short the growing season, it is a killing freeze.

freezing rain/drizzle — rain or drizzle that falls in liquid form and then freezes upon striking the ground or objects that are at 32°F (0°C) or colder.

front — the transition zone between two distinct air masses.

frost (hoarfrost) — a covering of ice produced by sublimation (to change from a gaseous state to a solid without becoming a liquid) on exposed surfaces when the air temperature falls below the frost point (the dew point is below freezing).

frozen dew — the transformation of liquid dew into tiny beads of ice when the air temperature drops below freezing.

funnel cloud — a rotating cone-like cloud that extends downward from the base of a thunderstorm. When it reaches the surface, it is called a tornado.

graupel — ice particles between .08–.20 inches (2 and 5 mm) in diameter that form in a cloud. Snowflakes that become rounded pellets due to riming (being frosted over) are called graupel or snow pellets.

gust front — a boundary that separates a cold downdraft of a thunderstorm from warm, humid surface air. On the surface, its passage resembles that of a cold front.

hailstones — transparent or partially opaque particles of ice that range in size from that of a pea to that of golf balls and larger.

haze — fine dry or wet dust or salt particles dispersed through a portion of the atmo- sphere. Individually these are not visible, but cumulatively they diminish visibility.

heat index (HI) — an index that combines air temperature and relative humidity to

determine an apparent temperature — how hot it actually feels.

humidity — a general term that refers to the air’s water vapor content.

hurricane — a severe tropical cyclone having winds in excess of 64 knots (74 mph).

hurricane warning — a warning given when it is likely that a hurricane will strike an area within 24 hours.

hurricane watch — a hurricane watch indicates that a hurricane poses a threat to an area (often within several days) and residents of the watch area should be prepared.

jet stream — relatively strong winds concentrated within a narrow band in the atmo- sphere.

knot — a unit of speed equal to 1 nautical mile per hour (1 knot = 1.15 mph).

lake-effect snows — localized snowstorms that form on the downwind side of a lake. Such storms are common in late fall and early winter near the Great Lakes as cold, dry air picks up moisture and warmth from the unfrozen bodies of water.

lightning — a visible electrical discharge produced by thunderstorms.

mean annual temperature — the average temperature at any given location for the entire year.

mean daily temperature — the average of the highest and lowest temperature for a 24- hour period.

meteorology — the study of the atmosphere and atmospheric phenomena as well as the atmosphere’s interaction with the earth’s sur- face, oceans, and life in general.

Special Features

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