909
FXUS65 KRIW 111724
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1124 AM MDT Mon Aug 11 2025

.KEY MESSAGES...

- A bit warmer today with isolated showers and thunderstorms in
  Johnson and Natrona Counties.

- Rather hot Tuesday through Thursday, with elevated fire
  weather possible on Wednesday and Thursday.

- Coverage of thunderstorms increases Wednesday and likely peaks
  on Friday.

&&

.DISCUSSION...
Issued at 231 AM MDT Mon Aug 11 2025

All in all, things look fairly quiet today across the area. There
is one exception, and that is across Johnson and northern Natrona
Counties where there could be a few showers and thunderstorms
this afternoon where some moisture is lingering. With higher heights
today, coverage looks sparse though (less than a 1 in 5
chance). Elsewhere, we removed the POPs. We can`t rule out a
stray shower, but most models are mainly dry. The NAM Nest has
some showers, but it`s middle name may as well be overdone
orographics as precipitable waters are under a half an inch in
most of these locations and there is no real trigger other than
some weak diurnal upslope flow. Anything that forms may just be
cumulus and maybe some virga. There will be a gusty breeze at
times today in northern Wyoming, the result of a gradient
between a trough moving eastward over the northern Plains states
and high pressure over the West Coast, The areas will the wind
will be the most moist though, so no fire weather highlights
will be needed today. Temperatures should average close to
normal.

Temperatures will increase somewhat as flow begins to turn
southwesterly on Tuesday. Many places East of the Divide will see
highs in the 90s on this day. As for convection, a weak shortwave
brushing by to the north may bring a few showers and storms.
However, southwest flow will also bring in drier air, with
precipitable water values dropping about 10 to 20 percent when
compared to Monday. So, we have some in the northern mountains but
coverage remains isolated (less than a 1 in 4 chance).

Wednesday looks like the warmest day at this point as the ridge
flattens and southwest flow really increases. A southwesterly breeze
will increase and bring highs well in the 90s East of the Divide,
with a few locations flirting with 100. Mid and high level moisture
will also increase on this day, especially across the west. So, POps
are higher this day. However, the surface remains rather dry and
precipitable waters are at best near normal. As a result, any storms
would be of the high based variety and have more wind than rain.
With the low humidity, elevated to critical fire weather will become
a concern, especially across the Rock Springs to Casper wind
corridor.

Thunderstorm coverage should increase on Thursday as a trough and
cold front approaches from the west. More cloud cover should
also bring somewhat cooler temperatures, especially West of the
Divide. Hot temperatures are expected to continue East of the
Divide though. Precipitable water levels do rise on this day but
only back to near climatological averages. As a result, there
will be a more widespread chance of showers and storms but the
chance in any given location remains low (generally less than 1
out of 3). In addition, humidity may remain low enough for some
elevated to critical fire weather, especially in the windier
locations.

Friday may be the most active day as precipitable waters peak on
this day. Temperatures should fall back close to normal for all
locations as well. Following that, most guidance shows a
gradually fall in coverage as drier air moves into the area as
ridging builds northward across the Rockies for the weekend and
early next week. Temperatures through this period should average
near to somewhat above average. &&

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1125 AM MDT Mon Aug 11 2025

VFR conditions are expected at all TAF sites throughout the
forecast period, with a very small (10%) chance of MVFR
conditions due to MVFR ceilings at sites east of the divide
overnight. North-northwest flow is over western and central WY
today, with moisture moving from south-central MT into north-
central WY toward the SSE. With mostly clear skies west of the
divide and some breezy northwest wind, skies will be partly to
mostly cloudy east of the divide with breezy north-northeast
winds at times. KCOD/KWRL/KCPR will see some gusty north winds
during the middle and late afternoon and perhaps into the early
evening hours, but only 15-20 kts are expected. Models are
indicating some light showers over the northern Absarokas and
the Bighorns late this afternoon and into the evening, with
only a 5% chance of showers getting into KCOD and KCPR.

Overnight should see mostly clear west of the divide,
with mostly cloudy east of the divide as the weak shortwave
trough moves to the SE. Winds will be light overnight as the
mean flow shifts more the the west on Tuesday. Clouds are
expected to be heavier over the northern part of the state, with
some weak showers possible along the MT/WY border, which may
impact KCOD around 13/00Z. The southwest WY TAF sites will see
gusty west winds in the afternoon with mostly clear skies.

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.

&&

$$

DISCUSSION...Hattings
AVIATION...McDonald