Severe Thunderstorm Warning 87, NWS Cheyenne, WY

Area Forecast Discussion
National Weather Service Cheyenne WY
152 PM MDT Sat Jun 20 2026

.KEY MESSAGES...

- Scattered strong to severe thunderstorms are anticipated this
  afternoon and evening across much of the area.

- All severe weather hazards are possible today, but the
  greatest concern is the risk for large hail.

- Daily chances for showers and thunderstorms will continue
  through much of the week ahead with temperatures near average
  west of I-25, and cooler than average east of I-25.

&&

.SHORT TERM /THROUGH SUNDAY NIGHT/...
Issued at 150 PM MDT Sat Jun 20 2026

Active weather is on track to return to the area this afternoon.
GOES satellite imagery shows a potent upper level low over the
northern Rockies approaching the area today. A dry slot to it's
south is pushing into south central Wyoming at this time, while
plentiful moisture is entrenched over the High Plains. With a
surface high sitting over the northern Plains, south to southeast
flow dominates today, supporting the influx of low-level moisture.
Cloud cover has broken up west of a line from roughly Pine Bluffs to
Chadron, but low clouds remain fairly entrenched over the rest of
the Nebraska panhandle. Expect the cloud cover to continue to erode
this afternoon, but it may not totally clear out at all today. As a
result, the forecast temperature for portions of the Nebraska
panhandle was decreased considerably through the afternoon.

Looking towards the convective threat this afternoon, we will see
the dryline become better defined along the Laramie Range as drier
air mixes down to the surface in southern Carbon and Albany
counties. Ahead of the approaching shortwave trough, expect vertical
wind shear to increase as the day progresses, with strong synoptic
forcing for lift kicking up this afternoon as well. Potent
instability is already developing in southeast Wyoming, and this is
expected to grow in western Nebraska shortly. However, due to the
morning cloud cover, the capping inversion is still quite strong,
especially in Nebraska. West of the state line, CIN is expected to
break down by mid afternoon, but this may not occur at all to the
east. Normally this would prohibit thunderstorm development, but
today, the large scale ascent is substantial enough that we may be
able to sustain elevated convection overtop the low-level inversion.
MUCAPE is already pushing around 1000 to 2000 J/kg and progged to
climb towards 2000 to 3000 J/kg later this afternoon. So, we are
generally expecting surface based convection to develop around 1-2PM
along the Laramie Range (tied to the dryline), and then grow upscale
as they move eastward. Upon reaching the state line, storms will
either weaken as they lose surface instability, or they will be able
to tap into some elevated instability and maintain or strengthen.
It's difficult to say which storms will take which path at this
time, but expect to see a little of both occurring today. The
primary hazard will be large hail today, but all severe weather
hazards are possible. For Carbon, Albany, and Converse counties,
strong to damaging winds will be the primary concern, but isolated
hail will still be possible in these areas. Late this afternoon and
through the evening, east to southeast winds will increase, leading
to fairly potent low level shear over the High Plains. Even if
storms become elevated, this may allow for a few tornado spin-
ups, with the primary risk area remaining in far southeast
Wyoming and the southern Nebraska panhandle. Due to the strong
forcing, multiple rounds of thunderstorms will be possible.
While the primary window for severe weather is between 2PM and
10PM, a few storms may linger as late as 1AM. Due to these
expectations, a Tornado Watch has been issued for the southern
Nebraska panhandle, and a Severe Thunderstorm Watch has been
issued for remaining portions of the area.

Sunday will start off with a few areas of isolated fog across the
High Plains following the moisture return, but winds will turn
westerly shortly after sunrise following the passage of a surface
trough / weak cool front. Localized strong winds are possible (30%
chance) along the typical wind prone areas of I-80, with breezy
conditions anticipated elsewhere. Look for another round of
scattered afternoon showers and thunderstorms. A few storms will
have the potential to become strong to severe, but the risk will be
a bit lower thanks to vertically stacked winds.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
Issued at 150 PM MDT Sat Jun 20 2026

Monday into Tuesday, A low pressure system drops into
a the Northern Plains sending a frontal passage through our area.
This weak front will bring some cool air over the Intermountain West
keeping our temperatures mostly in the 70's for both days but some
isolated 80 temperatures will be possible as warm dry air starts to
also push in from the West. As more of the dry air begins to filter
in over night RH values West of I-25 will start to drop into the
teens while everything east will stay into the 30's and 40's. This
dry air will most likely follow the upper level ridge that sets up
on the West coast and slightly pushes east. The ridge does look to
compress on Thursday and Friday to allow for some continued chances
for rainfall as more troughs/system push into Pacific Northwest from
the Alaskan Bay. This active pattern could potential last through
the weekend if the ridge and dry airmass stay centered over the
southwestern part of the United States.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1152 AM MDT Sat Jun 20 2026

Low stratus is slowly lifting out of IFR and into MVFR range.
The plus side to this low stratus deck is that it may inhibit
severe convection this evening but we shall see. Today's severe
thunderstorm potential really lies over KCYS and the Nebraska
terminals. KLAR and KRWL may see some vicinity showers and
rumbles of thunder but that may be it as the models and dynamics
put the storm potential in the lower elevations today.

&&

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

&&

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

Special Weather Statement
National Weather Service Cheyenne WY
204 PM MDT Sat Jun 20 2026

WYZ104-109-202045-
Central Carbon County WY-Ferris/Seminoe/Shirley Mountains WY-
204 PM MDT Sat Jun 20 2026

...STRONG THUNDERSTORMS WILL IMPACT NORTH CENTRAL CARBON COUNTY
THROUGH 245 PM MDT...

At 204 PM MDT, Doppler radar was tracking a cluster of strong
thunderstorms 12 miles east of Lamont, or 28 miles north of Rawlins,
moving northeast at 35 mph.

HAZARD...Wind gusts of 50 to 55 mph and penny size hail.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects. Minor hail damage to vegetation is
         possible.

Locations impacted include...
Lamont, Seminoe Campground, Miracle Mile, Seminoe Dam, Kortes Dam,
Separation Lake, Dome Rock, Muddy Gap, and Seminoe State Park.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

A Severe Thunderstorm Watch remains in effect until 900 PM MDT for
south central Wyoming.

&&

LAT...LON 4243 10752 4244 10720 4243 10677 4202 10674
      4183 10715 4194 10750 4208 10751 4209 10753
TIME...MOT...LOC 2004Z 238DEG 32KT 4220 10723

MAX HAIL SIZE...0.75 IN
MAX WIND GUST...55 MPH

Natoli

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