Weather terms starting with M

219 terms

M 3000 In solar-terrestrial terms, the optimum high frequency radio wave with a 3000 km range, which reflects only once from the ionosphere (single hop…
M2/S2 m2/s2 (meters squared per second squared), unit of measure equivalent to J/kg (joules per kilogram).
Mackeral Sky The name given to cirrocumulus clouds with small vertical extent and composed of ice crystals. The rippled effect gives the appearance of fish scales.
Macroburst A convective downdraft with an affected outflow area of at least 2Â½ miles wide and peak winds lasting between 5 and 20 minutes.
Macroscale Large scale, characteristic of weather systems several hundred to several thousand kilometers in diameter.
Madden-Julian Oscillation (abbrev. MJO)- Tropical rainfall exhibits strong variability on time scales shorter than the seasonal El NiÃ±o-Southern Oscillation (ENSO).
MAFOR (Great Lakes Marine Forecast) - A National Weather Service coded summary appended to each of the Great Lakes Open Lakes forecasts.
Magflare In solar-terrestrial terms, a geomagnetic and/or cosmic storm has been associated with this flare
Magnetic Bay In solar-terrestrial terms, a relatively smooth excursion of the H (horizontal) component of the geomagnetic field away from and returning to quiet levels.
Magnetic pole Magnetic Pole Either of the two points on the Earth's surface at which magnetic meridians converge.
Magnetogram A magnetogram is an image of the Sun's magnetic flux. They are derived by using emission lines which are magnetically sensitive, which allows the magnetic…
Magnetopause In solar-terrestrial terms, the boundary layer between the solar wind and the magnetosphere.
Magnetosphere An area around a planet in which the planet’s magnetic field is stronger than the magnetic field carried by the solar wind.
Main Stem The reach of a river/stream formed by the tributaries that flow into it.
Main Synoptic Times The times of 0000, 0600, 1200, and 1800 UTC. Also known as the standard synoptic times.
MAINT Maintain
Major Flare In solar-terrestrial terms, this flare is the basis for the forecast of geomagstorm, cosmic storm and/or protons in the earth's vicinity
Major Flooding A general term including extensive inundation and property damage. (Usually characterized by the evacuation of people and livestock and the closure of…
Major Hurricane A hurricane which reaches Category 3 (sustained winds greater than 110 mph) on the Saffir/Simpson Hurricane Scale.
MALR Moist Adiabatic Lapse Rate- The rate at which the temperature of a parcel of saturated air decreases as the parcel is lifted in the atmosphere.
Mammatus Clouds Rounded, smooth, sack-like protrusions hanging from the underside of a cloud (usually a thunderstorm anvil).
Manure Dung and urine of animals that can be used as a form of organic fertilizer. See fertilizer, organic fertilizer.
MAP 1. verb: to determine the relative positions of loci (genes or DNA sequences) on a chromosome.
Mare's Trail The name given to thin, wispy cirrus clouds composed of ice crystals that appear as veil patches or strands, often resembling a horse's tail.
MAREP (MArine REPort) A voluntary marine observation program of the National Weather Service whose goal is to solicit meteorological and oceanographic…
Marginal Visual Flight Rules (Abbrev. MVFR) - In an aviation product, refers to the general weather conditions pilots can expect at the surface.
Marine climate Marine (maritime or oceanic) climate A climate dominated by the ocean. Because of the moderating effect of water, sites having this climate are considered…
Marine Inversion Temperature inversion produced when cold marine air underlies warmer air.
Marine Push A replacement of the current air mass with air from off the ocean. Temperatures are much cooler and relative humidities much higher.
Marine Small Craft Thunderstorm Advisory A marine warning issued by Environment Canada Atmospheric Environment Branch when the possibility of thunderstorms is greater than 40 percent.
Marine Small Craft Wind Warning A marine warning issued by Environment Canada Atmospheric Environment Branch for winds which are forecasted to be in the 20-33 knot range inclusive.
Marine Weather Statement A National Weather Service product to provide mariners with details on significant or potentially hazardous conditions not otherwise covered in existing…
Marine Zone Specific, defined over-water areas contained in the various NWS marine forecasts. These are the equivalent of "zones" in the public forecast program.
