Severe Thunderstorm Warning 166, NWS Denver/Boulder, CO

Area Forecast Discussion
National Weather Service Denver/Boulder CO
250 PM MDT Wed Jun 24 2026

.KEY MESSAGES...

- Numerous strong to severe thunderstorms expected today for the
  lower elevations, particularly late afternoon through tonight.
  Strongest storms may produce very large hail exceeding 2-3" in
  diameter.

- Additional round of strong to severe thunderstorms possible Thursday.
  Localized flash flood concerns will exist both Wednesday and
  Thursday.

- Critical fire weather conditions this afternoon in the mountains
  given warm, dry and breezy weather and the potential for
  isolated dry thunderstorms. Notably higher fire danger will
  develop this weekend as hotter and windier weather returns.

&&

.DISCUSSION /Through Wednesday/...
Issued at 147 PM MDT Wed Jun 24 2026

A rather conditional severe weather threat still exists across
most of the I-25 corridor and eastern plains this afternoon.

A broad belt of westerly/west-northwesterly flow aloft is evident
via GOES water vapor imagery and recent RAP analysis data.
Meanwhile, a well-defined surface boundary stretching from KAPA
through KDEN and into southeastern Weld County. While this
boundary has produced more of a shear zone than a true convergence
zone, there's been plenty of differential heating along the
boundary. With the DEN ASOS on the "warm" side of the boundary,
we've seen T/Td reach 89/55F, with temperatures in the upper 70s
to low 80s across the western Denver metro.

At this point, it appears likely that we'll see a first attempt at
convective initiation somewhere along the surface boundary in the
next couple of hours, with better probabilities of sustained
convection closer to Fort Morgan/Sterling. A recent ACARS
sounding, modified to the latest DEN observation suggest only
meager capping at 700-600mb remains, with ACARS and RAP
Mesoanalysis showing a fairly broad area of >3000 MLCAPE
stretching along and south of I-76. Combined with impressive deep
layer shear, any thunderstorms that can develop this afternoon
should quickly become strong to severe, with primarily a large
hail threat. Hodographs have slowly become more curved as the
low-level flow has increased, though overall hodographs are still
relatively straight-line and would favor splitting supercells with
the initial round of convection today. Still, there would be at
least a brief tornado threat, especially closer to any boundary
where sfc vorticity and effective SRH would be maximized.

A second round of thunderstorms is expected to develop in Wyoming
and move into our forecast area sometime between about 6-10 PM.
This should primarily be north and east of the metro (where SPC's
enhanced risk is). I would expect this to be the more significant
of the two waves of convection given a weakening cap and rather
impressive skew-t/hodograph combinations advertised by the WoFS.
While again this threat appears to be mainly north/east of the
I-25 corridor, we can't completely rule out strong to severe
storms this far west. Any sort of additional push of moist outflow
may be enough to break the remaining cap here, which has been
shown on and off by various high resolution models. We'll see if
any more meaningful trends emerge this afternoon but the threat in
the Denver metro is highly conditional.

A more organized round of sub-severe showers and thunderstorms is
likely overnight tonight as a shortwave moves across the region.
There could still be a strong storm or two left depending on how
much instability lingers overnight, but the severe threat should
diminish quickly after midnight. A combination of some showers,
stratus, fog/mist, and haze from wildfire smoke will likely
develop overnight and linger into Thursday morning.

The shortwave should move across the area through Thursday, with a
cooler/more stable airmass behind it. There should still be widely
scattered showers and thunderstorms in the afternoon, though any
severe potential will be determined by how quickly things can
destabilize following the morning stratus/fog.

Drier southwesterly flow aloft should develop by Friday, leading
to less convection across the region. The warming/drying trend is
likely to continue into the weekend as a strong upper trough
advances into the Pacific Northwest region during the weekend.
Strengthening mid/upper level flow is expected to bring gusty
winds to most of the forecast area, with the strongest winds over
the higher elevations. The combination of above normal
temperatures, a dry airmass, and gusty winds will likely lead to
critical fire weather conditions across a large portion of the
forecast area... and Fire Weather Watches may be necessary soon.

Little change is expected in the longer term forecast period as
dry southwesterly flow aloft continues.

&&

.AVIATION /18Z TAFS through 18Z Thursday/...
Issued at 1215 PM MDT Wed Jun 24 2026

Another complicated day is in store for the three airports. A
boundary is positioned just to the east of KDEN, with north to
NNE winds at KDEN. Over the last hour or so, this boundary has
migrated further to the NW. Guidance is having a difficult time
resolving the boundary, but we are currently thinking winds will
turn to the E and SE throughout the afternoon at KDEN as this
boundary moves further west. The timing could be slightly earlier
than what is currently in the TAF given the current position of
the boundary.

The next big focus is the thunderstorm chances this afternoon and
evening. Short-term models remain in pretty good agreement that
precipitation will likely occur at least near all three sites,
but timing is varying across run-to-run and model-to-model. Thus,
have stretched prob30s from about 21z to 8z at all three sites.
The highest chances look to be between about 00z and 04z, so we
may need to add in a tempo group if there is more confidence in
timing this afternoon. Gusty outflow winds of at least 30 kts will
be possible with any storms near KDEN and KAPA especially.

Finally, low ceilings/fog/haze look to develop with northeast to
east flow overnight. Ceilings could drop as low as about 005
generally after 10z. We will need to monitor the wind direction
overnight as the winds could turn more easterly or southeasterly,
which would limit the threat for lower ceilings. By tomorrow
afternoon, showers and thunderstorms will return to the area, but
we will address any needs to add -tsra in the next update.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning until 6 PM MDT this evening for COZ211>214-217-
218.

&&

DISCUSSION...Hiris
AVIATION...MV

Preliminary Local Storm Report
National Weather Service Denver CO
447 PM MDT Wed Jun 24 2026

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

0441 PM     Hail             5 N Adena School        40.19N 103.79W
06/24/2026  E2.00 Inch       Morgan             CO   Public

            Report from mPING: Hen Egg (2.00 in.).

&&

AA

Preliminary Local Storm Report
National Weather Service Denver CO
448 PM MDT Wed Jun 24 2026

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

0414 PM     Hail             1 SW Fort Morgan        40.25N 103.80W
06/24/2026  E1.75 Inch       Morgan             CO   Public

            Report from mPING: Golf Ball (1.75 in.) Time
            estimated from radar.

&&

AA

Preliminary Local Storm Report
National Weather Service Denver CO
506 PM MDT Wed Jun 24 2026

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

0426 PM     Tstm Wnd Gst     3 N Messex              40.46N 103.43W
06/24/2026  M61 MPH          Logan              CO   Public

&&

AA

Preliminary Local Storm Report
National Weather Service Denver CO
515 PM MDT Wed Jun 24 2026

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

0508 PM     Hail             1 SW Gary               40.06N 103.60W
06/24/2026  M1.50 Inch       Morgan             CO   Public

            Report from mPING: Ping Pong Ball (1.50
            in.).

&&

AA

Preliminary Local Storm Report
National Weather Service Denver CO
554 PM MDT Wed Jun 24 2026

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

0529 PM     Tstm Wnd Gst     1 NNW Akron             40.17N 103.22W
06/24/2026  M63 MPH          Washington         CO   AWOS

            AWOS station KAKO Akron.

&&

AA

Preliminary Local Storm Report
National Weather Service Denver CO
557 PM MDT Wed Jun 24 2026

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

0538 PM     Tstm Wnd Gst     1 W Akron               40.16N 103.23W
06/24/2026  M81 MPH          Washington         CO   Public

&&

AA