109
FXUS65 KRIW 032345
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
545 PM MDT Wed Jun 3 2026

.KEY MESSAGES...

- Increasing high clouds overnight as mid-level moisture streams
  across the state. A few virga showers are possible (10%
  chance) with brief gusty winds under these evaporating light
  rain showers.

- Isolated showers and thunderstorms are possible (20% chance)
  across northern WY Thursday afternoon. The rest of western and
  central WY will see mostly sunny and dry conditions with high
  temps from the mid 70s to mid 80s, and gusty west winds of
  25-35 mph for elevated fire weather conditions.

- Warm and dry conditions continue Friday into the weekend. with
  highs from the upper 70s to upper 80s. Low 90s are forecast
  Saturday east of The Divide, which will be the warmest day of
  the next 7 days.

- Gusty southwest winds will return Saturday afternoon with
  elevated fire weather conditions across all of western and
  central WY.

- Increasing moisture and clouds late Saturday and Sunday will
  bring isolated showers and thunderstorms Sunday afternoon.

&&

.UPDATE...
Issued at 1255 PM MDT Wed Jun 3 2026

Mostly sunny skies during the late morning hours are slowly
giving way to some areas of clouds this afternoon. With a bit of
cumulus around WY mountains, the most likely development is in
southwest WY where slightly higher moisture and weak instability
is starting to give rise to enhanced clouds around the Uintas. A
couple of the high-resolution models are indicating further
development this afternoon for some light showers between the
northeast Uintas and Rock Springs. Precipitation/hail is not
expected to be a player, but gusty outflow winds of 40-50 mph
are very possible given the 50+F surface dew point depression
over the area. The timing for impacts around Flaming Gorge are
from 1-4 pm, and for Green River to Rock Springs from 3-7 pm.
Otherwise, the rest of the area will see increasing west-
southwest winds this afternoon with 10-15 mph and 20-30 mph
gusts as humidity values drop to 10-12 percent in much of the
lower elevations. The exceptions will be across the northern
parts of the Bighorn Basin and the northern half of Johnson
County were moister northerly flow marks the boundary between
the two air masses. Additionally, the far NW parts of YNP could
see isolated showers from 7-10 pm as some weak convection from
SW MT makes it`s way eastward.

After sunset and the boundary layer stabilizes with a weakening
surface pressure gradient, the northern air mass will push back
southward into parts of central WY. As the overnight discussion
mentioned, a shortwave trough is expected to moves eastward
through Montana on Thursday. This will tighten up the mid-level
and surface gradients, increasing surface winds across the
western and central WY by late morning. The latest models are
showing convection starting over northern YNP and the northern
Absarokas around 2 pm, and spreading eastward during the
afternoon. The more vigorous convection should occur in southern
MT and Sheridan County, then into NE WY, though there is a small
chance that strong storms could occur in northeast Johnson
County, especially along the air mass boundary. As the trough
moves eastward, a cool front will push southward from northern
WY toward central WY, and potentially keep isolated showers and
storms going through 8-9 pm. The cool front will then push all
the way to the divide by midnight and then into Sweetwater
County during the early morning hours. Of broader concern though
is that much of central and southern WY (including western WY)
will see gusty west-southwest winds along with low humidities
for much of the afternoon, leading to elevated to critical fire
weather conditions. Gusts are likely in the 25-40 mph range
during the mid-afternoon. Winds will decrease somewhat during
the early evening and shift to the west-northwest before
diminishing by 10 pm, just as the cool front shifts the winds
even further and possibly becomes gusty again from the north-
northeast.

&&

.DISCUSSION...
Issued at 212 AM MDT Wed Jun 3 2026

The warm year we`ve had so far will continue today, as ridging
returns briefly between weather systems. Skies today will be
mostly sunny, with only fair weather CU along higher elevations
during the afternoon. Highs will again range from the mid 70s
west of the Divide, to the low to mid 80s east of the Divide.

Late Wednesday night, the next shortwave sweeps across the
Northern Rockies. The trough axis will be stretched across
central WY around noon, which will put most of the best lift
already into eastern WY, similar to today. With temperatures
still reaching the 80s east of the Divide tomorrow, the trough
will build more daytime CU, with tiny showers bubbling in the
instability. But with the trough already moving east early
afternoon, the threat for any stronger thunderstorms remains
limited to northern Johnson County, which could see a brief
threat for gusty winds and hail.

The passing trough will also bring a tighter gradient across the
state, so gusty winds will also ramp up, with frequent gusts
above 30 mph expected. This along with humidity levels of 10 to
15 percent in the afternoon will lead to an elevated to near
critical fire weather concern for most lower elevations
Thursday.

After the Thursday system sweeps through, the pattern changes as
a large-scale trough drops down into the PacNW. This will build
ridging across the Plains, with generally southwest flow across
Wyoming. The ridge placement will be favorable for building
temperatures aloft, especially on Saturday. H7 temps of 16 to 18
degrees C will translate to sfc temps in the 90s for the lower
elevations east of the Divide and mid to upper 80s for southern
WY. Southwest flow will be stronger as well, with current
forecast gusts of 30 to 40 mph across a wide swath of the state.
This southwest flow will also be very dry, with humidity levels
plunging to 5 to 10 percent in the afternoon. This points to a
near-critical fire weather day, especially those areas that
haven`t seen considerable rainfall so far this spring.

&&

.AVIATION /00Z TAFS THROUGH 00Z FRIDAY/...
Issued at 351 PM MDT Wed Jun 3 2026

VFR conditions through the period. Gusty winds should decrease
through the first few hours of the period. There will be a period of
passing high clouds between 00z/Thurs and 18z/Thurs. Winds increase
between 15z/Thurs and 18z/Thurs, with gusts generally 20 to 30 knots
through Thursday afternoon. No precipitation expected, though there
is currently a 15% chance at KCOD Thursday afternoon.

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.

&&

$$

UPDATE...McDonald
DISCUSSION...Straub
AVIATION...Wittmann