140
FXUS65 KCYS 280522
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1122 PM MDT Sun Sep 27 2026

.KEY MESSAGES...

- Unsettled weather returns to the area today, with chances for
  showers and thunderstorms this evening through at least
  Tuesday.

- A cooling trend begins Monday with near or slightly below
  average temperatures expected mid-week. Another warming trend
  will resume for the end of the week.

&&

.SHORT TERM /THROUGH TUESDAY/...
Issued at 220 PM MDT Sun Sep 27 2026

Most of our area is enjoying a pleasant day so far with temperatures
surging above seasonal averages for most of the area. A backdoor
surface front slowly moving into our High Plains zones from the
northeast has resulted in a stubborn low cloud deck pushing into the
northern Nebraska panhandle, and thus holding temperatures down in
the 60s. This airmass has plenty of moisture associated with it,
while the surface remains quite a bit drier southwest of the
boundary, which is parked somewhere around the North Platte River.
Meanwhile, GOES water vapor imagery shows a sprawling upper level
low moving into the Pacific coast, with southwest flow ahead pushing
abundant tropical moisture northward into our area. The approaching
trough will split in the coming days, with the northern shortwave
passing quickly to our north, while the southern shortwave closes
off and slowly migrates eastward. These features will keep unsettled
weather over the area for the next several days.

For this afternoon and evening, we can expect widely scattered
showers and isolated thunderstorms to kick up shortly, but coverage
looks fairly limited due to weak forcing. We have some minimal
instability west of the surface boundary, while those to the east
have a robust cap in place. Still, we can expect shower activity to
continue well into the evening and possibly into Monday morning. Due
to the influx of moisture, this activity will have the potential to
produce brief heavy downpours. In addition, the low-level jet will
kick up over the High Plains tonight with widespread gusty southerly
winds expected into Monday morning. This may be able to support
greater wind shear and thus an isolated strong to severe
thunderstorm overnight.

A cool front will very slowly move across the area Monday. Partial
sunshine in the morning will give way to a mostly cloudy afternoon.
As a result, expect temperatures to be cooler than today, but still
a touch above seasonal averages. Widely scattered shower activity
will be present even in the morning hours, but expect coverage to
increase after midday. A more potent surge of tropical moisture will
push in along with more organized forcing in the form of potent
positive mid-level theta-e advection ahead of the closed low in the
desert southwest. PoPs remain in the 30-60% range Monday and Monday
night, with scattered to possibly numerous showers and isolated
thunderstorms expected. If we can get enough sunshine Monday morning
to destabilize, there may be potential for a storm or two to become
strong to severe, but confidence is low. Shower activity will once
again continue all through the night as the surface front moves
through. Tuesday will be cooler, with thick cloud cover in the
southern part of the area, while sunshine works in north of Rawlins
to Chadron. While global models remain unimpressive with any
precipitation potential into Tuesday, a few Hi-res models
(particularly the HRRR) continue to show fairly widespread shower
activity continuing into Tuesday. This appears to be driven by
northeast upslope / isentropic ascent winds below 600-mb, but
this signal appears highly disorganized, and thus low
confidence.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
Issued at 220 PM MDT Sun Sep 27 2026

Tuesday night through the end of the work week could see a few
areas of showers trying to lift up into the region, but this
remains largely uncertain and low confidence as models remain
split on the evolution of low pressure to our south and how far
north moisture can make it. While some ensembles have begun to
push the low and moisture associated with what will be the
remnants of Hurricane Polo further northwards compared to the
last few runs, overall this system still looks to be too far
south to bring any further appreciable moisture to our area
beyond Tuesday outside of maybe our farthest southeast zones,
primarily Cheyenne County in the Nebraska Panhandle. The NBM
continues to keep us high dry as well, with the above scenario
remaining in the grids as of this writing. Still through
Thursday POP chances aren`t completely zero, but outside of the
I-80 corridor and southward it`s not looking favorable for any
meaningful moisture in the long term. Otherwise we`ll see a very
slight warming trend on Wednesday, with temperatures warming a
few degrees with widespread 60`s and a few 70`s expected, but a
second cold airmass should drop us right back down into the
widespread 60`s on Thursday. Friday and Saturday high pressure
over the southwestern US will allow for a warming and drying
trend, returning us to several degrees above normal with highs
in the 70`s across the region. Sunday flow turns more
northwesterly and a glancing upper level trough will help push a
weak cold front into the region, bringing temperatures back
down to near normal, but a lack of notable moisture will keep
our precipitation chances almost nil and provide little more
than a brief cool down to end the long term forecast.

&&

.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 1122 PM MDT Sun Sep 27 2026

A tricky forecast for this period as showers and storms will lift
across the region through the overnight hours and again by Monday
afternoon, with chances for all terminals. Any storms could bring
locally lowered VIS along with gusty and erratic winds. CIGs will
generally be mid-level as precipitation moves in, but will lower
tonight into Monday morning as an influx of moisture overspreads the
region. Low CIGs and VIS continues to plague KCDR, conditions should
improve through the nighttime hours as winds increase from the
south, look for AMDs in the TAF.

&&

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

&&

$$

SHORT TERM...MN
LONG TERM...CG
AVIATION...RZ