Darkflow (Evil Weather Supplement)
From D&D Wiki
 What is Darkflow?
Darkflow occurs only in arctic regions. Though it might require some particularly heinous act to create this sort of evil weather, it often appears with no apparent special prerequisites. Sometimes, though, it is caused by a celestial event (the stars are right...) or the rise of a new and malicious power. Darkflow begins as a fairly normal snowfall. The temperature, however, quickly drops one band (as much as fifteen degrees Celsius) and then the falling snow begins to turn black and hard as hail. When the black snow comes into contact with the previously fallen snow, it explodes and scatters as an ash-like powder, which then covers and taints the existing snow. Further, for the duration of the storm, and amid the explosion of new Darkflow, the cover of dark ash seems to writhe and flow across the surface of the snow is eddies and whirls; this is the distinct indication from which Darkflow takes its name.
 Game Rules
Area: Varies. Usually 10d10 x 100 square feet, but only in arctic regions.
Duration: Three months.
Massive Animation: Any and all creatures that have died in a body of snow adjacent to the Darkflow or whose remains are still buried beneath it will rise as undead versions of themselves and will seek out the area that was covered with the Darkflow.
Zone of Desecration: The blackened patch of Darkflow counts as being under the effect of a Desecrate with a Caster Level of 20.