This morning, between 8 and 10AM, New Orleans, Louisiana had a dusting to about an inch of snow as a vigorous early season winter storm moving from Louisiana towards  the mid-Atlantic pulled very cold air over the south central states while abundant moisture was moving in from the Gulf of Mexico. Snow in New Orleans is of course quite rare, having occurred only 17 times since 1850. New Orleans' last snow was a dusting on Christmas 2004, and before that they received 1-2 inches on December 22nd, 1989. The most in their recorded history was 5 inches on December 22nd, 1963. That makes this snowfall the earliest ever recorded in New Orleans. 

  Below are some weather charts that help explain why this highly unusual weather event occurred. Most striking is the very deep 500mb trough (Figure 3) with a developing cutoff low forming directly over southeastern Louisiana. Normally these troughs would not reach this far south with this strength in December. Also, note in the last surface chart, that with the exception of that isolated 31F reading in east central Texas, there are no freezing or below-freezing temperatures near the Gulf coast. In this case, there was a very shallow layer of above-freezing air at the surface, but much colder temperatures just above it that allowed the snow to reach the ground without melting.