Help me with this sentence from Harry Potter and the Deathly Hallows

Question

Autumn seemed to arrive suddenly that year. The morning of the first of September was crisp and golden as an apple, and as the little family bobbed across the rumbling road toward the great sooty station, the fumes of car exhausts and the breath of pedestrians sparkled like cobwebs in the cold air. Two large cages rattled on top of the laden trolleys the parents were pushing; the owls inside them hooted indignantly, and the redheaded girl trailed tearfully behind her brothers, clutching her father’s arm.

What does the phrase "crisp and golden as an apple" mean?

If golden meant dry day, why was their cold air?

Thanks in advance

Answer 1

This paragraph describes a particular time of year in northern Europe. 'Golden' comes from the leaves beginning to turn yellow, the apples ripening, and the sun being lower in the sky. And 'apple' sets up a sense of wholesome freshness to contrast with sooty station.
'Crisp' is a metaphor for the early morning hint of frost, the energy needed to face the cold, the alertness of the family on the move.

The same conditions can be found in other places of course, especially places where apples grow. The foothills of mountain ranges have crisp and golden days.