northeast radar from intellicastIf you were to look at this morning's radar map you might think a lot of rain is imminent. You'd be twenty percent right.

Radar works by sending out a weak microwave signal. When the radar beam hits a rain drop the signal returns to the radar station. The longer it takes the signal to make that trip the further away the rain is. Pretty simple, eh? Here's the catch and why this radar image is deceiving: Radar signals travel in straight lines. The signal is beamed out at a slight upward angle to avoid nearby objects like trees, buildings and hills, the so-called "ground clutter" TV weatherpeople are so fond of mentioning. Combine that with the curvature of the Earth and the radar beam is way above the ground a few miles out from the station.

The rain on this morning's radar is well above the ground. The air below is very dry. As the rain falls from above it is quickly evaporating in the drier air. Where the rain above is intense enough, some of the rain drops may reach the ground. Accordingly, the Weather Service is throwing in a 20 percent chance of light rain for today.

The rain on this map that is going to hit us is in the blob that's over the Ohio Valley. That should arrive this evening and last all day tomorrow. Showers will linger into Friday morning, but Saturday and Sunday are looking very nice –partly to mostly sunny with highs ranging from the the mid-70s to low-80s.

Radar image from