688
FXUS65 KRIW 181858
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1258 PM MDT Mon Aug 18 2025

.KEY MESSAGES...

- Hot and dry conditions begin to build over the state today.

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

- An influx of moisture looks to return to the region for the
  second half of the week bringing chances for showers and
  thunderstorms by the weekend.

&&

.UPDATE...
Issued at 1256 PM MDT Mon Aug 18 2025

The forecast looks to be on track with little deviation at this
time. High pressure builds over the region today which will bring
hot and dry conditions through much of the first half of the week.
Near record breaking heat is forecast for Tuesday and Wednesday with
some locations east of the Divide flirting with the century mark.
The current forecast shows highs on Tuesday in the mid to upper 90s
east of the Divide and around 90 west of the Divide. Higher
temperatures are expected Wednesday with highs in the upper 90s or
around 100 and the low 90s west of the Divide. Model guidance
is showing the best chances (30-60%) for temperatures to reach
or exceed 100 degrees being in portions of Johnson, Natrona, and
Fremont Counties along with the Bighorn Basin. Overall, both
Tuesday and Wednesday will see the potential for numerous daily
high temperatures records to be tied or broken.

The hot and dry conditions will bring some fire weather concerns as
Min RH values plummet into the single digits to teens. The good news
is winds look to remain marginal with periodic gusts of at most 10
to 20 mph. The lack of wind should hopefully allow for some ground
to be made against many of the rapidly growing fires across the
state at this time. Mainly clear skies this morning have revealed
some of the burn scars created by these fires. One of note being the
Red Canyon Fire which is nearly 100,000 acres and has created a
rather noticeable scar over southeastern Hot Springs County. The
smoke associated with these fires is expected to stagnate which has
created some air quality concerns. The greatest concern is across
portions of the Bighorn Basin where another Air Quality Alert has
been issued and will go into effect at 1PM Monday through 1PM
Tuesday.

A relief in the heat arrives for the second half of the week as
highs return to near seasonable values. At the same time an influx
of moisture will be ushered back into the region as high pressure
begins to breakdown. This increase in moisture will create
isolated chances for showers and thunderstorms starting
Thursday. Friday through much of the weekend will see greater
and widespread chances for showers and thunderstorms. However,
at this time there still is uncertainty regarding how potent the
influx of moisture will be and if we will actually see much
needed measurable precipitation.

&&

.DISCUSSION...
Issued at 130 AM MDT Mon Aug 18 2025

WV imagery starting to move towards a more broad and weaker
southwest flow across the CWA with a shortwave evident pushing
out of northern Wyoming into Montana through the overnight hours
into Monday morning. Otherwise, radar is becoming quiet with
much of the weak shower activity pushing northeast out of the
area into Montana and northeastern portions of Wyoming.

In wake of this shortwave, an upper level 595 dm high pressure
centered near the four corner region will start to build due to
increased convergence aloft. This will give way to a warming
trend and dry conditions through mid week Wednesday, although
some weak shower activity is possible across the Absarokas
(<10%) Monday afternoon. This high will keep the bulk of any
storm activity well to the north with the main jet across the
Pacific northwest and into southern Canada around a GOA low
making its way through the Alaskan Panhandle. Temperatures will
push back into the 80s west of the Divide and well into the 90s
east, and nearing the 100 degree mark for some by Wednesday
afternoon. Record high temperatures will be flirted with if not
broken Tuesday and Wednesday(the most likely afternoon).

The aforementioned high pressure will begin to weaken with
convergence aloft decreasing by Thursday and beyond through the
weekend. This will bring increased storm activity allowing for
an upper level low to skirt past the CWA to the north. Thursday
will see more isolated chances but becoming more scattered and
widespread for Friday and next weekend IAW the ensemble clusters
and longer term deterministic models. As such, this will be
what to watch for long term as the short term through mid week
will be all heat and no wet stuff, in which is needed for the
ongoing fires. However, synoptic nor outflow winds will be of a
concern Monday through Wednesday and hopefully give the break
that is needed for no new fire starts due to lightning nor gusty
outflows enhancing current ones.

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1107 AM MDT Mon Aug 18 2025

VFR conditions at all airports through the next 24 hours with
mostly clear skies. A few showers are still possible today on
the higher elevations west of KCOD, but should not impact the
aerodrome. Winds for most sites will switch more from the north
overnight, but winds will remain light 5kts or less. Winds
turn back from south during the morning, but remain light. Smoke
from the Red Canyon fire will be drifting north most of the day
today, which will bring some lowered vis to KWRL and KGEY,
possibly into the KU68/KPOY areas briefly.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
Air Quality Alert until 1 PM MDT Tuesday for WYZ004>007.

&&

$$

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