List of Terms & Acronyms Used Here, What is a Blizzard?
List of Terms & Acronyms Used Here, What is a Blizzard?
Jun 9 2015, 06:37 AM
Joined: 19-January 15
Member No.: 30,185
Glossary of Common Terms you will see referred to on the boards. Definitions taken from SOURCE
ALBERTA CLIPPER A fast moving, snow-producing weather system that originates in the lee of the Canadian Rockies. It moves quickly across the northern United States, often bring gusty winds and cold Arctic air.
BERMUDA HIGH A semi-permanent, subtropical area of high pressure in the North Atlantic Ocean that migrates east and west with varying central pressure. Depending on the season, it has different names. When it is displaced westward, during the Northern Hemispheric summer and fall, the center is located in the western North Atlantic, near Bermuda. In the winter and early spring, it is primarily centered near the Azores Islands. Related term: Azores High
BLOCKING HIGH The development of a warm ridge or cutoff high aloft at high latitudes which becomes associated with a cold high at the surface, causing a split in the westerly winds. Such a high will move very slowly, tending to move westward during intensification and eastward during dissipation. It prevents the movement of migratory cyclones across its latitudes. Related terms: cut-off high and Omega block
CENTRAL PRESSURE The atmospheric pressure at the center of a high or low. It is the highest pressure in a high and the lowest pressure in a low, referring to the sea level pressure of the system on a surface chart.
CLIMATE PREDICTION CENTER (CPC) A branch of the National Centers for Environmental Prediction,the Center maintains a continuous watch on short-term climate fluctuations and diagnoses and predicts them. For further information, contact the CPC, located in Washington, D.C.
CLOSED LOW A region of low pressure distinguished by a center of counterclockwise circulation (in the Northern Hemisphere), and is surrounded by one or more isobars or height contours. Closed lows aloft (i.e., above the surface) may become disconnected from the primary westerly flow and thus progress eastward more slowly. It is important to note that a cutoff low is a closed low, but not all closed lows are cutoff lows.
COLD AIR ADVECTION (CAA) The horizontal movement of colder air into a location. Contrast with warm advection.
COLD FRONT The leading edge of an advancing cold air mass that is under running and displacing the warmer air in its path. Generally, with the passage of a cold front, the temperature and humidity decrease, the pressure rises, and the wind shifts (usually from the southwest to the northwest in the Northern Hemisphere). Precipitation is generally at and/or behind the front, and with a fast-moving system, a squall line may develop ahead of the front. Related terms: occluded front and warm front
CYCLOGENESIS The process that creates a new low pressure system or cyclone, or intensifies a pre-existing one. It is also the first appearance of a trough.
DRY SLOT An area of dry, and usually cloud-free, air that wraps into the southern and eastern sections of a synoptic scale or mesoscale low pressure system. Best seen on a satellite picture, such as a water vapor image.
FRONTAL PASSAGE (FROPA) It is the passage of a front over a specific point on the surface. It is reflected by the change in dew point and temperature, the shift in wind direction, and the change in atmospheric pressure. Accompanying a passage may be precipitation and clouds. May be referred to as "fropa."
HUDSON BAY LOW An area of low pressure over or near the Hudson Bay area of Canada that often introduces cold air to the north central and northeast United States.
ICELANDIC LOW A semi-permanent, subpolar area of low pressure in the North Atlantic Ocean. Because of its broad area and range of central pressure, it is an area where migratory lows tend to slow down and deepen. It is strongest during a Northern Hemisphere winter and early spring, centered over Iceland and southern Greenland, and is the dominate weather feature in the area. During the summer, it is weaker, less intense, and might divide into two parts, one west of Iceland, the other over the Davis Strait between Greenland and Baffin Island. Then the Azores or Bermuda High becomes the dominate weather feature in the North Atlantic. Related term: Aleutian Low
LAKE EFFECT SNOW (LES) Snow showers that are created when cold dry air passes over a large warmer lake, such as one of the Great Lakes, and picks up moisture and heat.
NOR'EASTER A cyclonic storm occurring off the east coast of North America. These winter weather events are notorious for producing heavy snow, rain, and tremendous waves that crash onto Atlantic beaches, often causing beach erosion and structural damage. Wind gusts associated with these storms can exceed hurricane force in intensity. A nor'easter gets its name from the continuously strong northeasterly winds blowing in from the ocean ahead of the storm and over the coastal areas.
NOWCAST A short-term weather forecast for expected conditions in the next few hours.
OMEGA BLOCK A warm high aloft which has become displaced and is on the polarward side of the jet stream. It frequently occurs in the late winter and early spring in the Northern Hemisphere. The name comes from its resemblance to the Greek letter, Omega, when analyzed on upper air charts.
OVERRUNNING EVENT This occurs when a relatively warm air mass is forced above a cooler air mass of greater density. Weather generally associated with this event includes cloudiness, cool temperatures, and steady precipitation.
POLAR AIR MASS An air mass that forms over a high latitude region. Continental polar air (cP) is formed over cold surface regions and is typically very stable with low moisture. Maritime polar air (mP), produced over warmer waters, is less stable with high moisture.
POLAR JET Marked by a concentration of isotherms and strong vertical shear, this jet is the boundary between the polar air and the subtropical air. It often divides into two branches, the north and the south, and marks the high speed core of the prevailing westerlies. It is associated with the location and motion of the high and low pressure areas of the middle latitudes, and therefore, is variable in position, elevation, and wind speed. Its position tends to migrate south in the Northern Hemispheric winter and north in the summer, and its core winds increase during the winter and become less strong in the summer.
PRESSURE GRADIENT The amount of pressure change that occurs over a fixed distance at a fixed altitude.
QUANTITATIVE PRECIPITATION FORECAST (QPF) A forecast of rainfall, snowfall or liquid equivalent of snowfall.
RADIATIONAL COOLING The cooling of the earth's surface and the adjacent air. Although it occurs primarily at night, it happens when the earth's surface suffers a net loss of heat due to outgoing radiation. Related terms: terrestrial radiation
SNOW COVER The areal extent of ground covered by the snow. It is usually expressed as a percent of the total area of a given region.
TELECONNECTIONS Information used by forecasters to determine what the weather might be elsewhere when compared with past weather conditions at the same degree of longitude.
WARM AIR ADVECTION (WAA) The horizontal movement of warmer air into a location. VIRGA - Precipitation that falls from clouds but evaporates in dry air beneath the cloud before reaching the ground. Virga resembles streaks of water extending from the cloud.
Really helpful. Thanks for sharing.
San Francisco, CA, USA
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