Abbreviations & Acronyms & other Weather Gobbly Gook

If you want a question answered. If you know the answer to a question. This is the forum for it.
Please start a new thread for each weather question so we can all find the info quickly and easily.
WAWG Leadership Group
User avatar
Posts: 1439
Joined: Sat Aug 02, 2008 12:05 pm
Location: Margaret River West Australia

Abbreviations & Acronyms & other Weather Gobbly Gook

Postby nocky » Sun Jun 07, 2009 7:19 pm

The aim of this post is to give an idea of abbreviations and other weather terminology (Gobbly Gook) it will be added overtime and if anyone has anything to add please PM Me, info sourced from many places and help from members. Some references have links to another web site, these will be in bold blue, best way to access these is to right click on the link and select "open in another tab"
This thread will be Locked, post suggestions and comments IN THIS THREAD
Cloud Formations
There are four basic cloud categories observed in our atmosphere:

High-level clouds which form above 20,000 feet (6,000 meters) and are usually composed of ice crystals. High-level clouds are typically thin and white in appearance, but can create an array of colors when the sun is low on the horizon. Cirrus generally occur in fair weather and point in the direction of air movement at their elevation.
Nimbus comes from the Latin word meaning "rain". These clouds typically form between 7,000 and 15,000 feet (2,100 to 4,600 meters) and bring steady precipitation. As the clouds thicken and precipitation begins to fall, the bases of the clouds tend to lower toward the ground.
Clouds look like white fluffy cotton balls or heaps and show the vertical motion or thermal uplift of air taking place in the atmosphere. The level at which condensation and cloud formation begins is indicated by a flat cloud base, and its height will depend upon the humidity of the rising air. The more humid the air, the lower the cloud base. The tops of these clouds can reach over 60,000 feet (18,000 meters).
Strato-form "Stratus" is Latin for layer or blanket. The clouds consist of a feature-less low layer that can cover the entire sky like a blanket, bringing generally gray and dull weather. The cloud bases are usually only a few hundred feet above the ground. Over hills and mountains they can reach ground level when they may be called fog. Also, as fog "lifts" off the ground due to daytime heating, the fog forms a layer of low stratus clouds.

By convention, clouds are vertically divided into three étages (levels); low, middle, and high. Each étage is defined by the range of levels at which each type of clouds typically appears. The types of clouds are...
Cirrus (Ci), Cirrocumulus (Cc), and Cirrostratus (Cs) are high level clouds. They are typically thin and white in appearance, but can appear in a magnificent array of colors when the sun is low on the horizon.

Altocumulus (Ac), Altostratus (As), and Nimbostratus (Ns) are mid-level clouds. They are composed primarily of water droplets, however, they can also be composed of ice crystals when temperatures are low enough.

