In addition to the Altantic influence CaT mentions, the northern route of the jet stream seems to be locking in the cold weather in a polar loop around the great white north. The usual cold fronts just aren't able to drop south this winter.
Our lack of snow here in CA correlates pretty well with the La Nina condition we're experiencing (cooler water in the southern Pacific), which is the opposite of El Nino (above average water temp in the Southern Pacific). The oscillation back and forth between these two conditions is associated with well known weather patterns, but they are just trends. Last winter was also a La Nino signal and we had tons of snow.
Once these oceanic/atmospheric oscillations get established at an extreme end of the cycle, they tend to set up seasonal conditions and things don't change much for weeks or months.
The current La Nina is expected to remain until March-May, albeit a weak to moderate signal. Hopefully, the current equilibrium will break down and we'll get into a snow pattern. There's plenty of time to catch up if it gets started soon. Nothing on the horizon yet though.
Link to NOAA El Nino/La Nino Cycle
