(WHTM) — So, you are hearing for days that snow is coming and it’s going to impact travel and possibly close schools. But, when you look outside, it’s not snowing. So, you grab your phone or turn on the TV to check the latest radar scan, and it tells you it should be snowing.
So, why isn’t it snowing, when the radar clearly shows that it is?
The National Weather Service (NWS) states that weather radars work when a beam of energy, in the case of radio waves, is emitting from an antenna. As they strike objects, such as precipitation, the energy is scattered in all directions, with some of that energy being directed back to the radar.
The optical range of weather radars is limited to 3 -124 miles, according to IBM. This is due to the curvature of the earth. The radar beam travels in a straight line, meaning beyond its max range, it’s unable to detect objects close to the surface of the ground.
So, what you see on the radar screen is what the radar sees higher up in the atmosphere. So the radar isn’t lying. Precipitation is falling, just not at the surface.
The reason we don’t see snow at the surface on some occasions is due to the fact the air is too dry and as the snow falls, it evaporates and cannot penetrate the dry air mass that is in place. This is something called virga.
By definition, virga is streaks or wisps of precipitation that fall from a cloud but evaporate before reaching the ground. If the dry air is closer to the ground, rather than up in the atmosphere, the snow will fall and increase in intensity once the dry air is eroded by the precipitation.
This can also occur in the summer when the radar shows rain falling, but nothing is occurring at the surface.
So don’t get upset at the meteorologists when the radar shows one thing and you see another. Just have to be patient, and let the dry air erode away.