Subj : Wx Terms (M)(3) To : All From : Daryl Stout Date : Sat Oct 14 2017 12:05 am 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 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. Properly used, mesocyclone is a radar term; it is defined as a rotation signature appearing on Doppler radar that meets specific criteria for magnitude, vertical depth, and duration. It will appear as a yellow solid circle on the Doppler velocity products. Therefore, a mesocyclone should not be considered a visually-observable phenomenon (although visual evidence of rotation, such as curved inflow bands, may imply the presence of a mesocyclone). 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. Mesolow should not be confused with mesocyclone, which is a storm-scale phenomenon. 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. Horizontal dimensions generally range from around 50 miles to several hundred miles. Squall lines, MCCs, and MCSs are examples of mesoscale weather 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 intensity at night. The formal definition includes specific minimum criteria for size, duration, and eccentricity (i.e., "roundness"), based on the cloud shield as seen on infrared satellite photographs: * Size: Area of cloud top -32 degrees C or less: 100,000 square kilometers or more (slightly smaller than the state of Ohio), and area of cloud top -52 degrees C or less: 50,000 square kilometers or more. * Duration: Size criteria must be met for at least 6 hours. * Eccentricity: Minor/major axis at least 0.7. MCCs typically form 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 flooding. 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 more. MCSs may be round or linear in shape, and include systems such as tropical cyclones, squall lines, and MCCs (among others). MCS often is used to describe a cluster of thunderstorms that does not satisfy the size, shape, or duration criteria of an MCC. Mesoscale Discussion When conditions actually begin to shape up for severe weather, SPC (Storm Prediction Center) often issues a Mesoscale Discussion (MCD) statement anywhere from roughly half an hour to several hours before issuing a weather watch. SPC also puts out MCDs for hazardous winter weather events on the mesoscale, such as locally heavy snow, blizzards and freezing rain (see below). MCDs are also issued on occasion for heavy rainfall, convective trends, and other phenomena, when the forecaster feels he/she can provide useful information that is not readily available or apparent to field forecasters. MCDs are based on mesoscale analysis and interpretation of observations and of short term, high resolution numerical model output. The MCD basically describes what is currently happening, what is expected in the next few hours, the meteorological reasoning for the forecast, and when/where SPC plans to issue the watch (if dealing with severe thunderstorm potential). Severe thunderstorm MCDs can help you get a little extra lead time on the weather and allow you to begin gearing up operations before a watch is issued. The MCD begins with a numerical string that gives the LAT/LON coordinates of a polygon that loosely describes the area being discussed. 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 minimum that defines the mesopause (the base of the thermosphere). MET 1) Meteorological 2) MOS (Model Output Statistics) guidance based on Environmental Modeling Centers ETA model 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. The time series meteogram can be constructed using observed data or forecast data. Meteoric Water Water derived from precipitation. Meteorologist A person who studies meteorology. There are many different paths within the field of meteorology. For example, one could be a research meteorologist, radar meteorologist, climatologist, or operational meteorologist. Meteorology The science dealing with the atmosphere and its phenomena. A distinction can be drawn between meteorology and climatology, the latter being primarily concerned with average, not actual, weather conditions. METRO Metropolitan MeV Mega (million) electronvolt. A unit of energy used to describe the total energy carried by a particle or photon. MEX 1) GFS Model Guidance 2) Mexico MI 1) Mile 2) Michigan MIC Meteorologist In Charge Microbarograph A instrument designed to continuously record a barometer's reading of very small changes in atmospheric pressure. Microburst A convective downdraft with an affected outflow area of less than 2 miles wide and peak winds lasting less than 5 minutes. Microbursts may induce dangerous horizontal/vertical wind shears, which can adversely affect aircraft performance and cause property damage. Microclimate The climate of a small area such as a cave, house, city or valley that may be different from that in the general region. Micron Unit of length equal to one thousandth (1/1000) of a millimeter; one millionth (1/1000000) of a meter (1x10-6 m). Microscale Pertaining to meteorological phenomena, such as wind circulations or cloud patterns, that are less than 2 km in horizontal extent. Microwave A type of electromagnetic radiation with wavelengths between those of infrared radiation and radio waves. Microwave Burst In solar-terrestrial terms, a radiowave signal associated with optical and/or X-ray flares. MID Middle Mid-Flame Wind Wind 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 Areas Areas between 30ø and 60ø north and south of the Equator. Mid-level Cooling Local 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 all other factors are equal. --- þ Synchronet þ The Thunderbolt BBS - wx1der.dyndns.org .