An example of an omega block near North America in May 2006

Blocks in meteorology are large scale patterns in the atmospheric pressure field that are nearly stationary, effectively "blocking" or redirecting migratory cyclones. Meteorology (from Greek grc μετέωρος metéōros, "high in the sky" and grc -λογία -logia) is the Interdisciplinary They are also known as blocking highs or blocking anticyclones. A high pressure area (also called a high or high-pressure is a region where the Atmospheric pressure is greater than surrounding areas In Meteorology, an anticyclone (that is opposite to a Cyclone) is a Weather phenomenon in which there is a descending movement of the air and ^[1] These blocks can remain in place for several days or even weeks, causing the areas affected by them to have the same kind of weather for an extended period of time (e. g. - precipitation for some areas, clear skies for others). ^[2] In the Northern Hemisphere, extended blocking occurs most frequently in the spring over the eastern Pacific and Atlantic oceans. Northern Hemisphere is the half of a Planet that is North of the Equator —the word hemisphere literally means 'half ball' Spring is one of the four Temperate Seasons Spring marks the transition from Winter into Summer. The Pacific Ocean is the largest of the Earth 's Oceanic divisions ^[1]

Omega blocks

Omega blocks are so-named because the height fields associated with them resemble the Greek letter omega. The Greek alphabet (Ελληνικό αλφάβητο is a set of twenty-four letters that has been used to write the Greek language since the late 9th or early The typical pattern for this is low-high-low, arranged in the west-east direction. ^[2]

Rex blocks

An example of a rex block off the coast of North America in January 2007

Rex blocks consist of a high situated to the north of a low. Very often both the high and the low are closed, meaning that the isobars (or constant geopotential height lines) defining the high/low close to form a circle. Geopotential height is a vertical coordinate referenced to Earth's Mean sea level — an adjustment to geometric height ( Elevation above mean sea level using the ^[3] Rex blocks are not so-named because they are considered the "king of blocks" (see Rex), but rather they were named after the meteorologist who first identified them. ^[4]

Cut off Highs and Lows

When an upper level high or low pressure system becomes stuck in place due to a lack of steering currents, it is known as being "cut off". A ridge is a geological feature that features a continuous elevational crest for some distance The usual pattern which leads to this is the jet stream retreats to the north, leaving the then cut off system behind. ^[5] Whether or not the system is of high or low pressure variety dictates the weather that the block causes. Precisely this situation occurred over the southwestern United States in late spring and early summer of 2007, when a cut off low system hovering over the region brought unusually cool temperatures and an extraordinary amount of rain to Texas and Oklahoma (see June 2007 Texas flooding). Texas ( is a state geographically located in the South Central United States and is also known as the Lone Star State. Oklahoma ( is a state located in the South Central region of the United States of America. In June 2007 repeated Flooding took place in the US state of Texas.

If the block is a high, it will usually lead to dry, warm weather as the air beneath it is compressed and warmed; and rainy, cooler weather if the block is a low. ^[6]

See also

• Geopotential height
• Ridge (meteorology)
• Trough (meteorology)

References