Alert archive / Colorado / Flash Flood Warnings in 2026

Flash Flood Warning 1, NWS Denver/Boulder, CO

May 21, 2026Washington County, Colorado

NWS Denver/Boulder, CO issued this flash flood warning at May 21, 2026, 6:51 PM MDT for Washington County, Colorado. It was in force for 6 hr. No storm report in the archive falls inside the area while it was in force.

The area

The outline as issued.

The facts

Issued: May 21, 2026, 6:51 PM MDT (00:51 UTC)
Expired: May 22, 2026, 12:45 AM MDT
In force: 6 hr
Issued by: NWS Denver/Boulder, CO
Area: Storm-based polygon
Flood severity: None

County Washington County, CO

The radar

The Goodland radar (KGLD), 119 km from the middle of the area, began a volume at 00:51 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

The archived warnings, watches and discussions in force at that minute are drawn over the scan, this one among them.

Did it verify

Not verified. The Iowa Environmental Mesonet's Cow found no qualifying storm report inside this flash flood warning while it was in force. That is not proof nothing happened: reports are thin where few people live.

Cow counts a report within 15 km of the polygon while the warning was in force: a tornado for a tornado warning; hail of 1 inch or more, a gust of 58 mph or more or wind damage for a severe thunderstorm warning; a flash flood report for a flash flood warning.

The nearest sounding before it

N. Platte/Lee Bi, NE (KLBF), launched 00:00Z, 0.9 hours before the alert went out and 263 km from the middle of its area. This is the routine balloon launch nearest before it, the air the forecaster had in hand, not a measurement taken for the alert.

Skew-T log-p

Temperature in red, dew point in green, the mixed-layer parcel dashed.

Hodograph

The wind turning with height, colored by layer: ground to 1 km, 1 to 3 km, 3 to 6 km, 6 to 10 km.

Mixed-layer CAPE: 0 J/kg
Mixed-layer CIN: No buoyant parcel
Mixed-layer LCL: 1093 m above ground
0-6 km bulk shear: 48 kt
0-1 km storm-relative helicity: 14 m²/s²
0-3 km storm-relative helicity: 149 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

580 
WGUS55 KBOU 220051
FFWBOU
COC121-220345-
/O.NEW.KBOU.FF.W.0001.260522T0051Z-260522T0345Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/

BULLETIN - EAS ACTIVATION REQUESTED
Flash Flood Warning
National Weather Service Denver CO
651 PM MDT Thu May 21 2026

The National Weather Service in Denver has issued a

* Flash Flood Warning for...
  Southeastern Washington County in northeastern Colorado...

* Until 945 PM MDT.

* At 651 PM MDT, Doppler radar indicated thunderstorms producing
  heavy rain across the warned area. Between 2 and 3 inches of rain
  have fallen. Additional rainfall amounts of 0.5 to 1 inch are
  possible in the warned area. Flash flooding is ongoing or expected
  to begin shortly.

  HAZARD...Flash flooding caused by thunderstorms.

  SOURCE...Radar indicated.

  IMPACT...Flash flooding of small creeks and streams, gulches,
           roads, and poor drainage and low-lying areas.

* Some locations that will experience flash flooding include...
  Cope.

This includes the following streams and drainages...
  Arikaree River, North Fork Arikaree River and Gordon Creek.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Move to higher ground now. Act quickly to protect your life.

Be aware of your surroundings and do not drive on flooded roads.

&&

LAT...LON 3971 10315 3974 10280 3957 10280 3957 10315
      3971 10317

FLASH FLOOD...RADAR INDICATED

$$

63

4 follow-up statements

075 
WGUS75 KBOU 220154
FFSBOU

Flash Flood Statement
National Weather Service Denver CO
754 PM MDT Thu May 21 2026

COC121-220345-
/O.CON.KBOU.FF.W.0001.000000T0000Z-260522T0345Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Washington CO-
754 PM MDT Thu May 21 2026

...FLASH FLOOD WARNING REMAINS IN EFFECT UNTIL 945 PM MDT THIS
EVENING FOR SOUTHEASTERN WASHINGTON COUNTY...

At 754 PM MDT, Doppler radar indicated thunderstorms had ended over
southeastern Washington county.  Between 2.5 and 4 inches of rain
have fallen. Flash flooding is ongoing or expected to begin shortly.

HAZARD...Flash flooding caused by thunderstorms.

SOURCE...Radar indicated.

