Mammatus clouds are also known as mammatocumulus or translated from Latin to english: “mammary cloud” or “breast cloud”.
Breast clouds usually form at around 4 kilometers above the sea level when rain falls onto a dry layer of air and and instantly evaporates thus creating these eerie mammatus clouds.
Last week, these mammatus clouds were triggered by an active jet stream, causing rainfall over Israel. These eerie clouds are normally associated with severe storms and rain.
I haven’t heard about apocalyptic weather, but only about heavy rains.