Lander, Wyoming 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

328
FXUS65 KRIW 101125
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
525 AM MDT Tue Jun 10 2025

.KEY MESSAGES...

- Unseasonably warm temperatures will continue for the next 7
  days, with highs consistently from the upper 70s into the 80s
  in the lower elevations. Temperatures are expected to reach
  the low 90s in parts of the Bighorn Basin over the weekend.

- A series of disturbances will bring afternoon showers and
  thunderstorms to the region Tuesday and Wednesday.

- Confidence continues to increase regarding chances for strong
  to severe thunderstorms on Wednesday with an SPC Marginal
  Risk (15% probability) for severe storms across much of the
  state. Gusty winds will be the primary severe weather threat.

- Elevated fire weather conditions with stronger wind and low
  humidities are expected to return to parts of central and
  southern WY Friday through Sunday.

&&

.DISCUSSION...
Issued at 243 AM MDT Tue Jun 10 2025

Now that we are solidly into June, we start to bid farewell to the
wintery weather patterns and see the emergence of Summer weather
hazards. This week, we get to see severe weather hazards and fire
weather hazards show us their colors, as we see the first widespread
severe weather risk day(s) and first extended critical fire weather
period of the season.

The ridge axis slides overhead by this evening, as it does so, a
weak shortwave will also track across the region. A weak low also
develops over western TX, which will act to draw Gulf moisture into
the state. Combined with the shortwave, this will result in the
development of scattered showers and thunderstorms during the
afternoon. Latest hi-res model trends initiate convection beginning
around 19 to 20Z (1300 to 1400L) primarily along the Absarokas. By
21Z to 22Z, convection becomes much more widespread, with storms
generally tracking west to east. Instability will generally be weak,
however, with ML CAPE only approaching 500 J/kg for most locations.
Shear also will be lacking across most of the state, with best 0-6km
shear values around 30kts across far northern portions of the state.
That is not to say we won`t se any severe storms, but limited CAPE
and shear will certainly lessen the probabilities. Hence, SPC has
continued to keep the Marginal risk probs to our northwest in MT.
The area of greatest concern for supercell development would be
Johnson County, where the best shear (30 to 35kts) and CAPE (800 to
1000K/kg) look to exist. PWATs will also approach 0.8 to 0.9" across
Johnson County, which is above the 75th percentile, and will help
fuel any storms that do develop. Steering flow will be fairly weak
(10 to 15kts), so could see the potential for flash flooding, given
anomalously high PWATs, but generally only if training storms occur.
Will give today`s flash flood threat generally less than 10% chance
of occurrence. The primary severe threat will be wind. Dewpoint
depressions will be around 40 to 45F and DCAPE will be >500J/kg
even approaching 100+J/kg across southwest WY, so where moisture is
lacking and where there are collapsing storms (which will be common
due to lack of shear to sustain long-duration supercells), expect
outflow straight-line wind gusts 40 to 55 mph to be somewhat common
today. Lack of shear and thus short-lived storms, I would also
anticipate most convection to be outflow driven and pulse-y.

Once diurnal heating starts to wane towards sunset, convection
should quickly diminish and end. A quiet night should then be in
store. Cannot rule out localized fog Wednesday morning where precip
falls in the evening with mostly clear skies overnight, but chances
are low enough (less than 10%) that I did not include fog in the
forecast, except in the favored low valleys of YNP.

Wednesday will see the second of the pair of shortwaves track across
the region. This shortwave is more defined, and will also be able to
tap into Gulf moisture, allowing PWATs to soar to 90th percentile
values across much of the region. Steering flow remains weak, so
given significant PWATs, with stronger moisture fetch and increased
convective coverage (due to the stronger shortwave), would give a
higher likelihood (20%) for flash flooding on Wednesday. Given the
ingredients in place, SPC continues with a Marginal (15%
probability) risk of severe across much of the region for Wednesday
afternoon. Dewpoint depressions will again be 40 to 50F with
significant DCAPE and limited shear, so outflow winds 50 to 60kts
will remain the primary threat. There will be some better shear on
Wednesday, especially across western and northern WY, so could see
some small hail in stronger storms in those locations as well.

Diurnal heating will again be a primary driver of convection, and
looks to be generally simultaneous with the shortwave trough axis,
so once the axis pushes east and diurnal heating diminishes (both
look to occur by 04Z Wednesday night), convective threats will
quickly wane.

Though afternoon convection will continue to be possible through the
rest of the week and into the weekend, chances are much lower as
there are no indications of a stronger shortwave that would bring
more likely severe weather chances. The ridge will thus remain in
place and stall over WY through the end of the weekend. This will
keep temperatures 10 to 15 degrees above normal through that time.
High temperatures in the 80s will be common for nearly all lower
elevation locations through the weekend, with temperatures
approaching 90 across east of the Divide basins, particularly across
the Bighorn Basin over the weekend. Winds will generally remain
light, however in southwest flow, favored locations along the
typical Rock Springs to Casper Wind Corridor will see gusts 20 to 30
mph common most afternoons. RH values will also plummet to less than
10% across much of SW WY nearly every afternoon. This means near
critical fire weather conditions are expected Friday through Sunday.
Fuels are still in green-up so fire weather highlights are not
expected.

&&

.AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 523 AM MDT Tue Jun 10 2025

Mostly clear skies and VFR conditions will prevail through this
morning. Shower and thunderstorm development is then expected by
19Z, kicked off by a disturbance within the westerly flow. While
confidence on direct terminal impacts is not particularly high
anywhere, areal coverage is expected to be widespread enough that we
have included vicinity and PROB30 groups for the majority of sites
today. With a dry boundary layer, the primary concern will be strong
outflow wind gusts as storms move from west to east through the
afternoon. This activity will decrease after sunset, though
unsettled conditions and isolated showers will continue into the
early morning hours.

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.

&&

$$

DISCUSSION...Hensley
AVIATION...Myers