567
FXUS65 KCYS 281441
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
841 AM MDT Tue Jul 28 2026

.KEY MESSAGES...

- Marginal Risk of Severe Thunderstorms Tuesday afternoon and
  evening. Strong gusty winds will be the primary threat.

- Monsoon moisture will remain in place through the middle of
  the week. Heavy rainfall and localized Flash Flooding
  possible Tuesday through Wednesday night.

- More heat returns this weekend through Monday, with some near
  record high temperatures possible.

&&

.UPDATE...
Issued at 838 AM MDT Tue Jul 28 2026

Scattered showers and weak isolated thunderstorms are spreading
into western Laramie County per visible satellite imagery and
WSR-88D reflectivity, thus have massaged the grids to increase
POPS for the rest of the morning across Laramie County and
Cheyenne. Expecting this convective activity to remain rather
weak and disorganized due to the lack of instability and time of
day. Updated grids sent.

&&

.SHORT TERM /THROUGH THURSDAY/...
Issued at 135 AM MDT Tue Jul 28 2026

Persistent cloud cover and cooler temperatures on Monday were a
nice relief to the heat from this past weekend, although the
cloud cover suppressed widespread convection with only widely
scattered showers and thunderstorms observed across the area.
Some of this activity is lingering into the early morning hours
this morning over western Nebraska and near the mountains in
Carbon County across southern Wyoming. IR Satellite loop shows
slowly decreasing cloudiness over the area, which should result
in a more favorable environment for thunderstorms Tuesday
afternoon and evening.

Observations across the region show surface dewpoints in the
50s, pretty much everywhere across southeast Wyoming, with
dewpoints in the 60s over western nebraska and far eastern
Wyoming. Monsoon moisture is in place at the surface and aloft
with PWAT above the 90th percentile. This moisture is expected
to remain in place through at least Wednesday night. Best chance
for thunderstorms appears to be today and Wednesday with cloud
cover not as thick and widespread compared to Monday. In
addition, a 60 to 70 kt jet is expected to sneak into the
forecast area, with some enhanced dynamic lift in the upper
levels...but more importantly, increasing midlevel wind shear.
Wind shear still appears marginal based on forecast soundings
(RAP, NAM, and GFS), but convective parameters and PWAT suggest
multicell clusters and maybe a few linear segments with MLCAPE
over 2000 j/kg and 0-6km shear around 25 to 30 knots, at times,
as a potent shortwave/vort max moves east across the area. Very
heavy rainfall is also a concern in this pattern with a
marginal risk for flash flooding...especially far southeast
Wyoming and the southern Nebraska panhandle. Not going to
message this too aggressively quite yet due to the lack of
rainfall recently and low soil moisture. However, a day or two
of heavy rainfall in the same locations may warrant more
aggressive messaging in a day or two. Similar conditions
expected on Wednesday but slightly hotter, with very heavy
rainfall the primary concern. Shear values drop to below 20
knots even as a broad Pacific upper level trough axis ejects
northeast over the Front Range late Wednesday. A little more
concerned of flooding on Wednesday and Wednesday night as this
trough lifts northeast, but will see what rainfall amounts we
receive today. Isolated large or marginally large hail can`t be
ruled out both days, but appears unlikely at this time with the
lack of shear. At this time, nocturnal convection appears more
likely Wednesday night with the slow passage of the Pacific
upper level trough axis.

For Thursday, models show the upper level ridge axis building
over Utah, western Colorado, and western Wyoming behind the
Pacific trough. Some drier air should make it into central
Wyoming with a slight increase in westerly winds. Further east,
models tend to dry things out too fast under weak northwesterly
flow, so added 20 to 35 percent POP over the eastern plains for
widely scattered thunderstorms. Model soundings show areas along
and east of the I-25 corridor hanging onto the low to midlevel
monsoon moisture for another day. Hot temperatures on Thursday
as the upper level ridge builds northward with highs in the
upper 80s to mid 90s.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
Issued at 216 PM MDT Mon Jul 27 2026

Thursday night through Monday: Monsoonal moisture retreats out
of our County Warning Area (CWA) as a drier and hotter air mass
returns producing nearly dry conditions with only minimal
chances for isolated to scattered thunderstorms over and near
our Snowy, Sierra Madre, and Laramie Ranges due to differential
orographic processes. Temperatures will soar once again,
especially for Sunday and Monday, with some locations possibly
approaching near record maximum temperatures, and perhaps the
long standing all time record high temperature of 100 degrees at
Cheyenne, that has been achieved four times, the most recent in
the 1950s.

&&

.AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 545 AM MDT Tue Jul 28 2026

Monsoon moisture plume will remain over the area for at least the
next 48 hours. With less cloud cover today, there is a better chance
of scattered to numerous showers and thunderstorms, especially
further south near the I-80 corridor this afternoon and this
evening. Can`t rule out some patchy fog late tonight in areas that
receive heavy rainfall.

HAZARDS/WEATHER TRENDS: Primary Aviation concern is timing and
coverage of thunderstorm activity this afternoon. Winds will remain
relatively light out of the east or southeast with occasional gusts
of 20 knots. Thunderstorms will form near the Laramie Range,
impacting KLAR and KCYS after 20z. These thunderstorms will push
over the western Nebraska terminals after 22z and may linger through
the late evening hours. Gusty winds and very heavy rainfall are
possible which may result in brief MVFR to near IFR VIS.

Kept fog and low CIGS out of the TAF tonight due to low confidence
(5% to 10%) in rainfall amounts and coverage. The most likely
terminals to see some fog is KSNY and KCYS.

&&

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

&&

$$

UPDATE...RUBIN
SHORT TERM...TJT
LONG TERM...RUBIN
AVIATION...RZ