Chazal tell us that Chanukah was instituted as a day of both hallel and hoda’ah. The Sefas Emes asks: don't these two expressions mean the same thing – giving thanks to G-d. Why do Chazal use both expressions when one would suffice?
Sefas Emes answers that hallel and hoda’ah in fact mean different things. Hallel is praise for what everyone recognizes immediately as a miraculous, wonderful outcome; hoda’ah is what you realize to be good only upon reflection and the passage of time. In the story of Chanukah, the defeat of the Greeks and the miracle of the menorah were immediately appreciated as great events that required the recitation of hallel. But that’s only half of the picture. Chazal are telling us that the subjugation by the Greeks, which at the time seemed to be a horrible gezeirah, is something that also needs to be appreciated as chasdei Hashem. That perspective only comes with time and reflection; that perspective gives rise to hoda'ah (more in the Sefas Emes here, and see this post on the relationship between viduy and hoda’ah that he alludes to.)
For some, the storm passed with little damage and it was possible to say hallel immediately afterwards. For others, hopefully this is a day of hoda’ah, of coming to grips with the loss incurred and being able to see chasdei Hashem in retrospect.