518
FXUS65 KRIW 192200
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
400 PM MDT Wed Aug 19 2026

.KEY MESSAGES...

- Warming temperatures and dry conditions are expected to
  prevail across the Cowboy State today.

- Elevated fire weather conditions are possible this afternoon
  and evening mainly in portions of southern WY.

- Above normal temperatures return for Thursday and Friday with
  widespread highs in the 90s. Any thunderstorms would be
  confined to in and near the mountains.

- Deeper monsoonal moisture returns for the weekend and into
  next week, bringing an increased chance for daily showers and
  thunderstorms.

&&

.UPDATE...
Issued at 1125 AM MDT Wed Aug 19 2026

Not much to add regarding to forecast especially for the
remainder of the work week into the weekend. Warm and dry
conditions are expected to make their return. Temperatures will
gradually warm up Thursday and Friday with highs returning to
above normal values. Currently, highs are forecast to get into
the low to mid 90s Thursday and then the mid to upper 90s for
Friday. Precipitation chances remain low with possibly an
isolated virga shower or two mainly across the higher elevations
Thursday and Friday. Chances for precipitation do increase for
the weekend but at this time there still remains uncertainty as
to how much moisture the state may see. Overall, the nice period
of autumn like weather will come to an end with summer heat
returning.

&&

.DISCUSSION...
Issued at 1230 AM MDT Wed Aug 19 2026

We still have a few showers out there early this morning, but these
should be gone by sunrise. It finally looks like we will get a break
from the monsoon, but it is like a shark. It is only leaving for a
brief interlude, it will be back for more, but there will be
break.

The main concern the next few days looks like it will
shift to more hot temperatures. A ridge across the desert
southwest will slowly build to the north, and bring a gradual
rise in temperatures over the next few days. The rise in
temperatures begins today, with widespread mid to upper 80s
across most of the lower elevations, with a few locations
possibly touching 90. As for precipitation, we can`t completely
rule it out but the chance will be close to zero for 95 percent
of the area. We did add some slight chance POPs across southern
Lincoln and western Sweetwater Counties where just enough
moisture may linger for an isolated shower. With the dry low
levels, it would likely only be virga. But even here, the
chance is only 1 out of 6. Normal to below normal precipitable
water levels should keep the rest of the area rain free. There
is one other concern. There will be a bit of breeze developing
in southern zones, and relative humidity will be falling to
around 15 percent. This raises some concern for fire weather. At
this time, the chance of getting 3 hours of critical fire
weather is less than 1 out of 3, so we will not issue any fire
weather highlights. Elevated fire weather will be likely for a
few hours this afternoon though.

As we head to Thursday and Friday, the main concern will be heat as
700 millibar temperatures approach 20 celsius in portions of the
area. On Thursday. most of the population centers below 6000 feet
will have at least a 1 in 2 chance of high temperatures over 90.
Friday still looks like the hottest day, with locations below 6500
feet having at least a 3 out of 5 chance of high temperatures over
90. Areas below 5000 feet will have a 1 in 2 chance of high
temperatures over 95. The good news is this will be Wyoming heat,
meaning humidity will remain low, meaning it should not be dangerous
heat. As for potential convection, chances will increase each day as
monsoonal moisture begins to creep back in. However, as per the
usual progression, it will be largely at the mid levels first.
Through Friday, most convection would be confined to the mountains
with nothing more than a 1 out of 3 chance in any particular
spot. And with many of the showers, rain may not even reach the
ground. As for fire weather concerns, wind should remain light
to moderate so critical fire weather is not expected despite the
low humidity.

We will should be back in the monsoonal pattern on Saturday as
deeper moisture spreads back over the area. Precipitable waters have
the potential to climb over 150 percent of normal starting on
Saturday and continuing through much of next week. All areas will
have a chance of showers and storms starting on Saturday. As for the
most impacted areas, the majority of guidance favors the maximum
impact in western Wyoming this weekend, but confidence on this is
low. There will be the usual ebbs and flows in the coverage of
convection into next week, and it is difficult to nail down details
this far out as to what day will be the most active. As for
temperatures, with more cloud cover temperatures should begin to
cool starting Saturday. Overall though, temperatures should remain
largely above average into next week. So after around a three day
break, the monsoonal pattern of diurnal convection likely returns
this weekend.

&&

.AVIATION /00Z TAFS THROUGH 00Z FRIDAY/...
Issued at 400 PM MDT Wed Aug 19 2026

VFR conditions expected throughout the entirety of the period. A
few to scattered high clouds with relatively light winds 10kts
or less, except a 25kt gust at RKS the remainder of the evening
through sunset. With radiational cooling and mainly clear skies,
expect light winds and dry conditions to persist after 03Z
through the rest of the period into Thursday morning. Winds
increase once again after 18-20Z during peak heating and mixing
at JAC/RKS/CPR. Otherwise, no other weather elements expected
at this time.

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 1230 AM MDT Wed Aug 19 2026

A combination of an afternoon breeze and humidity falling to
around 15 percent across portions Unita, Sweetwater, Sublette
and southern Lincoln Counties will bring elevated to near
critical fire weather this afternoon. Although relative humidity
will remain low through Friday, lighter wind should improve fire
concerns somewhat.

&&

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

&&

$$

UPDATE...Dziewaltowski
DISCUSSION...Hattings
AVIATION...Lowe
FIRE WEATHER...Hattings