105
FXUS65 KRIW 181740
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1140 AM MDT Tue Aug 18 2026

.KEY MESSAGES...

- Showers and storms are possible through this evening. Some
  could be strong with 50 to 70 mph wind gusts, hail, and
  moderate to heavy rain.

- Drier Wednesday through Friday with any isolated convection
  confined largely the mountains. Hot temperatures return with
  many locations having highs in the 90s Thursday through
  Saturday.

- Deeper moisture returns for the weekend and early next week
  with another increased chance of showers and thunderstorms.

&&

.UPDATE...
Issued at 1124 AM MDT Tue Aug 18 2026

Lots of clouds across the area today, with showers and thunderstorms
in various locations through the morning. Widespread chances (15-45%)
continue through this afternoon. Latest hi-res models still have
strong wind gusts up to around 70 mph possible with storms this
afternoon and evening, mainly across the Bighorn Basin, Johnson
County, and Natrona County. Some isolated stronger winds 50 to
60 mph could also occur over Teton/Park Counties and into the
Wind River Basin, but chances are less than the aforementioned
locations. Small hail is also possible for the stronger storms.
This activity should quickly diminish this evening, with only a
few lingering showers over central Wyoming through about
midnight.

&&

.DISCUSSION...
Issued at 145 AM MDT Tue Aug 18 2026

Over the past six weeks or so, the main weather story has been one
of two things: heat, some record breaking; and the monsoonal
moisture which as stuck around a long time and is wearing out
its welcome like an house guest that won`t leave. Some days it
was one or the other, other days it was both. And the next seven
days will be no exception.

Today looks rather active. Dew points are rising across the area as
another plume of the moisture moves into the area. One difference
today is we will have a subtle shortwave moving across the area,
providing some additional lift. Just about everyone will have a
chance of a shower or thunderstorms today, but, much like many of
the previous days, not everyone will see one. As for threats, there
could be heavy rain with any storm, with precipitable water values
rising close to an inch in some locations, which approaches 175
percent of normal. However, we do have decent wind at the mid
levels, approaching 40 knots in some areas. So these storms will
have movement, and this should mitigate the threat of flooding
somewhat. However, we do have some other possible threats today. We
do have a marginal risk of severe weather roughly along and east of
a Cody to Shoshoni to Rawlins and eastward. The main threat looks to
be strong wind. Dew point depressions are not all that large
(generally 30 to 40 degrees), however lapse rates are rather steep
(over 8C/Km). Sounding also have somewhat of an inverted V signature.
Hodographs are also largely straight with wind fairly well aligned.
With the moist atmosphere, I also can`t rule out some hail, but
the threat of this smaller. Western portions of state look to have
the most storms during the afternoon, with the greatest coverage
shifting to the east in the evening. And a few storms could linger
well into the afternoon before ending after midnight. As for
temperatures, they should run fairly similar to yesterday,
fairly close to seasonal averages.

Then, for the next three days or so, the main concern shifts toward
temperatures. Almost all guidance shows the monsoonal moisture
getting suppressed to the south and east as high pressure over the
desert southwest builds northward. This will lead to temperatures
going up and the chances of showers and storms dropping. At this
point, Wednesday looks like the driest day as we finally get a day
of below normal precipitable water across most of the area. We can`t
completely rule out a stray shower or thunderstorm across far
southern Sweetwater County, but even here the chance is less than 1
out of 6. With the ridge building back northward, 700 millibar
temperatures will be climbing again, likely peaking on Friday when
some areas each 20 celsius. This will lead to a period of above
normal temperatures starting on Wednesday and peaking on Friday. Most
areas East of the Divide will likely see highs in the 90s starting
on Thursday and lasting through at least Saturday. Friday looks to
be peak of the heat with most locations with elevations less than
5000 feet having at least a 1 in 2 chance of highs of 95 or over. A
bit more moisture may return on Thursday or Friday, but almost
all convection on these days will be confined to the western
mountains and chances will be rather low, generally less than 1
out of 4 each afternoon at any particular location.

Concerns then shift to a another return of the monsoon for the
weekend and into next week. Recent models have slowed the return of
the moisture a bit for Saturday, with precipitable water values
generally 20 percent less than yesterday. The current forecast for
Friday night is likely too wet, the deepest moisture looks to return
Saturday and into Sunday and early next week. There is some
disagreement in the guidance in regards to the details of the
most active day of the monsoon as well as placement of the most
numerous convection, as would be expected this far out. However,
precipitable water values look to remain above normal for much
of next week. Temperatures should also lower somewhat with more
cloud cover, but will likely remain near to somewhat above
normal through the period. So, if I could sum up how the next
week has compared to much of the summer, it would be more of the
same.

&&

.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 1107 AM MDT Tue Aug 18 2026

VFR conditions are expected to prevail across most terminals through
much of the TAF period. Showers and thunderstorms continue to move
through the state this afternoon. All terminals will have chances 20-
40% for a shower or thunderstorms this afternoon and evening. There
may be brief periods of MVFR to even IFR conditions especially if
any storms move overhead any terminals. The main concerns with any
showers or storms today will be strong gusty outflow winds possibly
in excess of 35 knots, frequent lightning, and moderate rainfall.
Showers and thunderstorms are expected to linger into the late
evening hours Tuesday mainly for terminals east of the Divide such
as KWRL, KRIW, KLND, and KCPR. Winds are forecast to remain light
through the overnight into Wednesday morning with speeds around 5 to
10 knots. Conditions should dry out by Wednesday morning with VFR
conditions expected to prevail through the remainder of the TAF
period. Mountains are likely to be obscured at times Tuesday with
conditions improving through the overnight into Wednesday 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...Dziewaltowski