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Posted at 12:55 PM ET, 02/19/2009

Snow With Sunshine: The Explanation

By Steve Tracton

* Snow With Sun: The Pictures | Full Forecast Through Weekend *

In his post earlier today, CWG photographer Kevin Ambrose displays neat photographs of the sunrise on Feb. 16 (Presidents' Day) that show snow falling from a blue sky above -- the third time this winter Kevin has observed this phenomenon.

We normally think of sun showers as when rain falls while the sun is shining. This occurs mostly in the warm season when, for example, thunder clouds are nearly overhead with sunshine reaching our eyes at an angle through a cloudless region of the sky.

Sun snow showers differ in the sense that snowflakes can land before your very eyes with clear blue sky overhead, as in the case Kevin describes.

Keep reading to find out how snowflakes or rain droplets can fall from a cloudless sky...

I'll consider the rather straightforward explanation for these phenomena in the context of a question sent in recently by Gary Allen of Williamsburg, Va. -- namely, "Can you have rain without clouds?"

Gary said that on Jan. 19 he could see, feel and hear small rain drops falling on his glasses, the back of his hands, and nearby objects. Although the sky had been cloudy and "dampish" about an hour earlier, he reports, it was perfectly clear in all directions at the time light rain was occurring -- and there were no trees or structures from which the drops might have dripped or obscured his view.

"Waaaait a minute," Gary thought, "this cannot be ... it was a singular experience that likely would have amazed any weather-aware person as it did moi."

My reply to Gary explained that snowflakes have several thousand feet to fall once they become heavy enough to do so. Many factors contribute to the fall speed of snowflakes (e.g., size, shape) and distance traveled (e.g., wind speed, rate of any melting) before reaching the surface.

A reasonable estimate is that it can take up to an hour or more for a snowflake to reach the ground and can land up to 25 miles or more from where it originated. I suspect what happened in Gary's case was that there were snow showers from clouds well out of sight, with snowflakes melting to tiny raindrops just before reaching Gary. Hence, it's quite possible that a person can be hit by snowflakes or rain droplets even if the sky is cloudless from the observer's point of view.

On the other hand, the much larger and heavier raindrops emerging from the base of a thunderstorm reach the ground in a minute or less. Thus, it's very unlikely to be seriously rained on without the rain-generating cloud nearly overhead, though of course it can be clear all around.

Like Kevin, I'd much prefer a real snowstorm to a few isolated snow showers. But one thing is sure, when the flakes are flying with the sun out, it can certainly make for some picturesque scenes. Additional examples are found here.

Have a weather question? E-mail us at Ask the Gang.

By Steve Tracton  | February 19, 2009; 12:55 PM ET
Categories:  Tracton  
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Next: PM Update: There's a Cold Wind a Blowin'


Good to know!

Posted by: --sg | February 19, 2009 8:29 PM | Report abuse

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