Cumulus (Cu), Stratocumulus (Sc), Stratus (St), and Cumulonimbus (Cb) are low clouds composed of water droplets.
Level........................................Approx Hieght
High...............................16,500-40,000 Feet (5-13 km)
Middle..............................6,500-23,000 Feet (2-7 km)
Low................................Surface-6,500 Feet (0-2 km)
BOM Cloud Chart
Weather Elements
Precipitation: any or all of the forms of water, whether liquid (e.g. rain, drizzle) or solid (e.g. hail, snow), that fall from a cloud or group of clouds and reach the ground.
Showers:Image Usually begin and end suddenly. Relatively short-lived, but may last half an hour. Fall from cumulus clouds, often separated by blue sky. Showers may fall in patches rather than across the whole forecast area. Range in intensity from light to very heavy.
Rain:Image In contrast to showers, rain is steadier and normally falls from stratiform (layer) cloud. Liquid water drops greater than 0.5 mm in diameter. Rain can range in intensity from light to very heavy.
Drizzle:Image Fairly uniform precipitation composed exclusively of very small water droplets (less than 0.5 mm in diameter) very close to one another.
Frost:Image Deposit of soft white ice crystals or frozen dew drops on objects near the ground; formed when surface temperature falls below freezing point.
Mist:Image Similar to fog, but visibility remains more than a kilometre.
Smog:Image Smog (contraction for 'smoke fog') is a fog in which smoke or other forms of atmospheric pollutant have an important part in causing the fog to thicken, and have unpleasant and dangerous physiological effects.
Thunderstorms:Image Thunderstorms are one or more convective clouds in which electrical discharge can be seen as lightning and heard as thunder by a person on the earth's surface.
A severe thunderstorm produces one or more of :-
* hail at the ground with diameter of 2 cm or more;
* wind gusts at the ground of 90 km/h or more;
* tornadoes; or
* very heavy rain likely to cause flash flooding.
Tornado: A tall, rapidly rotating column of air between 5 and 1000 metres in diameter which is attached to the base of a cumulonimbus or large cumulus cloud and which is capable of producing damage at the earth's surface. Tornadoes may form water spouts when they occur over water.
Blizzard:Image Violent and very cold wind which is laden with snow, some part, at least, of which has been raised from snow covered ground.
Change: Signified by a transition between two air masses over a relatively short time period, usually when a cooler air mass replaces a warmer air mass over an area. A change may or may not be accompanied by rain, and is characterized by a rapid change in wind direction usually from warm north to northwesterly to cooler south east to southwesterly. A change differs from a sea breeze in that it is most often associated with the passage of a front or low pressure trough and affects a large area over a period of a day or more, as distinct from a sea breeze, which characteristically only affects areas up to around 60 km inland from the coast for a period of hours.
Windy:Image A prolonged period of average wind speeds exceeding 40km/h during the day.
Intensity of Precipitation
Drizzle Intensity

