This is weird. This represents a change over a mere ten year period.
My zone hasn't changed (still 6b), but USDA states the lowest T has gone up 5F (-10,-5) to (-5,0).
Last winter we had -10F for a week. This winter we had -20F for a week.
What I find strange is that the interval from the last assessment is small, only 10 years. And yet in two of those we broke records in the opposite direction of that reported. Note that USDA is not reporting the average, but the coldest temps likely to be encountered.
Even if the winter is trending warmer, I would think two record breaking cold winters in a ten year span would change my local data downwards, not up.
This has affected me. For three years I have tried planting chicago hardy figs. For three years we've had chicago like winters and the figs didn't make it (chicago hardy needs a couple of mild winters to withstand chicago temps).