Weather & Roads

Why is it that storms so frequently adhere to the boundaries provided by highways? Think about it - happens all the time. Here are a few examples, paraphrased from weather reports I've heard both in the DC Metro and Boston:

"A line of thunderstorms along I-95"
"Areas North and West of I-95 can expect some snow accumulation"
"South of the Mass Pike and 128 will get a dusting to an inch, while the Northern side will see as much as six inches"


I just grabbed this image from Weather.com's very cool interactive maps this morning, showing a storm that has so far remained obediently to the East of I-95, all the way from Richmond up into Delaware. Not to worry - later in the day, they predict that only areas West of I-95 will get any substantial accumulation of snow.

Is there something scientific going on? Do cars on highways produce enough turbulent air to actually cordon off an advancing storm? Or are storms just very well-trained to look both ways before crossing?