Flash Flood Warning 38, NWS Denver/Boulder, CO

435 
WGUS75 KBOU 230252
FFSBOU

Flash Flood Statement
National Weather Service Denver CO
852 PM MDT Tue Sep 22 2026

COC005-035-230302-
/O.CAN.KBOU.FF.W.0038.000000T0000Z-260923T0430Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Arapahoe CO-Douglas CO-
852 PM MDT Tue Sep 22 2026

...FLASH FLOOD WARNING IS CANCELLED FOR WESTERN ARAPAHOE AND DOUGLAS
COUNTIES...

The heavy rain has ended. Flooding is no longer expected to pose a
threat. Please continue to heed any remaining closures.

&&

LAT...LON 3962 10490 3962 10489 3964 10489 3965 10488
      3964 10488 3966 10485 3966 10487 3967 10487
      3967 10488 3966 10488 3966 10489 3968 10488
      3968 10487 3960 10472 3958 10470 3945 10474
      3938 10485 3945 10496
PARTITION...408005

$$

09

Area Forecast Discussion
National Weather Service Denver/Boulder CO
639 PM MDT Tue Sep 22 2026

.KEY MESSAGES...

- Isolated to scattered showers/thunderstorms this afternoon and
  evening.

- A disturbance moves through Wednesday and Thursday bringing
  increased chances for showers/storms (40-70%) and cooler
  temperatures Thursday.

- Drier and warmer this weekend, but isolated showers and
  thunderstorms each afternoon and evening can't be ruled out.

&&

.DISCUSSION /Through Tuesday/...
Issued at 242 PM MDT Tue Sep 22 2026

Water vapor imagery shows moisture starting to advect into
Southwestern Colorado associated with the disturbance in New
Mexico/Southeast AZ. Showers and storms are currently developing in
the higher terrain. With the influx of moisture in the southwest
flow aloft, more showers/thunderstorms are expected this afternoon
in the higher terrain. Isolated high-based showers/storms could
drift off the foothills and track eastward into the I-25 corridor
and Denver Metro (15-20% coverage), but scattered (25-35%) coverage
on the Palmer Divide. The eastern plains may also have a
shower/storm linger into the late evening. Models this afternoon
indicate DCAPE values in the 1000-1100 range, so gusty winds up to
~25-35 mph are possible with any showers/storms today. Forecast
soundings indicate the urban corridor remains limited in
instability, but MLCAPE is forecasted for 500-900 and MLCIN to be
quite minimal in the eastern plains so an isolated strong storm is
possible but quite low. High temperatures today will favor upper 70s
and lower 80s.

Deterministic and ensemble model guidance are in good agreement for
precipitable waters to increase Wednesday afternoon/late evening
bringing our highest moisture for the week. Additionally, models
indicate a shortwave moving through around Wednesday evening into
Thursday morning before transitioning out of our area rather quickly
by Thursday evening. The right entrance region of a jet streak
moving through in the afternoon should also provide some additional
lift. PWATs are expected across the forecast area in the 1.0-1.3
range with the highest values in the eastern and southern plains.
More southerly flow in the eastern plains is modeled Wednesday
afternoon advecting greater moisture into the area increasing
dewpoints near 60F while the Denver metro should be in the upper
50s. We still think the greatest chance for localized heavy rainfall
will remain over the east Colorado plains. This will increase rain
chances Wednesday afternoon (~30%) for the urban corridor before
increasing further towards the evening near 50-60% for most of the
night. We decided to increase chances for rain mostly for the
eastern plains into Wednesday night and Thursday morning since model
guidance favors the area. However, we are still concerned about
abundant cloud cover limiting instability leading to much less storm
coverage.

By Thursday morning low-level moisture will peak and cloud cover
will dominate much of the forecast area. Nonetheless a round of
showers/storms is modeled to move through Thursday morning in the
eastern plains (70-80%). Isolated storms could produce localized
heavy rainfall as warm cloud depths increase to 4,000-6,000 feet.
The urban corridor's chances remain slightly below the eastern
plains while the higher terrain should see shower development.
Temperatures will only reach the upper 60s with the aforementioned
cloud cover. We will likely see a slight decrease in shower coverage
in the afternoon, given the expected earlier passage of the
shortwave and less remaining instability for the eastern plains.

