Can you tell me why we have this temperature revision? Also, why does unseasonable weather happen anyway?
By temperature revision, I assume you mean the extra cold weather after the long run of 80s and the nose dive the temperatures took!
Your question would require a book chapter to fully answer, so I'll try to cut it very short, which means I will cut a few corners as well. But I think you will have a simplified picture of how these rare Arctic blasts can make it to the Gulf Coast.
Several times each winter, an extremely cold air mass builds over the northern Canadian Plains, the Canadian Yukon, the North Pole, and/or even sometimes over Siberia. Rather than normally moving with the rest of the atmosphere (the usual situation), the cold air mass stays put and keeps getting colder and colder. The colder it gets, the "heavier" it gets.
At some point it will finally start moving, and once it starts moving, its "extra weight" (from being extra cold) gives it extra momentum as it starts moving southward. Occasionally those Siberian air masses will first head north, cross the North Pole, and then head south across Canada! These tend to be the WORST/COLDEST air masses to hit North America.
If the upper air pattern begins to develop a decent trough (a deep, southward dip in the jet stream), the bitter cold air mass can travel even farther south. Over the Easter weekend, all the ingredients were in place to bomb the Southeast U.S. with record cold, as the jet stream reached all the way into the Gulf, allowing the bitter-cold air mass a free rise this far south!
While we did miss the "freeze" that I was concerned about for Easter Sunday, we did get a record-late winter precip ("sleet & snow") here in the greater Baton Rouge area! What makes this all the more unusual was that this was the first really bitter-cold Arctic blast since early December!