Weather is kind of crazy, as usual.
Ken here's a possible explanation from the extreme ridges and troughs we've been having in the jetstream, which cause temperature extremes in a short period of time and may even be responsible for the blocking highs and heat we experienced in North American last summer.
Not arguing whether this is true. Just a possible explanation.
http://www.climatecentral.org/news/arctic-warming-is-altering-weather-patterns-study-shows