There’s a brooding force that often lurks over Canada’s inland sea, subtly reshaping the weather hundreds of miles away. It’s called the Hudson Bay low, and you’ve probably felt its influence without realizing it.

The Hudson Bay low is a large, semi-permanent area of low pressure that often forms over Hudson Bay in northeastern Canada, particularly during the late fall, winter and early spring. It develops as cold Arctic air spills southward over the relatively warmer (but still frigid) waters of Hudson Bay.

Because Hudson Bay is a vast, shallow body of water surrounded by land, it often acts like a cold-air reservoir, helping lock this low in place for days or even weeks. It can have major impacts on everything from precipitation to temperatures for millions.

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The Hudson Bay low plays a key role in steering weather systems across much of eastern North America. It can act like a block, redirecting storms southward into the Midwest or northeastern U.S., and also contributes to cold air outbreaks in Canada and the northern U.S.

By reinforcing the dip in the jet stream, it helps pull Arctic air deeper into the continent. While not as well-known as the Bermuda high or Aleutian low, the Hudson Bay low quietly influences a lot of the cold-season weather many North Americans experience.

Jennifer Gray is a weather and climate writer for weather.com. She has been covering some of the world's biggest weather and climate stories for the last two decades.