There shouldn't be any correlation between a particular season and prices, but, for a fact for some reason prices begin to increase in the end of autumn and keep growing during the winter season (my own observation), so now is probably the best time to purchase Bitcoin as well as some altcoins and hold for 5-6 months. You can see the red market yourself - it's a good sign, buy during the downtrend. This has already happened in 2013, 2015 and, of course, the last year, but the uptrends and downtrends are becoming more and more steep as the years are passing, so better hurry and don't miss the perfect moment.