Exodus 9:14

For at this time I will send upon thee a plague from the heavens, and all My plagues Wherewith I have plagued thee thou wilt cause to return upon thy heart, and upon thy servants, and upon thy people, (plagues) which have been sent from before Me, and not from the magic of the sons of men, that thou mayest know that there is none like Me in all the earth.

מגפותי, different damage causing plagues, such as fire, hail, and brimstones, snow and heavy smoke.

כי בפעם הזאת, this time when I demonstrate My power over the third category of phenomena, the atmosphere and what it contains, אני שולח את כל מגפותי אל לבך ובעבדיך ובעמך, every plague which I am about to send will affect each one of you even after the plague itself departs. The damage caused by the plague while it was active will be felt long after the plague has departed. The after-effect could be felt because of the vegetables remaining having suffered damage from the hail. The unnatural type of darkness would also leave behind it unpleasant after-effects, as the whole atmosphere would have been affected during the period of no light. If we consider that for three days running no one could even rise from his chair or bed, we can imagine that this was not merely an absence of daylight. The plagues that had preceded the hail had not left behind them permanent after-effects.

בעבור תדע כי אין כמוני בכל הארץ, this realisation will come to you when you observe how I enjoy complete mastery of the atmosphere. G’d reserved the demonstration that He also had complete control of all the phenomena in outer space, or in extra terrestrial regions for the time when He split the Sea of Reeds. When the Egyptians observed the movements of the pillars of fire and the columns of cloud, all of which moved in a manner which reflected that they were being directed by a higher power.