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FXUS65 KCYS 071130
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
530 AM MDT Mon Sep 7 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 308 AM MDT Mon Sep 7 2026

Today might be uneventful with some light rain showers. The upper
level low is taking its sweet time moving up and over our ridge and
the models may yet again be too progressive than what is actually
going to happen. The upper level low is pulling moisture and cloud
cover over the Intermountain west as it rotates through Idaho and
moves east-northeast into Montana and eventually the Canadian
providences. Following the upper level low is a trailing cold front
that is expected to push through this afternoon and evening. The
cloud cover will limit any severe thunderstorm for most of the area.
Through the holes in the cloud cover will provide some chances for
the region to destabilize. The RAP however only has a few hundred
joules of CAPE and its mainly over the Panhandle with Southeast
Wyoming effectively a dead zone as far as CAPE is concerned. Looking
at satellite, Cheyenne and Kimball county are effectively in a clear
slot with not very many clouds further south. As the Low slowly
lifts the Panhandle may be clear by the afternoon just like how
Cheyenne and Kimball county are clear right now. When the cold front
eventually pushes through our forecast area, depending on the
timing, we might get a sub-severe thunderstorm out in the Panhandle
or more of a stratiform rain if the sun is already down. The Storm
Prediction Center must have the same thoughts because almost all of
the forecast area is in a general thunder while the Marginal risk is
just outside Cheyenne county on both the south and east side.
Southeast Wyoming is looking at mostly stratiform rain today while
the Panhandle may have an isolated risk for thunderstorms this
evening. Another factor to this isolated to no risk of thunderstorm
is our downsloping winds today. As the upper level low gets closer
to us, the height/pressure gradient will tighten giving us some
downsloping dry winds. Our downsloping winds will probably mitigate
or cancel out the small feed of moisture also by the upper level
low. Afternoon RH values may reach into the low 20`s by 3-4pm today
in our northern counties and mid 20`s in the southern counties. SPC
fire has put an Elevated fire condition for us today because of the
breezier  downsloping winds.

If everything moves the way models are showing then Tuesday will be
breezy and dry. The Low pressure system is supposed to be pushing
into the Dakotas to set us up with our gusty but dry westerly flow.
The gradient will really be compressed as the low passes north and
east of us. The 700mb jet will set up to give us pretty gusty
downsloping winds. While the wont be our high winds by any means it
will still be rather windy with the RH dropping into the low teens
for a majority of the forecast area. Near critical to critical fire
conditions will be possible tomorrow. As the upper low moves into
the Great lakes region, a shortwave looks to push through our
forecast area that may trigger some weak showers in the overnight
period.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
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 /12Z TAFS THROUGH 12Z TUESDAY/...
Issued at 532 AM MDT Mon Sep 7 2026

Some early morning showers that are slowly weakening as the heat
Northeast from KCDR and KAIA. Winds are light now but around 17z
wind gusts are expected to hit around 20-30kts for the Wyoming
terminals and KCDR. A second set of showers is expected to roll
through from 23z to 05z today affecting KCYS and the Nebraska
Terminals. Slight chance for thunderstorms around KSNY and KAIA
starting at 23z and goes until 02z. Tuesday winds are mainly
going to breezy from the west but clearing skies in the morning.

&&

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

&&

$$

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