In a story beginning like this, the bright cold day in April could serve as a metaphor for the state of the world or the characters' lives within the novel. It could imply that things seem promising on the surface (the brightness) but are actually rather harsh (the cold). This could be related to the society in the story, where there are outward signs of progress or beauty, but beneath it all, there are underlying problems. The story might then explore how the characters navigate this complex situation, whether they try to change it or are simply swept along by it.
Well, it might lead to a story where the coldness of the day affects the characters' actions and decisions. For example, they could be seeking warmth, either literally or metaphorically. And since it's a novel, there could be a complex plot that unfolds against this April backdrop. Maybe a character is on a journey, and this day is a significant part of that journey, either as a turning point or a moment of realization.
Perhaps it could be a story full of contrast, with the bright yet cold day setting a mood of unease or mystery. The month of April often symbolizes new beginnings, so there might be a character starting a new chapter in their life.