474
FXUS65 KCYS 011752
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1152 AM MDT Fri Aug 1 2025

.KEY MESSAGES...

- There is a Slight Risk (Level 2 of 5) for severe weather
  Friday afternoon and evening east of the Laramie Range. All
  modes of severe weather are possible: hail, winds, tornadoes,
  and flash flooding.

- There is a Marginal to Slight Risk of severe weather for
  Saturday, mainly across western Nebraska. Primary hazards look
  to be hail, wind, and flash flooding.

- Drier and warmer conditions return mid-week and continue
  through the weekend.

&&

.SHORT TERM /THROUGH SATURDAY NIGHT/...
Issued at 159 AM MDT Fri Aug 1 2025

Mostly quiet across the CWA tonight though some low stratus is
developing along and just east of the Laramie Range as skies
continue to clear. Some locations in the Panhandle are starting to
see low stratus develop. Widespread stratus development across the
Panhandle is expected through the overnight hours. Winds are fairly
calm across much of the area, introducing a slight chance for patchy
fog to develop east of the Laramie Range where ample moisture
remains. Temperatures are mild in the 50s and 60s across the region.

Another round of severe weather is possible today as the Storm
Prediction Center has highlight much of the Panhandle in a Slight
Risk (Level 2 of 5) with remaining portions of the CWA, east of the
Laramie Range, in a Marginal Risk (Level 1 of 5). Additionally, the
Weather Prediction Center has highlight much of the region in a
Marginal Risk for excessive rainfall, due to the high amount of
moisture in place east of the Laramie Range. Severe weather chances
are being fueled by an upper-leve trough pushing into the region,
oriented nearly west to east. In addition to this, a long fetch of
upper-level flow from the Pacific Ocean is funneling additional
moisture into the region and increasing surface dewpoints well into
the 50s to near 60s for most locations east of the Laramie Range. A
subsequent 500mb shortwave will push through the region as the upper-
level shortwave begins to move overhead. This shortwave will bring
ample 500mb cyclonic vorticity advection to the region, allowing the
shortwave to dig through and produce synoptic-scale rising motion
east of the Laramie Range. 700mb flow remains mostly unimpressive at
this time, with only a slight low-level jet showing up in some of
the models around 00 to 03Z this evening. Very weak warm air
advection is present at 700mb throughout the day, allowing
additional weak synoptic lift to much of the region. South-
southeasterly to southeasterly flow near the surface will enable
some upslope development this afternoon and evening, though will
likely act to bring in low stratus this morning. Fog is not
anticipated at this time as the surface pressure gradient across
eastern portions of the region are fairly strong at this time,
leading to gustier winds expected into the early morning hours.
Temperatures will rise into the low- to mid-80s across the region,
prior to convective initiation around 18 to 21Z this afternoon.

MLCAPE values will increase into the 1800 to 2200J, according to the
HRRR and RAP, range this afternoon, assuming low-level clouds move
out of the region earlier enough in the morning hours. If not,
convective initiation may be delayed and potentially weakened.
Forecast RAP soundings suggest a nice low-level wind profile across
the Panhandle wil good turning in the low-levels. The soundings
itself shows a favorable shape for severe weather this afternoon,
though calling it a "loaded gun sounding" is a bit of a stretch.
Ample CAPE exists in the 0 to -20C range, indicating and increased
potential for large hail. Additionally, 0-6km bulk shear is modest,
around 40 to 45kts, in most locations, suggesting a better chance
for storms sustaining themselves and not being completely
stationary. 0-1km storm relative helicity is maxes out around 60,
which is enough for an increased tornado threat across much of the
Panhandle. DCAPE, unsurprisingly, is around 1500J which suggests an
additional wind threat. The terrain-induced dryline will likely act
as the main catalyst for low-level lift, though with bulk shear
vectors nearly perpendicular to the dryline storms will mostly like
start off as isolated before growing upscale into a line or multi-
cellular clusters. Given this storm development, all modes of severe
weather will be possible across the region this afternoon, though
the Panhandle is more favorable for tornadic development than
southeast Wyoming.

