* Arctic (A) air masses: These originate over the Arctic Ocean and are extremely cold and dry. They bring the most severe cold waves, often associated with frigid temperatures and heavy snowfall.
* Continental Polar (cP) air masses: These form over the interior of Canada and are also cold and dry. They are less extreme than Arctic air masses but can still bring significant cold spells.
* Maritime Polar (mP) air masses: While they are considered "polar," they are often associated with milder temperatures than cP or A air masses due to their origin over the North Atlantic Ocean. They can bring chilly, damp conditions and occasional snow, but they are not the primary drivers of major cold waves.
How these air masses cause cold waves:
* Movement of air masses: During the winter months, a strong pressure gradient develops between the cold, high-pressure air masses over the Arctic and Canada and the lower pressure systems over the southeastern United States. This pressure difference drives the movement of cold air southward.
* Jet stream pattern: The position and strength of the jet stream, a ribbon of strong winds high in the atmosphere, influence the movement of air masses. A strong jet stream positioned further south allows the cold air to penetrate deeper into the United States, bringing cold waves to the central and eastern regions.
* Lake-effect snow: When cP air masses move over the Great Lakes, they pick up moisture, leading to lake-effect snow, which can exacerbate cold conditions.
Note: While these air masses are the primary contributors to cold waves, other factors like the El Niño-Southern Oscillation (ENSO) and La Niña patterns can also influence the severity and frequency of cold waves.
