FXUS65 KCYS 202113

AFDCYS



Area Forecast Discussion

National Weather Service Cheyenne WY

313 PM MDT Sun Sep 20 2026



.KEY MESSAGES...



- Much cooler temperatures expected on Today and Monday behind 

  a strong cold front.



- Strong winds will be possible Tuesday night into Wednesday

  morning across the western Nebraska Panhandle with a stout

  low-level jet expected to develop.



&&



.SHORT TERM /THROUGH MONDAY NIGHT/...

Issued at 257 PM MDT Sun Sep 20 2026



Today will be the last day of consistently stormy weather across the 

area as the low pressure center spins over Casper, WY. Storms are 

already ongoing, thanks to the low pressure system pulling moist, 

southerly flow into the mid-levels out ahead of it. With cooler 

temperatures being observed today, that atmosphere is more stable, 

making strong to severe storms less likely later today. Hi-Res 

guidance still shows the potential for an isolated strong storm

or two, but model soundings from the GFS show an environment 

with only about 500 to 700 J/kg of MUCAPE. This is enough 

instability to get thunderstorms, but not strong ones. Showers 

and storms will continue into the evening hours for locations in

the Nebraska panhandle as the low pressure system slowly spins 

eastward into South Dakota. Once the system makes it east of the

CWA, wrap around moisture could produce a few light showers 

overnight in the vicinity of the Pine Ridge from Lusk to 

Chadron.



As the trough/low pressure system moves eastward into the center of 

the country, shallow ridging will begin to build into the Rockies. 

As a result, temperatures on Monday will be a few degrees warmer 

compared to Sunday, but still cooler than average for this time of 

year. The ridge will also help clear clouds out of the area, lead to 

a partly to mostly sunny day across the forecast area. Precipitation 

chances are not anticipated, however, a few lingering showers will 

still be possible in the Pine Ridge area from the low pressure 

system moving out. Overnight, winds will turn southeasterly, 

ushering in low-level moisture with fog and low stratus potential in 

the Nebraska panhandle.



&&



.LONG TERM /TUESDAY THROUGH SATURDAY/...

Issued at 257 PM MDT Sun Sep 20 2026



By Tuesday morning, there's is an area of high 

pressure that begins to form over the Great Lakes region as our 

former low pressure system enters the Northern plains causing a 

traffic jam over the east coast. This becomes our problem as the 

ridge builds over us it blocks the weak low pressure system off the 

west coast. Multiple shortwaves will be pushing through the 

Intermountain west with the first one starting late Tuesday evening 

through Wednesday morning for possible light rain showers. With the 

later timing off this wave its going to be hard to maintain higher 

energy levels needed for severe thunderstorms as the sun angle is 

slowly starting to decline. Wednesday afternoon through Thursday 

evening looks pretty dry as the Intermountain maintains southwest 

flow on the front edge of the ridge advecting in the dry airmass of 

the desert southwest. Thursday night into Friday morning another Low 

pressure system is progged to push into the Pacific Northwest to 

cause some light rain showers to possibly occur Friday. Daily high 

temperatures will fluctuate as 700mb temperatures bounce between 6 

and 12 degrees C. So on our dry days expect temperatures to range 

between the 70's and low 80's to 60/70's on our rainy days. 

Overnight temperatures will remain relatively stable with the 

overnight lows to remain in the 40's to with some areas reaching the 

low 50's. This weekend is starting to trend warmer and drier with 

the global models wanting to amplify the ridging pattern over us 

shifting the potential Low pressure system from Friday further north 

into the Canadian Provinces.



&&



.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...

Issued at 1150 AM MDT Sun Sep 20 2026



The upper level low is pretty much over Casper right now. This

low is slowly pushing east but as this thing rotates expect on

and off showers through the Panhandle through 04z for KCDR and

00z for everyone else. However, for the Southeast Wyoming

terminals showers are going to be pretty much done by 19z with a

brief shower possible until 21z just to account for any stray

pop up shower that forms and dies as the low is also rotating.

Also if didnt predict this as well, winds will also be variable

around 10kts with the afternoon gust after this low departs our

area. Some low stratus may also develop again for the Panhandle

at around 12-15z tomorrow morning but should really start to

burnoff by the afternoon.



&&



.CYS WATCHES/WARNINGS/ADVISORIES...

WY...None.

NE...None.



&&



$$



SHORT TERM...SF

LONG TERM...MM

AVIATION...MM