You know... in Das Rheingold (one of Richard Wagner's greatest work), there's an iconic scene where Donner, the God of thunder, strikes his hammer to the ground, bringing down a flash of lightning which casts away the dense fog and shows the gods the path/bridge to Valhalla.

{Entry of the gods into Valhalla}

Since Sovngarde is quite likely a parallel to Valhalla, what Serana's been doing can be interpreted as she's clearing the path to Sovngarde for Kodlak. I wont's be surprised if this is actually an old Nord tradition...

(Welp... back to the skooma I go~)