The difference between a blizzard and other snowstorms is that in a blizzard, it is the wind that causes most of the trouble by keeping the snow airborne to such an extent that visibility is reduced to nearly nothing. In a ground blizzard, such as the one last Wednesday night, there is little to no falling snow and the blizzard is caused by the wind being strong enough to pick up already-fallen snow and keep it airborne for several hours.
Blizzards are hard to predict and ground blizzards are especially hard because the strongest winds are usually caused by turbulent, downward transport of strong winds higher up in the atmosphere where there is not a lot of wind data. Forecasters often resort to saying things like "blizzard conditions are possible," and only rarely are we able to forecast blizzard conditions with certainty. Even in the hours leading up to last Wednesday night's ground blizzard, there was some uncertainty as to how bad it would get.