GENERAL WEATHER TERMS
Cold air funnel - A funnel cloud or (rarely) a small relatively weak tornado that can develop from a small shower or thunderstorm when the air aloft is unusually cold. They are much less violent than other types of tornadoes.
Crest - The highest level of a flood wave as it passes a point.
Degree Day - Gauges the amount of heating or cooling needed for a building using 65 degrees as a baseline. To compute degree days, the average temperature for a day is taken and referenced to 65. An average temperature of 50 yields 15 heating degree days, while an average temperature of 75 would yield 10 cooling degree days.
Dew Point - A measure of atmospheric moisture. It is the temperature to which air must be cooled in order to reach saturation (assuming pressure and moisture content are constant).
Doppler Radar - Radar that can measure radial velocity, the instantaneous component of motion parallel to the radar beam (i.e., toward or away from the radar).
Downburst - A strong downdraft from a thunderstorm resulting in an outward burst of damaging winds on or near the ground. Downburst winds are often 50 to 100 mph and in a few cases, 100 to 150 mph. They can do as much damage as a small tornado.
- Microburst - a small downburst affecting an area less than 2 1/2 miles in diameter with peak winds lasting generally less than five minutes.
- Macroburst - a large downburst affecting an area greater than 2 1/2 miles in diameter with peak winds generally lasting five minutes or longer.
Flood Stage - The level or stage at which a stream overflows its banks or the stage at which the overflow of a stream begins to cause damage.
Freezing Rain/Freezing Drizzle - Rain or drizzle which falls in liquid form and freezes on impact with cold surfaces to form a glaze on the ground and exposed objects.
Enhanced Fujita Scale or EF-Scale - A scale of wind damage intensity in which wind speeds are inferred from analysis of wind damage. All tornadoes and most other windstorms are assigned a numerical rating from this scale according to the most intense damage caused by the storm.
||65-85 mph, light damage
||86-110 mph, moderate damage
||111-135 mph, considerable damage
||136-165 mph, severe damage
||166-200 mph, devastating damage
||Over 200 mph, incredible damage
Funnel Cloud - A rotating column of air, extending from a towering cumulus or cumulonimbus cloud, that is not in contact with the ground.
Gustnado - A gust front tornado. A small, weak, short-lived tornado that occurs along a gust front - the leading edge of a thunderstorm, caused by rain-cooled air flowing out from the storm's downdraft. A gustnado is often visible as a debris cloud or dust whirl.
Hail - Precipitation in the form of lumps of ice that form during some thunderstorms.
Heat Index - The apparent temperature that describes the combined effect of high temperatures and high levels of humidity, which reduces the body's ability to cool itself.
Lake Breeze - A local wind blowing from the cooler surface of Lake Michigan to warmer inland areas, usually during the afternoon in spring and summer.
Lake Effect Snow - Snow that occurs to the lee of the Great Lakes when cold air moves across relatively warm waters of the lakes.
Rain/Showers - Rain is a nearly steady and uniform fall of precipitation over an area. Showers are intermittent and/or scattered convective rainfall of varying intensity.
Seiche - An oscillation of the surface of southern Lake Michigan usually caused by a squall line moving rapidly south-southeast down the Lake. Rapid changes in the lake level pose a serious threat to marinas and people on piers and breakwaters.
Relative Humidity - The ratio of the amount of water vapor actually present in the air to the greatest amount possible at the same temperature.
Sleet - Sleet or ice pellets are solid grains of ice formed from the freezing of rain or the refreezing of melted snow, which bounce off the ground and other objects.
Squall line - A line of thunderstorms or squalls which may extend over several hundred miles.
Tornado - A violently rotating column of air, from a thunderstorm, in contact with the ground.
Waterspout - In general, a tornado occurring over water. Specifically, it refers to a small, relatively weak rotating column of air over water beneath a towering cumulus or cumulonimbus cloud. They occasionally occur over Lake Michigan in late summer with unusually cold air aloft.
Wind Chill - An apparent temperature that describes the combined effect of wind and low temperature on exposed skin.