'Arctic Express' vs. 'Siberian Express'

Dear Tom,
You refer to cold outbreaks from the north as the "Arctic Express" or the
"Siberian Express." Any difference?
Arthur Hitt, Richland Center, Wis.
Dear Arthur,
"Arctic Express" and "Siberian Express," while pleasingly descriptive, are
colloquial, non-technical terms whose definitions have never been formally
or precisely stated -- and add "Pineapple Express" to the list, because it
often occurs simultaneously with the other two.
Those terms describe patterns of upper "steering winds" (generally 15,000 to
30,000 feet aloft) that direct surface air masses from the tropical Pacific
Ocean to Alaska (Pineapple Express), from the Alaskan/Canadian Arctic deep
into the Lower 48 (Arctic Express) or from eastern Siberia and the
Alaskan/Canadian Arctic similarly deep into the Lower 48 (Siberian Express).
"Siberian" implies an air-mass origin northward from Alaska and Canada.