466
FXUS65 KCYS 062100
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
300 PM MDT Sun Sep 6 2026

.KEY MESSAGES...

- Chances for afternoon and evening thunderstorms continue
  through Monday afternoon. Strong gusty winds and brief heavy
  rainfall are the primary threats.

- A temporary drying trend begins Tuesday and possibly
  continuing through the end of the week.

&&

.SHORT TERM /THROUGH TUESDAY/...
Issued at 250 PM MDT Sun Sep 6 2026

Another warm afternoon today with readings generally in the 80s
to low 90s, warmest across far eastern Wyoming. Western Nebraska
is a little cooler with high dewpoints and breezy south to
southeast upslope winds. Meso Analysis shows quite a bit of BL
CIN across western Nebraska with model soundings showing a
strong temperature inversion just above 800mb. It`s likely going
to take a while to weaken this inversion, especially with any
shortwave/vort energy aloft taking its sweet time moving into
the the eastern high plains later this afternoon. Current KCYS
radar loop shows some shower activity starting to get going near
the southern Laramie Range, but nothing too intense noted at
this time. Models have trended higher with 0-6 km bulk shear,
particularly across the far eastern Wyoming plains and near the
NE/WY border. With expected MLCAPE values between 1000 to 1500
j/kg, expect the I-25 corridor eastward to the Nebraska side of
the WY/NE border to be the most favorable region to see strong
to marginally severe thunderstorms today. With the late arrival
of the upper level vort max, expect this activity to be a little
more isolated compared to yesterday. Excessive rainfall is also
less of a concern today due to the faster storm motion. Otherwise,
strong gusty winds and some large hail (0.75 to 1.50 inches in
diameter) possible with the stronger cells. Thunderstorms may
continue to develop and push northeast after midnight across
western Nebraska. Further west, a surface Pacific cold front
will move into Carbon and Albany counties, generally after
midnight. May see some rain shower activity as early as this
evening with gusty winds ahead of, and behind, the cold front
through tonight.

Drier airmass forecast to push into the area on Monday behind
the front with some cooler air. Expect a lower coverage of
thunderstorms, mainly located south along the I-80 corridor and
the mountains as the front briefly stalls before accelerating
eastward Monday night. High temperatures in the mid 70s to mid
80s are expected for most of southeast Wyoming, with highs in
the low 90s for western Nebraska. It will be windy during the
day with southwest winds between 25 to 35 MPH with gusts around
45 MPH likely along and west of Interstate 25. Kept POP around
20 to 40 percent for the morning hours and into the afternoon
hours across far southeast Wyoming and the southern Nebraska
panhandle. High res guidance shows some bands of light rain in
the morning along the cold front, with some shower and thunderstorm
activity for the afternoon and evening hours. A few strong
thunderstorms can`t be ruled out Monday evening across western
Nebraska, but confidence is pretty low due to limited coverage.

Models show a drier airmass moving into the area on Tuesday
behind the cold front, with dewpoints lowering into the 30s and
40s along the I-80 corridor and as low as 25 degrees across
central and east central Wyoming. Other than some fire weather
concerns, pleasant weather is expected with temperatures a
little cooler and generally in the mid 70s to mid 80s over most
of the region. It will be windy along and west of Interstate 25
with gusts around 45 MPH possible.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
Issued at 200 PM MDT Saturday SEPTEMBER 6 2026

Going into Tuesday evening and overnight a few storms may be
possible in the southern most portions of the area. Low temperatures
are progged to be in the mid 40s west of I-25 and in the 50s east.
With mostly clear skies we could see a few high elevation spots get
into the high 30s. A zonal flow west flow aloft on the north edge of
a ridge will keep things mostly dry. Wednesday afternoon humidity
values drop into the teens for our northern and western fire zones.
Thursday looks even drier with single digit humidity values with
poor overnight recoveries. If a shortwave is timed to pass during
any of these day`s afternoon hours, enhanced 700 mbar flow could mix
down to the surface increasing wind gust potential. Therefore,
elevated to critical fire weather conditions are likely to manifest
during this time frame through Friday evening. Model ensemble
probabilities for below 25 percent RH and wind gusts above 25 mph
are between 70-100 percent generally along and west of I-25 at this
timeframe, which is rather aggressive from that guidance. There is a
chance that Friday could feature a little more atmospheric moisture
from Hurricane Marie as upper level moisture from it is advected
well east over the intermountain regions. That would be the better
of chances to see showers and storms during this stretch.

Saturday could be the soonest we see improvements to the dry
conditions. An upper level trough is being hinted at in global
models to approach the Pacific Coast. The timing and magnitude of
this trough is largely unknown with high variance in each model and
from run to run. The shutoff of the monsoonal flow thanks to the
placement of the upper level ridge to the south could make getting
moisture north ahead of this possible system a challenge. Being so
far in the future that detail will resolve as we get closer.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1123 AM MDT Sun Sep 6 2026

Scattered showers and storms are anticipated to originate near
I-25 this afternoon, primarily effecting the KLAR and KCYS
terminals. These diurnal storms are expected to be widely spaced
given the weak forcing for ascent. The better forcing will be
later this evening when the shortwave trough passes through.
Starting around 01z showers and storms should start becoming
more numerous near KRWL and spreading eastward. A cluster of
storms are then anticipated to develop along I-25 north of KCYS
and move northeast to potentially impact the Nebraska Panhandle
terminals, except KSNY. These storms may drop visibility to 3SM
or lower and reduce CIGs to IFR. A few of these storms may
carry the risk of wind gusts greater than 50 kts and large hail.
Storms clear the area around 9z. Continued showers and mist at
KRWL, KLAR, and KCYS in the morning hours is possible. Then
winds pick up at these same terminals, plus KBFF, around noon
with gusts to 25-35 knots out of the northwest.

&&

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

&&

$$

SHORT TERM...TJT
LONG TERM...RV
AVIATION...RV