A cloud, with its base on the surface, which reduces visibility to 1/4 of a mile or less.

Cloud or rain droplets containing pollutants, such as oxides of sulfur and nitrogen, to make them acidic.

The horizontal transport of air or atmospheric properties. Commonly used with temperatures, i.e., "warm air advection", or moisture, i.e., "moisture advection".

Issued for weather situations that cause significant inconveniences but do not meet warning criteria and, if caution is not exercised, could

A large body of air having similar horizontal temperature and moisture characteristics.

An instrument that measures wind speed.

A large area of high pressure around which the winds blow clockwise in the Northern Hemisphere.

An instrument for measuring atmospheric pressure.

A storm lasting about 3 hours or longer with sustained winds 35 mph or greater with frequent gusts to 35 mph or greater; and considerable falling and/or blowing snow frequently reducing visibilities to less than 1/4 mile.

Small particles of dust or sand which are caused by strong winds blowing over dry ground, that has little or no vegetation.