Most pagan religions had a celebration on or following the spring equinox, and on December 25th. I kinda like this one the best:

Ishtar (which is pronounced "Easter"), the Bablyonian goddess of fertility, love, and war, came out of heaven in a giant egg, landed in the Euphrates river at sunrise on the first Sunday after the vernal equinox, and turned a bird into an egg laying rabbit. The priests would then sacrifice infants, take the eggs and die them in the blood of the sacrificed infants. Ishtar became impregnated by the rays of the sun-god Baal and gave birth to her son, Tammuz, on th 25th of December.

Tammuz was killed, resurrected and descended into the sky to be with is father. When he died, some of his blood fell on the stump of an evergreen tree and the stump grew into a full new tree overnight. Do you see where this is going yet?

I don't think anybody would need a cloud large enough that a 747 is required to carry all the necessary chemicals, I think most seeding is done with much smaller planes (think crop duster) and/or rockets.

"(Evergreen International Airlines) is completing final modifications on a Boeing 747-200 aircraft modified to be a Supertanker to fight fires. The airline was awaiting final approval from the FAA, which arrived in the last week of October 2006. With this it will be adding a giant aircraft to its current fleet of fire fighting aircraft. This Supertanker will offer at least seven times more drop capability as compared to the current largest airtanker. Its capacity to carry a large volume of Fire retardant will considerably decrease the time taken in fighting large fires."

http://en.wikipedia.org/wiki/Evergreen_International_Airlines

I think that's what this is. It was so high up probably because it was a demo or test run.