Weather Alert in Oregon
Air Quality Alert issued August 12 at 12:17PM PDT by NWS Portland OR
AREAS AFFECTED: Clackamas, OR; Multnomah, OR
DESCRIPTION: The Oregon Department of Environmental Quality has issued an Air Quality Advisory, which is IN EFFECT UNTIL 8 PM PDT THIS EVENING. An Air Quality Advisory for Ozone has been issued. High levels of ozone in the lower atmosphere in the region combined with forecasted conditions will cause air quality to reach unhealthy levels at times through 8 PM PDT this evening. Pollutants can cause burning eyes, runny nose, aggravate heart and lung diseases, and aggravate other serious health problems. Limit outdoor activities and keep children indoors if it is smoky. Please follow medical advice if you have a heart or lung condition. More information about air quality can be found at: www.orcaa.org www.swcleanair.gov www.oregon.gov/DEQ www.lrapa.org
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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