Severe Thunderstorm Warning 302, NWS Denver/Boulder, CO

Area Forecast Discussion
National Weather Service Denver/Boulder CO
132 PM MDT Sat Aug 9 2025

.KEY MESSAGES...

- Scattered thunderstorms this afternoon through tonight across
  the urban corridor and eastern plains. Some storms will be
  strong/severe.

- Another round of strong to severe thunderstorms possible Sunday
  across the urban corridor and eastern plains.

- Elevated to locally critical fire weather conditions across the
  northern mountains and high valleys this afternoon.

&&

.DISCUSSION /Through Saturday/...
Issued at 1250 PM MDT Sat Aug 9 2025

We finally got a reprieve from the blistering heat today, with
morning temperatures ranging from high 50s to low 60s across the
plains. The forecast area should stay below 90 degrees today: mid-
high 80s for the plains and low 60s to low 80s for the
mountains/valleys. Elevated to near critical fire weather conditions
are expected across the northern mountains and high valleys (see
Fire Weather Discussion). However, the main concern today is the
severe weather potential across the urban corridor and plains this
afternoon and evening.

The first round of storms will likely occur in the next hour or so.
Current radar imagery shows a well established Denver cyclone
just east/northeast of DIA, with the associated convergence zone
south of the cyclone and over the Palmer Divide. With continuous
moisture advection into the plains this morning from the E/SE
winds, there is a nice spread of mid 50s to low 60s dewpoint
temperatures. Hi-res guidance has MUCAPE between 1500-2500 J/kg,
EBWD >30 kts and steep mid-level lapse rates above 8 deg C/Km.
This environment would support multiple supercells capable of
producing 1-2" hail and damaging wind gusts up to 60 mph. The
tornado threat is low, but cannot rule out a brief one occurring,
especially along the DCVC. We expect storms to initiate off the
convergence zone on the Palmer Divide and travel east through the
late afternoon/evening. Another area of storm development will be
in northern/northeastern Colorado along a boundary along the
border between Wyoming, Nebraska, and Colorado. We will likely
have a watch out in the near future.

The second round of thunderstorms is expected for the urban corridor
and plains this evening and overnight. However, the severe threat
will be conditional. An upper level shortwave (currently in southern
Idaho) will enter the state tonight, forcing convective initiation
along the foothills/urban corridor and northern plains. With daytime
heating destabilizing the atmosphere, but no afternoon storms to
"use up" that energy, a few strong to potentially severe
thunderstorms are possible. Guidance is in good agreement of MLCAPE
values expected to be up to 2,000 J/kg, EBWD >40 kts and steep lapse
rates. Hail up to 2" will be the main threat again, along with
strong outflow wind gusts. Storms will travel east and could
continue to the early morning hours.

Another round of thunderstorms is expected for Sunday late morning
and early afternoon as the upper level shortwave travels across
the state. The severe threat will be dependent on how long the
overnight storms linger in our forecast area. Models are trending
towards instability building in the morning hours before
convective initiation starts around 11 AM/noon. MLCAPE values
could get up to 1500 J/kg and bulk shear between 30-40 kts. All
severe hazards will be possible, with large hail as the biggest
threat. However, if overnight storms linger past sunrise, initial
storm development could remain sub-severe along southern urban
corridor and Palmer Divide. Regardless of the severe threat, brief
moderate to heavy rain is expected with storms that develop. Due
to the multiple rounds of storms expected today combined with the
storms tomorrow, WPC has introduced a slight risk for excessive
rainfall for parts of Lincoln and Elbert counties. Although,
localized flooding issues are also possible across the eastern
plains.

Below normal temperatures are expected for Sunday and Monday, with
Sunday being our coolest day of the forecast period. Highs should be
in the mid-upper 70s across the plains. On Monday, flow aloft will
turn northerly behind the exiting shortwave, which will keep
temperatures in the low 80s. Scattered showers/thunderstorms are
also possible but should stay sub-severe.

By Tuesday, an upper level ridge will begin to rebuild over the
western United States, which will bring back warm and briefly dry
conditions. Highs are expected to reach mid-high 90s each day.

