557
FXUS65 KRIW 040335
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
935 PM MDT Wed Jul 3 2024

.KEY MESSAGES...

- An unsettled weather pattern continues through this week as a
  trough remains over Wyoming.

- Scattered rain showers and thunderstorms have developed across
  northern Wyoming this afternoon. Small hail and gusty wind is
  possible with these storms. Elevated fire weather conditions
  are occurring across southern Wyoming and will through this
  afternoon.

- The weather pattern favors breezy to windy conditions for the
  next 7 days and mostly dry conditions beyond Thursday. A heat
  wave is looking more likely to begin next week as a strong
  ridge moves into the region.

&&

.DISCUSSION...
Issued at 155 PM MDT Wed Jul 3 2024

Troughing will be the general weather pattern through this weekend,
with several waves within the trough sliding through Wyoming.
Independence Day (The 4th of July) looks pleasant temperature-wise
as cooler air moves into the area behind the weather system
moving through today. The current high temperature forecast is
for upper 60s to middle 70s across the area.

The wave today has resulted in scattered rain showers and
thunderstorms across the northern half of the area. Who gets a good
wetting rain with these showers and storms will depend on where they
develop, but about from YNP eastward through the Bighorn Basin and
into Johnson County is likely to have measurable precipitation from
Wednesday through Thursday. Currently, the SPC has a Marginal risk
of severe weather in the Bighorn Basin eastward into Johnson County
for large hail and damaging wind, but this threat looks to be very
low based on how things have developed this afternoon. Still, it is
best to stay alert, especially in northern Johnson County where the
best chance of severe weather exists. Once the wave passes by on
Thursday the cooler air aloft will allow for isolated convection to
develop. The best chance will be along/near the Absaroka
Mountains/Bighorn Mountains where afternoon upslope will contribute
to lift. Localized heavy rain will be a threat on Thursday,
especially in or near the Bighorns as northwest flow sets up and may
lead to the formation of some training convection in the Bighorns.
PWAT`s don`t look excessive, so not expecting widespread flash
flooding.

Model guidance has diverged on the flow pattern for Friday. The GFS
shows northwest flow greatly weakening, whereas the ECMWF now has a
wave/weak upper-low clipping the area. Am leaning toward the GFS
solution which would be more of a consistency forecast since
models have been showing weaker flow with that wave further
north and east. As such, mostly clear skies on Friday will allow
for temperatures to get back to about normal. Model guidance
has another wave coming down in northwest flow this weekend,
which will bring low chances for isolated convection to mainly
northeastern portions of the area. This looks like the last gasp
for the trough that has been sitting over the region as a large
amplified ridge pushes into the western US early next week.
This ridge will bring hotter temperatures back to Wyoming and
heat will become the most impactful weather well into next week
based on what long-range model guidance is depicting.

&&

.AVIATION /06Z TAFS THROUGH 06Z FRIDAY/...
Issued at 930 PM MDT Wed Jul 3 2024

Any remaining showers across the area will end by 08Z. Winds
will also continue to subside through the rest of the night.
West- northwest winds, with gusts around 25 kt, will return to
KBPI/KPNA and KRKS by 18Z, while winds will keep a northerly
component across areas east of the Divide. Showers and
thunderstorms will be possible again across northern portions
Thursday afternoon, but coverage may not be as widespread as
today. Confidence remains too low to include in any terminal
forecast at this time. Winds west of the Divide will begin to
subside after 01Z, with light winds across the forecast area by
the end of the TAF period.

Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for
the latest information on smoke, icing, and turbulence
forecasts.

&&

.FIRE WEATHER...
Issued at 155 PM MDT Wed Jul 3 2024

Elevated fire weather conditions will continue across southern fire
zones this week. The worst days will be today and Saturday as wind
increases ahead of weather systems and RH will drop into the teens
each afternoon. For northern zones, wetting rain is possible
(40-50%) this afternoon/evening and even into Thursday for The
Absaroka Mountains/Bighorn Mountains. Lightning will be
frequent with thunderstorms on Wednesday and Thursday, but the
storms should have a good amount of moisture with them, so the
chance of dry lightning is low (<10%). Smoke dispersal looks to
be at least good in the afternoon for the next few days at
least.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

DISCUSSION...Rowe
AVIATION...LaVoie
FIRE WEATHER...Rowe