964
FXUS65 KRIW 160350
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
950 PM MDT Sat Aug 15 2026

.KEY MESSAGES...

- Scattered showers and thunderstorms will continue through the
  evening, with the best chances across northwestern Wyoming and
  along and east of the Continental Divide. 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 /06Z TAFS THROUGH 06Z MONDAY/...
Issued at 949 PM MDT Sat Aug 15 2026

A few showers will linger across western Wyoming tonight into Sunday
morning, but should not impact any terminals. Outside of
thunderstorms conditions will remain VFR through the TAF period. The
strongest storms may drop conditions down to MVFR at times Sunday
afternoon. These showers and storms will not be as widespread as
moisture slowly decreases over the next few days.

Wind will generally be around 10 knots or less through the TAF
period. Some gusts near 20 knots will occur at KCPR and KRKS Sunday
afternoon. Outflow driven wind, with gusts up to 40 knots will be
possible with the strongest storms Sunday afternoon. Fog and low
clouds are possible at KJAC again Sunday morning thanks to more
rainfall this afternoon. Kept this threat as VCFG and SCT001 as
clouds may keep it from fully saturating across the whole valley
tonight/Sunday morning.

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...Rowe