A stationary front extended from a low near Amarillo east northeast to just south of Canadian, TX in the afternoon.  The lower levels of the atmosphere were moistening from southeast surface winds into the stationary front and the edge of the southwest United States monsoon moisture plume was also present across the area.  Weak to moderate instability was found along and behind the front along with weak wind shear which was greatest in the far northern Panhandles and into Kansas. Thunderstorms initially developed near Amarillo around 2 pm as a weak upper level disturbance passed through the area.  These storms were slow-moving and they were interacting with outflow boundaries.  Some severe storms trained along and outflow boundary collision across the western side of Amarillo causing flooding.  In addition, a couple of storms with large hail (up to 2 inches in diameter) moved northward across Lipscomb and Beaver Counties during the late afternoon/early evening where the better dynamics and wind shear were located.

Hail in LIPSCOMB, TEXAS
From 21-AUG-21 15:44:00 to 21-AUG-21 15:57:00 (CST-6)
Location: BOOKER
Magnitude: 2.00 
Reported by: Fire Department/Rescue

A picture with the hail measurement was sent to the NWS office over social media. Numerous reports of golf ball size hail in an around Booker were also received.

Flash Flood in RANDALL, TEXAS
From 21-AUG-21 15:36:00 to 21-AUG-21 16:20:00 (CST-6)
Location: AMARILLO
Flood cause: Heavy Rain
Property damage: 50.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Road closed from 45th to Hillside on Coulter  with 3 to 4 feet of water. Firefighters were helping motorist escape from flooding and stalled vehicles. An additional report was submitted by the public for water filling up West Hill Park with some  roads around the park  impassable.

Flood in POTTER, TEXAS
From 21-AUG-21 14:34:00 to 21-AUG-21 14:34:00 (CST-6)
Location: AMARILLO
Flood cause: Heavy Rain
Property damage: 20.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Trained spotter had reported street/road  flooding, along with road closures and vehicles stranded.

Flood in POTTER, TEXAS
From 21-AUG-21 15:09:00 to 21-AUG-21 15:09:00 (CST-6)
Location: AMARILLO
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Storm Chaser

Heavy flooding was reported under the bridge at I-40 and  Bell, with traffic at a standstill in the  west bound lane.

Hail in RANDALL, TEXAS
From 21-AUG-21 14:44:00 to 21-AUG-21 14:44:00 (CST-6)
Location: TIMBERCREEK CANYON
Magnitude: 1.25 
Reported by: Trained Spotter

Hail in HUTCHINSON, TEXAS
From 21-AUG-21 14:50:00 to 21-AUG-21 14:50:00 (CST-6)
Location: BORGER
Magnitude: 0.88 
Reported by: Trained Spotter

Hail in RANDALL, TEXAS
From 21-AUG-21 14:50:00 to 21-AUG-21 14:50:00 (CST-6)
Location: AMARILLO
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Thunderstorm Wind in POTTER, TEXAS
From 21-AUG-21 14:55:00 to 21-AUG-21 14:55:00 (CST-6)
Location: AMARILLO
Magnitude: 65.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Received report of widespread tree damage near  Avondale Elementary and there was at least one large  tree was completely uprooted.

Hail in RANDALL, TEXAS
From 21-AUG-21 14:54:00 to 22-AUG-21 14:56:00 (CST-6)
Location: TIMBERCREEK CANYON
Magnitude: 1.25 
Property damage: 60.00K
Crop damage: 0.00K
Reported by: NWS Employee

A NWS employee reported 1.25 diameter hailstones at their house in southwest Amarillo.