784
FXUS65 KCYS 061739
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1139 AM MDT Sun Sep 6 2026

.KEY MESSAGES...

- Chances for afternoon and evening thunderstorms continue until
  mid week. Strong gusty winds and brief heavy rainfall are the
  primary threats.

- A temporary drying trend begins Mid-week and possibly
  continues through the end of next week.

&&

.SHORT TERM /THROUGH MONDAY NIGHT/...
Issued at 344 AM MDT Sun Sep 6 2026

The deepening low is slowly inching its way into the Northern Rocky
Mountains. Midlevel Water Vapor shows a stream of dry air covering a
majority of the forecast area, however as this system slowly lift
the stream of moist inflow will be pulled into our area feeding the
next wave to develop our next severe weather event this afternoon
and evening. With this low creeping forward the storm coverage is
expected to be a bit more scattered. Areas along and east have
almost equal chances of seeing rain today if that moisture stream is
pulled northward. RAP model soundings are putting up massive CAPE
values in the southern half of the Nebraska Panhandle. By 21-00z the
estimated CAPE values are expected to be between 3500 to 4000 joules
with about 1500 joules available around 04z. DCAPE values is around
1000 to 1500 joules once again. The Hi-Res models are kind of
divided but presents two scenarios. The HRRR goes right through the
CWA with a cluster of storms moving northward placing thunderstorms
(possibly severe) right through Platte, Goshen, and Niobrara with
the Western most Panhandle counties also getting in the path before
spreading out to steam roll Sioux and Dawes county. The RRFS and NBM
(mpas edition) also depict this scenario. The Nam-Nest, FV3, and ARW
bring the storms further west and have the storms develop in Albany,
Carbon, and Converse county. Despite the NAM-Nest being one of the
better models during Monsoonal moisture events, the current
placement of the stream of moisture on Water Vapor better supports
the HRRR scenario making it the most likely scenario currently. The
newly created lake that resides in Alliance from the torrential
rainfall will also have more moisture at the surface that will be
available to lift than what the models are anticipating. SPC
currently has in a Marginal Risk today for Wind gusts up to 60 mph
and hail sized up to one inch. Don`t be surprised when 0615am MDT
rolls around and they put a Slight Risk over the Panhandle. Today
looks to be another 2.0 to 2.5 inch hail today as the UH tracks are
slightly more elongated than last nights depiction.

Monday will be interesting to say the least. So the upper level low
is expected to have flattened our ridge even more and be traveling
between Montana or into the Canadian Providences. This low
(depending on the track) may provide enough synoptic support to
produce light rain that pushes the through the Forecast area from
west to east. Then in the afternoon/ evening the trailing cold front
is expected to produce another phase of showers/storms. The question
will be does the cold front get hung up on our mountains and
pinwheels around the forecast area moving north to south now. Much
like a person walking from Carbon county stumbles in Albany and is
now falling towards Colorado. The other question is will we become
too cloudy from the first phase to really become unstable enough to
produce storms instead of a more steady light rain. If we don`t stay
clouded up then those areas with clear skies have a better chance of
seeing storms initiated by the trailing cold front. But if we stay
cloudy across the Forecast area then it will be more likely that
majority of the area sees more of steady rain, maybe some embedded
thunderstorms as opposed to seeing severe thunderstorms with clear
skies.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
Issued at 344 AM MDT Sun Sep 6 2026

In the long term the upper level low that was
responsible for our rainy weekend and start to the week starts to
push in the Great lakes region by Tuesday. Tuesday looks rather dry
as we enter a more zonal westerly flow aloft. This dry westerly flow
is expected to last until Thursday as agreed upon by the Global
models. However, they are still continuing to trend with another low
pressure system moving into the Pacific Northwest to give us another
possible Friday and last through the weekend. The models haven`t come
to an agreement on timing and intensity as it tracks through the
Intermountain West. So while we could still use the moisture for our
farms and reservoirs  The details of this system still remain
undecided.

&&

.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...MM
LONG TERM...MM
AVIATION...RV