Now, and over the next few months is the best time to buy lightweight toppers if you're in the Northern hemisphere. By May, when you're actually looking for them because it's warm enough to wear them, stores are picked over and focus on "naked" clothing. In other words, from May onwards, retail focuses on skimpier Summer tops and bottoms, and there's barely a Summer topper in sight. Just lots and lots of classic cardigans.
Trust me on this as I learned the hard way. In Seattle, I'm shopping for toppers with clients throughtout the year in all sorts of weights. We have learnt to shop for Summer toppers much sooner. xo