日本のどこでも雪が降るのかどうか尋ねられたら、単純に「Not necessarily」（そう言う訳ではない）と返すのが一番無難で、万能かと思います。
もし延長して言うなら、「It doesn't necessarily snow all across Japan」になりますが、「Not necessarily」と返した方が簡単かつ自然かと思います。
Just because it snows in some places in Japan doesn't mean it snows everywhere
「～わけではない」は一番大切なポイントです。英語もこういう表現をよく使える。"It doesn't mean that" という表現は「～わけではない」と同じ意味です。
「日本のどこでも雪が降るというわけではありません」と翻訳したら、" Just because it snows in some places in Japan doesn't mean it snows everywhere" になります。
他の例文：
Just because I don't want to eat it now doesn't mean I don't like it 「今食べたくないけれど、好きじゃないわけではありません。」
The three sentences you see provided above are terrific ways to express to your listener that it does not snow everywhere in Japan. In the third sentence you will see the word throughout. This means in every part of a place or thing. This word is appropriate for both formal and informal settings. It would make an awesome addition to your vocabulary.
When you want to explain that it only snows in certain parts of Japan but not everywhere; then you may answer in the following ways:
-It doesn't snow in every part of Japan
-No. It doesn't snow everywhere
-Only certain parts of Japan snow. Others don't
「日本では雪が降る地域と降らない地域がある」と説明したいなら、次のように言えます。
-It doesn't snow in every part of Japan（日本では雪が降らない地域もあります）
-No. It doesn't snow everywhere（いいえ、日本では雪が降らない地域もあります）
-Only certain parts of Japan snow. Others don't（日本では雪が降る地域と降らない地域があります）
In some regions of Japan it snows but not everywhere.
"Region" is another word for "area." You don't need to repeat "in Japan" after everywhere because it is implied and we don't like to repeat ourselves. I hope that this helps. :)
When asked "Does it snow everywhere in Japan?", you want to say that it snows in some places but it doesn't in others.
You use one of the above suggested responses.
イギリス 
アメリカ合衆国 
南アフリカ 
