The sun was up in the sky, there were no clouds and it looked as if it was going to be a wonderful day.

as 在这里是连词，表示"如同"或"像"的意思，用于引导比较状语从句。 if 在这里也是连词，表示"好像"或"似乎"的意思，常与as连用构成固定搭配。 as if 是一个固定搭配，意思是"好像""仿佛"，用来引导方式状语从句，表示某种假设或推测的情况。