Light: Up to 0.2 mm per hour. Can be felt on the face but is not visible. Produces little run off from roads or roofs. Generally visibility is reduced, but not less than 1000 m.
Moderate: 0.2 mm to 0.4 mm per hour. Window and road surfaces streaming with moisture. Visibility generally between 400 and 1000 m.
Thick or Heavy: Over 0.4 mm per hour. Visibility reduced to less than 400 m.
Rain or Showers Intensity
Light: Up to 2 mm per hour. Individual drops easily identified, puddles form slowly, small streams may flow in gutters.
Moderate: 2.2 mm to 6 mm per hour. Rapidly forming puddles, down pipes flowing freely, some spray visible over hard surfaces.
Heavy: 6.2 mm to 50mm mm per hour. Falls in sheets, misty spray over hard surfaces, may cause roaring noise on roof.
Violent: Over 50mm mm per hour. Gutters and downpipes overflowing, spray to height of several centimetres over hard surfaces, may cause roaring noise on roof.
Wind direction: Direction is based on true north orientation. Direction is where the wind is blowing from, for example a northerly wind is blowing from the north. Some forecasts may use abbreviations to describe the wind direction. (N, NE, NW, E, S, SE, SW W)
Gust: A gust is any sudden increase of wind of short duration, usually a few seconds.
Squall: A squall comprises a rather sudden increase of the mean wind speed which lasts for several minutes at least before the mean wind returns to near its previous value. A squall may include many gusts.
Windy: A prolonged period of average wind speeds exceeding 40km/h during the day.
Tending: A gradual change.
Shifting: A relatively abrupt change.
Wind Speed Descriptions
Calm 0kmh
Light winds 1-19kmh
Moderate Winds 20-29kmh
Fresh Winds 30-39kmh
Strong Winds 40-62kmh
Gale 63-87kmh
Storm 88-117kmh
Hurricane 118+kmh
Abbreviations and Brief Descriptions
AT Apparent Temperature (Heat Index): The apparent temperature (AT), invented in the late 1970s, was designed to measure thermal sensation in indoor conditions. It was extended in the early 1980s to include the effect of sun and wind. Only the modification due to wind is taken into account on this site. The AT index used by the Bureau is based on a mathematical model of an adult, walking outdoors, in the shade. The AT is defined as; the temperature, at the reference humidity level, producing the same amount of discomfort as that experienced under the current ambient temperature and humidity.
AHD Australian Height Datum: In 1971 the mean sea level for 1966-1968 was assigned the value of zero on the Australian Height Datum at thirty tide gauges around the coast of the Australian continent. The resulting datum surface, with minor modifications in two metropolitan areas, has been termed the Australian Height Datum (AHD) and was adopted by the National Mapping Council as the datum to which all vertical control for mapping is to be referred. Elevations quoted using this datum are normally followed with the acronym (AHD)
AWS Automatic Weather Station.
BOM Bureau Of Meteorology: Australia's main source of weather info and warnings
CAPE Convective Available Potential Energy:CAPE is effectively the positive buoyancy of an air parcel and is an indicator of atmospheric instability, which makes it valuable in predicting severe weather. It is a form of fluid instability found in thermally stratified atmospheres in which a colder fluid overlies a warmer one. As explained below, when an air mass is unstable, an element of the air mass that is displaced upwards is accelerated by the pressure differential between the displaced air and the ambient air at the (higher) altitude to which it was displaced. This usually creates vertically developed clouds from convection, due to the rising motion, which can eventually lead to thunderstorms.
DALR Dry Adiabatic Lapse Rate: is the rate at which the temperature of unsaturated air changes as a parcel ascends or descends through the atmosphere.
The DALR is approximately 9.8 degree Celsius per 1 km.
DST Daylight Saving Time: Also known as summer time, Daylight Saving Time occurs when the time on local clocks is advanced forward by one hour at the beginning of the defined period of DST, and returned back by one hour at the end of DST. The exact dates between which DST is to apply can be obtained from the relevant Australian State governments. Within Australia DST across the three time zones is generally denoted by: EDT - Australian Eastern Daylight Time; CDT - Australian Central Daylight Time
ENSO El Niño-Southern Oscillation: 'El Niño' used here refers to the warming of the oceans in the equatorial eastern and central Pacific; Southern Oscillation is the changes in atmospheric pressure (and climate systems) associated with this warming (hence 'Southern Oscillation Index' to measure these changes). 'ENSO' is used colloquially to describe the whole suite of changes associated with an 'El Niño' event - to rainfall, oceans, atmospheric pressure etc.
GFS Global Forecasting System:is a global numerical weather prediction computer model run by NOAA. This mathematical model is run four times a day and produces forecasts up to 16 days in advance, but with decreasing spatial and temporal resolution over time (it is widely accepted that beyond 7 days the forecast is little better than guesswork).
