Abdullah ibn Umar (RA) narrated: The Messenger of Allah (ﷺ) heard a thunderclap or a loud noise like thunder. He would say:
اَللَّهُمَّ لَا تَقْتُلْنَا بِغَضَبِكَ وَلَا تُهْلِكْنَا بِعَذَابِكَ وَعَافِنَا قَبْلَ ذَلِكَ
Transliteration
Allaahumma Laa taqtulna bi-ghadabika Wa laa tuhlikna bi-adhaabika Wa aafina qabla dhalik
Translation
O Allah, do not kill us with Your wrath, and do not destroy us with Your punishment, and pardon us before that.
He said, Allahumma inni a'udhu bika min sharri ma anzalta wa min sharri ma akhrajta. This asks Allah to protect us from harm in what He sends and what comes out.
Say it as soon as you hear thunder or see lightning. Your heart stays with Allah. You feel calm during the storm.
Yes. It asks Allah to protect from all harm in His creation. This includes danger from thunder and lightning.
Yes. You can add other duas for safety. Like Bismillah alladhi la yadurru ma'a ismihi shay'un fil-ardi wa la fis-sama'i. This gives more protection.
It makes your faith stronger. It reminds you Allah controls nature. Your heart gets calm and peace during big storms.