Weather Glossary – M


MACROBURST – Large downbursts with 2.5 miles or larger outflow diameter and damaging winds lasting 5 to 20 minutes. Intense macrobursts could cause tornado-force damage.

MARINE PUSH – A regional phenomena where the heat low shifts east across the Pacific Northwest, along an onshore flow of cool, marine air to spill over the Cascades. It is characterized by a gusty winds and the potential of convection across the Inland Northwest.

MARITIME AIR MASS – Moist air mass originating over the ocean.

MCS– Mesoscale Convective System. A large cluster of thunderstorms and rain. Can be a squall line, multi-cells or a mesoscale convective complex.

MEASURABLE- Precipitation of 0.01″ or more.

MESOCYCLONE -The rotating updraft in a supercell thunderstorm

METEOROLOGY – The study of the atmosphere and atmospheric phenomena.

MIC – Meteorologist In Charge.

MICROBURST – Small downbursts, less than 2.5 miles in outflow diameter, with peak winds lasting 2 to 5 minutes. They may induce dangerous wind and downflow wind shears which can affect aircraft performance.

MICROWAVE RADIATION – electromagnetic radiation which comprises the highest frequency radio energy.

MID/UPPER LEVEL SUPPORT– This is in reference to either positive differential vorticity advection or a jet streak creating upper level divergence. These processes result in a dynamic lifting of air.

MILLIBAR – A unit of atmospheric pressure. 1 mb = 100 Pa (pascal). Normal surface pressure is approximately 1013 millibars.

MIST – very fine water droplets at ground level

MIXING DEPTH– The vertical distance the process of convection mixes the air from the surface to aloft. The mixing depth is often the same depth as the PBL. The mixing depth will increase with solar warming of the surface and increased low level wind speed. Could also be in reference to the depth of the “transition zone” between two air masses that are horizontally differentially advecting one over the other.

MOISTURE AXIS / RIDGE– : An area of higher moisture values, usually in the form of a ridge of higher dewpoints at the surface or 850 mb. Low level moisture axes enhance atmospheric instability, which in turn promotes thunderstorm development. Existing storms can intensify by moving into moisture axes. The concept is similar to dewpoint pooling.

MONSOON – A persistent seasonal wind, often responsible for seasonal precipitation regime.

MOS – Model Output Statistics (usually in reference to NGM model). These are numerical representations of expected weather such as forecasted temperatures and precipitation chances.

MOSTLY CLOUDY – Between 7/10 and 9/10 cloud cover.

MOSTLY SUNNY (MOSTLY CLEAR) – Between 1/10 and 3/10 cloud cover.

MM5 – the Mesoscale Model Version 5. One of these models is run at the Department of Atmospheric Sciences at the University of Washington which covers the weather over Washington, Oregon and most of Idaho.

MRF – Medium Range Forecast model generated every 12 hours by NCEP.

MSLP – Mean sea level pressure.