324
FXUS65 KRIW 301021
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
421 AM MDT Thu Jul 30 2026

.KEY MESSAGES...

- Remaining warm with scattered showers and thunderstorms today
  and Friday, although coverage decreases reach day, especially
  compared to today.

- Very hot this weekend, especially on Sunday with many
  locations over 100 degrees. Some all time record temperatures
  for August may be set at some locations.

- Increasing breezes on Sunday and into Monday along with low
  humidity may bring elevated to critical fire weather each
  afternoon.

&&

.DISCUSSION...
Issued at 132 AM MDT Thu Jul 30 2026

I`ve often talked about how meteorology is a mathematical science.
And one of the most often sited examples are long waves, which
are essentially sine waves. The weather often works that way,
with a pattern reaching a peak and then dropping to a trough,
and the upcoming several days are no exception. The chances of
convection reached the peak of the wave, and will generally only
drop over the next several days. Meanwhile, temperatures will
climb out of the trough today and reach a peak over the weekend,
before falling again early next week. And for fire weather
concerns, they start in the trough of the wave and then rise
toward the end of the weekend and even early next week.

Monsoonal moisture remains over the area right now, and we continue
to have some light to moderate showers ongoing overnight,
and even a stray flash of lightning, especially in northern Wyoming.
This will be the peak of the monsoon and probably the wettest period
for the next several days. Most guidance shows drier air moving in
from the west today, dropping precipitable water values by an
average of 20 percent across the area. This is still above
climatological means, but only around 125 percent of normal versus
the 150 to 175 percent yesterday. Meaning there will be still be
some showers and thunderstorms around. However, most locations will
have a less than 1 in 4 chance. The best chance also shifts East of
the Divide where deeper moisture will remain, especially across
Johnson County where there is as much as a 1 in 2 chance. With more
sunshine, temperatures will be a bit warmer as well, generally about
1 to 4 degrees warmer, quite warm but nothing unusual for late July.
Convection should also be an earlier show, with most done by sunset
and almost all done by midnight.

The progression on the sine wave continues Friday. Precipitable
water drops another 10 to 20 percent on this day, bringing even less
coverage of convection. The main areas of concern on these days
would be the northern mountains as well as Johnson and Natrona
County where there will be a bit more moisture. However, the chance
is even smaller this day, nothing more than 1 out of 4. And, it will
be another very warm day to close out July, with temperatures
similar to a couple of degrees warmer than on Thursday. Some of the
warmer spots, like the eastern Bighorn Basin, will get close to or
may reach the 100 degrees on this afternoon.

Over the weekend, we reach the peak of the sine wave for
temperatures. A heat dome will build back north over the area. The
500 millibar heights climb as high as 5970 meters with 700 millibar
temperatures as high as 22 to 23 degrees celsius. This will lead to
a very hot first weekend of August with some record breaking
temperatures possibly, including a few all time high temperatures
for August, especially on Sunday. As for specifics, most of the
Bighorn Basin and the Wind River Basin below 5500 feet have at least
a 1 in 2 chance of highs temperatures at or over 100 on Saturday. On
Sunday, this increases to include most locations below 6000 feet,a
and also includes much of Natrona and Johnson Counties as well as
the lower elevations of Sweetwater County. Elevations below 5300
feet have at least a 1 in 2 chance of high temperatures over 105 on
Sunday. This would be the day some all time record high temperatures
for August could fall. As for highlights, we will hold off for
now. We will likely need at least heat advisories for the
weekend. Leaning against extreme heat warnings though given how
low the humidity will be. This, also with the fact nights are
getting longer and there will be more time for cooling after
sunset. And there is one more concern for Sunday, as this
variable climbs up from the trough of the sine wave, fire
weather. A cold front will be approaching the area from the
north, and bringing a gusty southwest breeze ahead of it.
Humidity will be very low, possibly under 5 percent in some
areas in the afternoon. Wind gusts are borderline in some areas
though. All areas will have at least elevated fire weather
though with critical fire weather likely for some. There is
still time to decide on highlights though. And, with the very
dry air over the area, the chance of any showers this weekend is
almost zero.

The cold front will move southward into the area Sunday night and
into Monday. This should bring some relief from the possible record
heat, with some areas seeing as much as a 20 degree drop in high
temperatures compared to Sunday. It will take a bit more time to
reach West of the Divide, so it looks like another hot day on
Monday, but a few degrees cooler. The somewhat cooler temperatures
should last into Tuesday. After that, the ridge may begin to build
back northward, bring more above normal temperatures. And, through
the middle of next week, precipitable waters look to remain below
normal, so the chance of any convection remains slim to none. In
addition, it still looks breezy so at least elevated fire weather
looks to continue into early next week as the fire weather sine wave
reaches it`s peak.

&&

.AVIATION /12Z TAFS THROUGH 12Z FRIDAY/...
Issued at 413 AM MDT Thu Jul 30 2026

Largely VFR conditions will continue through 12Z Friday. One
exception will be in vicinity of KJAC where last evening`s rain
and a clearing sky has brought some patchy fog which will bring
occasional IFR to possible LIFR conditions until around 14 to
15Z when the July sun should burn it off. Otherwise, any light
night showers should be away from TAF sites by 12Z. With
lingering moisture there will be another chance of afternoon and
evening showers and thunderstorms (a 15 to 25 percent chance) at
all TAF sites, although the best chance will be East of the
Continental Divide. Have elected PROB30 groups since confidence
in placement of storms remains low. Wind should remain 12 knots
or less except in and around thunderstorms and around any
outflows. Brief MVFR conditions will be possible around any
shower or thunderstorm. This should be an earlier show with
almost all showers ending by 06Z Friday. Occasional mountain
obscurations will be possible around any shower or storm.

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

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

&&

$$

DISCUSSION...Hattings
AVIATION...Hattings