Why is Stalingrad so cold?

While watching WWII documentaries I see that Stalingrad's invaders greatly feared the "Russian winter".
But why would Stalingrad be so cold? It's relatively far south, farther south than London and Munich.
Is this one of those weird weather patterns that makes Washington state and London so rainy (it's caused by ocean currents)?
But why would Stalingrad be so cold? It's relatively far south, farther south than London and Munich.
Is this one of those weird weather patterns that makes Washington state and London so rainy (it's caused by ocean currents)?