Severe Thunderstorm Warning 99, NWS Denver/Boulder, CO

Area Forecast Discussion
National Weather Service Denver/Boulder CO
553 PM MDT Sat Jun 20 2026

.KEY MESSAGES...

- Critical fire weather conditions are expected for the mountains
  and high valleys today.

- Strong to severe storms possible across the eastern plains
  today and Sunday. For today, very large hail, damaging wind
  gusts, and a couple of tornados possible across the far
  northeast plains.

- Scattered coverage of showers and storms on Monday and most of
  next week across the plains.

- Elevated fire weather conditions possible for the mountains and
  high valleys most of next week.

&&

.DISCUSSION /Through Saturday/...
Issued at 1259 PM MDT Sat Jun 20 2026

Visible satellite imagery shows mid level clouds over the
northern and central mountains of Colorado indicating mid level
instability. Some weak showers have develop mainly over the
foothills with some briefly making it onto the plains before
dissipating. While a couple of these showers could grow strong
enough to create some lightning, they will stay below severe
limits across all of the foothills and I-25 corridor.

There are two other significant features to note in the
observations and satellite data. One is a DCVZ that has setup over
the far southeast side of the Denver metro. Winds remain from the
northwest to northeast to the north of this boundary with dew
points staying in the low 50s. To the south of this boundary,
southwest winds have developed with much warmer temperatures and
dew points in the 30s. This is the boundary that will create the
initial strong to severe storms today. Storms will begin in Elbert
and Arapahoe Counties and as they encounter much greater
instability in Lincoln and Washington Counties, they will grow
strong to severe. Large hail and strong winds will be the primary
threat from these storms although a tornado cannot be ruled out.

The other feature worth noting is a warm front-like feature that
is an east-west oriented boundary over the border of
Washington/Logan Counties and Phillips/Yuma Counties. Low clouds
have persisted for the entire morning to the north of this
boundary keeping temperatures in the low 70s to upper 60s and dew
points in the low 60s. To the south of this boundary, temperatures
are in the upper 80s to low 90s with dew points in the 50s. The
parameter space near and just north of this boundary is
exceptional for Colorado standards. Mixed-layer CAPE is forecast
to be around 2,500-3,000 j/kg. Deep layer shear will be above 50
knots to the north of this boundary and may approach 60 knots.
Plus, the boundary has greatly increased the low level helicity
with effective helicity values forecast to be 300-400 m2/s2. Any
storm that forms in this area will be capable of very large hail
up to baseball size, damaging wind gusts up to 70 mph, and a
supercell tornado. The Storm Prediction Center has highlighted
this area in an enhanced risk of severe weather for good reason. A
convective watch will be needed later this afternoon for this
area. The one factor that may limit the chance of severe weather
in this area is a lack of a lifting mechanism during the
afternoon. There is a somewhat significant cap on soundings and
convective initiation this afternoon is uncertain. Storms may not
form until later this evening when storms that initiate north of
Cheyenne, WY reach that area. If storm initiation doesn't occur
until this evening, the main risk would be very large hail.

A shortwave trough will move through our forecast area tonight
and there will be slight subsident flow tomorrow morning. West
winds will mix down in the morning hours which will clear any fog
or low clouds that develop across the eastern plains tonight. A
dryline will setup roughly from Sterling to Limon which may
initiate storms. Mixed-layer CAPE values around 1,500 j/kg will
support the formation of a couple of strong to severe storms to
the east of the dryline. The main threats would be large hail and
damaging wind gusts. Otherwise, temperatures will be slightly
above normal in the Denver metro with a limited chance of rain.

Low level winds will have an easterly component Monday through
Thursday of this upcoming week. This will keep healthy moisture in
place over the eastern plains of Colorado. The moisture and
upslope flow will generate daily afternoon/evening showers and
thunderstorms. This will also keep temperatures below normal most
days. There may be a severe threat from some of these storms but
any details about this threat is unknown at this time.

&&

.AVIATION /00Z TAFS through 00Z Monday/...
Issued at 545 PM MDT Sat Jun 20 2026

As forecasted, outflow boundaries have been moving through KDEN
and KAPA causing gusty winds at times. An outflow boundary pushed
through KDEN in the last hour bringing E to NE winds. Just to the
west of the airport, NW winds are occurring (including at KBJC and
KAPA) where a boundary is set up. This boundary could briefly
bring NW winds to KDEN as depicted by some models, but it will be
a close call.

Later tonight, winds will stay gusty with a slight lean to the NNE
as a front pushes through around 04 to 05z. Low stratus clouds
are still in the forecast for tonight impacting all three TAF
sites with ceilings as low as 1000 to 1500 feet starting as early
as 05z and lingering as late as 14z. Ceilings will likely lift
around sunrise as winds briefly turn to drainage. Tomorrow
afternoon, the winds should be out of the NW to N and gusty with
some gusts up to 25 kts looking likely for most of the afternoon.
There is a very low chance of showers/thunderstorms tomorrow
afternoon, but are currently expected to stay south and east of
the terminals.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning until 9 PM MDT this evening for COZ211>214-217-
218.

