Weather Alert in Oregon
Air Quality Alert issued August 23 at 1:09AM PDT by NWS Portland OR
AREAS AFFECTED: Tualatin Valley; West Hills and Chehalem Mountains; Inner Portland Metro; East Portland Metro; West Central Willamette Valley; East Central Willamette Valley; Benton County Lowlands; Linn County Lowlands; Lane County Lowlands
DESCRIPTION: The Oregon Department of Environmental Quality, and the Lane Regional Air Protection Agency have continued an Air Quality Advisory, which is in effect from 10 AM Saturday to 8 PM PDT Monday. An Air Quality Advisory for Ozone remains in effect. 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 Monday 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. Please follow medical advice if you have a heart or lung condition. More information about air quality can be found at: www.oregon.gov/DEQ www.lrapa.org
INSTRUCTION: N/A
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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
Weather Topic: What is Snow?
Home - Education - Precipitation - Snow
Next Topic: Stratocumulus Clouds
Snow is precipitation taking the form of ice crystals. Each ice crystal, or snowflake,
has unique characteristics, but all of them grow in a hexagonal structure.
Snowfall can last for sustained periods of time and result in significant buildup
of snow on the ground.
On the earth's surface, snow starts out light and powdery, but as it begins to melt
it tends to become more granular, producing small bits of ice which have the consistency of
sand. After several cycles of melting and freezing, snow can become very dense
and ice-like, commonly known as snow pack.
Next Topic: Stratocumulus Clouds
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