386
FXUS65 KRIW 092318
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
518 PM MDT Sun Jun 9 2024

.KEY MESSAGES...

- Showers and thunderstorms will continue this afternoon and evening,
  most numerous across the northern half of the area. Strong
  wind gusts and brief, heavy rain are the main concerns with
  this activity.

- Monday will see continued isolated showers and thunderstorms.

- Warmer and drier conditions expected Tuesday through most of the
  week. Elevated river and stream levels will continue.

&&

.DISCUSSION...
Issued at 236 PM MDT Sun Jun 9 2024

Scattered showers and thunderstorms are ongoing across much of
Wyoming in response to the arrival of a shortwave trough riding
along the upper level ridge. This activity is expected to
expand eastward through the afternoon with the best coverage
across the northern half of the area. With both Pacific and Gulf
of Mexico moisture advecting into the area, there will be
fairly decent moisture available for convection (107% of normal
per 12Z sounding at RIW). Accordingly, instability will increase
through peak heating, with MLCAPE values generally peaking in
the 500-1000 J/kg range (with some caveats - such as the Bighorn
Basin which will miss out on deeper theta-e advection). The
best environment will be across eastern portions of the area
which will see MLCAPE rise to the 1000-1500 J/kg range. Given
the well-mixed boundary layer, strong, gusty winds are the main
concern, though large hail can`t be ruled out with any stronger
storms.

As the current convection wanes this evening, another shortwave will
push into western Wyoming. This will bring another round of showers and
thunderstorms overnight, most focused on northern and western
portions of the area. This round could bring a little more rain
accumulation, though this is very dependent on individual cell
locations. A quarter to half an inch is not out of the question from
any one cell, though most of the area will see much less. This
activity will wane by sunrise.

Monday will see additional showers and thunderstorms develop in the
afternoon as the next wave clips northern Wyoming. Accordingly, most
of the activity will be focused on areas east of the Divide. Strong
wind will be the primary concern again, with a lower hail threat as
well. Otherwise, an increased surface pressure gradient will make
for a gustier west to northwest wind for most of the area Monday
afternoon.

Further ahead, weak ridging to fairly zonal flow will take over.
Accordingly, warmer and drier conditions are favorable Tuesday
through at least Thursday. Ensemble cluster guidance is hinting at
increasing troughiness by the weekend.

&&

.AVIATION /00Z TAFS THROUGH 00Z TUESDAY/...
Issued at 516 PM MDT Sun Jun 9 2024

Widely scattered showers and thunderstorms continue across the
region through the early part of the evening. Localized MVFR
conditions are expected during thunderstorms. Gusty and erratic
winds, small hail, and locally heavy rain are also possible with
stronger storms. TEMPO groups are included in the TAFs to cover
the best chances of showers and thunderstorms. Shower and
thunderstorm chances significantly decrease after 06Z, but hi-
res models continue to suggest that isolated showers and weak
thunderstorms may continue across the north and west through
much of the night. Have omitted any mentions of TS or SH after
06Z though due to low confidence in coverage and location of any
lingering shower and t-storm activity. KJAC, KCOD, and KWRL have
the best chance (20%) of any lingering showers or thunderstorms
after 06Z.

Winds increase across the region late Monday morning, with westerly
winds gusting 20 to 30kts across most west of the Divide terminals
and northerly winds gusting 20 to 25kts at most east of the Divide
terminals through the afternoon. Additional showers and
thunderstorms will be possible Monday afternoon, but will be much
more isolated than Sunday`s activity, and thus have only included
mentions at KCPR where the best chances (30%) for any of these
showers or storms exists.

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


&&

.HYDROLOGY...
Issued at 214 AM MDT Sun Jun 9 2024

Rivers and creeks will remain on the high side today at Action Stage
or below, but look to remain steady for now. SnoTel sites above 9000
ft remain below 10 inches of SWE and continue to drop. At this rate,
the remaining snow at these sites could be gone in the next couple
of days. The notable exception is sites in the Tetons and portions
of Yellowstone NP, where 20-30 inches remain on the ground.

&&

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

&&

$$

DISCUSSION...Myers
AVIATION...Hensley
HYDROLOGY...LaVoie