[CyberAnt]

Hi strela - I knew you would know. "low wind speed at altitude" - amazing!

I thought it might be the chemical composition of the fuel. I guess that proves I didn't take chemistry.

[strela]

I don't know for sure why the cloud hung around as long as it did. Low high-level wind speed just seemed a logical reason to me. Somebody like Physicist could probably tell you for sure why it happened.