Low pressure systems
A low pressure system (cyclone) develops where relatively warm air ascends from the Earth's surface. These are systems of closed isobars surrounding a region of relatively low pressure.
low pressure system: area of minimum air pressure, and cyclonic air movement.
Low Pressure System
An area of a relative pressure minimum that has converging winds and rotates in the same direction as the Earth...counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. Also known as a cyclone.
Low, Low Pressure Systems, Depression: opposite of high pressure system with the centre having the lowest pressure. Bulges and elongation in the circular pattern are known as Troughs of Low Pressure. The flow of wind around a depression is clockwise in the Southern Hemisphere.
low (low pressure system): area with lower atmospheric pressure than its surrounding areas; this makes air from surrounding areas to flow into the low, the end result of which is probably cloudiness and precipitation.
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BOMB- A ~ that decreases in central pressure by at least 24 millibars in a 24 hour period.
BOUNDARY LAYER- The layer of the troposphere closest to the earth's surface where friction is a significant force and wind tends to be gusty (irregular flow).
~s that originate in the panhandle region of Texas and Oklahoma which initially move east and then "hook" or recurve more northeast toward the upper Midwest or Great Lakes region. In winter, these systems usually deposit heavy snows north of their surface track.
~ - A whirling mass of warm, moist air that generally brings stormy weather with strong winds. When viewed from above, winds spiral into a low-pressure center in a counterclockwise rotation in the Northern Hemisphere.
Deep ~s can create a dome of water under the storm (much like the low pressure in a vacuum on a carpet). High winds along a coastline can also elevate the water levels at the shore, depending on the direction of the wind with respect to the coast.
When a ~ draws near, altostratus clouds will appear at about 3 km in altitude. These types of clouds consist of a mix of ice crystals and water drops. The cloud is relatively thicker, spanning horizontally up to several hundred kilometers, and it is capable of blocking sunlight.
Surface ~s will tend to be smaller in area and have stronger surface winds than a given high pressure system, due to the addition of surface friction to the pressure gradient force and coriolis effect that drive the circulation.
A strong ~ that affects the Mid Atlantic and New England States. It can form over land or over the coastal waters.
A shallow ~ caused by the strong heating of the earth's surface. These lows are usually weak and are strongest in the late afternoon. They can trigger afternoon or evening showers and thunderstorms.
A period of abnormally hot weather lasting several days.
A ~ that has its coldest temperatures at or near the center of circulation, and is thermally barotropic with respect to a horizontal plane. Also known as a cold core low. A cut off low is an example, where an isolated pool of colder air is located south of the main westerlies.
Cold Low- a ~ with cold air mass from near the surface to all vertical levels (also called a cold core low).
Combined Seas- the interaction of wind waves and swell; the combined seas height is equal to the square root of the sum of the squares of the wind waves and swell.
WAVE CYCLONE - A ~ with waves and / or fronts associated with it. Wave cyclones are almost always extratropical type storms associated with frontal systems or upper level disturbances. Also called a MID LATITUDE CYCLONE (or EXTRATROPICAL CYCLONE).
CLOSED LOW A ~ that is completely encircled by an isobar. They often move slowly, as they displaced south of the main westerlies.
A general increase in the central pressure of a ~.Fire WindA thermally driven wind blowing radially inward toward a fire, produced by horizontal temperature differences between the heated air above the fire and the surrounding cooler free atmosphere.
Pancake IceIn hydrologic terms, circular flat pieces of ice with a raised rim; the shape and rim are due to repeated collisionsPanhandle HookLow pressure systems that originate in the panhandle region of Texas and Oklahoma which initially move east and then "hook" or recurve more northeast ...
Texas HookerSame as Panhandle Hook - ~s that originate in the panhandle region of Texas and Oklahoma which initially move east and then "hook" or recurve more northeast toward the upper Midwest or Great Lakes region.
Lake-Effect Snow Advisory: This product is issued by the National Weather Service when pure lake effect snow (this is where the snow is a direct result of lake effect snow and not because of a ~) may pose a hazard or it is life threatening.
Cyclogenesis and Cyclolosis "Cyclogenesis" and "cyclolosis" are terms used by meteorologists to refer to stages of an extratropical cyclone or ~.
This index measures the anomalies in sea level pressure between the Icelandic low pressure system and the Azores high pressure system.
Jet Stream A narrow band of strong winds in the atmosphere that controls the movement of high and ~s and associated fronts. Jet Streams meander from time to time. Wind speeds can reach 200 mph or higher in certain cases.
Snow Advisory- This product is issued when a ~ produces snow that may cause significant inconveniences but do not meet warning criteria and if caution is not exercised could lead to life threatening situations. The advisory criteria varies from area to area.
Tropical cyclone is the name given to any ~ which is fueled by the heat released when moist air rises and condenses.
Subtropical cyclone: A ~ that develops in subtropical waters (north of 20 north degrees latitude) and initially has non-tropical features (see table below for a list of tropical features) but does have some element of a tropical cyclone's cloud structure (located close to the ...
Surface data indicates that a small scale ~, about 100 miles in diameter, probably accounted for the LEWP configuration. Supercells often form near or immediately northeast of such a low.
A ~ that develops over subtropical waters that initially has a non-tropical circulation but in which some elements of tropical cyclone cloud structure are present. Subtropical cyclones can evolve into tropical cyclones. Subtropical cyclones are generally of two types: ...
NOR' EASTER: An intense ~ that tracks along the east coast of the United States, producing strong northeast winds, large waves, and intense precipitation.
Cut-Off Low - An upper level ~ that is no longer in the normal west to east upper air flow. Usually a cut-off low will lie to the South of the established upper air flow.
Tropical Storm - An organized ~ in the tropics with wind speeds between 38 and 74 mph.
Tropical Storm Warning- A warning issued when sustained winds of 39 to 73 mph (34 to 63 knots) are expected within 24 hours.
Subtropical Cyclone: A non-frontal ~ that has characteristics of both tropical and extratropical cyclones.
Storm Track: The path followed by the centre of a ~ or cyclone over a given period of time, usually its lifetime.
JET STREAM: Strong winds concentrated within a narrow band in the atmosphere. The jet stream often "steers" surface features such as front and ~s.
KATABATIC WIND: Local winds a result of cold, dense air flowing downhill.
KNOT: One nautical mile per hour (1.15 mph).
Dry Slot - A zone of dry (and relatively cloud-free) air which wraps east- or northeastward into the southern and eastern parts of a synoptic scale or mesoscale ~. A dry slot generally is seen best on satellite photographs.
synoptic scale - Used with respect to weather systems ranging in size from several hundred kilometers to several thousand kilometers, the scale of migratory high and ~s (frontal cyclones) of the lower troposphere. See cyclonic scale.
Jet Stream: Strong winds concentrated within a narrow band in the upper atmosphere. It normally refers to horizontal, high-altitude winds. The jet stream often "steers" surface features such as front and ~s.
Jet Stream-A river of fast flowing air at high altitudes above the earth that generally flows from west to east over the mid-latitudes. The jet stream separates cold polar air from warmer air to the south and generally "steers" surface features such as fronts and ~s.
Warm fronts usually form on the eastern sides of ~s, create wide areas of clouds and rain, and move at an average speed of 15 mph.
See also: What is the meaning of Low pressure, Pressure, Low, Surface, Water?