Why Doesn’t Nuclear Steam Turn To Snow?

PHILADELPHIA (CBS) — It’s been so cold for so long around the Philadelphia region. But not cold enough to cause one particular phenomenon.

In the bitter cold, we were looking up at the cooling towers at the Limerick Nuclear Plant the other day, wondering, ‘The air is so frigid. Why doesn’t that steam turn to snow?’ We put that question to CBS 3 meteorologist Katie Fehlinger. And the answer?

“Oddly enough, it wasn’t cold enough here,” she said.

Really?

Fehlinger says with a dew point as low as 8 below zero, the air temperature would have to get to 25 or 30 below, before the air could become saturated enough to cause precipitation. Until then, that steam is simply evaporating.

“Any steam that would come off of those towers would effectively sort of blend in to the rest of the air because it’s so dry,” she explained. “It basically would try to just moisten up the atmosphere. So there’s just not enough vapor available for anything to precipitate.”

Snowfall from nuclear plant steam was reported near Pittsburgh five years ago. So it can happen, but it’s rare.