245
FXUS65 KCYS 160456
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1055 PM MDT Sat Aug 15 2026

.KEY MESSAGES...

- Another round of thunderstorms will bring the potential for
  localized flash flooding and isolated strong to severe
  thunderstorms this afternoon and evening.

- A Flood Watch & Severe Thunderstorm Watch are in effect
  through this evening for much of the High Plains.

- Isolated strong to severe storms and localized flash flooding
  will remain possible Sunday, though overall storm coverage
  will be lower.

- Drier weather and temperatures close to seasonal averages will
  return early next week.

&&

.SHORT TERM /THROUGH SUNDAY NIGHT/...
Issued at 216 PM MDT Sat Aug 15 2026

Another round of slow moving thunderstorms is in store for this
afternoon and evening. Looking at Water Vapor, the mid and lower
levels show plumes of moisture advecting through Colorado and
Arizona and into our region. This will drive our PWAT values into
the 1.0-1.25 inch range during the weekend as we are in Southwest
flow. 700mb flow will remain rather slow today, with generally
westerly to southwesterly flow expected. A messy, surface high
pressure system will attempt to develop west of the Rocky Mountains
over western Colorado before strengthening into the afternoon hours.
With ample moisture available due to continued monsoonal moisture
advection, the easterly flow will lead to very moist, upslope flow
along and east of the Laramie Range. 700mb and 500mb vorticity
maxima will be the major players in the synoptic forcing which is
expected to increase into the later afternoon hours. Heavy rainfall
is anticipated once again today, with the Weather Prediction Center
placing portions of the region in a Slight Risk of excessive
rainfall and a larger portion in a Marginal Risk of excessive
rainfall. With the sustained rainfall across the lower elevations
yesterday, the soils should be moderately saturated to aid in
localized areal and urban flooding. A Flood Watch was issued on the
overnight shift that is valid from 2PM through 10PM for nearly all
locations along and east of the Laramie Range, where Precipitable
Water values remain at and above the 90th percentile and moist,
upslope flow persists. In addition to the flooding risk today, the
Storm Prediction Center has placed far southeast Wyoming and western
Nebraska in a Slight Risk (Level 2 of 5) of severe weather this
afternoon. Primary hazards look to be isolated, large hail and
damaging wind gusts. Isolated pockets of MLCAPE and SBCAPE around
1000 J/kg will provide enough instability for stronger updrafts to
develop this afternoon, especially across western Nebraska. The
biggest question will be whether or not the early morning cloud
cover anticipated across the region puts a damper on the severe
potential this afternoon. Pockets of clearing skies occurred across
the forecast area to aide in some diurnal heating this morning and
strengthening the instability for the showers/thunderstorms later.
Forecasting the daily high temperatures and trying to get the hourly
trend will be rather difficult as these clouds push into the region
potentially cooling areas faster than the models could predict as
well.

For Sunday, slightly drier condition as the upper-level flow turns a
little more westerly, cutting off some of the monsoonal moisture
advection into the area. However, with the ample moisture present
over the past several days, plenty of residual moisture will be
present to get another round of showers and storms Sunday afternoon
into the evening hours. A few lobes of 500mb vorticity will advect
across the region Sunday afternoon, providing some forcing for
ascent. Slightly stronger 700mb warm air advection briefly develops
Sunday afternoon, adding an additional forcing for ascent for
showers and storms. Surface flow turns southerly Sunday afternoon
through much of the overnight hours, leading to weak ascent across
the Cheyenne Ridge, likely resulting in showers and storms
developing in this area once again. Precipitable water values look
to return towards more climatologically average values Sunday,
decreasing the threat for isolated flooding across the region.
However, with monsoonal moisture still in play, flooding potential
continues for Sunday with a Marginal Risk of Excessive Rainfall from
the Weather Prediction Center. Another round of strong to severe
storms will be possible Sunday, with a Slight Risk of severe weather
for much of the area and a small portion of the region under a
Slight Risk of severe weather once again.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
Issued at 216 PM MDT Sat Aug 15 2026

Drier air will work into the area on Monday, bringing us a break in
the stormy monsoon weather pattern. Expect mostly sunny skies to
return to the area with temperatures generally near seasonal
averages, in the lower 80s around Laramie and Rawlins, and mid to
upper 80s along and east of I-25. While isolated showers and/or
thunderstorms will still be possible, coverage will be significantly
lower than the preceding days. The boundary layer will be much
drier on the Wyoming side, which may lead to a dry microburst,
threat, while a few actual rain producing thunderstorms will be
possible mainly on the Nebraska side.

The monsoon tap recovers somewhat on Tuesday into Wednesday, though
the flow will remain largely westerly aloft. Still, some low to mid
level southerly flow over the Great Basin will help inject higher PW
into our area, pushing values back to around 0.75 and 1.2 inches or
so across the area. This will of course be not quite as high as the
current monsoon surge, but should be sufficient to kick up coverage
of showers and thunderstorms for Tuesday and Wednesday, especially
with some help from an upper level shortwave trough riding over the
top of the ridge Wednesday. While the boundary layer will still b on
the dry side during this period, there looks to be plenty of
moisture aloft so rain should still reach the ground even in the
drier areas. Tuesday should see temperatures climb just a smidge
above seasonal averages, while these values will fall by a few
degrees Wednesday with the aforementioned shortwave.

The upper level ridge will amplify to our west on Thursday, and
Friday, turning the flow aloft to a more dry, northwesterly flow.
Expect storm chances to become much more isolated once again as
temperatures climb back above seasonal averages. An early look at
700-mb temperatures appears fairly marginal for record highs
with this round with NAEFS means hovering around +15 to +18C, or
near the climatological 90th percentile.

&&

.AVIATION /00Z TAFS THROUGH 00Z MONDAY/...
Issued at 1055 PM MDT Sat Aug 15 2026

Showers and embedded thunder slowly weakening late this evening with
most of the activity finished by 09z. Low CIGS and fog will be the
primary concern between 06z and 12z Sunday before another round of
thunderstorms impacts the region Sunday afternoon.

HAZARDS/WEATHER TRENDS: Moderate confidence (25% to 50%) of low CIGS
and fog over the eastern plains terminals, including KCYS. Added
prevailing IFR conditions to most sites, but not certain how long
it`s going to last, or if conditions will fluctuate through the
night and into the early morning hours. Light winds and some
overnight convection might result in periods of low CIGS, but it may
not be persistent. Added prevailing IFR where there is more
confidence, and kept VCFG and/or MVFR conditions where confidence is
lower.

Another round of thunderstorms expected after 20z Sunday, but
coverage is expected to be much more isolated. Added PROB30 for TSRA
for KSNY, KCYS, and KCDR due to higher confidence. Gusty winds and
brief heavy rainfall will be the primary concerns.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Flood Watch until 10 PM MDT this evening for WYZ102-107-108-
     117>119.
NE...Flood Watch until 10 PM MDT this evening for NEZ002-003-
     019>021-054-055-095-096.

&&

$$

SHORT TERM...MM
LONG TERM...MN
AVIATION...TJT