I'm thinking warmer temperatures are causing it.
December's average daily high temp was 58, just 1 degree above normal but the average daily low was 5 degrees above normal. In fact, the lows for the last five days of December were mid 50's.
January's average daily high temp was also 58, just 1.5 degrees above normal but the average daily low was 5 degrees above the normal of 35. Unfortunately for young spears, two day stretches of lows in the mid 20's come through about once a week.
There's been asparagus out in the garden for about 20 years and I've never seen it come up this early.