Susan Despot, age 11, of Shreveport, Louisiana, for her question:

Why do cold fronts come from the northwest?

If you are a regular student of weather maps, you look for changes approaching from the west. Over most of North America, the good weather and the bad tends to move eastward across the land, sometimes all the way from the Pacific to the Atlantic. This is because most of North America lies within the belts of the prevailing westerlies. These westerly winds blow from the west to the east, circling around and around the globe. And this wide belt of prevailing winds tends to carry along pockets of good weather and bad.

Masses of cold air naturally form above the frozen Arctic region. The heavy, cold air tends to flow southeast for awhile. Sometimes such a cold mass reaches the westerly wind belt and the prevailing breezes waft it towards the east.