western Wyoming. Precipitable water
levels are expected to drop back to close to climatological
averages today as well. Instability parameters are also less
today, with CAPE peaking only around 700 J/KG and lifted indices
generally around minus 3. The highest values, are in the usual
location, Johnson County. So if there are any stronger storms,
this would be the location. Another area of concern is from the
western Bighorn Basin into the Wind River Basin, where low
level easterly flow will bring some upsloping and enhance the
chance of a few storms. Chances are low though, generally only
around 1 in 4 at the most except in the mountains. As for fire
weather, concerns remain low today since most humidity will
remain above critical levels and wind should remain light to
moderate.

Friday and into the weekend is where the sine wave and concerns
really flip as ridging builds into the area, with 500 millibar
heights possibly riding as high as 5970 meters. Much drier air will
spread into much of the area, with precipitable water values
possibly dropping as low as 50 percent of normal. This will really
limit any convection, keeping it mainly in and near the mountains
where high level heat source will increase instability somewhat. But
even here, most storms would produce more wind than rain and the
chance would not be more than 1 in 5 at any given location.
Temperatures will also be above normal, with widespread highs in the
90s in the lower elevations east of the Divide with a few
warmer spots possibly making a run at 100. The main concern here
becomes fire weather. The humidity will definitely be low, some
possibly in the single digits over the weekend. The limiting
factor looks to be wind. Looking at the 700 millibar winds on
Friday, I am only seeing 10 to possibly 15 knots. This is
probably not enough for critical fire weather so highlights look
unlikely here. The real day of concern looks to be Saturday as
a weak shortwave moves across the area, enhancing mixing. Here,
700 millibar winds increase to 20 to 25 knots, so critical fire
weather is more likely here (more than a 1 in 2 chance). So, I
would expect some fire weather highlights for this day. On
Sunday, wind decreases again, making this day a borderline
critical day. However, elevated fire weather will be very likely
(at least a 4 out of 5 chance) each day from Friday through
Sunday.

The sine waves may reverse again next week. Monday looks like
another hot day with low humidity, but again wind looks borderline
at best for any fire weather highlights. There are indications that
a cold front may make a run at the area on Tuesday and bring cooler
temperatures. Guidance is split on any possible showers or storms
with this system, with some bringing them over the area and other
keeping the best convection over the Northern Plains states.
Monsoonal moisture may return to the area for the middle of next
week, but timing it this far out is uncertain. So, an example
of how mathematics is associated with weather forecasting.

&&

.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/...
Issued at 948 PM MDT Thu Jul 24 2025

Lingering showers and storms will end by the start of the TAF
period. An area of showers exiting Sweetwater County could hold
together and reach KCPR by 06Z/07Z, but only have a 20%
confidence. VFR conditions prevail overnight and through the
day Friday. Drier air Friday will limit shower/storm chances.
The best chances (15% to 30%) will occur over northwest Wyoming.
Currently only have KCOD with a PROB30 group for afternoon
storms. FEW-SCT FL150-200 will continue across the area through
the evening Friday.

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

&&

.FIRE WEATHER...
Issued at 316 AM MDT Thu Jul 24 2025

Fire weather concerns should remain low to moderate today as
humidity and wind should should remain below critical levels.
Fire weather concerns rise Friday as much drier air spreads into
western and central Wyoming. Elevated fire weather is expected
each day from Friday through Monday as relative humidity falls
below 15 percent. Wind will be more borderline. At this point,
breezy conditions on Saturday look to be the best chance of
critical fire weather across portions of the area.

&&

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

&&

$$

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