Weather Glossary - M
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MacroburstA downburst affecting an area greater than 4 kilometres across and having damaging winds. Macrobursts are generally longer-lived than the smaller microbursts. |
MacroscaleThe meteorological scale covering an area ranging from a continent to the entire globe. |
Madden-Julian OscillationThe Madden-Julian Oscillation (MJO), also referred to as the 30-60 day or 40-50 day oscillation, is the main intra-annual fluctuation that explains weather variations in the tropics. The MJO affects the entire tropical troposphere, but is most evident in the Indian and western Pacific Oceans. The MJO involves variations in wind, sea surface temperature (SST), cloudiness, and rainfall. Because most tropical rainfall is convective, and convective cloud tops are very cold (emitting little longwave radiation), the MJO is most obvious in the variation of outgoing longwave radiation (OLR), as measured by an infrared sensor on a satellite. |
MammatusLatin - mammary |
MCCMesoscale Convective Complex.
MCC's typically develop during the afternoon and evening in the form of several isolated thunderstorms, during which time the potential for severe weather is greatest. During peak intensity, the primary threat shifts toward heavy rain and flash flooding. |
MCSMesoscale Convective System. A complex of thunderstorms which becomes organized on a scale larger than the individual thunderstorms, and normally persists for several hours or more. MCS's may be round or linear in shape, and include systems such as tropical cyclones, squall lines, and MCCs (among others). MCS is often used to describe a cluster of thunderstorms that does not satisfy the size, shape, or duration criteria of an MCC. |
Medium rangeIn forecasting, (generally) three to seven days in advance. |
Meridional flowLarge-scale atmospheric flow in which the north-south component (i.e., longitudinal, or along a meridian) is pronounced. The accompanying zonal (east-west) component often is weaker than normal. Compare with zonal flow. |
MesoComes from the Greek meaning 'middle'. A common prefix used in meteorology to describe features that are intermediate in size or position.See mesoscale |
Meso LAPSA high resolution version of LAPS. Meso-LAPS (or MLAPS) has a resolution of 12.5km and a smaller domain than LAPS. Meso LAPS runs out to 48 hours. |
MesocycloneA storm-scale region of rotation, around 3-10 kilometres in diameter and often found in the left rear flank of a supercell (or often on the eastern, or front, flank of an HP storm). The circulation of a mesocyclone covers an area much larger than the tornado that may develop within it. |
MesohighA mesoscale high pressure area, usually associated with MCSs or their remnants. |
Mesolow(or Sub-synoptic Low) A mesoscale low-pressure centre. Severe weather potential often increases in the area near and just ahead of a mesolow. |
MesoscaleUsed to describe weather systems that lie in between synoptic scale and local scale. This generally means weather features that are between 25km and 250km in size. Examples of mesoscale systems are mesoscale convective systems (MCS), squall lines and southerly busters. |
METARMETeorological Aviation Report. An evaluation of selected weather elements from a site on or near the ground according to a set of procedures. |
MeteogramWeather outlooks of temperature, rainfall, winds and relative humidity. Presented as a graph, these outlooks are extracted directly from the latest computer weather prediction models. |
MeteorologyThe science and study of the atmosphere and atmospheric phenomena. |
MicroburstA small, concentrated downburst affecting an area less than 4 kilometres across. Most microbursts are rather short-lived (5 minutes or so), but on rare occasions they have been known to last up to 6 times that long. |
MicroscaleThe smallest scale of meteorological phenomena that range in size from a few centimetres to a few kilometres. |
Mid latitudesThe areas between about 30 degrees and 55 degrees latitude. |
Mid level coolingLocal cooling of the air in middle levels of the atmosphere (roughly 8,000-25,000' or 2,000-8,000m), which can lead to destabilization of the entire atmosphere if all other factors are equal. Mid-level cooling can occur, for example, with the approach of a mid-level cold pool. |
Middle cloudsClouds with bases between 6000 and 18000 feet. |
Middle latitudesThe latitude belt roughly between 35° and 60° North and South. |
MirageA refraction phenomenon the makes an image appear to be displaced from its true position. It is most common close to the ground on hot days, when the surface layer of the atmosphere is much warmer than the layer above, resulting in lower density and different optical properties of this surface layer. |
MistSimilar to fog, but visibility is greater than 1 kilometre. |
Mixed layerUpper portion of the boundary layer in which air is thoroughly mixed by convection. |
MLAPSSee Meso LAPS. |
ModelSee GCM. |
Moisture advectionTransport of moisture by horizontal winds. |
Moisture convergenceA measure of the degree to which moist air is converging into a given area, taking into account the effect of converging winds and moisture advection. Areas of persistent moisture convergence are favoured regions for thunderstorm development, if other factors (e.g., instability) are favourable. |
MonsoonA seasonal wind in the tropics. The northern Australian monsoon season generally lasts from December to March. It is associated with the inflow of moist west to northwest winds into the monsoon trough, producing convective cloud and heavy rainfall over northern Australia. |
Morning GloryAn elongated cloud band common across Cape York Peninsula and the Gulf Country in northern QLD. It is visually similar to a roll cloud, usually appearing in the morning hours when the atmosphere is relatively stable. Morning glories result from perturbations related to gravitational waves in a stable boundary layer. They are similar to ripples on a water surface. Several parallel morning glories often can be seen propagating in the same direction. |
Mountain waveA wave in the atmosphere caused by a barrier such as a mountain. Is sometimes marked by lenticular clouds to the leeward side of a mountain. |
MRFMedium-Range Forecast model; one of the operational forecast models run at NCEP. The MRF is run once daily, with forecast output out to 240 hours (10 days). |
MSLMean Sea Level. It is necessary to convert the pressure readings to equivalent mean sea level pressures, otherwise the horizontal changes in pressure would be overwhelmed by vertical variations simply due to differences in altitude between observing stations. |
Multicell thunderstormA thunderstorm consisting of two or more cells, of which most or all are often visible at a given time as distinct domes or towers in various stages of development. |
Multiple vortex tornado(or Multi-vortex tornado) a tornado in which two or more condensation funnels or debris clouds are present at the same time, often rotating about a common centre or about each other. Multiple-vortex tornadoes can be especially damaging. See suction vortex. |
Mushroom[Slang] A thunderstorm with a well-defined anvil rollover, and thus having a visual appearance resembling a mushroom. |
Weather News
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Light snow is falling in southern parts of the Victorian Alps on Tuesday evening, in the wake of the cold front that moved through Melbourne around the middle of the day.
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