Think about a large body of air with similar temperature and moisture. These air masses typically originate in specific locations in North America and will represent the type of characteristics ...

There are five air masses across North America at any given time. (Courtesy of NOAA) Continental polar air, which originates in Canada, is the most common air mass we find here in New England.

So how does this effect winter's in the northern U.S. Well Spokane, and the PNW gets air that originates from the north Pacific which is maritime polar, and the Midwest U.S. gets continental polar.

Air masses are huge, usually extending hundreds, occasionally thousands, of miles. Four kinds of air masses–Arctic, Canadian, Gulf and Pacific–dominate Chicago’s climate.

– cA (Continental Arctic): This air mass is the driest and coldest of all air masses. They are the northernmost air masses over land. You’ll find this over northern Canada, north of ~80N.

Viennese meteorologists: Transport of air mass from the Pacific Ocean explains weather conditions associated with El Niño in North America, South America and Australia The El Niño phenomenon ...

Cold air masses can settle in more frequently, leading to extended periods of chill. Storms: New England sees a mix of dry periods and intense winter storms during La Niña.