Chiefly in the Northern Territory, knock ’em down rains are violent thunderstorms in the Top End, with strong winds, lashing rain and plenty of lightning and thunder. These usually occur at the end of the wet season in the north of the NT.
Our Australian Word Map offers up some contributor etymology of the term in that it is so called because it
refers to the rain knocking down the tips of the spear grass that has just started turning brown at this time of year, the rain knocks the seedy heads off for next year’s spear.
and
the heavy rain storms at the end of the Wet which knocked down all the (6ft) tall grass.
