Severe Thunderstorm Warning 112, NWS Denver/Boulder, CO

Area Forecast Discussion
National Weather Service Denver/Boulder CO
559 PM MDT Sun Jun 21 2026

.KEY MESSAGES...

- Strong to severe storms possible across the far eastern plains
  today with large hail, gusty winds, and brief landspouts.

- Increasing coverage of afternoon thunderstorms early to mid
  week, with continued potential for severe thunderstorms,
  especially in the plains.

- Smoke aloft from the wildfires in Utah will bring intermittent
  hazy skies.

- Elevated fire weather conditions will persist through much of
  the week in the high country.

&&

.DISCUSSION /Through Sunday/...
Issued at 231 PM MDT Sun Jun 21 2026

A weak shortwave will graze northeast Colorado this afternoon,
bringing the potential for scattered showers and thunderstorm
activity. Current radar imagery shows showers and strong
thunderstorms starting to develop over eastern Colorado where SBCAPE
values are already in the 1000-2000 J/kg range. Dewpoint values over
the Denver area have plummeted from the mid 50s to the mid 30s due
to the mixing of drier dewpoints aloft. Therefore, the better
surface moisture for today's convective potential will be over the
easternmost counties of our CWA, where a Severe Thunderstorm Watch
is in effect until 8pm. Modest shear (30-40KT 0-6km) and steep mid-
level lapse rates will be conducive to a few strong supercells that
could produce very large hail, gusty winds, and brief landspouts.

There will be daily chances for severe thunderstorms through at
least Thursday this week, given the generally weak and zonal flow
aloft combined with low-level moisture advection from the southeast.
However, tomorrow looks to be the best chance for a more widespread
thunderstorm threat due to the better shear in place as well as 0-
3km SRH values in the 100-300 m^2/s^2 range over the northeastern CO
plains. Additionally, precipitable water values east of the
mountains will exceed the 75th percentile of climatology, with
values exceeding the 90th percentile at times (0.80"-1.00"). Large
hail, gusty winds, and landspouts will be possible again with any
strong thunderstorms that develop tomorrow afternoon and early
evening.

A cold front will advance through the region early Tuesday morning,
keeping afternoon temperatures in the low 80s for the lower
elevations. Isolated showers and thunderstorms will be possible
Tuesday afternoon if any low stratus behind the front are able to
clear off early enough for convective initiation to occur.

Long-range ensembles indicate a warming and drying trend arriving
late this week. While it is too early to tell with certainty,
widespread elevated to critical fire weather conditions appear to
return on Saturday as RHs drop into the teens and the pressure
gradient tightens due to a closed upper level low sliding through
the Pacific Northwest.

&&

.AVIATION /00Z TAFS through 00Z Tuesday/...
Issued at 555 PM MDT Sun Jun 21 2026

The current radar as of 1750z shows an outflow boundary located
just to the east of the KDEN property moving to the west. This
boundary will likely cause erratic and gusty winds over the next
few hours at KDEN with gusts of 25 to 30 kts possible.
Additionally, isolated thunderstorms have been firing off to the
east of this boundary for the last hour or two. Thunderstorms
remain possible in the vicinity of all three sites, particularly
KAPA and KDEN, until about 02z tonight.

Winds should then settle down some and stay in a more NNE/NE
direction before turning to near drainage early tomorrow morning.
The NE winds could bring in some lower clouds to about 5000 feet
(possible IFR to MVFR conditions) with even the possibility for
some briefly patchy fog. Wildfire smoke could also return tomorrow
morning between 06z and 12z as well as tomorrow evening after
00z, potentially impacting slantwise visibility at times, but
currently looks to have minimal near surface impacts.
Additionally, a cyclone could form early tomorrow morning, but
confidence is low on this solution at this time.

Tomorrow afternoon should be similar to this afternoon with
strong NW winds gusting to about 20 kts by about 18z to 19z. A
boundary along the Palmer Divide will be the initial focus for
thunderstorm development before spreading northward later in the
afternoon. There is now enough confidence to include VCTS at all
three sites with a prob30 for -tsra and some stronger wind gusts
at KDEN and KAPA for most of tomorrow afternoon. The showers and
thunderstorms should likely clear to the east of the sites by
about 00z tomorrow evening with strong winds still in place for at
least a few hours.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
None.