The model is run in two parts: the first part has a higher resolution and goes out to 180 hours (7 days) in the future, the second part runs from 180 to 384 hours (16 days) at a lower resolution. The resolution of the model varies in each part of the model: horizontally, it divides the surface of the earth into 35 or 70 kilometre grid squares; vertically, it divides the atmosphere into 64 layers and temporally, it produces a forecast for every 3rd hour for the first 180 hours, after that they are produced for every 12th hour.
ISA International Standard Atmosphere: is the 'average' atmosphere any pressure level has a standard corresponding altitude called 'pressure altitude' and temperature called the 'ISA temperature'.
MJOMadden-Julian Oscillation: also known as the 30-50 day wave. This is a periodic enhancement of rainfall over the Australian tropics, which progresses across tropical latitudes roughly every 30-50 days. Satellite cloud loops and atmospheric pressure changes can signal passage of the wave over Australia, signalling a burst in monsoon (rainfall) activity during the tropical wet season.
MSLMean Sea Level: It is necessary to convert the pressure readings to equivalent mean sea level pressures, otherwise the important horizontal changes in pressure would be overwhelmed by vertical variations simply due to differences in height between observing stations.
In this way, a Mean Sea Level Pressure (MSLP) map will then show pressures affected by changing weather conditions, not because of changing altitude.
NOAA The National Oceanic and Atmospheric Administration (NOAA, pronounced like "noah") is a scientific agency within the United States Department of Commerce focused on the conditions of the oceans and the atmosphere. NOAA warns of dangerous weather, charts seas and skies, guides the use and protection of ocean and coastal resources, and conducts research to improve understanding and stewardship of the environment.
PMF Probable Maximum Flood:The most severe flood that is likely to occur at a particular location. Such a flood would result from the most severe combination of critical meteorological and hydrological conditions.
PMP Probable Maximum Precipitation: The theoretically greatest depth of precipitation for a given duration that is physically possible over a given size storm area at a particular geographical location at a certain time of year.
QFE QFE is calculated by ajusting the station level pressure for the difference between the barometer level and the aerodrome reference level, assuming International Standard Atmosphere(ISA) conditions.
An Altimeter set to QFE will read zero when the aircraft is on the runway.
RCS Reference Climate Station: A climatological station, the data of which are intended for the purpose of determining climatic trends. This requires long periods (not less than thirty years) of homogeneous records, where human-influenced environmental changes have been and/or are expected to remain at a minimum. Ideally the records should be of sufficient length to enable the identification of secular (lasting for ages) changes of climate.
SALR Saturated Adiabatic Lapse Rate: is the rate at which the temperature of a parcel of air saturated with water vapour changes as the parcel ascends or descends.
The SALR is often taken as 1.5 degree Celsius per 1000ft, although the actual figure varies according to the amount of water vapour present.
SCO Seasonal Climate Outlook: These are outlooks of rainfall and temperature for three months ahead and are updated every month. See
SOI Southern Oscillation Index: The Southern Oscillation Index (SOI) is calculated from the monthly or seasonal fluctuations in the air pressure difference between Tahiti and Darwin.
Sustained negative values of the SOI often indicate El Niño episodes. These negative values are usually accompanied by sustained warming of the central and eastern tropical Pacific Ocean, a decrease in the strength of the Pacific Trade Winds, and a reduction in rainfall over eastern and northern Australia. The most recent strong El Niño was in 1997/98.
Positive values of the SOI are associated with stronger Pacific trade winds and warmer sea temperatures to the north of Australia, popularly known as a La Niña episode. Waters in the central and eastern tropical Pacific Ocean become cooler during this time. Together these give an increased probability that eastern and northern Australia will be wetter than normal.
SST(s) Sea Surface Temperature(s), also SSTA(s): Sea Surface Temperature Anomalies. Anomalies in the surface temperature are associated with changes in the heat exchange between atmosphere and ocean, or changes in ocean currents or upwelling, and these changes can drive large changes in rainfall and atmospheric circulation patterns. SSTAs are therefore often strongly related to the development and maintenance of unusual climate patterns, such as ENSO.
WBGT Wet Bulb Global Temperature: Human thermal comfort depends on many factors, only some of them environmental. The four environmental factors are air-flow (wind), air temperature, air humidity, and radiation (the sun and nearby hot surfaces). The exact response of a person to the environmental factors depends on other factors unique to themselves so there is no simple environmental index that can work for everyone under all conditions.
Nevertheless it can be useful to look at an index to help in determining if conditions are unfavorable to undertake strenuous sporting activity. Wet Bulb Global Temperature (WBGT) is a parameter that is often used for this purpose.
The WBGT values on the observation page is an approximation only and does not take into account variations in the intensity of solar radiation or of windspeed, and assumes a moderately high radiation level in light wind conditions.