&&

DISCUSSION...Danielson
AVIATION...MV

Special Weather Statement
National Weather Service Denver CO
342 PM MDT Sat Jun 20 2026

COZ046-202215-
North and Northeast Elbert County Below 6000 Feet/North Lincoln
County CO-
342 PM MDT Sat Jun 20 2026

...A STRONG THUNDERSTORM WILL IMPACT NORTHEASTERN LINCOLN COUNTY
UNTIL 415 PM MDT...

At 342 PM MDT, Doppler radar was tracking a strong thunderstorm 9
miles north of Arriba, or 22 miles northeast of Limon, moving east at
15 mph.

HAZARD...Wind gusts up to 50 mph and penny 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...
  Mainly rural areas of Northeastern Lincoln County.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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

&&

LAT...LON 3930 10335 3951 10342 3957 10323 3957 10315
      3933 10316
TIME...MOT...LOC 2142Z 249DEG 11KT 3940 10333

MAX HAIL SIZE...0.75 IN
MAX WIND GUST...50 MPH

63

Special Weather Statement
National Weather Service Denver CO
344 PM MDT Sat Jun 20 2026

COZ045-046-202215-
Central and East Adams and Arapahoe Counties CO-North and
Northeast Elbert County Below 6000 Feet/North Lincoln County CO-
344 PM MDT Sat Jun 20 2026

...A STRONG THUNDERSTORM WILL IMPACT ARAPAHOE AND NORTH CENTRAL
ELBERT COUNTIES UNTIL 415 PM MDT...

At 344 PM MDT, Doppler radar was tracking a strong thunderstorm 12
miles north of Kiowa, or 31 miles southeast of Denver, moving east at
20 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 damage to outdoor objects is
         possible.

Locations impacted include...
  Mainly rural areas of Arapahoe and North Central Elbert Counties.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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

&&

LAT...LON 3962 10449 3968 10422 3949 10417 3948 10420
      3949 10421 3948 10421 3945 10437 3946 10437
      3949 10436 3950 10437 3950 10441 3953 10442
      3954 10442 3952 10444 3953 10445 3954 10445
      3954 10447 3955 10446 3955 10447
TIME...MOT...LOC 2144Z 252DEG 17KT 3952 10443

MAX HAIL SIZE...0.75 IN
MAX WIND GUST...50 TO 55 MPH

63

Special Weather Statement
National Weather Service Denver CO
356 PM MDT Sat Jun 20 2026

COZ051-202230-
Phillips County CO-
356 PM MDT Sat Jun 20 2026

...A STRONG THUNDERSTORM WILL IMPACT SOUTHEASTERN PHILLIPS COUNTY
UNTIL 430 PM MDT...

At 356 PM MDT, Doppler radar was tracking a strong thunderstorm 11
miles south of Holyoke, moving northeast 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...
  Holyoke and Pleasant Valley.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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

&&

LAT...LON 4044 10236 4051 10242 4069 10214 4057 10205
      4044 10205
TIME...MOT...LOC 2156Z 226DEG 18KT 4043 10230

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

63

Preliminary Local Storm Report
National Weather Service Denver CO
419 PM MDT Sat Jun 20 2026

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

0410 PM     Hail             7 SE Holyoke            40.50N 102.20W
06/20/2026  M1.00 Inch       Phillips           CO   Trained Spotter

&&

KEB

Special Weather Statement
National Weather Service Denver CO
530 PM MDT Sat Jun 20 2026

COZ044-045-210000-
Central and East Adams and Arapahoe Counties CO-Morgan County CO-
530 PM MDT Sat Jun 20 2026

...A STRONG THUNDERSTORM WILL IMPACT SOUTHWESTERN MORGAN AND
NORTHEASTERN ADAMS COUNTIES UNTIL 6 PM MDT...

At 530 PM MDT, Doppler radar was tracking a strong thunderstorm over
Hoyt, or 24 miles southwest of Fort Morgan, moving northeast at 20
mph.

HAZARD...Wind gusts up to 50 mph and penny 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...
  Hoyt, Adena, Leader and Hoyt Beet Dump.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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

&&

LAT...LON 4000 10415 4011 10415 4019 10393 3996 10378
      3988 10407 4000 10416
TIME...MOT...LOC 2330Z 238DEG 17KT 3999 10408

MAX HAIL SIZE...0.75 IN
MAX WIND GUST...50 MPH

63

Preliminary Local Storm Report
National Weather Service Denver CO
758 PM MDT Sat Jun 20 2026

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

0754 PM     Hail             7 NNW Pawnee Buttes     40.92N 104.02W
06/20/2026  M1.75 Inch       Weld               CO   Storm Chaser

&&

KEB