Weather 101

Is frost the same thing as frozen dew?

No. The two weather phenomena are very different.

Frost: Courtesy MGN

Frost occurs when the dewpoint temperature reaches freezing or below.  When the temperature is that cold, the water vapor in the clouds goes directly from the vapor state, to a solid state.  This process is called sublimation, and will put a white crispy coat on vegetation, cars, and buildings.  The only variable in common between frost and frozen dew is the freezing temperatures.

Frozen Dew: Courtesy NASA

Frozen dew starts as liquid dew.  When the dewpoint temperature is reached, little droplets of water coats the vegetation.  However, if the air temperature starts to fall, and falls below freezing, the little droplets will freeze.  That’s when you would have tiny frozen beads.


Why is there a ring around the sun?

Summer has begun, which means more sunshine is beating down on the state.  Recently, a flood of e-mails and phone calls have come into the weather team about odd rings and rainbows in the sky.  So let’s explore what these strange sightings are.

First of all, these rings and rainbows are not unusual.  In fact, they are more common than you might realize.   However, it takes special conditions to see them.  All of the special features in the sky are properties of light.  When light is reflected, refracted, diffracted, or encounters interference, you’ll see optical phenomena.

How does light play a role?  Light emitted from the sun comes to our eye as “white” light.  It brightens the skies, and lights the land.  However, when you put light through dust, pollutants, water, ice, etc., the light wave is broken up into the colors it is composed of.  That’s when we can see various colors in the skies, such as pink sunsets and rainbows.

Courtesy Jarred Berger, Philomath

RAINBOW: A very common sight in Oregon, rainbows are when light is refracted through a raindrop, mist, or even lawn sprinkler.  This refraction causes an arc of colors to display.  To see a rainbow, put your back to the sun and look into the sun.  The best time in Oregon to see rainbows are nearly year round, but requires days with isolated showers where the sun and rain are both present.

Courtesy: Lisa Murphee

HALO: One of the most reported features to the Storm Tracker 9 Weather Team is the halo.  Halos are causes by the dispersion of sunlight through a thin layer of cirrus clouds.  Cirrus clouds are high into the sky where it is cold.  So instead of raindrops, halos are formed by light traveling through ice crystals.  The angle the sunlight travels through the layer of ice will determine the size and color of the halo.  Haloes around the moon occur also, but are less common. A similar formation as a halo is called a corona, which is a bright white disk centered on the sun or moon.  Coronas appear to have several rings and display colors on the outer edges of each ring.  Coronas form with lower, thicker clouds than haloes, and give the appearance of being filled in.  Unlike haloes, coronas form when light is passed through water droplets and is diffracted (bent).

Courtesy: NASA Photo of the Day: Joe Orman

SUN DOG: Often with haloes, sun dogs (or parhelia) form as well.  The same conditions for haloes are needed for sun dogs.  While they usually form in pairs, often sky conditions determine whether you can see both.  They form when sunlight goes into ice crystals at a 22-degree angle, and form in the same altitude as the sun.  Sun dogs are also nicknamed “mock suns” since it appears two to three suns exist at a time.

Courtesy: NASA Photo of the Day: Stan Richard

SUN PILLAR: Occurring at sunset or sunrise, sun pillars are a long shaft of light that extends from the sun.  Generally, the pillar will take on complimenting colors to the sunset.  To achieve this phenomenon, light is reflected by high altitude ice crystals.


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