SpaceWeather notes that Halloween is a cross-quarter date, one of the days that falls exactly between an equinox and a solstice. The other three are Groundhog Day (Candlemas or Imbolg), May Day (Beltane), and August 1st (Lammas).
The cross-quarter days establish offset seasons, sometimes called the solar seasons. Solar Winter starts today and ends, hog willing, on Groundhog Day, with the solstice in the middle. But in my experience, August 1st is still high summer. Halloween, while a chilly, wet day, is unlikely to produce snow, while the groundhog is frequently snowed in in his burrow come Groundhog Day. I’ll stick to the modern seasons.