g day Kevin, i have been enjoying your recent pics posted here
as for your mystery my thoughts only compound it;
CFN shows a strong jet stream from the SW flowing to the East over MacKay, and moderate southerly winds, so if a balloon above all that, 10km - 16km up.
Wikipedia says, weather balloons regularly go 18 km - 37 km and one went to 53 km, so maybeeee but at those distances would a weather balloon be as bright?
the brightness you describe sounds like the ISS but the few times i have identified the ISS it moved W to E.
interesting
regards, L