543
FXUS65 KRIW 171102
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
502 AM MDT Tue Jun 17 2025

.KEY MESSAGES...

- Tuesday will see cooler conditions with northwest-north winds,
  as well as showers and thunderstorms along and east of the
  Continental Divide. A strong or severe thunderstorm over the
  Wind River Basin or Natrona County cannot be ruled out this
  afternoon.

- High pressure returns to the area Wednesday through Saturday,
  with hot temperatures on Thursday and Friday, and elevated to
  critical fire weather conditions across southern and central
  WY.

- A cold front will move through Sunday, cooling temperatures
  into the 60s and 70s.

&&

.DISCUSSION...
Issued at 103 AM MDT Tue Jun 17 2025

Convection ended across much of the CWA earlier Monday night around
10pm. Very weak showers will continue to move over southern portions
from UT/CO this morning. This activity will get pushed eastward out
of the forecast area between 7am and 10am, as a shortwave trough
approaches the Cowboy State from ID. This will result in mostly dry
conditions across the area for a few hours. The flow aloft will turn
more northwesterly by this afternoon as a leeside low develops over
northeast CO/the NE Panhandle and the aforementioned
trough/associated cold front move across the area. Temperatures
today will be 5 to 10 degrees cooler as a result. Showers and
thunderstorms will then redevelop across northern portions between
12pm and 2pm, with other areas east of the Divide seeing similar
development through the rest of the afternoon as these storms move
to the southeast. Strong gusty winds, small hail and brief heavy
rain will be the main threats. Any strong thunderstorms are expected
in Natrona County and the Wind River Basin, where the residual
moisture from Monday continues to linger. However, instability will
not be as strong in these locations as has been the case the last
few days. With that being said, a severe thunderstorm cannot be
ruled out. MLCAPE will be 500-1000 J/kg, lifted indices as low as
minus 6, sfc dewpoints near 50F, and bulk shear values up to 35 kt
will be in place. Thus, large hail, wind gusts over 60 mph and
localized flash flooding could occur. Convection will end across the
area by midnight as high pressure builds into the region.

A strong ridge will then build over the Northern and Central Rockies
Wednesday, beginning a warming trend and drier conditions
through the rest of the week. Wednesday will be the quietest
day, with seasonal temperatures and mostly clear skies. Elevated
to critical fire weather conditions will develop by Thursday,
as temperatures rise into the 90s across much of the area and
relative humidity values drop below 15 percent over central and
southern portions of the CWA. Southwest winds, with gusts of 25
to 35 mph, will be mainly confined over southern portions.
Similar conditions return Friday, with of 35 mph being more
widespread across the south. By Saturday, these conditions
spread into the Bighorn Basin and southern Johnson County.
Overall winds will increase again, with gusts of 35 to 45 mph
occurring across the south and central portions. This will be
due to a digging longwave trough with a closed low over the
PACNW and a strong (596dm) high center over the Ohio Valley.
This will, in turn, strengthen the pressure gradient over the
Cowboy State and lead to the higher winds. Far western portions
will have some relief from the hot temperatures as a cold front
associated with the closed low will move over the area late
Friday night/early Saturday morning, resulting in high
temperatures in the 70s. The front will move across the area
Sunday, with precipitation chances being confined to mostly
northern portions of the CWA. Temperatures will be much cooler,
dropping 10 to 15 degrees. Needless to say, fire weather
conditions will not be as critical. The below normal
temperatures look to continue into Monday as the longwave trough
remains in place across the Intermountain West. This would be a
nice reprieve for this time of year, when we can see record
highs and heat waves in mid to late June.

&&

.AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 501 AM MDT Tue Jun 17 2025

VFR flight conditions are forecast this TAF period. A cold front
trekking across the region today will bring shower and thunderstorm
chances to all east of the Divide terminals. Thunderstorm
chances increase at KCOD beginning around 19Z followed by all
other east of the Divide terminals after 21Z. Thunderstorm
chances are reflected in a PROB30 group given the scattered
nature of convection and uncertainty in exact timing and direct
impacts. Any thunderstorms will be capable of producing gusty
outflows around 30 kts. An isolated stronger storm could produce
wind gusts up to 50 kts with large hail. A brief period of MVFR
visibilities cannot be ruled out with a heavier storm.
Thunderstorm chances diminish at all terminals by sunset.

Otherwise, winds increase at all terminals from the north or
northwest around 18Z. All west of the Divide terminals plus KRIW and
KWRL can expect gusts ranging from around 20-30kts. Winds decrease
around sunset at all terminals. There is potential for low clouds,
represented by a FEW020 group, at KCPR around sunset, however,
reduced flight conditions chances are low (20%) at this time.

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...LaVoie
AVIATION...Gerhardt