Is the polar vortex to blame for Arctic blast moving into Pittsburgh area?

PITTSBURGH — When it comes to bitter cold, the "polar vortex" generally gets the blame. It started making headlines in 2014, but it's not something new.

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The polar vortex is a large area of low pressure and cold air surrounding both of the Earth's poles. It's always there, though it weakens in summer and strengthens in winter. It affects our weather -- but it's located high above the ground in the troposphere, roughly five to 10 miles above the surface.

So, is the polar vortex to blame for this Arctic blast? Well, sort of. I mentioned the Polar Vortex is "strongest" in winter. Most of the time it works to bottle up or "block" the really cold air coming from the north. The polar jet stream flows around the polar vortex and works like a gate, keeping cold air well to the north. Sometimes, though, the polar vortex "weakens" in winter and, when that happens Arctic air and the polar jet stream shift south.

In the end, we can't directly blame the polar vortex for this cold stretch, but it does lead to colder than normal temperatures in winter.

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