@dougmac2 MS Edge is not very good Internet browser, and it is not supported by Windy. Consider please using Chrome/Firefox/Safari the latest version.
It is because you put negative speed (-2 kt) for your airplane.
Airplanes do not fly backwards (exept on Cobra maneuver! :) ).
The weather visualisation along a straight line is available with the Distance & planning feature, in the left Menu of the desktop version, not in the app.
This tool is also called Route planner as explained here:
Activate Distance & planning
Place 2 points on the map
Select your distance units
Choose your vehicle (Car, or other)
Select North up