863
FXUS65 KRIW 151731
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1131 AM MDT Sat Aug 15 2026

.KEY MESSAGES...

- Another day of showers and thunderstorms today, with most
  activity across northern Wyoming. Local heavy rain remains
  possible.

- Somewhat drier air moves in Sunday, bringing warmer
  temperatures and fewer showers and storms.

- Monsoonal moisture moves in and out next week, with Tuesday
  and Wednesday looking like the most active days, with the
  least coverage on Thursday and Friday.

&&

.UPDATE...
Issued at 1130 AM MDT Sat Aug 15 2026

Early day showers and thunderstorms become more widespread this
afternoon. Best chances still look to be across the northern half of
the area, with widespread 20 to 60 percent chances. Locally moderate
to heavy rainfall is possible with precipitable water values 0.75 to
1 inch for much of the area. Showers linger through this evening,
with most done by midnight. Current satellite shows the drier air to
the southwest making its way here, which will decrease rain chances
Sunday.

&&

.DISCUSSION...
Issued at 132 AM MDT Sat Aug 15 2026

The weather has been rather active over the past couple of days,
with some reports of flooding with the monsoonal moisture over the
area. It also brought some needed rain to portions of the area. And
this looks to continue, although there will be some fluctuations
over the next few days. As for now, we still have some showers and
embedded thunder out there right now, although they are slowly
weakening. A few showers may hang around until sunrise though.

We will still be under the monsoonal moisture today. However, the
core of it will shift a bit more to the north and east as some drier
air tries to punch in from the southwest. Precipitable water values
on average are around 15 to 20 percent lower than on Friday, with a
northeast to southwest gradient from most moist to the least (from
around a 1 in 6 chance in southern Wyoming to as much as 1 out of 2
in the northern mountains. So, the best chance of showers and storms
will be across northern Wyoming where we still have a marginal risk
of excessive rainfall today. There is still some steering flow so
this should cut the threat of flooding somewhat but it is still
possible in local areas. Temperatures will be similar to yesterday,
evening around 5 degrees below seasonal averages. Most guidance is
also showing an earlier show, with most convection over by sunset
and almost all showers and storms over by midnight.

Drier air should then push further eastward on Sunday, dropping the
chance of showers and storms even more. There will still be a few
around, but with precipitable water values returning close to
seasonal normals and dew points generally 10 to 15 degrees lower
than on Saturday, most locations should be rain free. There will
also be more sunshine along with somewhat warmer temperatures aloft.
This will allow for warmer temperatures, probably returning closer
to seasonal normals. At this point, things look largely quiet after
sunset on Sunday night.

Things may turn more active again on Monday, especially later and
into the night. Guidance shows precipitable water values climbing
back to around 130 to 150 percent of normal. At the same time,a
subtle shortwave will be moving through the area. As a result, the
chance of showers and storms increases again this day, and possibly
lasting into the nighttime hours as well. This more active pattern
looks to last into Tuesday and possible Wednesday as well,
especially across northern Wyoming where another shortwave may be
passing. Temperatures through this period look to be near to
possibly slightly below normal.

Following Wednesday, most guidance shows ridging over the desert
southwest building back northward into the central and northern
Rockies for the end of the work week. As a result, temperatures
should begin a warming trend starting on Thursday and especially
Friday and into next weekend, when above normal temperatures again
look likely for most of the area, with 90s across many of the lower
elevations East of the Divide. As for convection, Thursday and
Friday look largely dry at this point, with only isolated showers
over the higher elevations. Some monsoonal moisture may return for
the weekend, but this far out it uncertain is rather high. So, the
story for the next seven days will be the monsoon, and it`s ebbs and
flows over the period.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1027 AM MDT Sat Aug 15 2026

VFR conditions are expected across nearly all terminals throughout
much of the TAF period. Low clouds have lingered across KJAC this
morning but gradual improvement is expected over the next hour or so
after the start of the TAF period. Otherwise, monsoonal moisture is
expected to persist across the region today. This influx of moisture
will help fuel scattered showers and thunderstorms through the
afternoon and evening Saturday. Showers and thunderstorms have
already begun to develop across portions of western WY. Convection
will continue to spread east through around 00Z Sunday with nearly
all terminals having a 10-40% chance for a brief shower or
thunderstorm. MVFR to IFR conditions cannot be ruled out at times
especially if storms move directly overhead any terminals. Gusty
winds may occur nearby developing storms with gusts of 30 knots or
more possible. Conditions should improve after 00Z Sunday for nearly
all terminals with KWRL and KCPR possibly seeing showers or storms
linger to about 04Z. Conditions are expected to remain dry through
the overnight into the morning hours on Sunday. Winds are forecast
to remain light through this time period with speeds of 5 to 10
knots.

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

&&

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

&&

$$

UPDATE...Wittmann
DISCUSSION...Hattings
AVIATION...Dziewaltowski