The North American High (also ''Canadian High/Anticyclone'', sometimes in Europe ''Greenland High/Anticyclone'') is an impermanent
high-pressure area
A high-pressure area, high, or anticyclone, is an area near the surface of a planet where the atmospheric pressure is greater than the pressure in the surrounding regions. Highs are middle-scale meteorological features that result from interpl ...
or
anticyclone
An anticyclone is a weather phenomenon defined as a large-scale circulation of winds around a central region of high atmospheric pressure, clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere as viewed from ...
created
by a formative process that occurs when cool or cold dry air settles over North America. During summer, it is replaced with an
Arctic Low, or a
North American Low should it move over continental land.
Description
A North American High moves eastward across the continent, often in the company of one or more
low-pressure cell
In meteorology, a low-pressure area, low area or low is a region where the atmospheric pressure is lower than that of surrounding locations. Low-pressure areas are commonly associated with inclement weather (such as cloudy, windy, with possible ...
s or
cyclones. The cold, dense air does not extend usually above and is lower than the
Canadian Rockies mountain range.
Occasionally during winter, a North American High passes over the Rockies resulting in a cold front into Southwestern United States and Mexico, freezing crops and producing snow into Mexico's mountains, as far south as
Jalisco. The North American High's distance from the warm Pacific Ocean as well as its protection from the Rockies to its West reinforces its intensity. The average January sea level pressure at its centre is approximately 1,020
millibars
The bar is a metric unit of pressure, but not part of the International System of Units (SI). It is defined as exactly equal to 100,000 Pa (100 kPa), or slightly less than the current average atmospheric pressure on Earth at sea lev ...
(30.12 inches of mercury). The Canadian high often moves south-eastward until it reaches the Atlantic Ocean, where it merges with the
Azores High
The Azores High also known as North Atlantic (Subtropical) High/Anticyclone or the Bermuda-Azores High, is a large subtropical semi-permanent centre of high atmospheric pressure typically found south of the Azores in the Atlantic Ocean, at the Ho ...
.
During summer, the Canadian high circulates cool, dry air to the United States located east of the Rockies and parts of southern Canada.
The North American High is akin to the
Siberian High
The Siberian High (also Siberian Anticyclone; russian: Азиатский антициклон (''Aziatsky antitsiklon'')) is a massive collection of cold dry air that accumulates in the northeastern part of Eurasia from September until April. It ...
of
Eurasia
Eurasia (, ) is the largest continental area on Earth, comprising all of Europe and Asia. Primarily in the Northern and Eastern Hemispheres, it spans from the British Isles and the Iberian Peninsula in the west to the Japanese archipelago ...
, though much smaller, and has much less influence, merely affecting the weather of the Northern Hemisphere. The
sea-level pressure
Atmospheric pressure, also known as barometric pressure (after the barometer), is the pressure within the atmosphere of Earth. The standard atmosphere (symbol: atm) is a unit of pressure defined as , which is equivalent to 1013.25 millibars, 7 ...
(
atmospheric pressure
Atmospheric pressure, also known as barometric pressure (after the barometer), is the pressure within the atmosphere of Earth. The standard atmosphere (symbol: atm) is a unit of pressure defined as , which is equivalent to 1013.25 millibars, ...
) rarely, if ever, exceeds 1055 millibars (1055
hectopascals)(hPa)(
SI).
Often, in the winter months, cool or cold dry air settles over the land in the vicinity of the
Great Basin where it builds into a
high-pressure cell or
anticyclone
An anticyclone is a weather phenomenon defined as a large-scale circulation of winds around a central region of high atmospheric pressure, clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere as viewed from ...
that moves across the United States with a
cold front
A cold front is the leading edge of a cooler mass of air at ground level that replaces a warmer mass of air and lies within a pronounced surface trough of low pressure. It often forms behind an extratropical cyclone (to the west in the Northern ...
on its leading edge. After reaching the Atlantic Ocean, the moist environment results in a change of air quality and the dissipation of the high-pressure cell or
anticyclone
An anticyclone is a weather phenomenon defined as a large-scale circulation of winds around a central region of high atmospheric pressure, clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere as viewed from ...
as the cold air warms and becomes humid. In Europe, a portion of the North American/Canadian High commonly over
Greenland
Greenland ( kl, Kalaallit Nunaat, ; da, Grønland, ) is an island country in North America that is part of the Kingdom of Denmark. It is located between the Arctic and Atlantic oceans, east of the Canadian Arctic Archipelago. Greenland i ...
, called the Greenland High, affects northern European weather and may merge with the Scandinavian High.
See also
*
Siberian High
The Siberian High (also Siberian Anticyclone; russian: Азиатский антициклон (''Aziatsky antitsiklon'')) is a massive collection of cold dry air that accumulates in the northeastern part of Eurasia from September until April. It ...
*
Cold wave
A cold wave (known in some regions as a cold snap, cold spell or Arctic Snap) is a weather phenomenon that is distinguished by a cooling of the air. Specifically, as used by the U.S. National Weather Service, a cold wave is a rapid fall in tem ...
References
{{Cyclones
Anticyclones
Climate of Canada
Climate of Greenland