533
FXUS65 KRIW 211812
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1212 PM MDT Fri Jun 21 2024

.KEY MESSAGES...

- Scattered thunderstorms expected this afternoon ending before
  sunset with damaging winds and flash flooding the main
  concerns. Larger hail cannot be ruled out as well.

- Warming trend for the weekend and beyond with mainly dry
  conditions going forward.

&&

.DISCUSSION...
Issued at 1134 AM MDT Fri Jun 21 2024

IR currently depicts southwest flow across the CWA with ample
mid to upper level moisture pumping in from the base of the
trough. A strong PVA signature can be seen over northwestern
Colorado that will be the main trigger for thunderstorm develop
in the coming hours ahead into the afternoon. Radar shows some
dissipating rain showers and a couple isolated thunderstorms
from eastern Sweetwater County extending through Natrona.

Stronger storms are expected to continue to develop early this
afternoon across Sweetwater County with possible severe hail the
main concern being for supercellular in nature. Ample shear over
30kts and steep lapse rates yield to at least quarter to ping
pong ball size hail before storms cluster up and push
northeastward becoming more of a wind event. The atmosphere has
destabilized with clear skies further south extending north and
northeastward in the next couple hours. This will allow for
forecasted CAPE values to push well over 1,000 J/kg even upwards
to 1500 in parts of this area and further northeastward. CAMs
are showing storms cluster together by 3-4PM through central
portions of the CWA becoming more of a damaging winds over 60
mph and flash flooding concern going forward into the evening
hours. DCAPE values show similar conditions with PWAT values up
to an inch in some areas east of the Bighorns to the I-25
corridor. If this main upper level trough progs to stay more
progressive as models suggest, flooding may not be a high
concern going forward. Severe watches are currently issued with
more to come this afternoon and evening before storms weaken and
push east by 7-8PM towards sunset losing the ingredients with
radiational cooling.

Going forward, ridging builds back in from the subtropical high
over west Texas that will bring a warming trend and mainly dry
conditions to the CWA for the weekend and much of the next week.
Temperatures well into the mid to upper 90s for points east of
the Divide to include possible 100 degree through the Bighorn
Basin. An upper level low looks to come out of the Gulf of
Alaska down to the Pacific Northwest, but the main finger of the
PFJ looks to stay north only clipping any minor impacts to
northern parts of the CWA by week`s end in terms of light
precipitation and general thunderstorm activity for higher
elevations.

All in all, today is the last chance for widespread rainfall
going forward with dry conditions and elevated fire weather
becoming a concern for much of next week into the long term
outlook.

&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 1120 AM MDT Fri Jun 21 2024

A very active weather day across western and central WY for the
end of the work week. Isolated showers and thunderstorms early
this morning are persisting across central WY and should bring
some showers to KCPR through 19-20Z. Moisture is more than 100%
of normal and disturbances to the north and south are already
destabilizing the atmosphere late this morning and early
afternoon as the boundary layer heats up. Scattered to
widespread showers and thunderstorms are expected between 19z
and 02Z, moving from west to east, and impacting all TAF sites
except KJAC. Some storms could be quite strong and produce very
gusty outflow winds, brief heavy rain, and moderate-sized hail.
General VFR conditions will become MVFR under and near storms
and showers. KRKS and KCPR seem to have the best chance at the
strongest impacts. Lingering showers are expected into the
evening, with storms moving out of Johnson and Natrona Counties
by sunset.

Winds will decrease for the overnight hours and skies become
mostly clear Saturday morning. Dry westerly flow then moves in
Saturday, with isolated storms south of KRKS Sat afternoon, and
some mid-level clouds across the MT/WY border. Hot and dry then
moves in for the rest of the weekend.

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...Lowe
AVIATION...McDonald