756
FXUS65 KRIW 112110
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
310 PM MDT Thu Jul 11 2024

.KEY MESSAGES...

- Mid-summer near-record heat today through Sunday. Afternoon
  temperatures in the 90s to low 100s will be common.

- Isolated showers and thunderstorms will cause brief erratic
  wind gusts in the 45 to 60 mph range despite light winds
  outside of outflows.

- The air mass will be very dry over the next several days,
  leading to low relative humidities and increase fire weather
  danger.

&&

.DISCUSSION...
Issued at 255 PM MDT Thu Jul 11 2024

The big weather story for the region over the next several days
will be the mid-summer heat, with many locations in the 90s to
low 100s during the afternoons through Sunday. Heat Advisories
are in effect for locations east of the Divide where the Heat
will be most notable; however, even locations west of the
Divide will be 10 to 15 degrees above normal. Take precautions
if outside to avoid heat-related illnesses. It`s not until
Monday that the presiding upper level ridge flattens slightly,
leading to a slight cooling. That being said, temperatures will
still be above normal next week, with highs in 90s for many.

Isolated afternoon and evening showers and thunderstorms will be
a concern due to the very dry air in place. These will be
relatively rare, with most locations staying dry over the next 4
days; however, locations that do have a stray shower or
thunderstorm move overhead are at high risk of experiencing 45
to 60 mph erratic outflow wind gusts. Some of these dry
microbursts in past days have damaged shingles and thrown
objects across fields. Assume strong wind gusts with any nearby
shower or thunderstorm.

Another weather concern will be elevated fire weather danger.
Fuels are quickly drying, and the mid-summer heat combined with
dry air will lead to low relative humidities. This is especially
pronounced overnight when usually RH recovers; however,
midslopes and much of the higher terrain above valleys and
basins will only see RH rise into the 35 to 50 percent range,
allowing any fires to burn more efficiently overnight. The one
mitigating factor is a lack of widespread wind, but afternoon
showers and thunderstorms may provide the aforementioned brief
strong winds, along with a small chance (10% or less) of dry
lightning.

No major change in the pattern is expected in the next week,
with mid-summer heat and isolated thunderstorms remaining in the
forecast through next week.

&&

.AVIATION /18Z TAFS THROUGH 18Z FRIDAY/...
Issued at 1135 AM MDT Thu Jul 11 2024

West of the Divide...KBPI/KJAC/KPNA/KRKS Terminals

VFR conditions are expected for the next 24-30 hours with high
pressure building over the area under mostly clear skies. West-
northwest winds will increase this afternoon a should produce
gusts around 20 kts at all 4 sites. Decreasing winds are
expected around sunset with drainage flows overnight. WNW winds
should increase again by 12/18Z. Some scattered mid-level
cumulus is expected this afternoon, mainly around and to the
east of the mountains, and weak virga showers may create more
gusty outflow winds at KBPI and KPNA.

East of the Divide...KCOD/KCPR/KLND/KRIW/KWRL Terminals

For the most part, VFR conditions are expected at all TAF sites
throughout the forecast period, although there is a low chance
of MVFR at KCOD/KWRL/KCPR due to isolated showers and
thunderstorms from about 11/21Z-12/03Z. In general, winds will
increase this afternoon with gusts around 20 kts. Area showers
and thunderstorms could produce outflow winds and stronger
gusts over 40 kts. Feel that the best chances are across
northern WY and into the KCPR area. KCOD/KWRL to KBYG could see
showers linger through 12/06Z due to a disturbance moving
eastward across southern Montana. All sites should see some
north-northeast wind overnight due to a boundary moving south
from northern into central WY. Wind directions this afternoon
are somewhat uncertain at several of the TAF sites due to
conflicting forecast guidance as well as chaotic nature of
thunderstorm outflow.

Friday will see mostly clear skies once again with isolated
afternoon showers and thunderstorms. Breezy gusty and dry west-
northwest winds in the afternoon will give way to northeast
winds Friday evening.

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...
Heat Advisory until 10 PM MDT Sunday for WYZ004>006-010-011-
017-018-020.

&&

$$

DISCUSSION...VandenBoogart
AVIATION...McDonald