258
FXUS65 KCYS 182327
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
527 PM MDT Fri Jul 18 2025

.KEY MESSAGES...

- Scattered PM showers and thunderstorms are expected across the
  area on both Friday and Saturday. A few storms will have the
  potential to become strong to severe, mainly in the NE
  Panhandle.

- Quite warm conditions persist for Sunday through Friday, with
  almost daily chances for isolated to scattered late day
  showers and thunderstorms.

&&

.SHORT TERM /THROUGH SATURDAY NIGHT/...
Issued at 100 PM MDT Fri Jul 18 2025

Early afternoon visible satellite imagery reveals developing
convective cumulus cloud coverage over the higher terrain of
southeast Wyoming. Widely scattered mid and upper-level cloud
cover continues to drift from southwest to northeast over the
region, evidence in seasonably high mid-level moisture also
shown in forecast soundings. Aloft, a light zonal-flow pattern
is present over Wyoming and Nebraska, with the core of stronger
flow aloft located well to the north in the Dakotas and Montana.
Forecast soundings reveal a very shallow layer of upslope flow
in areas east of the high plains which is confirmed by surface
observations as of 19z. Overall, a very marginal convective
setup is in place today. West of I-25, forecast soundings show
fairly large dewpoint depressions and generally straight but
short hodographs. Isolated instances of gusty wind in the 40-60
mph range are possible with any stronger cores, with isolated
shower activity continuing overnight as a weak monsoonal plume
of mid-level moisture continues to sit over the central Rockies.
Farther east in the Wyoming high plains and Nebraska Panhandle,
thunderstorms will have a bit more low-level moisture to work
with, with smaller Td depressions and small but slightly more
curving hodographs seen in forecast soundings. CAM guidance is
in generally good agreement showing a weak clustered storm mode
and the possibility of a few cells containing pea to penny
sized hail and wind gusts up to 60 mph. The corridor of greatest
concern appears to be from Torrington/Lusk through Chadron
where locally backed and enhanced surface flow may help to
sustain a stronger storm or two through around 3z tonight.
Elsewhere, expect a few isolated showers to continue through the
evening as the aforementioned monsoonal plume remains in place
in the mid levels over all of southeast Wyoming and far western
Nebraska.

After a mild and partly cloudy overnight period, convection will
once again be a threat on Saturday. The 500mb jet will dip
southward through the morning and early afternoon, with h5 flow
around 25-35 knots over most of the high plains east of the
Laramie Range by 18z. Surface flow will remain out of the west
in the high-basins of southeast Wyoming. To the east, a battle
between drier westerly surface flow and lingering upslope will
take place, with a diffuse dryline setting up somewhere
along/east of the WY/NE state line in the NE panhandle. Exactly
where this dryline sets up and how sharp it becomes will
ultimately determine the convective threat in the Panhandle on
Saturday. A sharper dryline with more potent moisture return
(evidenced in CAMs such as the NAM Nest/WRF ARW would support a
greater thunderstorm threat in the panhandle. Supercells would
be possible in the CWA with large hail over 1 inch and gusty
outflow winds possible. However, models such as the HRRR, FV3,
and RRFS favor a more deeply mixed boundary layer and thus a
more diffuse dryline farther east of the CDR/AIA/SNY line. This
outcome would likely result in only weaker, high-based
convection for much of the CWA with only a minor high-wind
threat. The current trend of most HREF guidance favors the
farther east dryline and lower severe weather threat for the
eastern portions of the CWA on Saturday and PoPs/PoT guidance
has been adjusted accordingly. Still, folks headed outside to
enjoy summertime recreation weekend activities should be on the
lookout for briefly gusty winds and isolated lightning with any
thunderstorms that do form.

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
Issued at 100 PM MDT Fri Jul 18 2025

Sunday...Low amplitude shortwave ridging aloft develops. With drier
air moving in at low and mid levels, only isolated afternoon
thunderstorms will be possible near the southern Laramie Range,
otherwise dry. 700 mb temperatures near 17 Celsius will yield high
temperatures from the mid 80s to upper 90s.

Monday...Continued hot with southwest flow aloft and 700 mb
temperatures near 16 Celsius. Other than isolated late day
thunderstorms, warm temperatures aloft will produce enough
convective inhibition to limit convective development.

Tuesday...With slightly more atmospheric moisture, and cooler
temperatures aloft, we expect to see a little uptick in late day
showers and thunderstorms, along with slightly cooler temperatures.

Wednesday...As the flow aloft turns westerly, atmospheric moisture
increases, with a corresponding increase in late day showers and
thunderstorms, along with cooler temperatures.

Thursday...Similar temperatures compared to Wednesday with weak
ridging aloft. Still looks like adequate low and mid level moisture
for isolated to scattered afternoon and evening thunderstorms.

Friday...A few degrees warmer than Thursday as 700 mb temperatures
peak near 18 Celsius. Adequate atmospheric moisture for isolated to
scattered late day showers and thunderstorms, mainly east of
I-25.

&&

.AVIATION /00Z TAFS THROUGH 00Z SUNDAY/...
Issued at 522 PM MDT Fri Jul 18 2025

West flow aloft will continue.

Wyoming TAFS...Scattered to broken clouds from 7000 to
10000 feet will prevail. Occasional thunderstorms will occur at
Rawlins and Cheyenne until 02Z, producing wind gusts to
35 knots. Outside of thunderstorms, winds will gust to 25 knots
at Rawlins until 03Z, and to 25 knots at all terminals after
15Z Saturday.

Nebraska TAFS...Scattered to broken clouds from 6000 to
12000 feet will prevail. Thunderstorms will be in the vicinity
until 03Z. Winds will gust to 23 knots at Chadron and Alliance
until 03Z, and to 25 knots at all terminals after 15Z Saturday.

&&

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

&&

$$

SHORT TERM...MAC
LONG TERM...RUBIN
AVIATION...RUBIN