272
FXUS65 KRIW 262040
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
240 PM MDT Wed Jun 26 2024

.KEY MESSAGES...

- Showers and a few thunderstorms continue to bubble across the
  state. Some thunderstorms may contain gusty winds.

- A more widespread threat for stronger thunderstorms expected
  on Thursday for nearly all of the state. Western and Central
  WY will have the threat for very gusty winds and hail.

- Ridge builds back across the state for the weekend, with a
  return of much warmer and drier conditions. Gusty winds will
  increase the fire weather threat both Friday and Sunday.

&&

.DISCUSSION...
Issued at 202 PM MDT Wed Jun 26 2024

Shortwave continues to transit the state this afternoon, with
enough instability to spark a few showers. Main push has been
held back until current time due to building of daytime heating,
but more convective activity is setting up across central WY,
and another area developing quickly in NE ID. SPC did bring a
marginal sever threat into far NW WY this afternoon, with gusty
winds being the main threat. Any precip should be fairly light,
but a brief downpour may occur in stronger storms.

Thursday turns to a more potent day across the state as a
larger trough sweeps in off the PacNW Coast into the far
southern Canadian Prairies. Ahead of the trough, sfc moisture
will be building across the state, with dewpoint temperatures
starting the day in the 50s. Related PW values running 2 to 3
standard deviations above normal indicate plenty of fuel to
generate thunderstorms. Mostly clear morning skies will help
quickly destabilize this layer. As the trough sweeps to the east
during the day, diffluence ahead of the trough will bring good
lifting aloft, tapping the unstable sfc moisture layer. drier
air aloft will try to wrap in from behind during the afternoon,
trying to form a modest dryline-type boundary advancing across
the state. Storms would be able to tap the approaching 100 jet
to mix very gusty winds down to the sfc. Some hail is also a
threat, but this may be confined farther north closer to the
cold pool near the trough center. SPC already has marginal SVR
risk for nearly all of western and central WY, with slight risk
just to the east of the I-25 corridor. Main forecast issue is
where storms fire first. Initial showers may already form along
the WY/ID border midmorning, but the main building will
probably fire along the western mountains and quickly push east
during the afternoon, tapping the unstable sfc moisture. The
thunderstorm activity will be moving quickly, so most activity
should be well off to the east and southeast by early evening.

Friday will see the trough continue east into the Northern
Plains. Some lingering moisture and daytime heating may bring a
few showers along the higher elevations of the Bighorns, and for
southeastern Sweetwater County, but most other will see a nice
day with temperatures in the 70s and 80s. Friday will be windy
and drier, so some fire weather concerns may develop during the
afternoon. Saturday and Sunday will continue the warming and
drying trend, with temperatures back in the 90s. Sunday will see
gusty winds again in advance of the next trough sweeping into
the PacNW, so more fire weather concerns are noted here, as
gusts could approach 40 mph at times, while humidity levels fall
to near 10 percent.

Still watching with interest that next trough for late Sunday
and Monday. Current forecast does bring a good amount of Pac
moisture with it, but strongest lift occurs overnight, so peak
heating will be minimized as it passes.

&&

.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 1122 AM MDT Wed Jun 26 2024

Shower and thunderstorm chances continue to spread eastward through
the afternoon. All sites have at least a 15% chance to see a shower
or thunderstorm today. Locations with closer to 30% chances have
TEMPO or PROB30 groups in the TAFs. Shower chances will persist
overnight, but will be less than 20% for all terminals (except KRKS)
after 03Z. KRKS has the best chance to see thunderstorms after 03Z.
Then, shower and thunderstorm chances increase again late in the
period. West to southwest winds also increase late Thursday morning
as a shortwave passes through the area.

Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for
the latest information on smoke, icing, and turbulence
forecasts.

&&

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

&&

$$

DISCUSSION...Straub
AVIATION...Hensley