By John Francis
John Rodgers is a math and science teacher at Bruce Peninsula District School; has been for decades. As with most scientists, his mind never stops. He has a passion for understanding the world around him (also for Monty Python).
He grew up on the Ferndale Flats. Snowsqualls have been part of his life as long as he can remember. He has always felt there should be a better way of understanding/predicting where and when they will happen.
OK, everybody thinks there should be a better way of predicting snow squalls. But John Rodgers has actually done it.
Most weather wonks have a nest of pages that they can “open in tabs” so they all come up at once. Two of the most important are Britt Radar (https://weather.gc.ca/radar/index_e.html?id=WBI) and Windy/Windity (https://www.windy.com/?44.983,-81.250,5,i:pressure or just www.windy.com to start. Zoom in to get local winds over Lake Huron). I load these two, among a host of others, several times a day. Despite all that looking, I had never noticed a coherent pattern.
John Rodgers spotted the pattern.
Windity shows the direction and speed of the winds: the direction with little moving streaks, the speed with colours. Watch on Windity for areas where the winds converge and/or slow down. Thought experiment: imagine what must be happening when winds converge and slow down. Answer: all that air can’t occupy the same space so some of it gets forced upwards. When air rises, it cools. If it was only a couple of degrees above dewpoint to begin with, it won’t take much of a rise to trigger condensation. Ergo: a cascade of tiny little snowflakes that stays still, downwind of the point of conversion. (You can get the dewpoint spread from Environment Canada’s Tobermory forecast page: https://weather.gc.ca/city/pages/on-157_metric_e.html)
Look at the photos at left. The windity photo on the left shows two areas of convergence and a lot of slowing down. The biggest convergence is out over Lake Huron, northwest of Tobermory. A less pronounced convergence is over Lake Huron, west of Port Elgin to Sauble. The wind is slowing from 30+ knots (red) to 20+ knots (orange) to 18 knots (green).
The map above at right shows where the snowsqualls were.
But it gets better. Windity will also predict wind speed and direction into the future. Just move the slider at the bottom of the page. Watch where the convergences are going to be — there will be snowsqualls downwind of that point.
Amaze your friends. Even better: amaze yourself!
John Rodgers assures me that Windity’s predictions of future winds are pretty accurate for the first 24 hours or so, somewhat less so beyond that.
Have fun with this!