Severe Thunderstorm Warning 129, NWS Denver/Boulder, CO

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1127 PM MDT Mon Jun 16 2025

.KEY MESSAGES...

- Still a couple strong thunderstorms over northeast Colorado
  overnight. Isolated severe storm threat.

- Severe storms with a high wind threat grow Tuesday. Cooler as a
  storm system moves through. At least a chance (30-50%) of
  showers/storms across the metro and plains.

- Strong signal for record breaking heat from Thursday into next
  weekend, along with potential for critical fire weather
  conditions.

&&

.DISCUSSION /Through Monday/...
Issued at 126 PM MDT Mon Jun 16 2025

Current satellite imagery shows cumulus clouds developing over the
Front Range mountains as light elevated convective showers are
just initiating, primarily in Larimer county. These showers will
continue for the next couple of hours, spilling across I-25
corridor and Denver metro. Severe threat is low at this time, as
SPC mesoanalysis shows decent CIN just east of the foothills due
to a weak cap still in place. However, daytime mixing will
eventually erode the cap. As these storms travel east, primarily
into eastern Weld, Logan Sedgwick and Phillips counties, they will
be entering into an environment that will support supercell
development. MLCAPE is expected to increase to 3,000+ J/Kg with
model Skew-T soundings showing 9 degrees C/km 500-700 mb lapse
rates and bulk shear >30 kts. Due to these expected conditions,
strong wind gusts up to 70 mph and large hail (golfball sized) are
possible, mainly between 6 PM and 10 PM. Tornado threat is very
low, but cannot rule out a brief spin up.

Overnight, a cold front will cross the region bringing gusty winds
and a few scattered light showers in the morning. Tuesday will be
a lot cooler than the past couple of days, with ensemble guidance
being in good agreement of the plains reaching up to the mid 70s.
An upper level shortwave is expected to track across the region
Tuesday afternoon, which could bring scattered thunderstorms. A
deep moisture field will be advected into the region from the
southeast, bringing dewpoint temperatures into the high 50s (and
low 60s far northeast), with MLCAPE values up to 2,000 J/Kg and
steep lapse rates. The only parameter that is lacking is bulk
shear, as models indicate less than 30 kts. If guidance starts
trending towards increasing shear, confidence will increase for
severe storms over the plains. If these storms do materialize,
wind and hail will be the primary threat.

The cooldown will be very brief as we will start warming up again
on Wednesday. Temperatures should reach up to the mid 80s across
the plains, with mostly dry conditions. However, the main concern
towards the end of the week will be the possibility of a heat
wave Thursday through the weekend. Ensemble guidance has continued
to trend towards multiple days of 97+ degree temperatures across
the lower elevations. Friday should have the best chance reaching
100 degrees, as each member of the ECMWF has the max temperature
being over 100 degrees. There is still a little uncertainty
however, as the GEFS has most of their members reaching up to 99
degrees. Regardless, it will be very hot until we get into next
week, as guidance has indicated a system moving through sometime
Monday or Tuesday.

Another concern with the scorching heat, is the fire weather
threat. As an upper level ridge travels east, southwesterly flow
aloft will bring dry conditions to the mountains and plains.
Relative humidity values could get as low as the single digits and
breezy wind gusts could bring about critical fire weather
conditions. We will continue to monitor.

&&

.AVIATION /06Z TAFS through 06Z Wednesday/...
Issued at 1127 PM MDT Mon Jun 16 2025

A couple surges of cooler and more moist northeast to northerly
winds should bring a return of stratus and MVFR ceilings to the
TAF sites starting 10Z-12Z. There will even be a chance of showers
or a rare isolated morning thunderstorm Tuesday morning as that
higher moisture content airmass moves in. The main concern will
then shift to thunderstorms Tuesday afternoon, and possible severe
storms. Those could start as early as 19Z and then organize into
a linear storm complex which would potentially produce 50+ kt
gusts as they move east across the I-25 Corridor. We have beefed
up the winds for now to G38kts in a TEMPO group, but a 10-20% of
reaching severe thresholds (50 kts) at KDEN. We think the main
threat of storms would be pushing east of the TAF sites by 23Z,
but still a chance of a lingering shower/isolated storm til 02Z
Wednesday. Then gradual clearing and lighter drainage winds
developing beyond 02Z.

&&

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

&&

DISCUSSION...Ideker
AVIATION...Barjenbruch

Hazardous Weather Outlook
National Weather Service Denver/Boulder CO
844 AM MDT Mon Jun 16 2025

COZ030>051-171445-
Jackson County Below 9000 Feet-
West Jackson and West Grand Counties Above 9000 Feet-
Grand and Summit Counties Below 9000 Feet-
South and East Jackson/Larimer/North and Northeast Grand/
Northwest Boulder Counties Above 9000 Feet-
South and Southeast Grand/West Central and Southwest Boulder/
Gilpin/Clear Creek/Summit/North and West Park Counties Above
9000 Feet-Larimer and Boulder Counties Between 6000 and 9000 Feet-
Jefferson and West Douglas Counties Above 6000 Feet/Gilpin/Clear
Creek/Northeast Park Counties Below 9000 Feet-
Central and Southeast Park County-
Larimer County Below 6000 Feet/Northwest Weld County-
Boulder And Jefferson Counties Below 6000 Feet/West Broomfield
County-
North Douglas County Below 6000 Feet/Denver/West Adams and
Arapahoe Counties/East Broomfield County-
Elbert/Central and East Douglas Counties Above 6000 Feet-
Northeast Weld County-Central and South Weld County-Morgan County-
Central and East Adams and Arapahoe Counties-
North and Northeast Elbert County Below 6000 Feet/North Lincoln
County-
Southeast Elbert County Below 6000 Feet/South Lincoln County-
Logan County-Washington County-Sedgwick County-Phillips County-
844 AM MDT Mon Jun 16 2025

This hazardous weather outlook is for northeast and north central
Colorado.

.DAY ONE...Today and Tonight

Well above normal temperatures will continue today, with highs in
the low 90s across the lower elevations.

Strong to severe storms are possible this afternoon and evening,
primarily in Logan, Sedgwick, Phillips and northern Washington
counties. Large hail and damaging wind gusts (up to 70 mph) are
the main hazards.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday

A storm system will bring cooler weather along with a chance of
thunderstorms across the area Tuesday into Wednesday.

Hot weather is likely to return by late this week, with high
temperatures in the mid to upper 90s possible from Thursday
through Saturday.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will not be needed today and tonight, but
reports of any hail or gusty winds will be appreciated.

Special Weather Statement
National Weather Service Denver CO
157 AM MDT Tue Jun 17 2025

COZ038-043-170830-
Larimer County Below 6000 Feet/Northwest Weld County CO-Central
and South Weld County CO-
157 AM MDT Tue Jun 17 2025

...A STRONG THUNDERSTORM WILL IMPACT WEST CENTRAL WELD AND EAST
CENTRAL LARIMER COUNTIES UNTIL 230 AM MDT...

At 157 AM MDT, Doppler radar was tracking a strong thunderstorm near
Severance, or 9 miles east of Fort Collins, moving east at 10 mph.

HAZARD...Wind gusts up to 40 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...
  Eastern Fort Collins, Windsor, Eaton, Severance, Ault, Pierce,
  Timnath, Nunn, Black Hollow Reservoir and New Windsor Reservoir.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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

&&

LAT...LON 4050 10499 4070 10499 4071 10473 4050 10470
TIME...MOT...LOC 0757Z 262DEG 10KT 4060 10491

MAX HAIL SIZE...0.75 IN
MAX WIND GUST...40 MPH

RPK

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