757
FXUS65 KCYS 161944
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
144 PM 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.

- Another slight cool down with scattered PM showers and
  thunderstorms is expected Tuesday and Wednesday. A few storms
  may have the potential to become strong to severe.

- Warmer and drier weather will return to the area Thursday and
  Friday.

&&

.SHORT TERM /THROUGH MONDAY NIGHT/...
Issued at 142 PM MDT Sun Aug 16 2026

The upper level pattern has flattened to a more westerly flow aloft.
This will increase the downsloping drying effect near the surface.
The humidity will become a touch more dry today because of it but
nothing to noticeable. Dewpoints have been relatively stable in
the 50`s with some drier spots in the 30`s and 40`s west of I-25.
Sidney and Kimball however must have a decent cap over them still
as their dewpoints are still in the low 60`s keeping residual
moisture near the surface in the southern panhandle. Looking at
mid-level water vapor, a plume of dry air is making its way to the
Intermountain west. This dry air aloft may limit any storm potential
over our area increasing confidence in the high-res outputs of some
weak showers and may be one or two supercells. As far as synoptic
forcing goes, there really isn`t any strong vort maxes, warm air
advection, or isentropic lift to help storms develop. Mid-level
lapse rates are also kind of unhelpful as they range from 7.5 to 8C
with a couple hundred joules of CAPE. So not the best environment
but a couple storms may be able to develop especially with the 30-40
knots of bulk shear. The southern Panhandle and possibly Laramie
county look to be the best locations to get a supercell for this
evening. Some the hi-res guidance wants to place something
developing in the Northern Panhandle but it`s looks like if anything
exciting up there happens it will most likely be a gracious gift
from South Dakota. 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. Past 6pm the environment really
starts to degrade and we could possibly be done before 11pm.

Westerly flow aloft returns 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 142 PM MDT Sun Aug 16 2026

After a briefly warmer and drier day on Monday, a series of
shortwave troughs aloft will move over the top of the ridge and
flatten it a bit, lowering heights aloft and 700-mb temperatures for
Tuesday and Wednesday. While the flow direction aloft will remain
westerly, we should see a fetch of better recycled monsoon moisture
moving into the area. Precipitable water will nudge up slightly for
Tuesday, back to between 0.75" and 1.1" in Wyoming and 1.0" to 1.25"
in Nebraska. The boundary layer (especially on the Wyoming side)
will probably remain fairly dry Tuesday as remnants of Monday`s
drier airmass remain in place, but fairly plentiful moisture will
push in aloft. Forcing from the passage of the upper level shortwave
trough will support scattered showers and thunderstorms developing
in the afternoon and evening hours, likely greater coverage than
Monday`s activity. Rainfall will not have trouble reaching the
ground despite the drier boundary layer due to the high precipitable
water. Wednesday will bring a fairly similar setup, but probably
with better surface moisture due to models picking up on slightly
more organized southerly flow across the High Plains. While it is
still early, parameters look somewhat favorable for strong to severe
thunderstorms both Tuesday and Wednesday, despite lower overall
thunderstorm coverage compared to the monsoon surge our area has
been under for the last several days. The ECMWF ensemble Extreme
Forecast Index for combined CAPE-Shear is around 0.7 to 0.85 for
much of the High Plains both Tuesday and Wednesday, indicating that
a large proportion of ECMWF ensemble members have combined CAPE-
shear values that are climatologically unusual to extreme. We will
need to continue to watch this period in the coming days.

A more defined upper level shortwave trough will pass through the
area Wednesday evening. Behind this feature, the upper level ridge
over the southwest will begin to re-amplify to our west, initiating
a drier, northwest flow pattern for the remainder of the week.
Precipitable water won`t be terrible during this weather pattern, so
we should still see at least a few isolated PM showers and storms
Thursday and Friday, but expect those two days to be considerably
drier. Temperatures will also begin to climb once again. 700-mb
temperatures climb back to near the climatological 90th percentile
by Friday into Saturday, peaking around +16 to +18C across the area.
Expect high temperatures to climb above seasonal averages Thursday,
and then closer to 5 to 10 degrees above average Friday and
Saturday. Since we`ll be somewhat on the periphery of this heat
wave, current forecasts do not challenge daily record highs, but
this could still change in the coming days. Over the course of
Thursday through Saturday, the upper level ridge should start to
very slowly meander back to the east. Once this moves east of the
Four Corners, the monsoon should surge back to the north, and we may
see precipitation chances increasing again by Saturday.


&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1138 AM MDT Sun Aug 16 2026

Thunderstorm activity will be more limited today than the last
few days, but still anticipate isolated to widely scattered
showers and thunderstorms to develop by mid afternoon. CYS and
SNY have the highest probability for impacts and thus have TEMPO
groups for the hazard, though the probability is only around 50
to 60%. Lower probabilities for impacts exist at all other
terminals, generally between 20 and 40%. PROB30 groups are
maintained for BFF, AIA, and CDR for this possibility. Winds
will be impacted by thunderstorm outflows through the middle
evening hours. The High Plains may see some breezy southwest
winds overnight, but the chance for fog / low CIGs tonight is
lower.

For Monday, expect winds to turn westerly in the morning, but
should remain on the light side.

&&

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

&&

$$

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