Max Parcel Level (MPL)This signifies the highest attainable level that a convective updraft can reach; therefore, it is a good indication of how tall a thunderstorm may reach.
Maximum Spillway DischargeSpillway discharge (cfs) when reservoir is at maximum designed water surface elevation.
Maximum Sustained Surface WindWhen applied to a particular weather system, refers to the highest one-minute average wind (at an elevation of 10 meters with an unobstructed exposure)…
Maximum TemperatureThis is the highest temperature recorded during a specified period of time. Common time periods include 6, 12 and 24 hours.
Maximum Unambiguous RangeThe range from the radar at which an echo can be known unquestionably as being at that range.
Maximum Unambiguous VelocityThe highest radial velocity that can be measured unambiguously by a pulsed Doppler radar.
MAXTHigh temperature for the day. Usually forecast out 7 days in advance.
MCCMesoscale Convective Complex. A large MCS, generally round or oval-shaped, which normally reaches peak intensity at night.
MCSAbbreviation for multiple cloning site. See: polylinker.
MDMesoscale Discussion- When conditions actually begin to shape up for severe weather, SPC (Storm Prediction Center) often issues a Mesoscale Discussion…
Mean Areal Precipitation(abbrev. MAP)- The average rainfall over a given area, generally expressed as an average depth over the area.
Mean Daily TemperatureThe average of the highest and lowest temperatures during a 24-hour period.
Mean DepthThe average depth of water in a stream channel or conduit. It is equal to the cross-sectional area divided by the surface width.
Mean Doppler VelocityReflectivity-weighted average velocity of targets in a given pulse resolution volume. Usually determined from a large number of successive radar pulses.
Mean Low Water(MLW) - A tidal datum. The average of all the low water heights observed over the National Tidal Datum Epoch.
Mean Lower Low Water(MLLW) - A tidal datum. The average of the lower low water height of each tidal day observed over the National Tidal Datum Epoch.
Mean Sea Level(MSL) - The arithmetic mean of hourly water elevations observed over a specific 19-year tidal epoch.
MeanderBig bend and loops in a river channel as the river snakes through a flat land area.
Meander BeltThe area between lines drawn tangential to the extreme limits of fully developed meanders.
Measured CeilingA ceiling classification applied when the ceiling value has been determined by an instrument, such as a ceilometer or ceiling light, or by the known…
Mechanismthe means by which an effect or change is produced.
Medium Frequency(abbrev. MF)- That portion of the radio frequency spectrum from 0.3 to 3 MHz.
Medium RangeIn forecasting, (generally) three to seven days in advance.
melting layerThe layer below the 0°C isotherm where snowflakes melt and turn into raindrops.
Melting LevelThe altitude which ice crystals and snowflakes melt as they descend through the atmosphere.
Melting PointThe temperature at which a solid substance undergoes fusion, changing from a solid to a liquid state. Contrast with freezing point.
MeniscusThe curved top of a column of liquid in a small tube caused by surface tension.
Mercury BarometerAn instrument for measuring atmospheric pressure. The instrument contains an evacuated and graduated glass tube in which mercury rises or falls as the…
meridian(meh-RID-ee-un) In traditional Chinese medicine, one of 20 channels that form a network through which qi (the body's vital energy) flows and that connect…
Meridional circulationMeridional circulation An atmospheric circulation in a vertical plane oriented along a meridian.
Meridional FlowLarge-scale atmospheric flow in which the north-south component (i.e., longitudinal, or along a meridian) is pronounced.
MESOMesocyclone- A storm-scale region of rotation, typically around 2-6 miles in diameter and often found in the right rear flank of a supercell (or often on…
MesoclimateThe climate of a small area of the earth's surface which may differ from the general climate of the district.
Mesocyclone(abbrev. MESO)- A storm-scale region of rotation, typically around 2-6 miles in diameter and often found in the right rear flank of a supercell (or often…
MesohighA relatively small area of high atmospheric pressure that forms beneath a thunderstorm. It is usually associated with an MCS or its remnants.
