We have this problem in Ireland also. It might be sunny in the morning and raining in the afternoon! Therefore the weather frequently changes.
Frequently- Often
In Ireland if something ''changes like the weather'' it means that it changes very often.
Example:
His mood changes like the weather.
アイルランドでもこの問題があります。朝は晴れていても、午後には雨が降ることがあります。ですので、天気が頻繁に変わります。
Frequently- よく、頻繁に
アイルランドで ''changes like the weather''（天気と同じように/頻度で変わる）と言うと、とてもよく変わることを意味します。
例：
His mood changes like the weather.
彼の気分はよく変わる。
Unpredictable: means that don't know what will happen next. One second it would be sunny and the next it would be raining. Unpredictable can be used in other situations like
"This boy is so unpredictable. He changes his mind all the time!"
You can also say that "The weather is always changing." and it would convey the same message.
Hope this helps!
Unpredictableとは、次に何が起こるかわからないという意味です。一瞬晴れても、次は雨が降っているということです。 Unpredictableは、以下のような状況でも使うことができます。
"This boy is so unpredictable. He changes his mind all the time!"
この男の子は読めない。いつも気が変わる！
また以下のようにも言うことができます。
"The weather is always changing."
天気がよく変わる。
これは、同じ意味を表します。
Weather in Boston is unpredictable and can change in an instant.
Unpredictable means that it is difficult to tell what is going to happen with something. In this case it is the weather that we find unpredictable. One moment it could be sunny, the next it is pouring with rain.
Instant is another way of saying 'very quickly'.
The weather in Boston changes all the time, it is never the same.
Boston's weather is never the same.
This is a way of saying that you cannot simply follow the weather report because the weather changes all the time and because of this you must always be prepared for anything.
This sentence or phrase is showing that the weather is not able to be predicted.
When something is predictable it means that it follows a pattern that often can easily be determined. For example the weather in a desert is predictable; it is a very unlikely for it to rain there.
In contrast to this the weather in Boston cannot be predicted. This is the weather from many urban countries.
"The weather in Boston is always changing"
This sentence implies that the weather in Boston Is always changing, the weather is not always the same.
"Boston weather is very unpredictable"
This is explaining that the weather in Boston is 'Unpredictable', meaning that the weather is always changing, something that you don't know what will happen next.
"The weather in Boston is always changing"（ボストンの天気は変わりやすい）
は「ボストンの天気は変わりやすい」と伝えています。
"Boston weather is very unpredictable"（ボストンの天気は予測がつかない）
では「ボストンの天気は 'Unpredictable' だ」と言っています。これは「ボストンの天気は変わりやすい、予測がつかない」という意味です。
イギリス 
アイルランド 
カナダ 
南アフリカ 