&&

DISCUSSION...AA
AVIATION...MV

Special Weather Statement
National Weather Service Denver CO
546 PM MDT Sun Jun 21 2026

COZ045-220030-
Central and East Adams and Arapahoe Counties CO-
546 PM MDT Sun Jun 21 2026

...A STRONG THUNDERSTORM WILL IMPACT ARAPAHOE AND SOUTHEASTERN ADAMS
COUNTIES UNTIL 630 PM MDT...

At 546 PM MDT, Doppler radar was tracking a strong thunderstorm near
Deer Trail, or 33 miles northwest of Limon, moving east at 20 mph.

HAZARD...Wind gusts up to 50 mph and nickel size hail.

SOURCE...Radar indicated.

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

Locations impacted include...
  Deer Trail.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Monitor the weather situation closely and be alert for threatening
weather conditions.

&&

LAT...LON 3958 10415 3975 10410 3972 10381 3957 10388
      3957 10406
TIME...MOT...LOC 2346Z 286DEG 15KT 3965 10406

MAX HAIL SIZE...0.88 IN
MAX WIND GUST...50 MPH

63

Special Weather Statement
National Weather Service Denver CO
622 PM MDT Sun Jun 21 2026

COZ044-048-049-220100-
Washington County CO-Logan County CO-Morgan County CO-
622 PM MDT Sun Jun 21 2026

...A STRONG THUNDERSTORM WILL IMPACT NORTHEASTERN MORGAN...
SOUTHWESTERN LOGAN AND NORTH CENTRAL WASHINGTON COUNTIES UNTIL 7 PM
MDT...

At 622 PM MDT, Doppler radar was tracking a strong thunderstorm 7
miles north of Hillrose, or 17 miles northeast of Fort Morgan, moving
east at 20 mph.

HAZARD...Wind gusts up to 50 mph and nickel size hail.

SOURCE...Radar indicated.

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

Locations impacted include...
  Merino, Hillrose, Prewitt Reservoir, Snyder, Messex, Union and
  Fremont Butte.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Monitor the weather situation closely and be alert for threatening
weather conditions.

&&

LAT...LON 4033 10374 4052 10365 4052 10358 4054 10358
      4047 10314 4022 10325
TIME...MOT...LOC 0022Z 283DEG 18KT 4043 10355

MAX HAIL SIZE...0.88 IN
MAX WIND GUST...50 MPH

63

Special Weather Statement
National Weather Service Denver CO
703 PM MDT Sun Jun 21 2026

COZ048-049-220130-
Washington County CO-Logan County CO-
703 PM MDT Sun Jun 21 2026

...A STRONG THUNDERSTORM WILL IMPACT SOUTHEASTERN LOGAN AND
NORTHEASTERN WASHINGTON COUNTIES UNTIL 730 PM MDT...

At 703 PM MDT, Doppler radar was tracking a strong thunderstorm 8
miles southeast of Sterling, moving east at 25 mph.

HAZARD...Wind gusts up to 50 mph and nickel size hail.

SOURCE...Radar indicated.

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

Locations impacted include...
  Eastern Sterling, Burdett, St Petersburg, Lone Star and Reiradon
  Hill.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Monitor the weather situation closely and be alert for threatening
weather conditions.

&&

LAT...LON 4038 10324 4064 10319 4062 10275 4044 10277
      4044 10278 4035 10278 4035 10279 4032 10279
TIME...MOT...LOC 0103Z 279DEG 22KT 4052 10310

MAX HAIL SIZE...0.88 IN
MAX WIND GUST...50 MPH

63

Preliminary Local Storm Report
National Weather Service Denver CO
731 PM MDT Sun Jun 21 2026

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

0730 PM     Hail             5 SSE Reiradon Hill     40.51N 102.99W
06/21/2026  E1.00 Inch       Logan              CO   Trained Spotter

&&

KEB

Preliminary Local Storm Report
National Weather Service Denver CO
736 PM MDT Sun Jun 21 2026

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

0730 PM     Hail             4 SE Reiradon Hill      40.53N 102.99W
06/21/2026  M1.75 Inch       Logan              CO   Trained Spotter

&&

KEB

Preliminary Local Storm Report
National Weather Service Denver CO
804 PM MDT Sun Jun 21 2026

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

0743 PM     Hail             1 SW St Petersburg      40.54N 102.84W
06/21/2026  E2.75 Inch       Logan              CO   Trained Spotter

&&

KEB