IMPACT...Flash flooding of small creeks and streams, gulches, roads,
         and poor drainage and low-lying areas.

Some locations that will experience flash flooding include...
  Cope.

This includes the following streams and drainages...
  Arikaree River, North Fork Arikaree River and Gordon Creek.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Move to higher ground now. Act quickly to protect your life.

Be aware of your surroundings and do not drive on flooded roads.

&&

LAT...LON 3971 10315 3974 10280 3957 10280 3957 10315
      3971 10317

FLASH FLOOD...RADAR INDICATED

$$

63

671 
WGUS55 KBOU 220328
FFWBOU
COC121-220645-
/O.EXT.KBOU.FF.W.0001.000000T0000Z-260522T0645Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/

BULLETIN - EAS ACTIVATION REQUESTED
Flash Flood Warning
National Weather Service Denver CO
928 PM MDT Thu May 21 2026

The National Weather Service in Denver has extended the

* Flash Flood Warning for...
  Southeastern Washington County in northeastern Colorado...

* Until 1245 AM MDT.

* At 928 PM MDT, Doppler radar and automated rain gauges indicated
  thunderstorms producing heavy rain across the warned area. Between
  2.5 and 4.5 inches of rain have fallen. Flash flooding is ongoing
  or expected to begin shortly.

  HAZARD...Flash flooding caused by thunderstorms.

  SOURCE...Radar and an automated gauge that has reported over 4
           inches of rain.

  IMPACT...Flash flooding of small creeks and streams, gulches,
           roads, and poor drainage and low-lying areas.

* Some locations that will experience flash flooding include...
  Cope.

This includes the following streams and drainages...
  Gordon Creek, North Fork Arikaree River and Arikaree River.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Move to higher ground now. Act quickly to protect your life.

Be aware of your surroundings and do not drive on flooded roads.

&&

LAT...LON 3971 10315 3974 10280 3957 10280 3957 10315
      3971 10317

FLASH FLOOD...RADAR AND GAUGE INDICATED

$$

22

496 
WGUS75 KBOU 220508
FFSBOU

Flash Flood Statement
National Weather Service Denver CO
1108 PM MDT Thu May 21 2026

COC121-220645-
/O.CON.KBOU.FF.W.0001.000000T0000Z-260522T0645Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Washington CO-
1108 PM MDT Thu May 21 2026

...FLASH FLOOD WARNING REMAINS IN EFFECT UNTIL 1245 AM MDT FRIDAY FOR
SOUTHEASTERN WASHINGTON COUNTY...

At 1108 PM MDT, Doppler radar and automated rain gauges indicated
thunderstorms producing heavy rain across the warned area. Between
2.5 and 5 inches of rain have fallen. Flash flooding is ongoing or
expected to begin shortly.

HAZARD...Flash flooding caused by thunderstorms.

SOURCE...Radar and automated gauges.

IMPACT...Flash flooding of small creeks and streams, gulches, roads,
         and poor drainage and low-lying areas.

Some locations that will experience flash flooding include...
  Cope.

This includes the following streams and drainages...
  Gordon Creek, Arikaree River and North Fork Arikaree River.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Move to higher ground now. Act quickly to protect your life.

Be aware of your surroundings and do not drive on flooded roads.

&&

LAT...LON 3971 10315 3974 10280 3957 10280 3957 10315
      3971 10317

FLASH FLOOD...RADAR AND GAUGE INDICATED

$$

Meier

114 
WGUS75 KBOU 220509
FFSBOU

Flash Flood Statement
National Weather Service Denver CO
1109 PM MDT Thu May 21 2026

COC121-220645-
/O.CON.KBOU.FF.W.0001.000000T0000Z-260522T0645Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Washington CO-
1109 PM MDT Thu May 21 2026

...FLASH FLOOD WARNING REMAINS IN EFFECT UNTIL 1245 AM MDT FRIDAY FOR
SOUTHEASTERN WASHINGTON COUNTY...

At 1109 PM MDT, Doppler radar and automated rain gauges indicated
thunderstorms producing heavy rain across the warned area. Between
2.5 and 5 inches of rain have fallen. Flash flooding is ongoing or
expected to begin shortly.

HAZARD...Flash flooding caused by thunderstorms.

SOURCE...Radar and automated gauges.

IMPACT...Flash flooding of small creeks and streams, gulches, roads,
         and poor drainage and low-lying areas.

Some locations that will experience flash flooding include...
  Cope.

