931
FXUS65 KCYS 181141
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
540 AM MDT Fri Sep 18 2026

.KEY MESSAGES...

- Active with scattered to numerous showers and thunderstorms
  into the weekend. Strong to marginally severe thunderstorms
  may return to the area as a potent Pacific storm system moves
  into Wyoming Saturday and Saturday night.

- Friday will be the warmest day with low to middle 80s
  possible across the lower elevations.

- Active weather with cooler temperatures expected for much of
  the upcoming week.

&&

.SHORT TERM /THROUGH SATURDAY NIGHT/...
Issued at 200 AM MDT Fri Sep 18 2026

Current IR Satellite loop this morning shows the remnants of
the tropical disturbance over South Dakota and northern
Nebraska, producing moderate to heavy rainfall. In our area, we
got some heavy rainfall for portions of western Nebraska, but
nothing terribly widespread as many locations reported under
0.25 inches of liquid. Believe the thick cloud cover resulted in
a more stable environment compared to what models were showing.
The track of the tropical disturbance wasn`t favorable either,
with the best lift further north and east. Pretty quiet early
this morning with the rainfall finished until Friday afternoon.
Surface observations show areas of fog across the Nebraska
panhandle and east central Wyoming, which saw the best rainfall
amounts with this system. Visibilities generally range from one
quarter mile to 6 miles. May need a Dense Fog Advisory, but that
looks unlikely at this time with isolated and brief reports of
one quarter mile. Fog and low clouds are expected to lift after
900 am.

For the rest of today (Friday), all models show the slow moving
upper level trough, currently entering the western Great Basin
Region, slowly meandering eastward into Idaho and northern Utah
through this afternoon. Low to midlevel moisture expected to
remain in place over the area. Although NAEFS PWAT isn`t quite
as high as yesterday, it still shows 95th to 99th percentile
PWAT over most of the forecast area into this evening. A potent
midlevel shortwave is still expected to eject northeast ahead
of the main trough over the Front Range. With current IR
Satellite loop showing clearing skies across most of central
Wyoming and portions of eastern Wyoming this morning, expect
higher coverage of showers and thunderstorms with more
instability present due to the lack of morning cloud cover.
Western Nebraska will likely be fighting some CIN due to morning
low clouds and fog, but expect activity to push into the high
plains later in the day as the shortwave disturbance lifts
northeast. Heavy rainfall, gusty winds, and frequent lightning
possible with stronger thunderstorm activity through this
evening. Remnant showers are then expected after 1000 PM and
past midnight. Kept POP between 50 to 70 percent today through
late this evening, especially for southeast Wyoming and far
western Nebraska.

For Saturday, models show some drier air starting to sneak into
central Wyoming, with PWATs lowering to around 0.75 in the
afternoon. Further east, still expect PWATs close to 95th
percentile of climatology. Also, instability will be higher with
more jet dynamics as the main Pacific upper level trough moves
across Wyoming through the evening hours. Not only is another
round of showers and thunderstorms likely, expect a higher
chance for strong to marginally severe thunderstorms with 0-6 km
shear of 30 to 40 knots and MLCAPE around 1000 to 1500
j/kg...which is solid for this time of the year. Very heavy
rainfall, strong gusty winds, and even some hail possible
Saturday afternoon through Saturday night. Pretty good chance
for some nocturnal convection as the main trough axis moves into
the forecast area late Saturday evening. Increased POP between
60 to 90 percent, especially across the eastern high plains with
a good chance for widespread moderate rainfall. May see some
snowfall on the highest mountain peaks as 700mb temperatures
drop below 5c, but minimal accumulation is expected at this time.
After a pretty warm Friday, high temperatures will be closer to
average for mid September on Saturday with early afternoon
highs in the upper 60s to mid 70s.

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
Issued at 1251 AM MDT Fri Sep 18 2026

An upper-level low will move west to east across the CWA throughout
the day Sunday. The upper-level jet on the backside of this system
will strengthen Sunday evening into Sunday night as it dives
southeastward into the Central Plains. A slight intensification of
the 700mb winds will be possible during this time, though the 700mb
jet remains fairly weak. 700mb temperatures cool into the single
digits with this low, bringing in a nice cool down with high
temperatures in the 60s and 70s. The cold front will bring
widespread precipitation chances to the region as moisture will be
quite good with this system, with precipitable water values in the
90th percentile per NAEFS guidance. A cool, rainy day will certainly
start bringing the fall vibes back to southeast Wyoming and western
Nebraska. These fall vibes will continue for Monday as temperatures
remain quite cool behind the system. Additionally, winds will turn
easterly as a high strengthens over Iowa and Minnesota. Stout,
easterly flow will result in continued upslope develop throughout
the day Monday before winds turn back southerly for Tuesday.

Tuesday onwards, the upper-level pattern will remain quite
progressive with multiple systems moving through the region. Daily
precipitation chances will continue through much of the week.
Tuesday will start off a warming trend across the region, with highs
in the low- to upper-70s, followed by low-70s to low-80s Wednesday,
and mid-70s to mid-80s Thursday and Friday. Luckily, winds look to
remain fairly calm despite the systems moving through the region.
Most of the systems will be fairly weak, with limited 700mb jet
strength.

&&

.AVIATION /12Z TAFS THROUGH 12Z SATURDAY/...
Issued at 540 AM MDT Fri Sep 18 2026

A Pacific upper level trough will continue to move towards the
Front Range today and this weekend. Another round of showers
and thunderstorms will form between 18z and 21z across southeast
Wyoming, and push east across the high plains of western Nebraska
after 00z Saturday.

HAZARDS/WEATHER TRENDS: Areas of dense fog and LIFR conditions will
continue to impact the western Nebraska terminals until 15z, with
fog lifting/gradual clearing by 16z. Another line of showers and
thunderstorms will develop near KLAR and KCYS between 19z and 21z,
and push east into western Nebraska after 00z. Brief MVFR VIS is
possible as this line moves east and gradually weakens by 06z. Kept
PROB30 groups in the TAFs for now due to questionable impacts and
low confidence on coverage. Low clouds and some patchy fog may
redevelop after 06z for KCDR, KAIA, and KBFF late this evening.

&&

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

&&

$$

SHORT TERM...TJT
LONG TERM...AM
AVIATION...TJT