Weather Alert in Illinois
Air Quality Alert issued July 14 at 10:11PM CDT by NWS Chicago IL
AREAS AFFECTED: McHenry; Lake; Kane; DuPage; Kendall; Grundy; Northern Cook; Central Cook; Southern Cook; Northern Will; Southern Will; Eastern Will
DESCRIPTION: The Illinois Environmental Protection Agency has issued an Air Pollution Action Day for Tuesday July 15th for the greater Chicago metropolitan area. A Chicago area "Air Pollution Action Day" is declared when weather conditions are such that widespread ozone and or particular levels are expected to be at or above the Unhealthy for Sensitive Groups (USG) category of the Air Quality Index (AQI) for multiple days. Ozone is expected to be the primary pollutant of concern. Active children and adults, especially people with pulmonary or respiratory disease such as asthma, should limit prolonged outdoor activity. Area residents are urged to reduce pollution levels. Air quality forecasts, current air quality, and tips on how you can reduce your emissions can be found at www.airnow.gov. Media contact...Illinois EPA.
INSTRUCTION: N/A
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Weather Topic: What is Precipitation?
Home - Education - Precipitation - Precipitation
Next Topic: Rain
Precipitation can refer to many different forms of water that
may fall from clouds. Precipitation occurs after a cloud has become saturated to
the point where its water particles are more dense than the air below the cloud.
In most cases, precipitation will reach the ground, but it is not uncommon for
precipitation to evaporate before it reaches the earth's surface.
When precipitation evaporates before it contacts the ground it is called Virga.
Graupel, hail, sleet, rain, drizzle, and snow are forms of precipitation, but fog
and mist are not considered precipitation because the water vapor which
constitutes them isn't dense enough to fall to the ground.
Next Topic: Rain
Weather Topic: What are Shelf Clouds?
Home - Education - Cloud Types - Shelf Clouds
Next Topic: Sleet
A shelf cloud is similar to a wall cloud, but forms at the front
of a storm cloud, instead of at the rear, where wall clouds form.
A shelf cloud is caused by a series of events set into motion by the advancing
storm; first, cool air settles along the ground where precipitation has just fallen.
As the cool air is brought in, the warmer air is displaced, and rises above it,
because it is less dense. When the warmer air reaches the bottom of the storm cloud,
it begins to cool again, and the resulting condensation is a visible shelf cloud.
Next Topic: Sleet
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