Other Gobbly Gook
Anemometer A device used to measure wind speed.
Anti Cyclone Atmospheric circulations that rotate anti-clockwise in the southern hemisphere. Anticyclones are areas of higher pressure and are generally associated with lighter winds and fine and settled conditions.
Barometer An Instrument that measures air pressure.
Beaufort Wind Scale A scale that uses observations of the effects of wind to estimate its speed
Cold Front In some regions along the polar front, cold dense air advances equatorwards, causing warm air to be forced aloft over its sloping surface. This portion of the polar front is known as a cold front.
Cold polar air is replacing warm tropical air.
Cyclogenesis The rapid development of a low or intensification of a pre-existing one
Cyclone Atmospheric circulations that rotate clockwise in the southern hemisphere, and anti-clockwise in the northern hemisphere. Cyclones are areas of lower pressure and generally associated with stronger winds, unsettled conditions, cloudiness and rainfall.
Delta-T Delta T is used by the agricultural industry. It is an important indicator for acceptable spraying conditions. It is indicative of evaporation rate and droplet lifetime. Delta T is calculated by subtracting the wet bulb temperature from the dry bulb temperature.
Dew-Point Temperature This is a measure of the moisture content of the air and is the temperature to which air must be cooled in order for dew to form. The dew-point is generally derived theoretically from dry and wet-bulb temperatures, with a correction for the site's elevation.
If the dry-bulb temperature is the same as the dew-point, the air is said to be saturated and the relative humidity is 100%.
Dry Bulb Temperature This is the shade temperature (degrees Celsius) registered by a mercury-in-glass thermometer exposed in a white louvered box or meteorological screen which is raised on legs one metre above the ground.
El Nino Nowadays, the term El Niño refers to the extensive warming of the central and eastern Pacific that leads to a major shift in weather patterns across the Pacific. In Australia (particularly eastern Australia), El Niño events are associated with an increased probability of drier conditions.
Geostrophic wind When the wind is steady, horizontal, and flowing parallel to straight isobars it is called the geostophic wind. Where the Pressure Gradient force is exactly balanced by the Coriolis force.
Gradient wind A steady, horizontal wind flowing along curved isobars is called gradient wind. Where there is imbalance between the pressure gradient and Coriolis forces.
When the pressure gradient force is greater than the Coriolis force, the flow takes on a curved path around low pressure.
When Coriolis is the larger force, the curved flow is around high pressure.
High pressure Atmospheric circulations that rotate anti-clockwise in the Southern Hemisphere. Anticyclones are areas of higher pressure and are generally associated with lighter winds and fine and settled conditions.
Hydrology An earth science concerned with the occurrence, distribution and circulation of waters on and under the earth's surface, both in time and space, their biological, chemical and physical properties, their reaction with the environment, including their relation to living beings.
Hydrometeorology The study of the atmospheric processes that affect the water resources of the earth, including the study of the atmospheric and land phases of the hydrological cycle with emphasis on the interrelationships involved.
Indigenous Weather Indigenous Australians have long held their own seasonal calendars based on the local sequence of natural events.
Inversion, temperature A temperature inversion occurs when the temperature of air increases with increasing height. Generally the temperature decreases with height in the lower atmosphere, called the troposphere. Low-level inversions generally form on clear calm nights due to cooling of the ground through loss of heat by radiation. The warm air on the ground is replaced by cooler air at the surface resulting in a temperature inversion. The inversion creates a boundary layer that restricts vertical motion and mixing of air between the two air masses either side. Low-level inversions act like a lid to trap pollutants resulting in smog over our cities. For further information please read
Isobars Lines on weather maps joining places which have the same air pressure.
Jet stream A flat, tubular current of air located in the tropopause, the area in the Earth's atmosphere located between the troposphere and the stratosphere. These powerful winds are generated by strong pressure gradients which reflect the great temperature differences at high altitudes
Knot Unit of speed equal to one nautical mile per hour (1.852kmh).
Køppen's classification of climates Classification of climate based on annual and monthly means of temperature and precipitation (rainfall) which also takes into account the vegetation limits. It is a tool for presenting the world pattern of climate and for identifying important deviations from this pattern.
La Nina The extensive cooling of the central and eastern Pacific Ocean. In Australia (particularly eastern Australia), La Niña events are associated with increased probability of wetter conditions.
Low pressure Atmospheric circulations that rotate clockwise in the southern hemisphere. Cyclones are areas of lower pressure and generally associated with stronger winds, unsettled conditions, cloudiness and rainfall.