Yet another round of severe weather is possible on Saturday as an
upper-level shortwave trough propagate through the broad upper-level
zonal flow. With the fetch of moisture still from the Pacific Ocean
into the Intermountain West, above average moisture is still
expected. Several 500mb vorticity maxima will eject out ahead of the
shortwave pushing through, allowing cyclonic vorticity advection to
return to the region once more. 700mb flow remains rather modest,
though a 700mb cold front is progged to push through the region
Saturday afternoon into the evening hours, acting as significant
forcing for storms. Strong southerly flow is expected near the
surface, especially across the Panhandle, suggesting that low
stratus and fog may not be players for Saturday morning ahead of the
storms, increasing the potential that storms could be severe.
Surface temperatures will warm into the mid-80s to low-90s east of
the Laramie Range ahead of the cold front, with cooler temperatures
in the low- to mid-80s west of the Laramie Range. Southeasterly
surface flow will help increase storm potential as the cold front
collides with the moist, southerly flow in the afternoon. Bulk shear
vectors remain mostly parallel to the cold front, so storms will
most likely grow into a line upscale, but may initially be isolated
in nature. However, forecast sounding from the RAP are not as
favorable for severe weather as the forecast soundings for this
afternoon and evening. Much drier low-level will be present on
Saturday, though a decent amount of CAPE exists in the hail growth
zone, suggesting a better chance for hail and strong winds, with
minimal tornado threat for Saturday. DCAPE values will once again be
above 1500J, further favoring a wind threat across the region. The
Storm Prediction Center has highlight most of the region east of
the Laramie Range in a Marginal Risk for severe weather, while
Cheyenne County is currently in a sliver of a Slight Risk. The
Weather Prediction Center has highlight much of the Panhandle in a
Marginal Risk for excessive rainfall, due to the high amount of
moisture in place across the Panhandle.

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
Issued at 159 AM MDT Fri Aug 1 2025

Sunday onwards looks to be hotter and drier across much of the
region as an upper-level ridge move into the Intermountain West and
the moisture fetch from the Pacific Ocean dissipates with the
disruption from the ridge. 700mb temperatures will surge back into
the 17 to 20C range by mid-week, leading to much warmer temperatures
mid-week onwards as the ridge remains in place overhead. Wednesday
and Thursday look to be the hottest day of the week with low- to
upper-90s returning to much of the area as 700mb temperatures rise
into the 18 to 20C range once more. With the warmer and drier
conditions, fire weather concerns will return mid-week, especially
in locations that do not see rainfall over the next couple of days.
The next best chance for precipitation will be next weekend, as an
upper-level trough and subsequent 700mb low are progged to move into
the region. However, this is still over a week out and this
potential will likely change over the next several forecast
packages. Overall, looks like another hot and dry week for much of
southeast Wyoming and western Nebraska.

&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 1140 AM MDT Fri Aug 1 2025

Mostly VFR conditions expected over the next 24 hours, with the
exception of some lingering low clouds in the Nebraska Panhandle
that should lift within the next hour or two, and the threat of
thunderstorms again later today. Storms will be mostly likely
from KCYS and eastwards through KBFF and KSNY. These storms
could be strong to severe and include very large hail, strong
wind gusts, and even an isolated tornado. Cloud bases may also
drop back down to MVFR status, alongside heavy rainfall bringing
IFR visibility or worse. Storms also possible all other sites,
but should not be as strong, particularly at KRWL/KLAR where
any storm near these sites will be brief and not likely to be
severe. Decks should then lift this evening, and some low clouds
may be possible tomorrow morning but the threat for low decks is
less likely compared to previous days.

&&

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

&&

$$

SHORT TERM...AM
LONG TERM...AM
AVIATION...CG