Severe Thunderstorm Warning 115, 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

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

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

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

0835 PM     Hail             3 ENE Highland Center   40.55N 102.52W
06/21/2026  M2.00 Inch       Phillips           CO   Storm Chaser

&&

KEB

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