There are different answers to that.
The easy one: it will either rain or not rain - therefore 50 %.
Another easy: it will most likely rain somewhere in the US - therefore almost 100%.
The hard one: learn a lot about meteorology and collect a lot of data about rain. Do a lot of calculation.
Give Us Tomorrow was created in 1978.
There is no specified rain season in the US. Most US states have a series of seasons that contain rain.
tomorrow
rain on us is by Ernest Pugh
Tomorrow.
tomorrow
Mexico us going to play with Venezuela tomorrow at 10:00pm
The phrase "us ever after tomorrow's " is an awkward phrase, plus it makes "tomorrow's " a singular possessive. It shouldn't be used. You might say, "us for ever after", but even that becomes awkward in a sentence.
The adverb in that sentence is tomorrow. It's an adverb of time telling when Uncle Rico will visit.
It shows us the likelihood of the occurrence of specified events.
Our doctor told us the probability was 4%.
In the US its New York