Polar Vortex

 Supposedly this is the culprit responsible for our below-zero weather lately.

On Tuesday and Wednesday morning,

we had wind chill temperatures of 10 below zero.

This morning, it was 14 degrees.... a veritable heat wave.

According to meteorologist Brandon Miller, a Polar Vortex is "...circulation of strong, upper-level winds that normally surround the northern pole in a counterclockwise direction -- a polar low-pressure system.  These winds tend to keep the bitter cold air locked in the Arctic regions of the Northern Hemisphere. On occasion, this vortex can become distorted and dip much farther south than you would normally find it, allowing cold air to spill southward.  The upper-level winds that make up the polar vortex change in intensity from time to time. When those winds decrease significantly, it can allow the vortex to become distorted, and the result is a jet stream that plunges deep into southern latitudes, bringing the cold, dense Arctic air spilling down with it. This oscillation is known as the Arctic Oscillation and it can switch from a positive phase to negative phase a few times per year. This oscillation -- namely the negative phase where the polar winds are weaker -- tends to lead to major cold air outbreaks in one or more regions of the planet."

Or, put more simply, it's an icy wind that blows up your skirt at the trolley stop

and makes you want to die.  A truly negative phase in your day.