Why has it been so cool this late in the year?

In my 46 years of existence I don't remember it ever being this cool this late in the year. Snow just the other week in Pennsylvania. Highs were I live at times barely reaching 65*F when the average for this time of year is 85*F. Gardens are late to have growth. Frost has ruined cherries for the year. Lawn grass isn't growing as fast even with rain. Usually by this time my yard could be mowed twice a week. I am now mowing every other week. Just the other night I was shocked to see my breath in the cool air. I have never, ever seen that in the month of June. Lows around here average 60*F at this time of year.