777
FXUS65 KRIW 271830
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1230 PM MDT Thu Jun 27 2024

.KEY MESSAGES...

- Isolated to scattered showers and thunderstorms are expected
  this afternoon, and some storms may become strong to produce
  very strong outflow winds with some large hail. Northern WY
  and far southern WY should expect the strongest storms.

- Friday will be cooler with below normal temperatures in the
  60s and 70s, yet winds will be breezy and gusty out of the
  north and northwest.

- Elevated fire weather conditions will return Saturday and
  Sunday with warming temperatures, drier air, and gusty winds.

- Another storm system will impact the area late Sunday into
  Monday, bringing cooler temperatures and a chance of
  precipitation to the northern half of the state.

&&

.DISCUSSION...
Issued at 1230 AM MDT Thu Jun 27 2024

With the trough axis moving quickly from eastern WA/OR into
Idaho today, strengthening and moistening west-southwest flow
has moved into western and central WY with the expectation of
isolated to scattered showers and thunderstorms through the
afternoon and early evening. A very big change from the previous
shift is that the Storm Prediction Center has drastically cut
back the slight risk of severe storms over the forecast area to
now only include the NE corner of Johnson County instead of 90
percent of the CWA. The 12Z models are indicating less
instability across the central portions of the forecast area,
concentrating the convection from west-central WY toward north-
central WY, as well as across the southern half of Sweetwater
County toward southern Natrona County. WSW have already picked
up across much of the area ahead of the trough and thunderstorms
will soon move into Star Valley. High resolution models as well
as the NAM/GFS combo are inline with the latest thinking. In
areas where strong storms could develop (since we still have a
marginal risk of severe storms over much of the forecast area),
strong outflow winds over 40 mph are the most likely threat.
Next, some storms may produce hail larger than an inch in
diameter, and these storm are mostly likely over the Bighorn
Basin into Johnson County. For the most part, the triggers for
the storms quickly move eastward with the storms out of the area
by 800 pm, with lingering convection remaining across far
southern Sweetwater County until after midnight. Winds will
generally decrease around sunset as well with a northerly push
into the northern Bighorn Basin and Johnson County late this
afternoon.

Friday will see the trough axis over the state and moving
eastward with much cooler mid-level and surface temperatures
over the area, dropping high temps down to the mid 60s to upper
70s in the lower elevations. The flow pattern will continue
breezy and gusty winds across the area from the WNW. During the
afternoon, another "cool front" will move into northern WY as a
secondary trough moves through WY. The Bighorn Basin and Johnson
County will see gusty north winds of 30-40 mph during the
afternoon and evening hours, with the north winds pushing
southward into central WY during the evening. Models continue to
show showers and thunderstorms across southern Sweetwater County
Friday afternoon and evening until the north winds push them
south.

While Saturday starts off cool with mostly clear skies, the
ridge axis quickly moves over the state from the WSW and
southerly surface to SW and southern WY during the early
afternoon. Temperature will warm back to near normal with some
mid- and high-level clouds over the norther parts of the state.
Sunday will see temperatures increase again to the 90s as S-SW
flow increase over the forecast area. The advecting air from the
Great Basin will be drier as well with afternoon humidities
dropping to the low teens. These elements will create elevated
fire weather conditions over much of western and central WY.
Another trough from the PacNW into MT will increase clouds over
NW WY late Sunday, and bring showers and isolated thunderstorms
to NW and northern WY late Sunday into Monday. Temperatures will
cool again as showers linger across northern WY into Monday
evening. A generally dry and warm westerly flow pattern then
sets up for Tuesday through Thursday, elevating fire weather
conditions across western, southwest, and southern WY. Models
are hinting at cooler and moister air from the northern plains
backing into northeast WY to keep some areas east of the divide
from otherwise hot and dry conditions. Will wait and see however
on the westward movement of this air mass.

&&

.AVIATION /18Z TAFS THROUGH 18Z FRIDAY/...
Issued at 1134 AM MDT Thu Jun 27 2024

Showers have begun to re-ignite over the Wind River Range and along
the ID/WY border late Thursday morning as mid-level clouds have
cleared and surface heating has increased. The overall trend will be
toward scattered showers and isolated thunderstorms across west-
central and southwest Wyoming by 21Z/Thursday, eventually
shifting to KCPR around 23Z. Gusty outflow wind around 40kts
will be the primary hazard. Additionally, westerly surface wind
of 15-30kts will be common for most terminals by 20Z. The
prevailing surface wind and scattered convection persist until
02Z-03Z/Friday. VFR and quiet conditions anticipated after that
time through the remainder of the forecast period.

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...McDonald
AVIATION...CNJ