millibar (mb) — a unit for expressing atmospheric pressure. Sea level pressure is normally close to 1013 mb.
northeaster — a name given to a strong, steady northeast wind that is accompanied by rain and inclement weather. It often develops when a storm system moves northwest- erly along the coast of North America.
overrunning — a condition that occurs when air moves up and over another layer of air.
pressure tendency — the rate of change of atmospheric pressure within a specified period of time, most often three hours. Also known as barometric tendency.
rain — precipitation in the form of liquid water drops that have diameters greater than that of drizzle.
rainbow — an arc of concentric colored bands that spans a section of the sky when rain is present and the sun is behind the observer’s back.
Rain Gauge — an instrument designed to measure the amount of rain that falls during a given time interval.
relative humidity — the ratio of the amount of water vapor actually in the air compared to the amount of water vapor the air can hold at that particular temperature and pressure. The ratio of the air’s actual vapor pressure to its saturation vapor pressure.
sea breeze — a coastal local wind that blows from the ocean onto the land. The leading edge of the breeze is called a sea breeze front.
sea level pressure — the atmospheric pressure at mean sea level.
severe thunderstorms — intense thunderstorms capable of producing heavy showers, flash floods, hail, strong and gusty surface winds, and tornadoes.
shower — intermittent precipitation from a cumuli form cloud, usually of short duration but often heavy.
sleet — a type of precipitation consisting of transparent pellets of ice .20 inches (5 mm) or less in diameter. Also known as ice pel- lets.
smog — air that has restricted visibility due to pollution, or pollution formed in the presence of sunlight — photochemical smog (originally smog meant a mixture of smoke and fog).
snow — a solid form of precipitation composed of ice crystals in complex hexagonal forms.
snowflake — an aggregate of ice crystals that falls from a cloud.
snow flurries — light showers of snow that fall intermittently.
snow squall (shower) — an intermittent heavy shower of snow that greatly reduces visibility.
squall line — any
standard atmospheric pressure — pressure of 1013.25 millibars (mb), 29.92 inches of mercury (Hg), 760 millimeters of mercury (mm), 14.7 pounds per square inch (lb/in), 101,325 pascals (Pa).
station pressure — the actual air pressure computed at the observing station.
supercell storm — an enormous severe thunderstorm whose updrafts and down- drafts are nearly in balance, allowing it to maintain itself for several hours. It can produce large hail and tornadoes.
temperature — the degree of hotness or coldness of a substance as measured by a thermometer. It is also a measure of the
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