710
FXUS65 KRIW 171830
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1230 PM MDT Sun Aug 17 2025

.KEY MESSAGES...

- One more day of afternoon showers and thunderstorms, with the
  main concern being widespread gusty outflow winds and
  frequent lightning strikes.

- Hot and dry conditions are forecast to build in over the
  region for much of the upcoming week.

- Near record high temperatures are possible for Tuesday and
  Wednesday with some locations east of the Divide flirting with
  the century mark.

&&

.UPDATE...
Issued at 1229 PM MDT Sun Aug 17 2025

Another day, another round of afternoon showers and thunderstorms.
The overall forecast remains on track with little change. Lingering
morning showers have gradually weakened with cloud cover dissipating
allowing for sunshine to break through. Temperatures are forecast to
reach the upper 80s east of the Divide and upper 70s west of the
Divide. Showers and storms are expected to begin developing across
western WY early in the afternoon. Activity will eventually spread
east of the divide lingering through the evening into the early
morning hours Monday. Similar to the last few days the main concerns
with any developing showers or storms will be strong gusty outflow
winds and frequent lightning strikes. Moisture has increased across
the region which should limit the strength of outflow winds but
temperature and dewpoint depressions still look to range from 40 to
50 degrees. This will lead to widespread outflow winds of 30 to 45
mph with isolated gusts of 50 mph or more possible. The increase in
moisture and instability may allow for some stronger storms to
produce small hail. Overall, widespread gusty outflow winds,
frequent lightning, and isolated small hail will be the main
hazards associated with convection this afternoon and evening.

The upcoming weeks forecast remains on track with little change as a
period of hot and dry conditions is expected to build in over the
region. This is the result of an area of high pressure prevailing
over the area hindering moisture. Temperatures are forecast to
climb to above normal values by the middle of the week. Current
model guidance shows portions of the Wind River Basin, Bighorn
Basin along with Johnson and Natrona Counties having a 20 to 50
percent chance of seeing highs near 100 degrees for Tuesday and
Wednesday. Lower but still above normal temperatures are
forecast west of the Divide with highs in the low 90s. Looking
at climate data for numerous sites across the state, there looks
to be a good chance for multiple daily high temperature records
to be in jeopardy. Elevated to near critical fire weather
conditions will be the other story for the upcoming weeks
weather. The one positive is that winds look to be marginal
through the week, which should slightly limit fire weather
concerns. This will need to be monitored as very dry fuels
prevail across the state with little needed to start and rapidly
grow any fires.

&&

.DISCUSSION...
Issued at 130 AM MDT Sun Aug 17 2025

Water vapor imagery continues to show the southwest difluent
flow aloft extending out of northern Utah into Wyoming. IR has
quited down for the overnight hours with the next shortwave
evident coming off Uintas to impact the CWA come Sunday
afternoon and evening. Otherwise, some sporadic and very
isolated in nature rain showers continue to persist across
Sweetwater County that will dissipate by sunrise Sunday morning.

Storm initiation Sunday around the noon time frame looks to be
in decent agreement with the HiRes models across portions of
Sublette County before pushing east and northeast over the
Divide. Storms will become more widespread after around 4-5PM
coming off the Winds pushing east of the Divide through sunset.
The main concerns once again will be frequent lightning for
starting new fires, and gusty outflow winds for the ongoing
ones, especially the one near Thermopolis pushing over the Owl
Creeks for the 6-7PM timeframe. The more enhanced storms could
be for northern portions of Johnson County where the gusts may
push over 50mph. The better instability and shear values will be
into eastern Montana and the Dakotas in the stronger upper level
difluent flow. Storms weaken towards sunset and push out of the
CWA by 10PM to midnight exiting out of Johnson County. Weak
synoptic winds outside of storm outflows and temperatures again
remain not as warm with the 70s west of the Divide and up to
the mid 80s to the east.

Clearing skies and weak winds overnight into Monday morning will
give way to building higher heights centered over the Colorado
Rockies with the ever increasing confluence aloft. This will
start a warming trend and dry conditions Monday and beyond
pushing to near 100 degrees for some locations Wednesday east of
the Divide. Increasing fire danger as relative humidity values
decrease with the warming trend, but thankfully, no stronger
winds are expected to reach critical conditions. Some mountain
showers possible Thursday afternoon as the aforementioned upper
level high starts to weaken and retreat southeastward. This will
allow the GOA low to skirt by to the north and increase the
monsoonal moisture for Friday and into next weekend. As such,
storm chances rise as well for a more widespread event after a
hot and dry work week.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1127 AM MDT Sun Aug 17 2025

Showers and thunderstorms have already started to bubble across
western WY, and will continue to drift northeast across the
state. Best chances at local airports will be locations closest
to mountain ranges (KBPI, KCOD, KLND), so have added TEMPO
groups at these locations. Any locations would have the
potential for gusty and erratic winds through the afternoon.
Conditions will improve by early evening, with light winds
overnight.

&&

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

&&

$$

UPDATE...Dziewaltowski
DISCUSSION...Lowe
AVIATION...Straub