Wind Chill Advisory - dangerous wind chills of 15 below to 24 below zero are expected.

Wind Chill Warning - potentially life threatening wind chills of 25 below zero or colder are expected.

Frost Advisory - damaging frost is expected during the growing season.

Freeze Warning - below freezing temperatures are expected during the growing season.

Ice Storm Warning - dangerous accumulations of ice will occur and are expected to result in hazardous travel, extended power outages, and damage to trees.

Heavy Snow Warning - snow accumulations of six inches or greater, which will result in hazardous travel conditions.

Winter Weather Advisory - cold, ice, and/or snow (two to five inches) are expected.

Winter Storm Watch - severe winter weather, such as heavy snow or ice, is possible within the next day or two.

Winter Storm Warning - severe ice and/or snow (six inches or more) have begun or are about to begin.

Blizzard Warning - heavy snow and strong winds will produce a blinding snow, near zero visibility, deep drifts, and life-threatening travel conditions.

Tornado Watch - conditions are favorable for the development of tornadoes.

Tornado Warning - a tornado has been reported by spotters, or National Weather Service (NWS) meteorologists have determined that one is about to form in the next several minutes. Go to a substantial shelter immediately.

Severe Thunderstorm Watch - conditions are favorable for the development of severe thunderstorms containing large hail and damaging wind.

Severe Thunderstorm Warning - large hail and/or damaging wind has been reported by spotters, or is about to develop. Go to a substantial shelter immediately.

Flood/Flash Flood Watch - conditions are favorable for flooding in the next day or two. Flash floods occur very quickly, usually as a result of heavy rainfall in a short period of time.

Flood Warning - flooding is expected to threaten life and property a few hours after the onset of heavy rain, ice jams, reservoir releases or snowmelt. Flood warnings may be in effect for days or even weeks depending on weather and soil conditions, land topography, and river size.

Flash Flood Warning - rapidly rising water which poses an immediate threat to life and property within a few hours due to small stream or urban flooding and dam or levee failures. Quickly move to higher ground or stay away from flooded areas - especially in vehicles.

Flood Statement - ponding of water in urban areas or minor flooding of streams is occurring. Also used to convey supplemental information, updated observations, and impact information for Flood Warnings.

Heat Wave - A period of abnormally and uncomfortably hot and unusually humid weather. Typically a heat wave lasts two or more days.

Excessive Heat Watch - Issued by the National Weather Service when heat indices in excess of 105ºF (41ºC) during the day, combined with nighttime low temperatures of 80ºF (27ºC) or higher, are forecast to occur for two consecutive days.

Heat Advisory - Issued within 12 hours of the onset of the following conditions: heat index of at least 105°F but less than 115°F for less than three hours per day, or nighttime lows above 80°F for two consecutive days.

Excessive Heat Warning - Issued within 12 hours of the onset of the following criteria: heat index of at least 105°F for more than three hours per day for two consecutive days, or heat index more than 115°F for any period of time.

Heat Index - The heat index is an apparent temperature, or a measure of how hot it feels when temperature and humidity are combined. The heat index is the mostly commonly used method of measuring heat. It is the result of extensive biometeorological studies, taking into account many parameters, including body size and shape, core and body surface temperatures, clothing and the skin's resistance to heat and moisture transfer. The heat index values used in National Weather Service forecasts and warnings and in heat index tables assume an average size adult with clothing, in the shade, with a 5-mph wind. Being in full sun or in an area with no air movement can significantly increase the apparent temperature.

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Glossary sources: National Weather Service and Illinois Emergency Management Agency