Maritime Air Mass An air mass influenced by the sea. It is a secondary characteristic of an air mass classification, signified by the small "m" before the primary…
Maritime Polar Air Mass An air mass characterized by cold, moist air. Abbreviated mP.
Maritime Tropical Air Mass An air mass characterized by warm, moist air. Abbreviated mT.
MAROB A voluntary marine observation program of the National Weather Service in the early stages of development whose goal is to solicit meteorological and…
MARS Machine Assisted Reference Section
Mass balance The application of the principle of the conservation of matter.
Massif A compact portion of a mountain range, containing one or more summits.
Mauna Loa An intermittently active volcano (elevation: 13,680 feet; 4,170 meters) on the island of Hawaii.
MAV AVN MOS Guidance
MAX Maximum
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 Discharge Spillway discharge (cfs) when reservoir is at maximum designed water surface elevation.
Maximum Sustained Surface Wind When 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 Temperature This is the highest temperature recorded during a specified period of time. Common time periods include 6, 12 and 24 hours.
Maximum Unambiguous Range The range from the radar at which an echo can be known unquestionably as being at that range.
Maximum Unambiguous Velocity The highest radial velocity that can be measured unambiguously by a pulsed Doppler radar.
MAXT High temperature for the day. Usually forecast out 7 days in advance.
MB Millibar
MCC Mesoscale Convective Complex. A large MCS, generally round or oval-shaped, which normally reaches peak intensity at night.
MCS Abbreviation for multiple cloning site. See: polylinker.
MD Mesoscale Discussion- When conditions actually begin to shape up for severe weather, SPC (Storm Prediction Center) often issues a Mesoscale Discussion…
MDFY Modify
MDLS models
MDNGT midnight
MDT Moderate (or) Mountain Daylight Time
Mean A statistics term. The average value in a set of measurements. The mean is the sum of a set of numbers divided by how many numbers are in the set.
Mean Annual Temperature The average temperature for the entire year at any given location.
Mean Areal Precipitation (abbrev. MAP)- The average rainfall over a given area, generally expressed as an average depth over the area.
Mean Daily Temperature The average of the highest and lowest temperatures during a 24-hour period.
Mean Depth The 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 Velocity Reflectivity-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.
Meander Big bend and loops in a river channel as the river snakes through a flat land area.
Meander Belt The area between lines drawn tangential to the extreme limits of fully developed meanders.
Measured Ceiling A ceiling classification applied when the ceiling value has been determined by an instrument, such as a ceilometer or ceiling light, or by the known…
Mechanism the 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 Range In forecasting, (generally) three to seven days in advance.
MEGG Merging
melting layer The layer below the 0°C isotherm where snowflakes melt and turn into raindrops.
Melting Level The altitude which ice crystals and snowflakes melt as they descend through the atmosphere.
Melting Point The temperature at which a solid substance undergoes fusion, changing from a solid to a liquid state. Contrast with freezing point.
Meniscus The curved top of a column of liquid in a small tube caused by surface tension.
Mercury Barometer An 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 circulation Meridional circulation An atmospheric circulation in a vertical plane oriented along a meridian.
Meridional Flow Large-scale atmospheric flow in which the north-south component (i.e., longitudinal, or along a meridian) is pronounced.
MESO Mesocyclone- 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…
Mesoclimate The 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…
Mesohigh A 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.
Mesonet A regional network of observing stations (usually surface stations) designed to diagnose mesoscale weather features and their associated processes.
Mesopause The top of the mesosphere, corresponding to the level of minimum temperature in the atmosphere found at 70 to 80 km.
Mesoscale Size 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 Discussion When conditions actually begin to shape up for severe weather, SPC (Storm Prediction Center) often issues a Mesoscale Discussion (MCD) statement anywhere…
Mesoscale High Winds These high winds usually follow the passage of organized convective systems and are associated with wake depressions or strong mesohighs.
Mesosphere The 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…
MET An approximate unit of heat produced by a resting person, equal to about 18.5 Btu per square foot per hour.
metadata Metadata 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) The components of the ARM data system that collect and report data stream metadata. Formerly known as the Site Ops Log.
METAR An international code (Aviation Routine Weather Report) used for reporting, recording and transmitting weather observations.
Meteogram A graphical depiction of trends in meteorological variables such as temperature, dew point, wind speed and direction, pressure, etc.