I recently wrote a column about the radar situation here in Atlantic Canada: More radars… not on the radar
The next day, Ron emailed with an observation and a comment.
Ron lives in Nova Scotia, along the Minas Basin shore. He says he often checks out the local radar image before heading out on the road, especially in the winter. The other day, he had a look before getting in his car. He wasn’t more than five minutes down the road when he drove right into a snow squall.
I remember that day very well, Ron. I was expecting snow squalls as the cold, dry wind picked up moisture over the water then made landfall along the northwest-facing coastlines. I didn’t see anything on the radar, so I checked the local surface observations and visible satellite imagery and, sure enough, there they were: snow squalls! In this case, the lack of precipitation data was not related to sparse radar coverage. So, where were the snow squalls?
Most of you are familiar with the expression “flying under the radar.” In ordinary terms it means to go without being noticed or detected. But the term is an old aviation expression coined by pilots. Originally it meant that you were flying an aircraft at a lower altitude than a radar beam was able to detect. You were, therefore, literally flying under the radar.
The radar structure is composed of an open lattice steel tower with a 12-metre diameter radome (an enclosure that protects the radar antenna) on top. The total height varies from one site to another, depending on the location and surroundings. Generally, the weather radars will be about 40 metres high or the equivalent of a 12-storey building.
Back to the snow… In the case of lake- or sea-effect snow squalls, intense bands of snow can be associated with clouds that are quite close to the ground. In such cases, the radar beam can overshoot the streamers or bands of snow.
Radar imagery is very useful, but does have its limitations. It becomes a better tool when supported by other methods of detection and backed by good old “ground-truthing.”