The atmosphere only allows for a little cooling at night. You need a continual period of shorter days, longer nights and lower sun angle to get a winter.

But you just proved its round with your comment. 1000 miles north means that it's further away from the sun, ie further from the center which is closer to the sun due to the curve. Which is why it's hotter in Florida than Pennsylvania. During winter, you are facing away from the sun, but it still spins so it stays hotter towards the center because its curved and closer to the sun. Then you have to factor is different climates due to water sources and wind patterns in weather in relation to where it's located on the curve. Thats why you have deserts in certain areas and tropical climates in others on the same longitudinal lines.

Read: angle of insolation

Wow.