Ice Crystal - Any one of the crystalline forms of ice large enough to be seen with the naked eye. An ice crystal may be in the form of a column, crystal, needle, or platelet, and it is usually six-sided (hexagonal).
Ice Crystal Cloud - A cloud, such as cirrus, composed entirely of ice crystals.
Ice Crystal Haze - A light ice fog made up of ice crystals only and sometimes seen up to heights over 4 miles.
Ice Fog - A fog which is rare above temperatures of -22 degrees Fahrenheit and which is composed of suspended ice particles partly ice crystals between .007874 and .03937 inch in diameter but mostly droxtals between .00047244 and .007874 inch diameter. Ice fog occurs mainly at high latitudes during clear, calm weather.
Ice Needle - A long, thin ice crystal.
Ice Pellets - Precipitation which consists of either transparent or translucent pellets of ice about .20 inch or smaller in diameter. There are two kinds of ice pellets. One kind, formed from the freezing of raindrops or refreezing of mostly melted snowflakes as they fall from a warmer layer of air aloft into a colder layer near the earth's surface, is known commonly as sleet and consists of usually transparent grains of ice. A second kind of ice pellets is known as small hail (not to be confuesed with hail from thunderstorms) and consists of translucent snow pellets which have been covered with a thin layer of ice.
Springfield Missouri Ice Storm of Jan. 12-14, 2007. Photo from Springfield National Weather Service Forecast Office.
Ice Storm - A storm consisting of a steady fall of freezing rain which coats exposed objects with a rather heavy layer of glaze usually resulting in a variety of hazards.
Cumulonimbus with incus (anvil) by Nathan Webb. Photo from Louisville, Kentucky NWS photo library.
Incus - A supplementary cloud feature commonly called anvil where the thunderstorm cloud (cumulonimbus) top flattens out into an anvil shape.
Indian Summer - A period of unseasonably warm weather during mid or late autumn following a period of cool weather.
Inferior Mirage - A type of mirage resulting from the layer of low density air being below the observer's eye, such as when a hot road surface appears to be covered with water.
Insolation - Generally, solar radiation received at the surface of the earth. The term is short for incoming solar radiation.
Instability - The state of the atmosphere which allows convection to take place spontaneously and results in the formation of clouds and, often, precipitation.
Cotton Region Instrument Shelter from the Tallahassee, Florida NWS.
Instrument Shelter - A box type structure painted white and having louvered sides designed to protect certain weather instruments from exposure to direct sunlight while permitting air to flow freely through it. The shelter is always positioned so that the door faces north.
Intertropical Convergence Zone - The boundary line which separates the southeast trade winds of the Southern Hemisphere from the northeast trade winds of the Northern Hemisphere.
Intracloud Flash - A lightning flash between a positive charge center and a negative charge center within the same cloud.
Inversion - The condition which exists in the atmosphere when there is an increase of temperature with height.
Ionosphere - The region of the atmosphere whose base is at a height of about 43 to 50 miles above the earth's surface and which contains a high concentration of ions and electrons.
Iridescent Clouds around the sun. Photo by Commander John Bortniak from NOAA Photo Library.
Iridescent Clouds - Clouds composed of ice crystals and which display bright spots or borders of colors, mainly red and green. Such phenomena can usually be seen up to approximately 30 degrees from the sun.
Iron Winds - Northeasterly winds frequent during February and March in Central America and which last several days.
Isallobar - A line of equal change in atmospheric pressure within a specific period of time.
Isobar - A line connecting points of equal atmospheric pressure.
Isodrosotherm - A line of equal dewpoint temperature.
Isohume - A line connecting points of equal humidity.
Isohyet - A line connecting points of equal precipitation.
Isotach - A line connecting points of equal wind speed.
Isotherm - A line connecting points of equal temperature.
Jet Stream - A meandering, narow band of very strong winds in the atmosphere. Wind speeds in a jet stream can hit speeds of 200 m.p.h. or more. Two jet streams are often mentioned. The primary one, known as the polar-front (or polar) jet stream is found in the middle and upper latitudes at a height of approximately 30,000 to 40,000 feet. A secondary jet stream, known as the subtropical jet stream, is usually found at a height of about 7 to 8 miles above the earth's surface and between 20 and 30 degrees latitude.
Jet Stream Core - Sometimes called a Jet Streak, this is a localized area of highest wind speeds within a jet stream.
Junk Wind - A south or southeast monsoon wind known in China, Japan and Thailand which is favorable for the sailing of junks (a Chinese sailing ship).
Juran - A cold, snowy wind which blows from the Swiss Jura Mountains toward Lake Geneva.
Copyright 2006 Ronald Hahn. All Rights Reserved