BLOG: Why is the radar green when it's snowing? - | WBTV Charlotte

BLOG: Why is the radar green when it's snowing?

(Source: Lyndsay Tapases) (Source: Lyndsay Tapases)
Newland, NC (Source: David Pittman) Newland, NC (Source: David Pittman)
Crossnore, NC (Source: Anserson Richard) Crossnore, NC (Source: Anserson Richard)

Great question! 

This morning I put out a call for viewer photos and/or reports of where there may be snow in the mountains, even though the radar was showing green, which would typically indicate rain. 

Blue on the radar means snow, so why wasn't blue showing up?

Well, here's how radar works.

The radar beam does its job in detecting where precipitation (rain or snow) is falling because when the beam hits a rain drop or snowflake along its path, it sends a signal back indicating that "hey, there is something there!"

But beyond that, the radar itself doesn't know what that something is.

When the radar is plotted on the map, there are post-treatment algorithms that are used to determine what the something is.

Based on the surface temperature and dew point profiles that are indicated, the program will then take its best guess at what form of precipitation that radar beam actually hit. But because winter weather is extremely sensitive to very minor fluctuations in temperature and moisture at different levels of the atmosphere that can mean the difference between rain, snow, or ice, the radar's "educated guess" isn't always accurate.

So in a case like this, the radar thinks that based on the best information available and the temperature profile present, there should be rain falling. But, due to small variations in temperature or moisture that it has no control of picking up on, it is actually snow.

You'll see the example from this morning's radar image attached. I circled a few areas I got snow photos in from while all the while the radar was telling me green. 

Fortunately, this doesn't happen too often, because most cases are more clear-cut than this morning's was.

But, in this case, I did greatly appreciate all of the viewers who answered my call with tweets, emails, and photos, and sure did enjoy seeing the beauty in the first snow of the season for some! 

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