On Friday, another weak shortwave will move through Colorado
promoting isolated to scattered showers/storms over the higher
terrain. A few showers/storms could develop in the plains, but with
the lack of moisture aloft and instability only isolated activity is
expected at this time. Temperatures across most of the area will
return to the upper 70s. Saturday and Sunday deterministic and
ensemble guidance depicts much drier weather with temperatures in
the lower 80s slightly above normal for this time of year. Monday
and Tuesday deterministic models depict a upper level trough
potentially cooling us back down Tuesday near 70, along with another
chance of showers and storms.

&&

.AVIATION /00Z TAFS through 00Z Thursday/...
Issued at 638 PM MDT Tue Sep 22 2026

Scattered storms and showers have been popping up off the Palmer
Divide and lingering in the vicinity of KAPA, producing heavy rain
and lowering cloud ceilings as low as 5000ft. Given the lack of
instability in the latest ACARS soundings and current radar
observations show storms weakening as they move northward, we expect
these storms to weaken as they approach KDEN; however, they could
still drop cigs to ~6000ft and reduce visibility over the airfield
as they pass. Additionally, storms approaching now are producing
gusts up to 35kts. After storms pass, winds are expected to be
variable and mainly outflow-driven until showers clear the area,
which is expected to be around 03Z.

Winds should then turn south overnight and become light and variable
in the early morning, around 12Z. Clouds are expected to linger
overnight, but ceilings should remain high enough for VFR to
prevail. Tomorrow afternoon/evening brings with it another chance
for scattered showers/storms. Current model guidance suggests most
precipitation will occur after 00Z, though we could see some showers
pop up starting around 22Z. There's still some uncertainty on this
timing and we'll be updating the current PROB30 and TEMPO groups
accordingly once we get a better idea of what tomorrow's instability
and moisture will be. Outside of any variability from storms, winds
should be predominantly easterly throughout the afternoon and
evening.

&&

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

&&

DISCUSSION...Schnell/20
AVIATION...AGS

Special Weather Statement
National Weather Service Denver CO
517 PM MDT Tue Sep 22 2026

COZ040-045-222345-
Central and East Adams and Arapahoe Counties CO-North Douglas
County Below 6000 Feet/Denver/West Adams and Arapahoe
Counties/East Broomfield County CO-
517 PM MDT Tue Sep 22 2026

...A SHOWER WILL IMPACT NORTHEASTERN ARAPAHOE AND SOUTH CENTRAL ADAMS
COUNTIES UNTIL 545 PM MDT...

At 517 PM MDT, Doppler radar was tracking a shower near Watkins, or
20 miles east of Denver, moving northeast at 15 mph.

HAZARD...Wind gusts up to 40 mph.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects.

Locations impacted include...
  Aurora, Bennett, Manila Village and Watkins.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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

&&

LAT...LON 3965 10457 3974 10468 3989 10453 3974 10436
      3966 10451 3966 10452
TIME...MOT...LOC 2316Z 225DEG 13KT 3973 10457

MAX HAIL SIZE...0.00 IN
MAX WIND GUST...40 MPH

09

Special Weather Statement
National Weather Service Denver CO
540 PM MDT Tue Sep 22 2026

COZ040-041-230015-
Elbert/Central and East Douglas Counties Above 6000 Feet CO-North
Douglas County Below 6000 Feet/Denver/West Adams and Arapahoe
Counties/East Broomfield County CO-
540 PM MDT Tue Sep 22 2026

...A STRONG THUNDERSTORM WILL IMPACT SOUTH CENTRAL ARAPAHOE...
NORTHWESTERN ELBERT AND NORTHEASTERN DOUGLAS COUNTIES UNTIL 615 PM
MDT...

At 540 PM MDT, Doppler radar was tracking a strong thunderstorm near
Castle Pines, or 21 miles south of Denver, moving northeast at 15
mph.

