Albert Barnes Commentary Jeremiah 4:11

"At that time shall it be said to this people and to Jerusalem, A hot wind from the bare heights in the wilderness toward the daughter of my people, not to winnow, nor to cleanse;" — Jeremiah 4:11 (ASV)

At that time - See (Jeremiah 4:7). Though the revelation of the certainty of Judah’s ruin wrings from Jeremiah a cry of despair, yet it is but for a moment; he immediately returns to the delivery of God’s message.

A dry wind - literally, A clear wind. The Samum is probably meant, a dry parching east wind blowing from the Arabian desert, before which vegetation withers, and human life becomes intolerable.

Not to fan... - The Syrian farmers make great use of the wind for separating the chaff from the grain: but when the Samum blows labor becomes impossible. It is not for use, but for destruction.