515
FXUS65 KCYS 160815
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
215 AM MDT Sun Aug 16 2026

.KEY MESSAGES...

- There is a Slight Risk (Level 2 of 5) of severe weather across
  the region today, mainly Cheyenne up to Torrington and points
  east.

- There is a Marginal Risk for Excessive Rainfall this
  afternoon, though the threat is much lower than previous days.

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

&&

.SHORT TERM /THROUGH MONDAY NIGHT/...
Issued at 214 AM MDT Sun Aug 16 2026

An upper-level pattern shift is in store as moist, southwesterly
flow fueled by the monsoon shifts west, becoming drier and warmer
across the region. Ahead of zonal flow returning aloft, the
southwesterly flow will advect in a touch more monsoonal moisture
before becoming largely cut off. This moisture will enable another
day of isolated to scattered showers and storms before drier
conditions and fire weather concerns return Monday. For today,
several 500mb vorticity maxima will eject across the region,
enabling synoptic forcing for portions of the region. 700mb flow
remains largely benign, turning westerly through the evening hours
and starting the drying process. Strong warm air advection is
anticipated at 700mb, leading to further forcing across the region.
Surface flow will remain largely southeasterly for areas along and
east of the Laramie Range, with locations west seeing largely
westerly flow at the surface. Southerly flow in the eastern portion
of the region will enable additional moisture to funnel in, despite
the monsoonal tap eroding during the afternoon hours. Instability
will increase this afternoon with portions of the Panhandle seeing
MLCAPE values around 1000 J/kg with some capping possible,
especially where morning cloud cover from departing storms limits
daytime heating and destabilization. Overall, shear looks to be
decent across western Nebraska with surface winds out of the south
and southeast and 700mb flow coming westerly by the afternoon hours.
With left over monsoonal moisture, heavy rain also looks likely with
any storms this afternoon. Precipitable Water values will increase
towards the 1 inch mark in the Panhandle. Gusty showers also cannot
be ruled out across southeast Wyoming with forecast RAP soundings
suggesting steep low-level lapse rates and DCAPE values around 1000
J/kg. Overall, damaging winds and large hail, mainly in the
Panhandle, are the primary threats for severe weather today, as
highlighted in the Slight Risk (Level 2 of 5) from the Storm
Prediction Center. Additionally, the Weather Prediction Center has
placed portions of the region in a Marginal Risk of excessive
rainfall yet again this afternoon.

Westerly flow aloft return in force on Monday as a ridge builds over
the western CONUS. Much drier conditions are anticipated to return
under this ridge as the monsoonal moisture tap gets largely cut off.
Afternoon humidity values will decrease dramatically, compared to
the past several days, with values in the 20s and 30s. With drier
conditions returns the threat for elevated fire conditions across
portions of the area. Areas west of the Laramie Range will see
elevated fire weather conditions Monday, but winds are expected to
be fairly light, limiting the fire concerns. Precipitation chances
will be quite low on Monday with drier conditions everywhere.
Temperatures will begin to increase as the upper-level ridge starts
to influence the region, though still remaining around the
climatological average for this time of year.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
Issued at 214 AM MDT Sun Aug 16 2026

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...Dense Fog Advisory until 7 AM MDT this morning for WYZ116-117.
NE...None.

&&

$$

SHORT TERM...AM
LONG TERM...MN/AM
AVIATION...TJT