Weather Alert in Oregon
Air Quality Alert issued August 22 at 4:03PM 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.orcaa.org www.swcleanair.gov www.oregon.gov/DEQ www.lrapa.org
INSTRUCTION: N/A
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Weather Topic: What is Rain?
Home - Education - Precipitation - Rain
Next Topic: Shelf Clouds
Precipitation in the form of water droplets is called rain.
Rain generally has a tendency to fall with less intensity over a greater period
of time, and when rainfall is more severe it is usually less sustained.
Rain is the most common form of precipitation and happens with greater frequency
depending on the season and regional influences. Cities have been shown to have
an observable effect on rainfall, due to an effect called the urban heat island.
Compared to upwind, monthly rainfall between twenty and forty miles downwind of
cities is 30% greater.
Next Topic: Shelf Clouds
Weather Topic: What is Sleet?
Home - Education - Precipitation - Sleet
Next Topic: Snow
Sleet is a form of precipitation in which small ice pellets are the primary
components. These ice pellets are smaller and more translucent than hailstones,
and harder than graupel. Sleet is caused by specific atmospheric conditions and
therefore typically doesn't last for extended periods of time.
The condition which leads to sleet formation requires a warmer body of air to be
wedged in between two sub-freezing bodies of air. When snow falls through a warmer
layer of air it melts, and as it falls through the next sub-freezing body of air
it freezes again, forming ice pellets known as sleet. In some cases, water
droplets don't have time to freeze before reaching the surface and the result is
freezing rain.
Next Topic: Snow
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