The recent cold snap has also brought snow to portions of the Southland that rarely see any. It stems, in part, from a weakening polar vortex — a wide expanse of swirling cold air in Earth’s poles. When the polar vortex is strong, there’s powerful west-to-east wind that traps cold air in the Arctic. If it weakens and the air is no longer a continuous band, cold air can spill out of the Arctic and move down to the West Coast, Swain said.

Source: Los Angeles Times March 01, 2019 00:09 UTC