Mesolow(or Sub-synoptic Low) - A mesoscale low-pressure center. Severe weather potential often increases in the area near and just ahead of a mesolow.
MesonetA regional network of observing stations (usually surface stations) designed to diagnose mesoscale weather features and their associated processes.
MesopauseThe top of the mesosphere, corresponding to the level of minimum temperature in the atmosphere found at 70 to 80 km.
MesoscaleSize scale referring to weather systems smaller than synoptic-scale systems but larger than storm-scale systems.
Mesoscale Convective Complex(abbrev. MCC)- MCC - Mesoscale Convective Complex. A large Mesoscale Convective System (MCS), generally round or oval-shaped, which normally reaches peak…
Mesoscale Convective System(MCS): A complex of thunderstorms which becomes organized on a scale larger than the individual thunderstorms, and normally persists for several hours or…
Mesoscale DiscussionWhen conditions actually begin to shape up for severe weather, SPC (Storm Prediction Center) often issues a Mesoscale Discussion (MCD) statement anywhere…
Mesoscale High WindsThese high winds usually follow the passage of organized convective systems and are associated with wake depressions or strong mesohighs.
MesosphereThe atmospheric shell between about 20 km and about 70 to 80 km, extending from the top of the stratosphere (the stratopause) to the upper temperature…
METAn approximate unit of heat produced by a resting person, equal to about 18.5 Btu per square foot per hour.
metadataMetadata is information about a particular data set which may describe, for example, how, when, and by whom it was received, created, accessed, and/or…
metadata system (MDS)(MDS)The components of the ARM data system that collect and report data stream metadata. Formerly known as the Site Ops Log.
METARAn international code (Aviation Routine Weather Report) used for reporting, recording and transmitting weather observations.
MeteogramA graphical depiction of trends in meteorological variables such as temperature, dew point, wind speed and direction, pressure, etc.
Meteorological elementMeteorological element Any one of the properties or conditions of the atmosphere which together specify the weather at a given place for any particular…
MeteorologistA person who studies meteorology. There are many different paths within the field of meteorology.
MeteorologyThe science dealing with the atmosphere and its phenomena. A distinction can be drawn between meteorology and climatology, the latter being primarily…
Methane (CH4)A hydrocarbon that is a greenhouse gas with a global warming potential most recently estimated at 23 times that of carbon dioxide (CO2).
Methane (CH<sub>4</sub>)A hydrocarbon that is a greenhouse gas with a global warming potential most recently estimated at 21.
Methanol (CH<sub>3</sub>3OH)A colorless poisonous liquid with essentially no odor and little taste. It is the simplest alcohol with a boiling point of 64.7 degrees Celsius.
MethanotrophicHaving the biological capacity to oxidize methane to CO2 and water by metabolism under aerobic conditions. See aerobic.
Methyl bromide (CH<sub>3</sub>Br)An effective pesticide; used to fumigate soil and many agricultural products. Because it contains bromine, it depletes stratospheric ozone when released…
Metric Ton(or tonne) 1000 kilograms. 1 metric ton = 2,204.62 lb = 1.023 short tons.
Mid-Flame WindWind measured at the midpoint of the flames, considered to be most representative of the speed of the wind that is affecting fire behavior.
Mid-Latitude AreasAreas between 30o and 60o north and south of the Equator.
Mid-level CoolingLocal cooling of the air in middle levels of the atmosphere (roughly 8 to 25 thousand feet), which can lead to destabilization of the entire atmosphere if…
Middle Clouds(or Mid-Level Clouds) - A term used to signify clouds with bases between 6,500 and 23,000 feet.
Middle Latitudes1) The latitude belt roughly between 35 and 65 degrees North and South. Also referred to as the temperate region.
Middle-level cloudsMiddle-level clouds (Ac and As) Altocumulus and Altostratus are the middle-level clouds.
Mie ScatteringAny scattering produced by spherical particles whose diameters are greater than 1/10 the wavelength of the scattered radiation.
MillibarA unit of atmospheric pressure equal to 1/1000 bar, or 1000 dynes per square centimeter.