Ok, it can change rather quickly.

Case in point... I'm heading from the Philly are to a spot just 2 hours away. The weather difference can easily be 10 degrees cooler in the other spot.

The weather on one side of the tunnel can often be quite different from the other. I can't begin to count how many times it would be raining on one side and sunny on the other. Snow on one, fog on the other... Etc...

Then, in the woods at the northern spot, a storm can blow through quite quickly and drop the temps down 20-30 degrees, then add in the wind chill.

Weather: You must respect it and be prepared for just about anything. Certainly helps to at least look at the weather trends and forecast before leaving home.