This is the 1744th most frequent Korean word.
전국에
"Nationwide"
In this sentence, "전국에" is used to express spatial distribution across the entire country.
전국에 많은 공원이 있습니다.
There are many parks across the whole country.
Here, "전국에" conveys the scope of the television broadcast as covering the entire nation.
전국에 방송되는 뉴스 프로그램이 시작되었습니다.
The news program broadcast nationwide has started.
In this context, "전국에" refers to the area affected by the action of raining, spanning the entire country.