This includes the following streams and drainages...
  Gordon Creek, Arikaree River and North Fork Arikaree River.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Move to higher ground now. Act quickly to protect your life.

Be aware of your surroundings and do not drive on flooded roads.

&&

LAT...LON 3971 10315 3974 10280 3957 10280 3957 10315
      3971 10317

FLASH FLOOD...RADAR AND GAUGE INDICATED

$$

Meier

What forecasters said that day

The local office's own words before this flash flood warning went out, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.

NWS Denver/Boulder, CO wrote its last area forecast discussion before this flash flood warning went out at May 21, 6:13 PM MDT, 38 minutes earlier. Its key messages:

Strong to locally severe thunderstorms expected late this afternoon through this evening in the plains, mainly east of I-25.
Elsewhere, weaker isolated to scattered showers/t-storms can be expected with and behind an early evening cold front.
Lingering showers into Friday, mainly south of I-70. Remaining cool.
Warmer and drier this weekend, with isolated showers possible Saturday afternoon.
Remaining mild next week but with a return of potential afternoon showers and thunderstorms.

Area forecast discussion, May 21, 6:13 PM MDT, 38 minutes before

Area Forecast Discussion
National Weather Service Denver/Boulder CO
613 PM MDT Thu May 21 2026

.KEY MESSAGES...

- Strong to locally severe thunderstorms expected late this
  afternoon through this evening in the plains, mainly east of
  I-25.

- Elsewhere, weaker isolated to scattered showers/t-storms can be
  expected with and behind an early evening cold front.

- Lingering showers into Friday, mainly south of I-70. Remaining
  cool.

- Warmer and drier this weekend, with isolated showers possible
  Saturday afternoon.

- Remaining mild next week but with a return of potential
  afternoon showers and thunderstorms.

&&

.DISCUSSION /Through Thursday/...
Issued at 1218 PM MDT Thu May 21 2026

Ingredients are coming together as anticipated to provide for an
active afternoon and evening for our plains in particular. Cloud
cover has reduced considerably across the urban corridor and will
continue to thin over the plains in the coming hours, helping to
destabilize the environment. Surface moisture remains a potential
limiting factor for portions of the I-25 corridor with dewpoints
falling below 40F this afternoon, capping MLCAPE below ~400 J/Kg
at most.

Thunderstorms remain on track to develop mid-afternoon, mainly
after 3-4pm, favoring initiation east of I-25 and off the Palmer
Divide, where a DCVZ will become increasingly pronounced as the
afternoon progresses. These will spread into a much more unstable
environment in the eastern plains where an axis of more favorable
low-level moisture (dewpoints exceeding 50F) is present, roughly
to the east of the north/south line from Fort Morgan to Agate.
Ample bulk shear of 45-60 kts should support sustained growth of a
few supercells into Lincoln/Washington/Logan Counties late
afternoon into early evening, capable of producing large hail to
~2" in diameter with the strongest storms, as well as isolated
strong wind gusts and/or a weak tornado.

For the urban corridor, the highest chances for showers and
thunderstorms will arrive in the evening as a cold front descends
south between 5-8pm, although any convection should be sub-severe.
However, the front will provide an opportunity for redevelopment
of strong thunderstorms into the plains, reinforced by a secondary
frontal surge mid/late evening associated with the upper level
trough axis. With time, convection should become less discrete in
nature, favoring some upscale growth into a broader area of
thunderstorms across the northeast plains, exiting into KS/NE
roughly after midnight. Post-frontal winds will remain robust
overnight across our plains with gusts 25-40 mph.

This evening's front will usher in cooler temperatures for Friday,
along with a more stable airmass that will significantly reduce
precipitation potential for most areas. Nonetheless, some pockets
of marginal instability could remain south of I-70, and upslope
flow combined with the passage of another (weaker) shortwave aloft
will promote some showers and potentially a few weak thunderstorms
in the late afternoon and evening, focused across the Palmer
Divide.

We'll trend noticeably warmer Saturday into Sunday, with the
latter seeing highs climb into the lower 80's for the plains and
urban corridor. Some lingering mid-level moisture and yet another
weak shortwave may support isolated and weak high-based convection
on Saturday, although most will stay dry, and that will certainly
be the case on Sunday as higher pressure settles in. A more
unsettled pattern looks to return as early as Monday with renewed
potential for diurnal showers and thunderstorms through much of
the week.

