101
FXUS65 KCYS 181830
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1230 PM MDT Tue Aug 18 2026

.KEY MESSAGES...

- There is a Marginal Risk (Level 1 of 5) of severe weather
  across portions of the region along and east of the Laramie
  Range. Large hail and damaging winds will be the primary
  hazards.

- Drier conditions start to return Wednesday as the upper-level
  ridge strengthens across the Intermountain West.

- An isolated storm or two cannot be ruled out Wednesday.
  Portions of the Panhandle are under a Marginal Risk of severe
  weather with large hail and damaging winds the primary
  hazards.

- Warmer, drier conditions continue through the end of the week,
  suggesting elevated fire danger may return.

&&

.SHORT TERM /THROUGH WEDNESDAY NIGHT/...
Issued at 210 AM MDT Tue Aug 18 2026

Upper-level ridging continues to build across the Intermountain West
today with a strong trough moving south out of Canada into the
Midwest. The upper-level jet between these two systems strengthens
today due to strong height gradients aloft, leading to stronger
winds and a more dynamic upper-level setup. An upper-level shortwave
will propagate through the larger upper-level trough, likely
impacting the Great Plains and portions of southeast Wyoming and
western Nebraska. A similar setup is expected at 500mb, with
multiple vorticity maxima ejecting through the 500mb flow and
traversing across the CWA. 700mb flow becomes slightly more dynamic
this afternoon as well, as the 700mb winds strengthen a touch as the
trough moves into the Midwest. Strong 700mb WAA will further promote
rising motion across the region before a backdoor cold front pushes
in from the east. With largely stacked westerly flow from the
surface through 250mb, RAP soundings suggests straight hodographs
across much of the region with Inverted-V soundings across southeast
Wyoming and more favorable soundings in western Nebraska. However,
instability looks to be an issue this afternoon as cloud cover
sticks around and limits daytime heating across much of the area.
The 700mb WAA and backdoor cold front should provide enough forcing
to get showers and storms to develop, but the overall setup is less
impressive than previous days. Despite this, any storm that develops
this afternoon will interact with straight hodographs and modest
bulk shear around 30 to 35kts. Therefore, splitting storms that
eventually grow upscale into several linear segments looks to be the
most favorable severe mode this afternoon. Multiple line segments
across the region will make radar look very busy, but only a few of
these storms may become severe. The Storm Prediction Center has
placed much of the area along and east of the Laramie Range in a
Marginal Risk (Level 1 of 5) of severe weather this afternoon with
damaging winds and large hail being the primary threats. Forecast
soundings suggest hail struggling to get very large, but stone
between 1 inch and 1.5 inches will be possible, especially further
east into the Panhandle. The best severe threat appears to have
shifted away from the CWA, so widespread severe weather is not
expected across the CWA today. This does not mean that no storms
will be severe. An isolated storm or two may become severe,
especially where there are breaks in the morning cloud cover.
Precipitable Water values remain around average for this time of
year as well, so while heavy rain cannot be ruled out in some of the
stronger storms, widespread flooding threats are not anticipated.

The upper-level ridge continues to build across the Intermountain
West on Wednesday, leading to warmer and drier conditions once more.
Northwesterly flow aloft develops for Wednesday, allowing multiple
lobes of 500mb vorticity to traverse overhead, resulting in sporadic
synoptic forcing for ascent. Northwesterly flow will persist at
700mb leading to drier conditions along and east of the Laramie
Range as downslope warming and drying take hold. The terrain-induced
dryline returns Wednesday and quickly pushes well to the east,
fueled by the stronger 700mb flow advecting drier air eastward.
Precipitation chances will be limited to none for most locations
across the region, though an isolated shower or storm could develop
across the eastern row of counties, from Chadron down to Sidney.
Currently, models are not overly excited about any form of
precipitation across the Panhandle on Wednesday, instead favoring
dry and breezy conditions. Elevated to near-critical fire conditions
are anticipated to develop across western portions of the CWA where
surface winds return to more "normal" speeds and afternoon minimum
humidity values drop into the 15 to 20 percent range. Decided not to
issue any Fire Weather headlines this morning due to low confidence
in achieving 3 consecutive hours of Red Flag conditions and due to
the fairly limited coverage of any critical fire conditions.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
Issued at 210 AM MDT Tue Aug 18 2026

The upper-level ridge looks to continue to strengthen through
the end of the week, with the monsoonal flow becoming largely
cutoff. This accelerates the onset of the next round of hot
temperatures as ridging builds in to our west. Expect highs to
climb 5 to 10 degrees above average for Thursday through
Saturday. We probably won`t be totally dry on Thursday and
Friday, but expect PM convection to be much more limited and
likely confined to areas in or near the higher terrain of
southern Wyoming. Attention will shift back to fire weather
during this period as well. Westerly winds moving into the area
behind Wednesday`s shortwave trough will lead to at least
elevated, if not critical, fire weather conditions along and
west of the Laramie Range. The winds appear a little lighter for
Thursday and Friday, but model guidance has been consistently
too low on winds in Carbon and Albany counties lately.

The upper level ridge will very gradually shift eastward over the
course of the week, sliding east of the Four Corners by the weekend.
This will allow a fresh tap of monsoon moisture to be pulled
northward into the Great Basin and Four Corners states, eventually
working its way over the top of the ridge and into our area. As a
result, look for increased coverage of PM shower and thunderstorm
activity for the weekend with temperatures remaining about 5 to 10
degrees above seasonal averages.

&&

.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 1204 PM MDT Tue Aug 18 2026

Primary challenges include ongoing showers as well as timing,
intensity and coverage of afternoon and early evening showers
and thunderstorms. A series of shortwave troughs aloft, also
known as an atmospheric perturbation, will move southeastward in
northwest flow aloft over the aviation district.

The primary shortwave trough aloft will affect the terminals and
aviation area from late afternoon through early evening,
producing scattered showers and isolated thunderstorms, with
some of the stronger storms producing winds gusts to 45 knots
with isolated strong thunderstorms, especially east of the
Laramie Range and the I-25 corridor, producing a few wind gusts
in excess of 50 knots. Showers and thunderstorms will exit the
forecast area by 06Z with clearing skies and lessening winds.

Wyoming TAFS...VFR prevails through the TAF period. High
confidence in the latest consistent HRRR timing of showers and
thunderstorms, as well as the latest 12Z NAM run. Confident
enough with timing of the HRRR to go with TEMPO groups at KRWL,
KLAR and KCYS, from 22Z to 00Z, 23Z to 01Z, and 00Z to 02Z,
respectively, with occasional MVFR due to visibilities and low
VFR ceilings, as well as erratic winds and some gusts from the
stronger storms up to 45 knots, with a few storms in the
aviation district supporting wind gusts in excess of 50 knots.
During the evening hours and overnight, expect decreasing cloud
cover with ceilings and visibilities becoming unrestricted.

Nebraska TAFS...VFR prevails through the TAF period. High
confidence in the latest consistent HRRR timing of showers and
thunderstorms, as well as the latest 12Z NAM run. Confident
enough with timing of the HRRR to go with TEMPO groups at KCDR,
KAIA, KBFF and KSNY, from 23Z to 02Z, with occasional MVFR due
to visibilities and low VFR ceilings, as well as erratic winds
and some gusts from the stronger storms up to 45 to 50 knots,
with a few storms in the aviation district supporting wind gusts
in excess of 50 knots. During the evening hours and overnight,
expect decreasing cloud cover with ceilings and visibilities
becoming unrestricted. -Rubin

&&

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

&&

$$

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