903
FXUS65 KCYS 212343
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
543 PM MDT Tue Jul 21 2026

.KEY MESSAGES...

- Widespread showers and storms are expected over the next
  several days. Monsoon moisture will lead to heavy rain with
  the potential for flash flooding. Isolated severe storms will
  also be possible.

- Numerous to widespread beneficial showers and scattered thunderstorms
  will occur Thursday afternoon and evening, with lesser
  coverage of late day shower and thunderstorm coverage for
  Friday through the weekend and into early next week.

- Maximum temperatures will be moderated by clouds and
  precipitation coverage for Thursday, then hot temperatures and
  possible Heat Advisories will return for Friday through
  Tuesday, east of I-25, due to lesser coverage of late day
  showers and thunderstorms and cloud cover. Maximum
  temperatures over the weekend and early next week will range
  from 90 to 105 degrees east of I-25, with mid 80s to near 90
  degrees west of I-25.

&&

.SHORT TERM /THROUGH WEDNESDAY NIGHT/...
Issued at 203 PM MDT Tue Jul 21 2026

The core of the upper level ridges is kind of centered over the
Oklahoma Panhandle/NW Texas area. Due to the clockwise motion of the
High this funnels all the warm pacific moisture into the
Intermountain West. This translates into an abundant source of mid
level moisture that will get translated toward the surface through
daily afternoon storm chances and diurnal mixing within the boundary
layer. Over the course of today and Wednesday, precipitable water
(PWAT) will bouncing between the 90 and 99th climatological average
at around 1 to 1.5 inches. NAEFs also shows strong 90th- 99th
percentile Integrated Vapor Transport (IVT) as well to really
capture the monsoonal moisture coming up from the South. With this
abundant moisture weak thunderstorms will be starting to redevelop
this afternoon. These showers/thunderstorms will be rather pulsy
with the lack of shear and projected CAPE values around 1000 joules.
Mid-level lapse rates are also expected to be kind of neutral this
afternoon at around 7.5 C/km. So these showers/thunderstorms are
going to very hit or miss as to whether they produce lightning but
surely aren`t expected to go severe. However, there are some
potential ponding and flooding in low lying areas across the
forecast area today especially near the WY/NE border where NAEFS
expects the highest IVT values to be. And this is mostly due to also
the lack of mid-upper level wind to really push these storms along.

Wednesday will be a wash, rinse, repeat of today. Some lingering
showers will be possible in the morning. But the "main show" will be
in the afternoon. There looks to be a little more synoptic forcing
as well as MUCAPE pockets ranging between 1000-1500 joules. Once
again there is virtually no shear so some a severe storm aspect, the
CAPE is kind of wasted in this environment. However, with it being
the Intermountain West I can`t rule out so BB to pea-sized hail if
one of the thunderstorms temporarily pulses up. The also big
difference is that the IVT and Moisture content will be a little
stronger than today so there`s a bigger risk for potential flooding
from these slow moving storms. Putting out a flood watch and
matching our neighbor office Riverton was on the mind. However,
their storms are likely to be stronger than ours with more of a
chance for torrential downpour to lead to flash/localized flooding.
WPC Excessive Rainfall Outlook does have a slight risk for us West
of the I-25 corridor and a Marginal risk for areas along and east of
I-25.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
Issued at 203 PM MDT Tue Jul 21 2026

Thursday...More beneficial rains are anticipated as a decent
positively tilted shortwave trough aloft passes overhead near peak
heating, and with beaucoup, plenty of low and mid level moisture and
decent upslope southeast winds advecting low level moisture
northwestward, expect to see numerous to widespread showers with
scattered thunderstorms in the afternoon and evening, focused once
again along the I-25 corridor and near the mountains where
orographics will coincide with the best 850/700 mb theta-e ridge
axis. POPS along the spine of the Laramie Range and the Interstate
25 corridor will range from 60 to 90 percent, and weak steering flow
aloft seen near 700 mb, around 10,000 feet Mean Sea Level, MSL, will
aid in some locally heavy rainfall and some training of storms.

Friday...Will see an abrupt cutoff to the low and mid level moisture
supply as drier air at low and mid levels advects into our counties
as the dominant ridge over Colorado and southern Wyoming reasserts
itself. Thus dry and hotter.

Saturday through Tuesday...Isolated to scattered afternoon and
evening showers and thunderstorms expected, with areal coverage
increasing each day due to increased mid level moisture.
Fortunately, more beneficial rains expected concentrated over and
near our Snowy, Sierra Madre and Laramie Ranges, with the best
chances for convection on Monday and Tuesday. Typical weak northwest
flow aloft on the northeast periphery of the ridge aloft will aid in
occasional passing shortwave troughs aloft near peak heating
resulting in increasing convective potential each day

&&

.AVIATION /00Z TAFS THROUGH 00Z THURSDAY/...
Issued at 529 PM MDT Tue Jul 21 2026

The dominant ridging of the past few days will continue to
weaken slightly and transition centered over northern Texas,
while low and mid level pseudo monsoonal moisture increases over
our counties, along with moist upslope east and southeast winds
near the surface, advecting low level moisture northwestward
into southeast Wyoming. Scattered to numerous afternoon and
evening showers and thunderstorms will affect locations west of
I-25 primarily this evening, with lesser coverage east of I-25.

Wyoming TAFS...For KRWL and KLAR, high confidence in scattered
showers and thunderstorms in the 00Z to 03Z timeframe, per the
NAM and HRRR models. Went with PROB30 at KRWL and TEMPO at KLAR
as the convection evolves. Strongest thunderstorms will produce
gusty and erratic wind gusts to 40 knots along with brief MVFR
visibilities. Clouds will decrease later this evening. Expect
typical gusty diurnal winds until sunset and after sunrise on
Wednesday.

For KCYS, NAM and HRRR show convective potential holding off
until the 05Z time frame, and confidence is moderate on much
convection reaching KCYS after 00Z, so maintained a TEMPO for
now from 02Z to 05Z. VFR prevails with scattered to broken
clouds from 6000 to 10000 feet AGL. Will see typical gusty
diurnal winds to 30 knots until late this evening.

Nebraska TAFS...Using the NAM and HRRR for timing, it appears
that widely scattered to scattered showers and thunderstorms
will develop or propagate across the terminals in the 03Z to
09Z timeframe, with lesser chances at KSNY, though high enough
chances to include VCTS there. VFR prevails with scattered to
broken clouds near 6000 feet prevailing. Will see typical gusty
diurnal winds up to 25 knots until early this evening, and again
after 15Z Wednesday.

&&

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

&&

$$

SHORT TERM...MM
LONG TERM...RUBIN
AVIATION...RUBIN