It's not as hot this summer.
This summer feels colder than last year.
We are having a cold spell this summer.
This is not a normal summer this year. It's much too cold.
I can't believe how cold this summer is.
I have never seen it this cold in summer.
Some areas have cold summer such as Wyoming, and Montana.
It's not as hot this summer.（今年の夏はそこまで暑くありません）
This summer feels colder than last year.（今年の夏は去年よりも涼しいと思う）
We are having a cold spell this summer.（今年の夏は冷夏になっています）
This is not a normal summer this year. It's much too cold.（今年の夏は普通ではありません。寒すぎます）
I can't believe how cold this summer is.（この夏は信じられないくらい寒いです）
I have never seen it this cold in summer.（こんなに寒い夏は初めてです）
Some areas have cold summer such as Wyoming, and Montana.（ワイオミングやモンタナなど一部の地域では冷夏になります）
Every year the weather can be different in temperature so if it is colder than other years you could refer to it as a 'cool summer' another way to say and describe this in detail is
'it's not as hot this summer'
毎年、気温が変わります。他の年より涼しい夏のことを、 'cool summer' （冷夏）と言います。
'it's not as hot this summer'
（今年の夏はそれほど暑くない。）
Every summer can be different each year so if you wanted to explain to someone about the summer being colder than last year you could say "Its a chilly summer this year"
夏といっても毎年毎年違いはありますね。もし普段よりも涼しいなら、"It's a chilly summer this year"（今年の夏は寒い）と言えます。
When talking about a cooler than normal summer you can say it is a "Mild summer".
"It has been a mild summer so far."
"Do you think it will be mild all summer?"
Mild means to not be as severe or warm.
"The heat has been severe this year."
"I cannot believe how warm it is today!"
例年に比べて涼しい夏は "Mild summer" と表すことができます。
"It has been a mild summer so far."（今年の夏は今のところそんなに暑くありません）
"Do you think it will be mild all summer?"（今年は最後まで冷夏になると思いますか）
"Mild" は 'to not be as severe or warm'（厳しくない、暑くない）という意味です。
"The heat has been severe this year."（今年の暑さは猛烈だ）
"I cannot believe how warm it is today!"（今日はすごく暖かい）
When summer is not as hot as it usually is during other years then we can say "the temperature has dropped."
There can be many different reasons for this taking place.
A cool summer is always great, most people don't like to feel too hot from the sun.
Temperate: moderate, cool.
Light: not heavy, breezy, refreshing
"This summer is much cooler than last!"
"What a temperate summer! usually, it is boiling hot by this time of year."
"I enjoy summer when it is this light."
夏がいつもの年よりも涼しいときは、"the temperature has dropped"（気温が下がった）と言うことができます。
これが起こる原因はいろいろです。
夏は涼しい方がいいですね。暑いのは苦手という人が多いです。
Temperate: 穏やかな、涼しい
Light: 軽い、そよ風の吹く、さわやかな
"This summer is much cooler than last!"（今年の夏は去年よりずっと涼しい）
"What a temperate summer! usually, it is boiling hot by this time of year."（今年の夏は過ごしやすいですね。いつもだとこのくらいの時期にはうだるような暑さなのですが）
"I enjoy summer when it is this light."（このくらい涼しい夏が好きです）
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