&&

.AVIATION /18Z TAFS through 18Z Sunday/...
Issued at 1146 AM MDT Sat Aug 9 2025

A boundary associated with the Denver Cyclone is very slowly
moving across the DEN airport grounds. The first storms of the day
are expected to form along this boundary later today. Models so
far have been a too aggressive moving this boundary eastward. Will
continue with the PROB30 beginning at 21Z just in case this
boundary stall over/near DEN. Behind this boundary, northerly
winds are expected to prevail until a southeast outflow produces a
wind shift around or after 00Z.

A second round of showers and thunderstorms are expected this
evening and overnight as an upper level trough pushes through.
Exact timing and locations are still a bit fuzzy from the models
and thus will continue with the PROB30 for tonight.

The best chance for thunderstorms looks to be early Sunday
afternoon. Storms could form as early as 18Z. For this, added a
tempo for thunderstorms 19-23Z Sunday.

&&

.FIRE WEATHER...
Issued at 1250 PM MDT Sat Aug 9 2025

Elevated to locally critical fire weather conditions are expected
across the high country, particularly in Jackson county. Minimum
relative humidity values will range from 9-20% today with breezy
wind gusts up to 25 mph. After sunset, winds will decrease and
moisture increase ahead of an approaching upper level shortwave.
Overnight showers are possible, which will help decrease fire
weather concerns for Sunday. But, with RH values expected to be in
the low teens and breezy wind gusts, elevated fire weather
conditions are possible, especially for areas that didn't see rain
overnight.

Looking at the beginning of next week, dry conditions should
prevail for the mountains/valleys with RH values in the teens to
low 20s. However, winds are expected to be generally light across
the forecast area.

&&

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

&&

DISCUSSION...Ideker
AVIATION...Meier
FIRE WEATHER...Ideker

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Preliminary Local Storm Report
National Weather Service Denver CO
302 PM MDT Sat Aug 9 2025

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

0237 PM     Hail             3 W Cedar Point         39.36N 103.87W
08/09/2025  M1.00 Inch       Elbert             CO   Public

            Report from mPING: Quarter (1.00 in.).

&&

Preliminary Local Storm Report...Summary
National Weather Service Denver CO
341 PM MDT Sat Aug 9 2025

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

0318 PM     Tstm Wnd Gst     2 NW Sterling           40.65N 103.25W
08/09/2025  M58 MPH          Logan              CO   Mesonet

0237 PM     Hail             3 W Cedar Point         39.36N 103.87W
08/09/2025  M1.00 Inch       Elbert             CO   Public

            Report from mPING: Quarter (1.00 in.).

0240 PM     Hail             7 W Cedar Point         39.35N 103.96W
08/09/2025  M1.00 Inch       Elbert             CO   Trained Spotter

            Measured with digital calipers.

0307 PM     Hail             3 SW Cedar Point        39.31N 103.84W
08/09/2025  E1.00 Inch       Elbert             CO   Public

            Report from mPING: Quarter (1.00 in.).

0326 PM     Hail             5 SSW Cedar Point       39.28N 103.83W
08/09/2025  M1.00 Inch       Elbert             CO   Storm Chaser

            Report via SpotterNetwork.

&&

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Preliminary Local Storm Report
National Weather Service Denver CO
411 PM MDT Sat Aug 9 2025

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

0401 PM     Hail             6 W Limon               39.23N 103.79W
08/09/2025  E1.50 Inch       Elbert             CO   Public

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

0404 PM     Hail             6 S Cedar Point         39.26N 103.85W
08/09/2025  M2.00 Inch       Elbert             CO   Trained Spotter

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

0408 PM     Hail             7 SW Limon              39.21N 103.79W
08/09/2025  E1.00 Inch       Elbert             CO   Public

            Report from mPING: Quarter (1.00 in.).

0409 PM     Hail             6 W Limon               39.23N 103.79W
08/09/2025  E2.00 Inch       Elbert             CO   Public

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

&&

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