The Targum Pseudo-Jonathan on Exodus 9:18, the Aramaic paraphrase long attributed to Yonatan ben Uzziel, does something the plain Hebrew text does not. It names the source of the hail.
"Behold, at this time tomorrow I will cause to come down from the treasures of the heavens a mighty hail, the like of which hath never been in Mizraim since the day when men were settled upon it until now."
Otzarot shemaya — the treasuries of heaven. The Targumist imagines the firmament not as empty space but as a series of storehouses, each containing an element the Holy One can release at will. Snow has a treasury. Wind has a treasury. Dew has a treasury. And hail, the Targum insists, comes from one of these sealed vaults, opened only when the Judge of the earth commands.
The image is important. Nature, in this theology, is not autonomous. The weather does not simply happen. It is dispensed.
And the Lord gives Pharaoh a full day's warning. Twenty-four hours to believe a prophet whose word has already been proven by blood, frogs, lice, wild beasts, cattle plague, and boils. The Maggid teaches: warning is itself a mercy. Every plague Egypt suffered came with an advance notice that Egypt chose to ignore.