Why all the winter annuals this year?

Had a question why winter annuals, specifically henbit, are so thick this year.  Two main factors: 1) ample moisture at the end of last year's growing season, and 2) a relatively mild winter.  Most winter annuals emerge in late August-September, in many years we don't have enough soil moisture to trigger germination.  That obviously wasn't an issue last year.  Frequently there can be relatively high mortality rates of winter annuals during the winter, but the combination of early-emergence and a mild winter would have minimized those losses.  Now specifically what favored henbit this year, I'm not quite smart enough to know that.