29 results. (Showing 1 - 20)
1.
macroburst
Large thunderstorm downbursts with a 2.5 mile diameter or greater outflow of damaging winds lasting 5 to 20 minutes.
2.
Madden-Julian Oscillation
(MJO )
Tropical rainfall exhibits strong variability on time scales shorter than the seasonal El Niņo-Southern Oscillation (ENSO). These fluctuations in tropical rainfall often go through an entire cycle in 30-60 days, and are referred to as the Madden-Julian Oscillation or intraseasonal oscillations. The intraseasonal oscillations are a naturally occurring component of our coupled ocean-atmosphere system. They significantly affect the atmospheric circulation throughout the global Tropics and subtropics, and also strongly affect the wintertime jet stream and atmospheric circulation features over the North Pacific and western North America. As a result, they have an important impact on storminess and temperatures over the United States. During the summer these oscillations have a modulating effect on hurricane activity in both the Pacific and Atlantic basins.
3.
Mammatus Clouds
Rounded, smooth, sack-like protrusions hanging from the underside of a cloud (usually a thunderstorm anvil). Mammatus clouds often accompany severe thunderstorms, but do not produce severe weather; they may accompany non-severe storms as well.
4.
Mean
The arithmetic average, or the middle point between two extremes.
5.
measurable
Precipitation of 0.01" or more.
6.
Medium Range
In forecasting, (generally) three to seven days in advance.
7.
Medium Range Forecast
(MRF )
Medium Range Forecast, usually a reference to a numeric model that extends one to two weeks into the future.
8.
Medium-Range Forecast
(MRF )
Medium-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).
9.
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.
10.
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. 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).
11.
Mesohigh
A mesoscale high pressure area, usually associated with MCSs or their remnants.
12.
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.
13.
Mesonet
A regional network of observing stations (usually surface stations) designed to diagnose mesoscale weather features and their associated processes.
14.
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.
15.
Mesoscale Convective Complex
(MCC )
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.
16.
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.
17.
meteorology
The scientific study of the physics, chemistry, and dynamics of the Earth's atmosphere, especially weather and climate.
18.
microburst
A small, concentrated downburst affecting an area less than 4 kilometers (about 2.5 miles) 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.
19.
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. Mid-level cooling can occur, for example, with the approach of a mid-level cold pool.
20.
millibar
A pressure unit of 1000 dynes cm-2, often used for reporting atmospheric pressure where one millibar equals 1 hectopascal (hPA).
