Flash Flood Warning 26, NWS Cheyenne, WY

Area Forecast Discussion
National Weather Service Cheyenne WY
601 PM MDT Sat Sep 5 2026

.KEY MESSAGES...

- Chances for afternoon and evening thunderstorms continue until
  mid week. Strong gusty winds and brief heavy rainfall are the
  primary threats.

- A temporary drying trend begins Mid-week and possibly
  continues through the end of next week.

&&

.SHORT TERM /THROUGH MONDAY/...
Issued at 235 PM MDT Sat Sep 5 2026

Not too many changes to the previous forecast package with
shower and thunderstorms, some strong with heavy rainfall,
remaining the primary concern today. Overall, strong upper
level ridge axis is forecast to remain across the central Great
Plains for much of the weekend. Fall-like upper level trough
will meander its way across the Pacific NW coastline and move
inland on Sunday. Ahead of this trough, some shortwave energy
will eject northeast over Colorado and Wyoming along with a 100
knot jet max nudging east into the northern Front Range Sunday
night and Monday. Generally expect a slow cooling trend Sunday
and Monday as some cooler air makes its way into Central
Wyoming. Further east, surface winds are expected to shift into
the east or southeast, resulting in some upslope flow and minor
cooling over mainly southeast Wyoming.

Shallow convection from this morning has lifted northeast of the
area and dissipated. However, radar loop shows activity starting
to fire up again over the northern and central Nebraska
panhandle early this afternoon. Expect this trend to continue
through late this evening as coverage is likely going to
increase across the entire Nebraska Panhandle. Convective
parameters look favorable for scattered to numerous showers and
thunderstorms, which may linger past midnight across portions of
the southern panhandle. Meso Analysis shows MLCAPE of 1000 to
2000 j/kg (slightly higher SB) over mostly western Nebraska,
with values increasing a bit more through the afternoon as we
near the peak heating of the day. Severe thunderstorm potential
looks limited today, but can't rule out a few marginally severe
multicell clusters developing into this evening. Main limiting
factor is shear with 0-6km and overall effective shear around 20
to 25 knots, maybe up to 30 knots. Hodographs are fairly
straight, with some curvature across the southern Panhandle this
evening. Generally expect some very heavy rainfall with gusty
winds as high res guidance shows clusters of thunderstorms
forming and then building upshear into this evening. Can't
totally rule out some hail producers (including large hail) in
this area, but its not the most favorable environment this time
of the year. There is some considerable concern for some areal
flooding or localized flash flooding. Area of concern is not
generally known for flash flooding issues however. Kept POP
above 35 percent through midnight for Alliance, Sidney, and
Kimball Nebraska.

Another warm day for Sunday, but not quite as warm as guidance
suggests due to east to southeast upslope winds across the
plains. Similar weather pattern during the day with even higher
dewpoints due to some low level moisture advection. Model
soundings show some lingering CIN in the low to midlevels on
Sunday, likely due to the nocturnal convection early Sunday
morning. Upper level shortwave/vort max is not as strong as
today's forcing and arrives a bit later in the day, so expect
more isolated coverage of thunderstorms. Shear looks even more
marginal with around 20 knots of Bulk Shear by mid to late
afternoon. A few strong thunderstorms are possible, but having a
hard time with the severe potential with such limited 0-6 km
shear. Further west, may say some gusty winds associated with
shower and isolated thunderstorm activity as the leading edge of
the Pacific cold front and jet max aloft moves into central
Wyoming by late Sunday evening. Increased POP across the whole
area, but mainly for later in the day (after 6 PM) due to the
better forcing.

Drier air forecast to push into the area on Monday behind the
front with some cooler air. Expect a lower coverage of
thunderstorms, mainly located south along the I-80 corridor and
the mountains. High temperatures in the mid 70s to mid 80s are
expected for most of southeast Wyoming, with highs in the low
90s for western Nebraska. It will be windy during the day with
southwest winds between 25 to 35 MPH with gusts around 45 MPH
likely along and west of Interstate 25.

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
Issued at 200 PM MDT Sat Sep 5 2026

The very persistent low pressure system loitering in the Pacific
Northwest will finally be ejecting eastward on Monday and Tuesday.
The models are trending towards a slightly more eastward and
amplified evolution of this low's passage, possibly influenced by a
stronger shortwave just ahead of it. Moisture content ahead of this
system seems to be on track with previous forecasts. PWAT values are
running about 2 to 3 standard deviations above climatology. The few
CAMs that go out to Monday evening do not show much in the way of
rainfall with most of the synoptic forcing staying well north of the
area. Regardless a few showers and storms from the afternoon will
linger through the early evening. Tuesday the western most lobe of
the upper level system will swing southeast to pass just north of
our area. With it a weak cold front will pass through. There is
enough moisture ahead of the front that a few storms are possible,
particularly for the southern NE Panhandle areas. No severe weather
is anticipated at this time for this round of storms before they
depart to our east. The front should cut afternoon highs by about 5
degrees, so that is nice. What isn't nice are the low humidity and
gusty winds behind it which could elevate fire weather conditions.

Post cold front Wednesday is also slightly cooler and drier.
The ridge that has been patiently waiting for its chance to
build back west will do so by Thursday. Downsloping flow from
the Intermountain West will act to heat us back up and keep us
dry. Continued gusty winds does mean fire weather will be the
topic of upcoming forecast. The type of pattern will continue
until our next Pacific upper level system arrives in the very
long term, hopefully with more rain.

&&

.AVIATION /00Z TAFS THROUGH 00Z MONDAY/...
Issued at 601 PM MDT Sat Sep 5 2026

Overall looking at an active evening for terminals east of the
Laramie Range. Hi-Res models show thunderstorms continuing
through the evening, with heavy rain, strong winds and large
hail the primary concerns. Heavy rain will cause visibility
drops down to IFR criteria. The storm threat will continue
through about 06Z. Terminals west of the Laramie Range will
likely see a quieter evening and overnight.

&&

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

&&

SHORT TERM...TJT
LONG TERM...RV
AVIATION...SF

Preliminary Local Storm Report
National Weather Service Cheyenne WY
529 PM MDT Sat Sep 5 2026

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0527 PM     Hail             9 SSW Alliance          41.98N 102.94W
09/05/2026  M1.00 Inch       Morrill            NE   Trained Spotter

            Trained Spotter reported 1 inch hail along
            Highway 385, 9 miles SSW of Alliance.

&&

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Preliminary Local Storm Report
National Weather Service Cheyenne WY
558 PM MDT Sat Sep 5 2026

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0548 PM     Flash Flood      Alliance                42.10N 102.87W
09/05/2026                   Box Butte          NE   Law Enforcement

            Alliance Police Department send out a
            statement saying residents are "urged to
            stop driving around town and remain where
            they are unless travel is absolutely
            necessary." This is in reference to the
            flash flooding ongoing around town.

&&

Preliminary Local Storm Report
National Weather Service Cheyenne WY
603 PM MDT Sat Sep 5 2026

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0601 PM     Hail             1 ENE Minatare          41.82N 103.48W
09/05/2026  M1.75 Inch       Scotts Bluff       NE   Trained Spotter

            Trained Spotter reporting golf ball sized
            hail falling east of Minatare at the time of
            the report.

&&

Preliminary Local Storm Report
National Weather Service Cheyenne WY
609 PM MDT Sat Sep 5 2026

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0608 PM     Hail             3.5 E Minatare          41.81N 103.43W
09/05/2026  M1.25 Inch       Scotts Bluff       NE   Trained Spotter

            Trained spotter reported half dollar sized
            hail falling east of Minatare.

&&