Subj : Wx Terms (M)(2)
To   : All
From : Daryl Stout
Date : Sat Oct 14 2017 12:05 am

Maximum Temperature
This is the highest temperature recorded during a specified period of
time. Common time periods include 6, 12 and 24 hours. The most common
reference is to the daily maximum temperature, or "high."

Maximum Unambiguous Range
The range from the radar at which an echo can be known unquestionably as
being at that range. As the radar sends out a pulse of energy, the pulse
hits a target and part of the energy bounces back to the radar, but part
of the energy may continue to travel away from the radar. The distance
to the target is computed by knowing the time that has elapsed since the
pulse was emitted. Then a second pulse of energy is transmitted. If some
of the energy from the first pulse strikes a target at a far range and
returns to the radar when radiation from the second pulse arrives, the
RDA misinterprets the returned first pulse as arriving from a target
near the returned second pulse. The maximum unambiguous range is related
to the amount of time that elapses between successive pulses of emitted
energy.

Maximum Unambiguous Velocity
The highest radial velocity that can be measured unambiguously by a
pulsed Doppler radar. The maximum unambiguous velocity is related to
the radar's successive pulses of emitted energy. When a target's
velocity exceeds the maximum unambiguous velocity, the velocity will
be "folded" to appear as a different velocity.

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. 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.

MCS
Mesoscale 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. MCSs may be round or linear
in shape, and include systems such as tropical cyclones, squall lines,
and Mesoscale Convective Complexes (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 Mesoscale Convective Complex.

MD
Mesoscale Discussion- When conditions actually begin to shape up for
severe weather, SPC (Storm Prediction Center) often issues a Mesoscale
Discussion 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.

MDFY
Modify

MDLS
models

MDNGT
midnight

MDT
Moderate (or) Mountain Daylight Time

Mean
The arithmetic average of a set of data (numbers), or the middle point
between its two extremes.

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
In hydrologic terms, 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. Also called mean radial (towards or away from
the antenna) velocity. Doppler velocity refers to spectral density
first moment, radial velocity to base data.

Mean Low Water
(MLW) - A tidal datum. The average of all the low water heights
observed over the National Tidal Datum Epoch. For stations with shorter
series, simultaneous observational comparisons are made with a control
tide station in order to derive the equivalent datum of 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. For stations
with shorter series, simultaneous observational comparisons are made with
a control tide station in order to derive the equivalent datum of 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
In hydrologic terms, the winding of a stream channel.

Meander Belt
In hydrologic terms, 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 heights of unobscured portions of objects, other than
natural landmarks, near the runway. See variable ceiling.

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 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
In hydrologic terms, the curved surface of the liquid at the open end of
a capillary column.

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 pressure of the atmosphere increases or decreases.

Meridian
An imaginary line on the earth's surface passing through both geographic
poles and through any given point on the planet, also called a line of
longitude.

Meridional Flow
Large-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.

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 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).


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