685
FXUS65 KRIW 300228
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
828 PM MDT Tue Jul 29 2025

.KEY MESSAGES...

- A few showers and storms linger in northern Johnson County
  until midnight. Skies will clear overnight.

- Unsettled and active weather persists through the week and
  into the weekend with daily afternoon and evening showers and
  thunderstorms. The best chances occur along and east of the
  Continental Divide.

- Beneficial rain will fall in many locations east of the Divide
  Wednesday and Thursday.

&&

.UPDATE...
Issued at 1220 PM MDT Tue Jul 29 2025

The forecast remains on track for showers and thunderstorms this
afternoon and evening with strong to severe thunderstorms possible
east of the Divide. As mentioned in the morning AFD discussion, the
front remains situated along the Divide. As of 18Z, post-frontal
dewpoints east of the Divide are in the upper 50s to low 60s due to
the easterly low-level flow. These high dewpoints will continue to
help the atmosphere destabilize. As of 18Z, satellite imagery shows
decent cloud cover across the region and this will limit some of the
daytime heating and the amount of destabilization. As skies clear,
convection will initiate off of higher elevations along and east of
the Divide and push east. Sufficient deep-layer shear of 30-50kts
and DCAPE values ranging from 1000-1500 J/kg favors large hail and
gusty winds of 50-60+ mph being the primary hazards. Johnson and
Natrona Counties continue to have the highest probability (around
50% chance) of severe thunderstorms, especially because some of the
morning cloud cover has dissipated. However, anywhere east of the
Divide could see severe thunderstorms. Heavy downpours are also
anticipated with precipitable water amounts around 120% of normal.
Isolated flash flooding is possible, especially across Johnson and
Natrona Counties, with any showers or thunderstorms. The reason
flash flooding will primarily be isolated is due to thunderstorms
moving relatively fast and not staying in one place for too long.

West of the Divide remains cut off from the substantial low-level
moisture, thus elevated fire weather conditions exist this
afternoon. Isolated showers and thunderstorms are possible during
the afternoon and early evening hours. Given dewpoint depressions of
50-60 degrees, showers and thunderstorms will largely be dry and
capable of 50+ mph gusty outflows. The rest of the forecast remains
on track with shower and thunderstorm chances each afternoon.

&&

.DISCUSSION...
Issued at 148 AM MDT Tue Jul 29 2025

After a quiet Monday across the Cowboy State activity is expected to
ramp up today. A weak cold front draped itself across portions of
the state on Monday eventually dissecting the CWA bilaterally with
one half being east of the Divide and the other west. Temperatures
will not be impacted to greatly as they remain near seasonable if
not slightly below normal with highs in the mid to upper 80s.

The location of the front is a key part in determining where the
best chances for showers and thunderstorm will be today. Currently
locations east of the Divide will have the highest likelihood
(30-60%). This is due to an influx of moisture filling in
behind the frontal passage. This can be seen with dewpoints
forecasted to be in the low to mid 50s east of the Divide and
low 30s west of the Divide, where the front has not moved
through. Forecasted PWATs range anywhere from 0.75 to nearly
1.25 inches which is well above normal for this time of year.
Winds will also be a factor as post frontal winds are from the
east/northeast while west of the Divide will remain
south/southwest. These post frontal winds will create some
upsloping mainly across the eastern slopes of the Bighorns and
Wind River Ranges. The other impact these winds will have is
creating some shear throughout the atmosphere. Upper-level flow
will be from the south/southwest but low-level flow in post
frontal locations as mentioned earlier will be from the
east/northeast. Temperatures in the mid 80s combined with
dewpoints in the low to mid 50s will have the potential to
create some potent areas of instability. CAMs are showing CAPE
values ranging from 1500 to 2500 J/kg with some locally higher
amounts in Johnson and Natrona Counties. Speaking of Johnson and
Natrona Counties these areas will likely have the best chances of
seeing a strong to severe storm or two today. SPC highlights this
with a slight risk drawn across these areas. Convection looks to
start developing by the late morning and early afternoon over parts
of western WY. Showers and thunderstorms will gradually spread east
of the Divide by the mid afternoon. Convection will continue to trek
east through the afternoon and evening eventually dissipating by the
late evening Tuesday. Overall, there is the potential for some
strong to severe storms developing during the afternoon and evening.
The best chances will be east of the Divide, especially in portions
of the eastern Bighorn Basin as well as Natrona and Johnson
Counties. The main hazards will be large hail, strong gusty outflow
winds, and localized heavy downpours. There is a small chance for
some flash flooding mainly across Natrona and Johnson Counties where
the most abundant moisture will be. One thing to monitor which
models have started to show is cloud cover lingering over Johnson
and Natorna Counties during the late morning and early afternoon. If
this cannot break up in time then the potential for strong to severe
storms may be hindered.

A trough will make its way across the western CONUS and gradually
move east through the week, this will keep things rather unsettled
and active over the region. Wednesday sees this unsettled weather
continue as above normal moisture lingers across areas east of the
Divide. Showers and thunderstorms develop again during the afternoon
and evening. The best chances remain east of the Divide where the
best moisture will be. An isolated strong to severe thunderstorm
cannot be ruled out as well. The overall concern is not too high as
there will not be as favorable dynamics in place to aid in storm
development. However, a strong storm or two may be capable of
producing small hail, gusty winds, and isolated heavy downpours.
Unsettled weather will persist through the remainder of the week
into the weekend. Coverage of these showers and thunderstorms will
decrease throughout the week becoming more scattered in isolated in
nature. Temperatures remain around seasonable values into the
weekend with no significant warm up insight.

&&

.AVIATION /00Z TAFS THROUGH 00Z THURSDAY/...
Issued at 537 PM MDT Tue Jul 29 2025

Cloud cover has hindered the development of strong/severe
thunderstorms late Tuesday afternoon, but recent trends are on
the upswing. Ongoing convection will spread east through at
least mid-evening Tuesday. For the most part, convection occurs
along and east of the Continental Divide where moisture and
instability are most favorable. Wide temperature-dew point
spreads west of the Divide support gusty outflow wind with any
showers and storms. Convection is east of the forecast area by
06Z/Wednesday. Any terminals that receive heavy rain before
clearing out toward Wednesday sunrise could be susceptible to
patchy fog and/or low stratus with KCPR the most likely
location. Forecast maintains some SCT decks to reflect this
possibility. Low-level, moist northeasterly flow pushes into
southwest Wyoming Tuesday night leading to 10-18kt surface wind.
Another round of convection returns around 21Z/Wednesday and
impacts mainly areas east of the Continental Divide.

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...Gerhardt
DISCUSSION...Dziewaltowski
AVIATION...CNJ