Weather Alert in Oregon
Red Flag Warning issued August 25 at 7:57AM PDT until August 25 at 8:00PM PDT by NWS Portland OR
AREAS AFFECTED: Central Oregon Cascade Foothills; Northern Willamette National Forest; Southern Willamette National Forest
DESCRIPTION: The National Weather Service in Portland has issued a Red Flag Warning for thunderstorms and high instability, which is in effect until 8 PM PDT this evening. * AFFECTED AREA...In Oregon, Fire Weather Zone 687 Central Oregon Cascade Foothills, Fire Weather Zone 689 Northern Willamette National Forest and Fire Weather Zone 690 Southern Willamette National Forest. * THUNDERSTORMS...Scattered thunderstorms with critically dry fuels. * OUTFLOW WINDS...Gusts up to 40 mph may travel outward up to 25 miles from thunderstorm cores. * IMPACTS...Thunderstorm outflow winds may result in unanticipated erratic fire spread. High instability may result in fire growth. Frequent lightning and critically dry fuels may result in numerous fire starts.
INSTRUCTION: A Red Flag Warning means that critical fire weather conditions are either occurring now, or will shortly. A combination of the above conditions can contribute to extreme fire behavior.
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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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