315
FXUS65 KCYS 302341
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
541 PM MDT Mon Jun 30 2025

.KEY MESSAGES...

- Isolated showers and storms are possible across southeast
  Wyoming this evening, but chances are low, around 15 to 20%.

- There is a Marginal Risk (Level 1 of 5) of severe weather
  Tuesday afternoon for portions of western Nebraska.

- Warm temperatures and daily chances for PM showers and
  thunderstorms will return for Tuesday onwards.

&&

.SHORT TERM /THROUGH WEDNESDAY NIGHT/...
Issued at 232 PM MDT Mon Jun 30 2025

Very quiet across the CWA this afternoon with clear skies for much
of southeast Wyoming and western Nebraska according to GOES visible
satellite imagery. Only a few scattered puffy clouds are present
across the southern Panhandle and the higher elevation of southeast
Wyoming. Light winds are present across western Nebraska with
slightly breezier conditions in southeast Wyoming. Temperatures have
warmed into the 70s area wide this afternoon and will continue to
warm a few more degrees as the sky remains clear. A few showers may
develop along and near the Laramie Range today, but will be isolated
in nature.

An upper-level ridge is sitting across the Intermountain West this
afternoon with broadly northwesterly flow aloft today. This ridge
will continue to slowly traverse eastward through Thursday morning,
ahead of the next system. Under this ridge, 700mb temperatures will
warm back into the 13 to 16C range, leading to warm temperatures
once again. Portions of the northern Panhandle will once again
approach the 100F mark, with highs on Wednesday in the mid-90s.
Wednesday looks to be the warmest day this week, with a slight cool
down expected in the long term forecast.

Per usual for this time of year, isolated to scattered afternoon
showers and storms are possible today, tomorrow, and Wednesday with
a Marginal Risk (Level 1 of 5) in place across portions of the
Panhandle on Tuesday. A 500mb shortwave on Tuesday afternoon with an
attendant vorticity maxima looks to be the primary forcing mechanism
tomorrow. Around 1000J of MLCAPE will be present with fairly minimal
CIN during the afternoon, according to the HRRR. The RAP and NAMNST
are a bit more extreme with MLCAPE values in the afternoon across
the Panhandle, maxing out around 2000J with little to no CIN in
place. However, the RAP and NAMNST have higher moisture present than
the HRRR, especially since the most recent runs had higher dewpoint
values than the HRRR. The HRRR was a closer match to current
dewpoints than either the NAMNST or RAP as of 18Z. Therefore, the
NAMNST and RAP may have a slight moisture bias or at least be
running a little "hot" for dewpoints, which would likely suggest the
higher CAPE values present in these models when compared to the
HRRR. Even with the more conservative HRRR CAPE values, 1000J is
still plenty to get severe storms, especially with minimal CIN and
southeasterly winds advecting in additional moisture overnight
tonight into the morning. HRRR soundings for 21Z tomorrow suggest
strong lapse rates throughout the atmosphere, but especially in the
lowest 3km where lapse rates are around 8 to 9 C/km. Bulk shear will
be fairly weak tomorrow, so some storm may struggle to get going and
collapse on themselves before growing into significant storms.
Therefore, strong winds will likely be the primary threat tomorrow,
but large hail cannot be completed rules out. Tornado potential
looks to be little to none, especially since SRH in the lowest three
kilometers is slim to none during peak severe hours tomorrow.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
Issued at 232 PM MDT Mon Jun 30 2025

Thursday and Friday, an upper level trough swings
through Thursday creating some leeward cyclogenesis off the Rockies.
This trough and the new system will be the main forcing behind
afternoon to evening scattered thunderstorms. With this trough and
system there also look to be lobes of vorticity to help drive
convection into the evening hours with the strongest development on
that Friday afternoon in the Nebraska Panhandle. Saturday will be a
mini break from the storms as a short lived ridging pushing through
the Intermountain West.  Storm chances are rejuvenated Sunday
evening with the passage of another trough to help spark convection
once again.

Temperatures remain in the upper 70`s to the mid 80`s across the
forecast area. 700mb temperatures stay around 16 celsius which
translate surface temperatures into the low to mid 80`s for the
lower elevations and upper 70`s to low 80`s for our more mountainous
regions.

&&

.AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 538 PM MDT Mon Jun 30 2025

Clear skies prevail this afternoon across the area. Gusty
southeast winds will continue through the evening at KLAR.
Expect winds further east to rotate around to southerly this
evening ahead of a modest nocturnal low-level jet event tonight
in the Nebraska panhandle. Gusty southerly winds are possible at
times during the night, but expect to find LLWS during periods
where the surface winds are light. Winds will mix down to the
surface consistently at all terminals by around mid morning
Tuesday. Expect another round of scattered showers and
thunderstorms Tuesday afternoon and evening, which is currently
handled with PROB30 groups at all terminals.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...None.
NE...None.

&&

$$

SHORT TERM...AM
LONG TERM...MM
AVIATION...MN