Weather Alert in Oregon
Winter Weather Advisory issued February 18 at 10:00AM PST until February 20 at 4:00AM PST by NWS Portland OR
AREAS AFFECTED: West Hills and Chehalem Mountains
DESCRIPTION: ...A SERIES OF WEAK SYSTEMS WILL BRING WIDESPREAD SNOW TO THE NORTHERN OREGON AND SOUTHERN WASHINGTON COAST AND CASCADE RANGES THROUGH AT LEAST THURSDAY NIGHT... .A broad area of low pressure will continue to bring widespread snow showers to elevations above 1000 ft through at least Thursday night. Given the showery nature of the precipitation and uncertainty as to the track of tonight's system, there is some variability in forecast total snow fall accumulations through Thursday night. While the forecast remains on track for overall snowfall totals, where exactly the highest snow accumulations occur remain in flux. * WHAT...Snow. Additional snow accumulations 1 to 3 inches. * WHERE...Portland West Hills and Chehalem Mountain. * WHEN...Until 4 AM PST Friday. * IMPACTS...Roads, and especially bridges and overpasses, will likely become slick and hazardous.
INSTRUCTION: Have a winter emergency driving kit readily available. Common items to include: flashlight, batteries, blankets, a shovel, water, non-perishable food items, tire chains, etc. Be aware that walking surfaces may be slick. Walk with extra care. For the latest road conditions and chain restrictions in Oregon, call 5 1 1, or visit: www.tripcheck.com. For the latest road conditions and chain restrictions in Washington, visit: wsdot.com/travel/real-time/map
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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
Weather Topic: What are Stratocumulus Clouds?
Home - Education - Cloud Types - Stratocumulus Clouds
Next Topic: Stratus Clouds
Stratocumulus clouds are similar to altocumulus clouds in their
fluffy appearance, but have a slightly darker shade due to their additional mass.
A good way to distinguish the two cloud types is to hold your hand out and measure
the size of an individual cloud; if it is the size of your thumb it is generally
an altocumulus cloud, if it is the size of your hand it is generally a
stratocumulus cloud.
It is uncommon for stratocumulus clouds to produce precipitation, but if they do
it is usually a light rain or snow.
Next Topic: Stratus Clouds
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