University Of Wyoming, Wyoming Weather Forecast Discussion

984
FXUS65 KCYS 132342
AFDCYS
Area Forecast Discussion
National Weather Service Cheyenne WY
542 PM MDT Sat Sep 13 2025
.KEY MESSAGES...
- Widespread rainfall and scattered thunderstorms for most of
  southeast Wyoming and western Nebraska Saturday afternoon
  through Sunday. A few strong thunderstorms possible across
  western Nebraska.
- Rainfall changing to snow above 10000 feet Saturday night.
  Snow accumulations up to 3 inches for the higher mountains of
  southeast Wyoming.
&&
.SHORT TERM /THROUGH SUNDAY NIGHT/...
Issued at 400 PM MDT Sat Sep 13 2025
Unsettled weather continues across the area this afternoon as the
upper level low over the Four Corners region slowly lifts off to the
northeast. The environment over most of the area is fairly marginal
for strong to severe thunderstorms, but the central/southern
Nebraska panhandle will need to be monitored. There, we have MLCAPE
approaching 1000 J/kg with around 30 knots of effective bulk shear.
This area has the best potential for a few isolated strong to severe
thunderstorms capable of producing large hail and strong winds.
Elsewhere, weaker instability and marginal shear in the place of
fairly strong forcing suggest widespread showers with scattered
(mainly sub-severe) thunderstorms. These area already expanding
across southeast Wyoming, and will continue to spread to the
northeast through the rest of the afternoon and evening hours.
Locally heavy rainfall, gusty winds, and small hail will be possible
in these areas, but lightning is probably the primary hazard.
Look for a messy synoptic setup overnight as the upper level low
moves across the area. Forecasts show a highly disorganized wind
field aloft, with a decent surface low trying to develop
underneath over our High Plains areas. Cyclogenesis over the
area generally means a fairly low confidence forecast as the
complex and fine scale dynamics can be difficult to pin down.
Most of the area should see thunder becoming more limited after
about 9PM, transitioning to more stratiform rainfall. However,
elevated instability will remain present over the Nebraska
panhandle, and we could see embedded thunder all through the
night there, most likely around the Chadron to Alliance area.
There is quite a bit of uncertainty regarding the coverage and
location of the overnight shower activity. Some models show a
weak signature loosely resembling a TROWAL developing over
southeast Wyoming and then moving into the Nebraska panhandle
Sunday morning. This would keep light to moderate rainfall (with
isolated heavier rainfall in cores that tap into the limited
instability remaining) going across much of the Nebraska
panhandle and southeast Wyoming along and south of the I-80
corridor. If this doesn`t materialize though, we may see much
more limited rainfall overnight into Sunday morning. PoPs were
dropped slightly with this update, mainly in Converse,
Niobrara, Goshen, and Sioux counties where there is lower
confidence in forcing supporting rainfall. Snow levels will also
be dropping down to around 10 kft tonight, which means that the
highest peaks of southeast Wyoming can expect to see some light
snowfall.
Heading into Sunday, look for chillier temperatures and breezy
northwest flow as the storm system departs. Scattered showers will
likely be lingering around the Nebraska panhandle in the morning.
Limited instability returning for Sunday afternoon may produce some
isolated showers and thunderstorms in the afternoon, but this is
expected to be fairly limited.
&&
.LONG TERM /MONDAY THROUGH SATURDAY/...
Issued at 400 PM MDT Sat Sep 13 2025
Monday...The next shortwave trough aloft moves into western Wyoming,
and with adequate low and mid level moisture, we expect to see
isolated to widely scattered afternoon and evening showers and
thunderstorms. It will be warmer based on the 700 mb temperatures.
Tuesday...The shortwave trough aloft moves overhead near peak
heating, sparking scattered showers and thunderstorms in the
afternoon and evening. Somewhat cooler in the wake of a cold front
and with more cloud cover and precipitation coverage.
Wednesday...The next shortwave trough aloft moves across Wyoming,
with somewhat drier air advecting in, thus only isolated afternoon
showers and thunderstorms are expected.
Thursday...Northwest flow aloft develops, with drier air moving in
at low and mid levels, producing a drier day. 700 mb temperatures
near 10 Celsius will produce a warmer day.
Friday...A slow warming trend continues as the ridge aloft moves
overhead, and the atmosphere remains relatively dry. 700 mb
temperatures rise to near 11 Celsius.
Saturday...Slightly cooler again as the next progressive shortwave
trough aloft passes overhead, along with a weak cold frontal
passage. Looks like enough low and mid level moisture to produce
isolated to scattered late day showers and thunderstorms.
&&
.AVIATION /00Z TAFS THROUGH 00Z MONDAY/...
Issued at 529 PM MDT Sat Sep 13 2025
A weather disturbance will move into northern Colorado
overnight, then to the western high plains on Sunday. Expect
scattered to numerous showers and some thunderstorms overnight
tonight.
Wyoming TAFS...Scattered to broken clouds from 4000 to
10000 feet will occur. Occasional thunderstorms will prevail at
Laramie and Cheyenne until 02Z, producing wind gusts to
35 knots, and visibilities to 3 to 4 miles. Showers will be in
the vicinity of the terminals until 15Z Sunday, with periods of
light rain at Laramie from 08Z to 14Z, reducing visibilities to
6 miles. Outside of thunderstorms, winds will gust to 25 knots
at the terminals after 11Z Sunday.
Nebraska TAFS...Ceilings will range from 4000 to 10000 feet.
Occasional thunderstorms will occur at Scottsbluff and Sidney
until 04Z, producing wind gusts to 35 knots and visibilities to
3 to 4 miles. Periods of showers will occur at Chadron and
Alliance from 07Z to 18Z, reducing visibilities to 5 miles.
Outside of thunderstorms, winds will gust to 23 knots at the
terminals after 14Z Sunday.
&&
.CYS WATCHES/WARNINGS/ADVISORIES...
WY...None.
NE...None.
&&
$$
SHORT TERM...MN
LONG TERM...RUBIN
AVIATION...RUBIN

NWS CYS Office Area Forecast Discussion