to get (very) cold; to get (much) colder
to feel very cold (of the body); to be chilled to the bone
to worsen (of relations, economic conditions, etc.); to decline
昨夜は急に冷え込んだ。
It got very cold suddenly last night.
今朝は特に冷え込んでいるから厚着が必要だ。
It is especially cold this morning, so dressing warmly is necessary.
北部では一月になると冷え込む夜が増えていく。
In the north, bitterly cold nights increase once January arrives.