Spring is, of course, one of the two transitional times of the year for the wardrobe. What is one to do in March or April when it's still cold, or in September or October when it's still hot?
Heavy Tweed Jacket just posted a new picture of himself today -- April 2 -- on his Tumblr, wearing a, well, heavy tweed jacket.
It makes more sense to dress for the weather than for the calendar.
For late summer/early fall, I like Will Boehlke's advice: ditch the overt summer items, like straw hats and spectator shoes, but continue to wear summer-weight clothing for as long as the weather requires it, but try to do so in more seasonless or autumnal colors -- such as a linen suit in navy or dark brown, instead of in light blue or tan.
For late winter/early spring, my opinion is to reverse the advise: maybe ditch overtly wintery items like tweed, but continue to wear winter-weight items in spring or seasonless colors, like a navy flannel blazer, as long as necessary. You could also mix them with some springier hues, like a light blue tie. I love HTJ's outfit, but I don't think I personally would wear it in April.
If this seems too confusing, or you don't have an extensive enough wardrobe to do it fully (I don't either), I suppose you can take solace in the fact that only hardcore clothing nerds like us even pay attention to such things; I suspect that the seasonal clothing distinction is lost on most people, who regard all classic clothing as "a suit." Sigh.