Weather Whys; Fronts

This is weather-wise. When the weather map on TV shows a front heading your way, from experience you might expect some change in the weather. That makes sense because fronts are imaginary lines drawn to show where different kinds of air are colliding. For instance, a typical cold front shows the boundary of a mass of cool, dry air, which is moving in on the warm, moist air ahead of it. Of course, there are no real boundaries, no walls holding the cold air in, so a front is actually a zone in which one type of air gradually gives way to another. There are four basic types of fronts, cold, warm, stationary, and occluded. Picture a weather map like you see on the local news. A huge storm system is bringing rain and thunderstorms to much of the nation's midsection. Here's the letter L showing the location of the low pressure center. The cold front extends south from there.

Warm, moist air is streaming northward to the east of the approaching cold front, and so the warm front on the map marks the leading edge of that warmer air. Now the cold front moves faster than the warm front, so eventually you see it overtaking part of the warm front, resulting in another zone called an occlusion. You can often see one of those spiraling out from the low pressure center with a cold and warm front branching off from it. The appearance of such a front often indicates the beginning of the end for a storm system. The fourth type of front is called stationary. As the name indicates, it moves very slowly or not at all. You can think of a front as a tree branch in a stream. If you hold the branch so it goes across the flow of the stream, you'll feel a fair amount of pressure on the stick as the water tries to sweep it downstream. But if you hold it in the same direction as the water flow, there will be less force pressing against it. A stationary front is simply a front which has gotten itself oriented sideways in the wind flow. For weather-wise, I'm Drew Barlow.