&&

.AVIATION /00Z TAFS through 00Z Saturday/...
Issued at 557 PM MDT Thu May 21 2026

Cold front is making its way through all terminals currently, with
gusts up to 30-35 kts behind it. Expect lighter northerly winds
by 01Z/02Z, however gusts up to 25 kts are still likely. A
secondary frontal push will occur by 04/05Z which will bring
another round of gusty winds up to 30 kts. Showers and
thunderstorms have increased in coverage with the arrival of the
cold front, however most of the convection has remained east of
the airports. Will keep the PROB30 in to account for isolated
showers/thunderstorms through this evening. Most likely chance for
the next round of precipitation will be with the arrival of the
secondary front.

Winds overnight should begin weakening by 08Z-10Z, remaining
generally north/northeast. Expect typical diurnal pattern in the
afternoon, with winds shifting to the southeast briefly before
returning to drainage. Evening showers are possible tomorrow,
however convection should remain south of the airport.

&&

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

&&

DISCUSSION...BRQ
AVIATION...MAI

In the hours before

Local storm report, May 21, 5:11 PM MDT, 1 hour 40 minutes before

Preliminary Local Storm Report
National Weather Service Denver CO
511 PM MDT Thu May 21 2026

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

0450 PM     Hail             5 S Last Chance         39.65N 103.59W
05/21/2026  E1.00 Inch       Washington         CO   Storm Chaser

            Report from mPING: Quarter (1.00 in.).

&&

Local storm report, May 21, 5:19 PM MDT, 1 hour 32 minutes before

Preliminary Local Storm Report
National Weather Service Denver CO
519 PM MDT Thu May 21 2026

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

0506 PM     Hail             5 SSE Last Chance       39.67N 103.53W
05/21/2026  M2.50 Inch       Washington         CO   Trained Spotter

&&

Local storm report, May 21, 5:23 PM MDT, 1 hour 28 minutes before

Preliminary Local Storm Report
National Weather Service Denver CO
523 PM MDT Thu May 21 2026

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

0519 PM     Hail             6 S Lindon              39.64N 103.41W
05/21/2026  M2.50 Inch       Washington         CO   Storm Chaser

            Report from mPING: Tennis Ball (2.50 in.).

&&

Local storm report, May 21, 5:46 PM MDT, 1 hour 5 minutes before

Preliminary Local Storm Report
National Weather Service Denver CO
546 PM MDT Thu May 21 2026

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

0535 PM     Tornado          3 WNW Thurman           39.61N 103.27W
05/21/2026                   Washington         CO   Trained Spotter

            Brief ground circulation. Report via
            NWSChat.

&&

Local storm report, May 21, 5:48 PM MDT, 1 hour 3 minutes before

Preliminary Local Storm Report
National Weather Service Denver CO
548 PM MDT Thu May 21 2026

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

0544 PM     Hail             2 WNW Thurman           39.61N 103.24W
05/21/2026  M2.75 Inch       Washington         CO   Trained Spotter

&&

Local storm report, May 21, 5:56 PM MDT, 55 minutes before

Preliminary Local Storm Report
National Weather Service Denver CO
556 PM MDT Thu May 21 2026

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

0547 PM     Hail             1 S Thurman             39.58N 103.22W
05/21/2026  E3.00 Inch       Washington         CO   Trained Spotter

            Report from mPING: Tea Cup (3.00 in.).

&&

The office that day

Everything else NWS Denver/Boulder, CO issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
May 21, 6:05 PM MDT	Tornado Warning	BOU	Logan	28 min
May 21, 6:25 PM MDT	Severe Thunderstorm Warning	BOU	Washington	35 min
May 21, 6:30 PM MDT	Severe Thunderstorm Warning Considerable damage threat	BOU	Washington	30 min
May 21, 7:01 PM MDT	Severe Thunderstorm Warning	BOU	Washington	18 min
May 21, 7:09 PM MDT	Severe Thunderstorm Warning Considerable damage threat	BOU	Adams, Arapahoe, Washington	36 min
May 21, 7:26 PM MDT	Special Weather Statement	BOU	Elbert	49 min
May 21, 7:57 PM MDT	Special Weather Statement	BOU	Lincoln	48 min
May 21, 8:39 PM MDT	Severe Thunderstorm Warning Considerable damage threat	BOU	Lincoln	36 min

Nearby

Flash Flood Warnings in Colorado, 2026 Every flash flood warning in 2026

Sources

The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.