1. The part of New Zealand I live in (Auckland) is subtropical.
2. New Zealand is in the Southern hemisphere, so it gets colder going south and warmer going north. Also, winter is in the middle of the year instead of at either end.

So, this winter, it's been somewhat cold and damp, as it usually is, and raining a lot as it usually does. However, there have also been (relatively speaking) some days which were quite warm. Then, all of a sudden, it's the coldest it's been all winter (in fact, colder than it's been any winter this far north for a long time) and it starts sleeting. This happened last night. It was mostly gone by the late morning today, but it's extremely surprising that it happened at all.