The emergence of cloud before Judgment

هَلْ يَنظُرُونَ إِلَّآ أَن تَأْتِيَهُمُ ٱلْمَلَٰٓئِكَةُ أَوْ يَأْتِىَ رَبُّكَ أَوْ يَأْتِىَ بَعْضُ ءَايَٰتِ رَبِّكَ ۗ يَوْمَ يَأْتِى بَعْضُ ءَايَٰتِ رَبِّكَ لَا يَنفَعُ نَفْسًا إِيمَٰنُهَا لَمْ تَكُنْ ءَامَنَتْ مِن قَبْلُ أَوْ كَسَبَتْ فِىٓ إِيمَٰنِهَا خَيْرًۭا ۗ قُلِ ٱنتَظِرُوٓا۟ إِنَّا مُنتَظِرُونَ

Are they waiting to see if the angels come to them, or thy Lord (Himself), or certain of the signs of thy Lord! the day that certain of the signs of thy Lord do come, no good will it do to a soul to believe in them then if it believed not before nor earned righteousness through its faith. Say: "Wait ye: we too are waiting."

فَٱرْتَقِبْ يَوْمَ تَأْتِى ٱلسَّمَآءُ بِدُخَانٍۢ مُّبِينٍۢ

Then watch thou for the Day that the sky will bring forth a kind of smoke (or mist) plainly visible,

يَغْشَى ٱلنَّاسَ ۖ هَٰذَا عَذَابٌ أَلِيمٌۭ

Enveloping the people: this will be a Penalty Grievous.