024
FXUS65 KCYS 132041
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
241 PM MDT Sun Sep 13 2026

.KEY MESSAGES...

- Temperatures warm on today and Monday with increasing
  precipitation chances.

- Severe weather chances return on today, with Monday seeing a
  potential critical fire weather environment alongside high
  winds.

- Much cooler on Tuesday with temperatures a few degrees warmer
  through the end of next week and daily chances of showers and
  thunderstorms.

&&

.SHORT TERM /THROUGH TUESDAY/...
Issued at 240 PM MDT Sun Sep 13 2026

Scattered thunderstorms are in store this afternoon through the
overnight hours as another shortwave passes through our neck of the
woods. Some strong to possibly severe thunderstorms could develop in
the late afternoon as a surface low moves northeast through our
forecast area. CAPE values look to be between 500 to 1,000 joules
with couple potential pockets of 2,000 joules as depicted by the RAP
between 3 to 7pm. The synoptic forcing of the surface low should
sustain the showers and thunderstorms through the evening. However,
in the morning we have a substantial cap to erode away in the
morning and afternoon before any strong to severe thunderstorms
could develop. It will be a little tough too since the forecasted
convective temperature is in the mid 80`s and the forecasted high
temperature are either at or below the convective temperatures. Most
of the area is still capped with the exception of Niobrara county
according to the latest RAP mesoanalysis. Most of the hi-res models
continue to show initiation around 20/21z with true scattered
thunderstorm coverage by 00z. Synoptic winds will start to pick up
this evening as the Upper level low moves into eastern Montana and
Western North Dakota. A high wind watch and a Red flag Warning go
into effect Monday afternoon as the pressure gradient tightens and
the upper level low drags drier air across Southeast Wyoming. RH
values are expected to drop into the teens as the 700mb flow starts
to reach 50-55 knots by mid morning. Most likely winds will be
westerly 20 knots gusting 45 knots but 53 knots or 60 mph wind gusts
will be possible in our wind prone areas however, not quite sure how
much of that jet will mix down hence why it was kept as a high wind
watch.  In-house random forest model guidance has kept its 30 to 40%
chance for elevated to high winds at Arlington, Rawlins, Bordeaux,
Coleman, and northern Carbon County. With these increased westerly
downsloping winds on Monday, high temperatures were raised higher
that what was being depicted by the global ensembles and the NBM.
Elevated downsloping winds are going to warm us up rather quickly
and may negate the effects of the colder airmass being pulled into
the Intermountain West behind the cold front.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
Issued at 240 PM MDT Sun Sep 13 2026

Tuesday and into the weekend, the upper level low
keeps migrating east into the Great Lakes and Hudson Bay region. The
counter clockwise circulation will begin filtering cold air from the
Arctic into the region undergoing some warming/modification as it
pushes south over us. 700mb temperatures will drop between 8 and 12C
translating daily surface temperatures into the cooler 60`s and
70`s and overnight temperatures into the 40`s and 50`s. Daily
rainfall chances start to occur Wednesday as a train of Low
pressure system system are expected to travel through the
Pacific Northwest over the next 7 days. This precession of low
pressure systems will push the ridge eastward into the central
and southern plains leaving the intermountain west susceptible
to multiple accompanied shortwaves but ahead and following each
progged low pressure system.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 240 PM MDT Sun Sep 13 2026

Scattered showers to possibly severe thunderstorms are expected
to start really evolving after 21z and looks to start affecting
terminals around 21z. These thunderstorms will start to decrease
in intensity around 03z with only a couple waves of scattered
showers around 06z. Some model guidance has the showers
persisting overnight and continuing into tomorrow morning. The
only terminals not really favored to be affected by the
thunderstorms looks to be KRWL and KSNY. However, if the showers
persist through the night then KSNY may see some rainfall
tomorrow morning. Model guidance has also hinted at low stratus
setting up across the Nebraska Panhandle tomorrow morning much
like Alliance airport today. MVFR ceilings were currently kept
into the TAF but IFR ceilings between 500 and 1,000 ft could be
possible.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Red Flag Warning from noon to 8 PM MDT Monday for WYZ417>423-
     427-432-433.
     High Wind Watch from Monday morning through Monday afternoon
     for WYZ106-109-110.
NE...None.

&&

$$

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