The event featured:
-Localized heavy rainfall
-Heavy thunderstorms at night
-A remote campground in a canyon next to a river, where many people likely had no warning devices
Here’s the summary from the Little Rock NWS.
Arkansas flash floods kill at least 20 people
By JILL ZEMAN BLEED (AP) – 56 minutes ago
CADDO GAP, Ark. — Floodwaters that rose as swiftly as 8 feet an hour rushed into a remote Arkansas valley early Friday, killing at least 20 people, many of them campers who became trapped by a devastating wall of water. Dozens more were missing and feared dead.
Heavy rains caused the normally quiet Caddo and Little Missouri rivers to climb out of their banks during the night. Around dawn, floodwaters barreled through the Albert Pike Recreation Area, a 54-unit campground in the Ouachita National Forest that was packed with vacationing families who were probably still asleep when their tents began to fill with water.
Two dozen people were hospitalized. Authorities rescued 60 others.
Check out the CNN description of the event. It does a good job of illustrating the dangers of flash floods.
You may remember the deadly August 2007 flood event in southeast Minnesota also occurred at night.