HAZARD...Wind gusts up to 40 mph and pea 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...
  Southern Centennial, Castle Rock, Parker, Lone Tree, The Pinery,
  Castle Pines, Franktown, Sedalia and Ponderosa Park.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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

&&

LAT...LON 3944 10496 3961 10488 3945 10457 3935 10485
      3942 10497
TIME...MOT...LOC 2339Z 231DEG 11KT 3944 10484

MAX HAIL SIZE...0.25 IN
MAX WIND GUST...40 MPH

09

Special Weather Statement
National Weather Service Denver CO
612 PM MDT Tue Sep 22 2026

COZ040-041-230045-
Elbert/Central and East Douglas Counties Above 6000 Feet CO-North
Douglas County Below 6000 Feet/Denver/West Adams and Arapahoe
Counties/East Broomfield County CO-
612 PM MDT Tue Sep 22 2026

...A STRONG THUNDERSTORM WILL IMPACT SOUTH CENTRAL DENVER...EASTERN
ARAPAHOE...NORTHWESTERN ELBERT AND NORTHEASTERN DOUGLAS COUNTIES
UNTIL 645 PM MDT...

At 612 PM MDT, Doppler radar was tracking a strong thunderstorm near
Castle Pines, or 18 miles south of Denver, moving northeast at 15
mph.

HAZARD...Wind gusts up to 40 mph and pea 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...
  Southwestern Aurora, Centennial, eastern Highlands Ranch, Parker,
  Greenwood Village, Lone Tree, The Pinery, Castle Pines, Foxfield
  and Cherry Creek Reservoir.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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

Heavy rain is occurring with this storm and may lead to flooding. Do
not drive your vehicle through flooded roadways.

&&

LAT...LON 3953 10495 3971 10487 3955 10457 3942 10483
      3951 10496
TIME...MOT...LOC 0012Z 225DEG 13KT 3948 10483

MAX HAIL SIZE...0.25 IN
MAX WIND GUST...40 MPH

09

Special Weather Statement
National Weather Service Denver CO
624 PM MDT Tue Sep 22 2026

COZ040-230100-
North Douglas County Below 6000 Feet/Denver/West Adams and
Arapahoe Counties/East Broomfield County CO-
624 PM MDT Tue Sep 22 2026

...A STRONG THUNDERSTORM WILL IMPACT EAST CENTRAL DENVER...
NORTHEASTERN ARAPAHOE AND SOUTH CENTRAL ADAMS COUNTIES UNTIL 7 PM
MDT...

At 624 PM MDT, Doppler radar was tracking a strong thunderstorm over
Arapahoe Park, or 14 miles east of Denver, moving northeast at 15
mph.

HAZARD...Wind gusts up to 40 mph.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects.

Locations impacted include...
  Eastern Aurora, Arapahoe Park, Watkins and Buckley SFB.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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

&&

LAT...LON 3960 10466 3969 10483 3982 10469 3972 10451
      3965 10451 3965 10452 3964 10452 3963 10451
      3963 10452 3962 10452 3960 10456 3962 10457
      3963 10458 3961 10460 3959 10460 3958 10461
      3958 10462 3959 10463 3960 10465
TIME...MOT...LOC 0024Z 225DEG 13KT 3965 10470

MAX HAIL SIZE...0.00 IN
MAX WIND GUST...40 MPH

09

Special Weather Statement
National Weather Service Denver CO
700 PM MDT Tue Sep 22 2026

COZ040-041-045-230145-
Elbert/Central and East Douglas Counties Above 6000 Feet CO-
Central and East Adams and Arapahoe Counties CO-North Douglas
County Below 6000 Feet/Denver/West Adams and Arapahoe
Counties/East Broomfield County CO-
700 PM MDT Tue Sep 22 2026

...A STRONG THUNDERSTORM WILL IMPACT SOUTHEASTERN DENVER...EASTERN
ARAPAHOE...SOUTH CENTRAL ADAMS...NORTHWESTERN ELBERT AND NORTHEASTERN
DOUGLAS COUNTIES UNTIL 745 PM MDT...

At 700 PM MDT, Doppler radar was tracking a strong thunderstorm near
Parker, or 20 miles southeast of Denver, moving northeast at 20 mph.

HAZARD...Wind gusts up to 40 mph and pea 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...
  Aurora, eastern Centennial, northern Castle Rock, Parker, Lone
  Tree, Arapahoe Park, The Pinery, Buckley SFB, Ponderosa Park,
  Franktown, Watkins, Castle Pines and Foxfield.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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

&&

LAT...LON 3947 10497 3982 10469 3968 10439 3933 10473
      3945 10498
TIME...MOT...LOC 0059Z 217DEG 16KT 3948 10477

MAX HAIL SIZE...0.25 IN
MAX WIND GUST...40 MPH

09