I think winfly is an acronym for winter fly-in. It’s the first flights of the season usually starting on the day the sun first comes over the horizon. With a little bit of light the flight crews can see the runway and it’s a bit safer than coming in twilight.
This year we had three flights. The first was delayed a day by a severe winter storm. The rest came in on time, but the last flight was close to being canceled for ground fog which sometimes forms at very low temps and no wind.