638
FXUS65 KCYS 291155
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
550 AM MDT Wed Jul 29 2026

.KEY MESSAGES...

- Monsoon moisture will remain in place through the end of the
  week across the high plains. Heavy rainfall and localized
  flooding possible through Wednesday night.

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

&&

.SHORT TERM /THROUGH THURSDAY NIGHT/...
Issued at 145 AM MDT Wed Jul 29 2026

Observations and IR Satellite this morning shows relatively
quiet conditions with remnant convection from Tuesday evening
weakening and drifting south across Colorado at this hour.
Dewpoints are still in the 60s, even over Cheyenne, Wheatland
and Douglas (I-25 corridor)...with dewpoints in the mid to upper
50s even in Laramie. Very moist airmass expected to remain over
the area today with southeast winds through the day. Can`t rule
out some low clouds and/or patchy fog with the I-80 Summit
reporting some fog at this hour. Added some fog to the forecast,
but with limited coverage since probabilities are still pretty
low. PWATs will remain between 1.00 to 1.60 inches, highest
across the western Nebraska Panhandle. Another day of scattered
to numerous showers and thunderstorms are expected Wednesday and
Wednesday evening across most of the area as MLCAPE ranges
between 1500 to 2500 j/kg. Models continue to show a broad
upper level trough and embedded shortwave lifting northeast
across the area today. However, upper level ridge axis is
expected to remain strong out ahead of this feature with pretty
low midlevel flow and the 70kt jet stream lifting north of the
forecast area. This will greatly limit 0-6km shear across the
region, so strong to severe thunderstorms appear unlikely at
this time. Still see some marginal shear for a few model
sounding locations across east central Wyoming, so may see some
marginally large hail and, most likely, brief gusty winds. Heavy
rainfall is still expected, but not seeing the same signals in
the high resolution model data as we saw yesterday. Only a few
locations in Morrill and Cheyenne Counties saw heavy rainfall
amounts over an inch, so not nearly as concerned as we were
yesterday. Some nocturnal convection is expected to linger past
midnight early Thursday morning, but activity should be more
isolated after 10 PM Wednesday evening. Forecast high
temperatures will be tricky further south along the I-80
corridor due to cloud cover, some fog, and early initiation of
convection. Lowered high temperatures by a few degrees along the
I-80 corridor with highs in the 80s to maybe low 90s further
east. Further north, high temperatures will generally remain in
the 90s with more sunshine.

For Thursday, models show the upper level ridge axis attempting
to rebuild 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 kept a slight chance of showers and
thunderstorms in the forecast through the evening hours. In
addition, the GFS and Canadian do show a subtle shortwave diving
southeast embedded in the northwest flow aloft. May be a strong
to marginally severe thunderstorm or two across east central
Wyoming and the northern Nebraska Panhandle Thursday afternoon
and evening. Temperatures will begin to climb over the whole
forecast area on Thursday, with highs in the upper 80s to middle
90s expected. Drier air will take it`s time moving into the
eastern plains with weak advection in the low to midlevels.

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
Issued at 201 PM MDT Tue Jul 28 2026

Friday...Monsoonal moisture plume stretches north to south across
far eastern Wyoming and western Nebraska, and with a ridge runner
shortwave trough aloft in northwest flow, we expect to see scattered
showers and thunderstorms generally east of a Douglas to Cheyenne
line.

Saturday and Sunday...Ridging prevails with a decrease in monsoonal
moisture and warm temperatures aloft will produce enough CIN,
Convective Inhibition, to prevent thunderstorm development. Hot
temperatures return with the hottest day being Sunday, and with 700
mb temperatures from 20 to 23 Celsius, high temperatures will range
from 95 to 105 degrees, with possible Heat Advisories needed east of
I-25 on Sunday.

Monday and Tuesday...Broad troughing aloft develops across the
northern Rockies with zonal flow over our counties. This will help
produce somewhat cooler temperatures as 700 mb temperatures lower to
13 Celsius. There may be enough low and mid level moisture to
produce isolated late day thunderstorms over and near the Laramie
Valley and southern Laramie Range.

&&

.AVIATION /12Z TAFS THROUGH 12Z THURSDAY/...
Issued at 550 AM MDT Wed Jul 29 2026

Patchy fog will dissipate shortly after sunrise early this morning
for mainly the eastern high plains. Another round of showers and
thunderstorms will develop over the mountains around 18z to 20z and
push east across the plains and high valleys this afternoon through
late this evening. Gusty winds and very heavy rainfall possible for
most terminals.

HAZARDS/WEATHER TRENDS: For early this morning, KAIA and KSNY
observing some low fog due to nearly saturated conditions and light
southeast winds. Expect conditions to improve to VFR after 14z.

VFR will prevail at all terminals through the late morning and
afternoon hours. Thunderstorms will develop over the mountains and
impact KRWL, KLAR, and KCYS after 19z. These thunderstorms will then
move into western Nebraska after 00z Thursday. Very heavy rainfall,
gusty winds, and IFR conditions possible (15% to 30% chance) for
most terminals, especially KCYS, KLAR, and KSNY until 03z Thursday.
Kept VCTS for the higher probability of thunder into this evening.

&&

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

&&

$$

SHORT TERM...TJT
LONG TERM...RUBIN
AVIATION...TJT