Is this a rare event or does it happen quite often?
Would not want to be in its path.
Oh yeah. Here in ABQ & other SW cities there are arroyos, paved channels that run downhill from the mountains (here the Sandias) to the rivers, here the Rio Grande, & it could be dry & sunny in town with huge storm on mts, & those dry channels become raging torrents. Foolhardy souls like to skateboard etc in the dry arroyos, causing the need for swift water rescues as the surge runs through town.