North American High
Encyclopedia
The North American High is an impermanent high-pressure area or anticyclone
created by anticyclogenesis (anticyclone + the Greek
word genesis, meaning "birth, origin"), a formative process that occurs when cool or cold dry air settles onto North America
.
North American Highs moves eastwards across the continent, often in the company of one or more low-pressure cells or cyclones. Its cold, dense air does not extend usually above 3 km (1.9 mi), lower than the Canadian Rockies
. Sometimes, in winter it breaks free and passes over the Rockies and brings a cold front into Southwestern United States and Mexico, freezing crops and bringing snow into Mexico's mountains as far south as Jalisco
. The high’s usual location east of the Rockies shelters it from the relatively warm Pacific Ocean
and helps it maintain its strength. The average January sea level pressure at its centre is about 1,020 millibars (30.12 inches of mercury). The Canadian high often moves southeastward until it eventually reaches the Atlantic Ocean
, where it merges with the Azores high
. In the summer the Canadian high circulates cool, dry air to the United States east of the Rockies and parts of southern Canada.
The North American High is akin to the Siberian High
of Eurasia
, but it is much smaller, and it has much less influence, merely affecting the weather of the Northern Hemisphere
. The sea-level pressure (atmospheric pressure
) rarely, if ever, exceeds 1055.0 millibars (1055.0 hectopascals)(hPa)(SI
).
Often, in the winter months, cool or cold dry air settles onto the land in the vicinity of the Great Basin
where it builds into a high-pressure cell or anticyclone
that moves across the United States
with a cold front
on its leading edge. After reaching the Atlantic Ocean
, the moist environment brings on changes of the qualities of the air and the dissipation of the high-pressure cell or anticyclone
as the cold air warms and becomes humid. The slow decay and disappearance of an anticyclone
is called anticyclolysis (anticyclone + the Greek word lyein, meaning "to dissolve"; it is used to form many other words, such as paralysis, e.g).
In Europe, a portion of the North American/Canadian high usually over Greenland
called the Greenland high which settles over Greenland affects northern European weather and may merge with the Scandinavian High.
Anticyclone
An anticyclone is a weather phenomenon defined by the United States' National Weather Service's glossary as "[a] large-scale circulation of winds around a central region of high atmospheric pressure, clockwise in the Northern Hemisphere, counterclockwise in the Southern Hemisphere"...
created by anticyclogenesis (anticyclone + the Greek
Greek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...
word genesis, meaning "birth, origin"), a formative process that occurs when cool or cold dry air settles onto North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
.
North American Highs moves eastwards across the continent, often in the company of one or more low-pressure cells or cyclones. Its cold, dense air does not extend usually above 3 km (1.9 mi), lower than the Canadian Rockies
Canadian Rockies
The Canadian Rockies comprise the Canadian segment of the North American Rocky Mountains range. They are the eastern part of the Canadian Cordillera, extending from the Interior Plains of Alberta to the Rocky Mountain Trench of British Columbia. The southern end borders Idaho and Montana of the USA...
. Sometimes, in winter it breaks free and passes over the Rockies and brings a cold front into Southwestern United States and Mexico, freezing crops and bringing snow into Mexico's mountains as far south as Jalisco
Jalisco
Jalisco officially Estado Libre y Soberano de Jalisco is one of the 31 states which, with the Federal District, comprise the 32 Federal Entities of Mexico. It is located in Western Mexico and divided in 125 municipalities and its capital city is Guadalajara.It is one of the more important states...
. The high’s usual location east of the Rockies shelters it from the relatively warm Pacific Ocean
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...
and helps it maintain its strength. The average January sea level pressure at its centre is about 1,020 millibars (30.12 inches of mercury). The Canadian high often moves southeastward until it eventually reaches the Atlantic Ocean
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...
, where it merges with the Azores high
Azores High
The Azores High is a large subtropical semi-permanent centre of high atmospheric pressure found near the Azores in the Atlantic Ocean, at the Horse latitudes...
. In the summer the Canadian high circulates cool, dry air to the United States east of the Rockies and parts of southern Canada.
The North American High is akin to the Siberian High
Siberian High
The Siberian High is a massive collection of cold or very cold dry air that accumulates on the Eurasian terrain for much of the year. It reaches its greatest size and strength in the winter, when the air temperature near the center of the high-pressure cell or anticyclone is often lower than...
of Eurasia
Eurasia
Eurasia is a continent or supercontinent comprising the traditional continents of Europe and Asia ; covering about 52,990,000 km2 or about 10.6% of the Earth's surface located primarily in the eastern and northern hemispheres...
, but it is much smaller, and it has much less influence, merely affecting the weather of the Northern Hemisphere
Northern Hemisphere
The Northern Hemisphere is the half of a planet that is north of its equator—the word hemisphere literally means “half sphere”. It is also that half of the celestial sphere north of the celestial equator...
. The sea-level pressure (atmospheric pressure
Atmospheric pressure
Atmospheric pressure is the force per unit area exerted into a surface by the weight of air above that surface in the atmosphere of Earth . In most circumstances atmospheric pressure is closely approximated by the hydrostatic pressure caused by the weight of air above the measurement point...
) rarely, if ever, exceeds 1055.0 millibars (1055.0 hectopascals)(hPa)(SI
Si
Si, si, or SI may refer to :- Measurement, mathematics and science :* International System of Units , the modern international standard version of the metric system...
).
Often, in the winter months, cool or cold dry air settles onto the land in the vicinity of the Great Basin
Great Basin
The Great Basin is the largest area of contiguous endorheic watersheds in North America and is noted for its arid conditions and Basin and Range topography that varies from the North American low point at Badwater Basin to the highest point of the contiguous United States, less than away at the...
where it builds into a high-pressure cell or anticyclone
Anticyclone
An anticyclone is a weather phenomenon defined by the United States' National Weather Service's glossary as "[a] large-scale circulation of winds around a central region of high atmospheric pressure, clockwise in the Northern Hemisphere, counterclockwise in the Southern Hemisphere"...
that moves across the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
with a cold front
Cold front
A cold front is defined as the leading edge of a cooler mass of air, replacing a warmer mass of air.-Development of cold front:The cooler and denser air wedges under the less-dense warmer air, lifting it...
on its leading edge. After reaching the Atlantic Ocean
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...
, the moist environment brings on changes of the qualities of the air and the dissipation of the high-pressure cell or anticyclone
Anticyclone
An anticyclone is a weather phenomenon defined by the United States' National Weather Service's glossary as "[a] large-scale circulation of winds around a central region of high atmospheric pressure, clockwise in the Northern Hemisphere, counterclockwise in the Southern Hemisphere"...
as the cold air warms and becomes humid. The slow decay and disappearance of an anticyclone
Anticyclone
An anticyclone is a weather phenomenon defined by the United States' National Weather Service's glossary as "[a] large-scale circulation of winds around a central region of high atmospheric pressure, clockwise in the Northern Hemisphere, counterclockwise in the Southern Hemisphere"...
is called anticyclolysis (anticyclone + the Greek word lyein, meaning "to dissolve"; it is used to form many other words, such as paralysis, e.g).
In Europe, a portion of the North American/Canadian high usually over Greenland
Greenland
Greenland is an autonomous country within the Kingdom of Denmark, located between the Arctic and Atlantic Oceans, east of the Canadian Arctic Archipelago. Though physiographically a part of the continent of North America, Greenland has been politically and culturally associated with Europe for...
called the Greenland high which settles over Greenland affects northern European weather and may merge with the Scandinavian High.