Why does it say "u'Va" (masculine)? Ra'ah is feminine!
Radak: We must say that it refers to Yom Ra'ah or Devar Ra'ah; the word Yom or Devar is omitted.
What is the meaning of "Lo Sede'i Shachrah"?
Rashi citing Targum Yonasan: You will not know to ask about it
What is "Hovah"?
Radak, Malbim: It is breakage.
What is "[Lo Suchli] Kaperah"?
Rashi: To clean it and remove it. Every expression of Kaparah is cleaning and removing.
Radak: It is removal, like "Achaperah Panav ba'Minchah" (Bereishis 32:21)
What is "Sho'ah [Lo Seda'i]"?
Radak: It is Shemamah (desolation).
Malbim: This is Machaneh Madai u'Faras, which fell suddenly on the city. They did not sense it beforehand.