"Then the Lord said to Moses, 'Stretch out your hand toward the sky so that hail will fall all over Egypt - on people and animals and on everything growing in the fields of Egypt.' When Moses stretched out his staff toward the sky, The Lord sent thunder and hail , and lightning flashed down to the ground. So the Lord rained hail on the land of Egypt; hail fell and lightning flashed back and forth. It was the worst storm in all the land of Egypt since it had become a nation. Throughout Egypt hail struck everything in the fields - both people and animals; it beat down everything growing in the fields and stripped every tree. The only place it did not hail was the land of Goshen, where the Israelites were." NIV translation
So, the Lord used Moses to bring about the worst storm in the history of Egypt. It affected the entire country except for the land where the Israelites lived. This is a reminder that God makes a clear distinction between His people and the world at large.
"Then Pharaoh summoned Moses and Aaron. 'This time I have sinned,' he said to them. 'The Lord is in the right and I and my people are in the wrong. Pray to the Lord, for we have had enough thunder and hail. I will let you go; you do not have to stay any longer." NIV translation
It appears that Pharaoh has "seen the light" and is repenting as he calls Moses and Aaron. Many will call out to the Lord or have someone else pray for them when they are in the middle of a tough situation.
"Moses replied, 'When I have gone out of the city, I will spread out my hands in prayer to the Lord. The thunder will stop and there will be no more hail, so you may know that the earth is the Lord's. But I know that you and your officials still do not fear the Lord God.'" NIV translation
Pharaoh wanted to be saved and even confessed that he was wrong but was not willing to repent. Moses recognized that as he agreed to pray for him and we see that repentance only comes from godly fear.