Weather Terminology: Unexpected Stratospheric Heating

A Sudden Stratospheric Warming (SSW) happens when temperatures in the stratosphere surge dramatically over just a few days. This phenomenon occurs as large atmospheric waves, called Rossby Waves, travel far north and rise to high altitudes, disrupting the stratospheric polar vortex.

Much like ocean waves, these Rossby Waves can "break" over the polar vortex, weakening it. In cases where the waves are particularly strong, the polar vortex winds may even reverse direction, shifting from westerly to easterly, which causes the trapped cold air to descend while the stratosphere warms rapidly.

The stratospheric polar vortex is a large pool of extremely cold air situated above the Arctic. When this vortex weakens, splits, or shifts position, the Arctic cold air can escape its usual confines and move southward. Historical examples of U.S. cold snaps linked to SSW events include the 2021 Texas Deep Freeze and the January 2024 Cold Air Outbreak.

Author: Gavin Porter