Meteograms Weather outlooks of temperature, rainfall, winds and relative humidity for any spot in Australia up to seven days ahead. Presented as a graph, these outlooks are extracted directly from the latest computer weather prediction models.
Occluded Front When the cold front moves faster than the warm front, and as it overtakes the warm front, the warm sector is closed and a combine front forms. This process is called occlusion. The front formed in this way is called an occluded front.
Relative humidity Is a traditional indicator of the air's moisture content. It is the ratio of the amount of moisture actually in the air to the maximum amount of moisture which the air could hold at the same temperature. Relative humidity is normally expressed as a percentage and at saturation the relative humidity will be very close to 100%. The air can hold more moisture at higher temperatures, hence the relative humidity alone does not give an absolute measure of moisture content.
Ridge A ridge is an elongated area of high pressure. It is indicated by rounded isobars extending outwards from an anticyclone and has associated with it a ridge line. The pressure at a point on the ridge is higher than at an adjacent point on either side of the line.
Squall A squall comprises a rather sudden increase of the mean wind speed which lasts for several minutes at least before the mean wind returns to near its previous value. A squall may include many gusts.
Supercell A persistent, single, intense updraught and downdraught coexisting in a thunderstorm.
TraceA trace of rain is reported by rainfall observers when a little precipitation can be seen in the rain gauge, but there is less than 0.1 mm in total. The precipitation could be from any source such as rain, drizzle, dew, melted frost, melted hail or melted snow. It is quite often reported as "tce" or "tr" in rainfall bulletins. Rainfall amounts between 0.1 mm and 0.2 mm are reported as 0.2 mm in rainfall bulletins.
Tropical cyclones Tropical cyclones are intense low pressure systems which form over warm ocean waters at low latitudes. Tropical cyclones are associated with strong winds, torrential rain and storm surges (in coastal areas). Tropical cyclones can cause extensive damage as a result of the strong wind, flooding (caused by either heavy rainfall or ocean storm surges) and landslides in mountainous areas as a result of heavy rainfall and saturated soil. Tropical cyclones are also known (in other parts of the world) as tropical storms. If they attain maximum mean winds above 117 km/h (63 knots) they are called severe tropical cyclones. In the northwestern Pacific severe tropical cyclones are known as typhoons and in the northeast Pacific and Atlantic/Caribbean they are called hurricanes.
Trough A trough of low pressure is an elongated area where atmospheric pressure is low relative to its immediate surroundings. A trough of low pressure is sometimes indicated on the synoptic chart by a centre line or trough line denoted by a dashed line e.g. - - - - -. The trough line often extends outward from a low pressure centre, or an enclosed area of relatively low pressure.
When moving across a trough from one side of a trough line to another, atmospheric pressure decreases as you approach the trough line. The atmospheric pressure increases again after you cross the trough line and move away. A change in wind direction will generally be observed as you cross from one side of the trough to the other.
Virga Precipitation that evaporates before it reaches the ground.
Vortex Rotating mass of air or water, such as water going down a plug hole.
Warm Front In other regions along the front, warm air of lower density moves polewards, sliding over its sloping surface. This portion is called a warm front.
Warm tropical air replaces cold polar air.
Wet bulb temperature Wet-bulb temperature is measured using a standard mercury-in-glass thermometer, with the thermometer bulb wrapped in muslin, which is kept wet. The evaporation of water from the thermometer has a cooling effect, so the temperature indicated by the wet bulb thermometer is less than the temperature indicated by a dry-bulb (normal, unmodified) thermometer.
The rate of evaporation from the wet-bulb thermometer depends on the humidity of the air - evaporation is slower when the air is already full of water vapour For this reason, the difference in the temperatures indicated by the two thermometers gives a measure of atmospheric humidity.
Water vapour pressure The atmospheric pressure which is exerted by water vapour (water in its gaseous state). It is one way of measuring the humidity of the air. At a given temperature, an increase of water vapour in the air corresponds to an increase in the humidity of the air.
Water vapour is supplied to the atmosphere by evaporation of water from oceans, lakes, wet land surfaces or from vegetation (transpiration). Water vapour absorbs the Sun's radiation. As a result, the sunlight received at the Earth's surface will be more intense in a drier atmosphere.
Zonal flow(1). Component of atmospheric circulation along a line of latitude, towards the east or west. (2). Atmospheric circulation along, or approximately along, parallels of latitude
Paul Nock wrote:This Reference page was original compiled by Paul Nock and is maintained by The WA Weather Group, all information has been sourced through the internet and member contributions.
Please post any comments or suggestions in THIS THREAD or PM Me

Return to Your Weather Questions

Who is online

Users browsing this forum: No registered users and 3 guests