Winds have a lot to do with how storms come and go (Chapter 5 goes into detail), but the weather forecast concerns itself mainly with the wind in your face. A forecaster describes what is expected of the wind’s direction and its speed.
Wind direction describes where the wind is blowing from. And so a north wind is coming out of the north and blowing toward the south. You get the idea. Weather forecasts commonly describe the direction of winds on an eight-point compass: north, northeast, east, southeast, and so on.
Winds that blow only up to 5 miles per hour are generally described as light, or light and variable, to indicate that they are kind of wafting around in different directions. Winds 15 to 25 miles per hour sometimes are described as breezy when it’s mild weather or brisk when it’s cold. The word for 20 to 30 miles per hour is usually plain windy, at 30 to 40 miles per hour they are very windy, and winds blowing 40 miles per hour or greater can be described as strong, damaging, dangerous, or high. Winds become “hurricane force” at 74 miles per hour, but they are dangerous well before then. (Stay out of them!)
Wind chill
Wind can make hot temperatures feel cooler and cool temperatures feel colder. This is the wind chill factor — how a wind makes the body feel that the air around it is colder. Wind chill can be an important indicator of the danger of severe cold winter conditions.
The warmth of the body actually creates a thin envelope of warm air around it, a little insulating comfort zone. Along comes the wind that whisks that envelope away, exposing the skin to the raw cold and accelerating the heat lost by the body. The stiffer the wind, the greater the heat loss, the colder the feeling of air.
Sky cover
When the sky will be free of all cloudiness or less than one-tenth cloudy, forecasters describe it as clear or sunny.
At three-tenths to six-tenths, the sky is partly cloudy or partly sunny or scattered with clouds.
At seven-tenths to eight-tenths, the sky is mostly cloudy or cloudiness is broken.
At nine-tenths to the whole shebang, it’s just plain cloudy or overcast.
How to Read a Weather Map
Weather maps have been around for the better part of two centuries, and for much of that time, they were the only way to visualize a lot of what was going on — or what forecasters thought was going on — in the atmosphere. But even now, when satellite images of actual storms and fronts are available, often a television forecaster and a newspaper weather page will display a simplified weather map to make clear to viewers and readers what’s going on.
The typical stripped-down version of a weather map highlights a few features of the weather picture across the nation. As Figure 2-2 illustrates, centers of high pressure and low pressure are designated simply by a large “H” or “L” on the map. Cold fronts lead with arrows ahead of them and warm fronts with semicircles along their leading edge. Areas of precipitation are often designated with hatch-marks or shaded sections. Some temperature readings often are included, and occasional arrows will point out the directions of surface winds. Chapter 3 goes into more detail about these weather features.
FIGURE 2-2: A typical weather map showing features and symbols that are common to most simplified maps used in televised forecasts today.
Chapter 3
Behind the Air Wars
IN THIS CHAPTER
If there is a personality that describes the atmosphere, the blanket of air where all the weather takes place, you might think of it as flighty or fickle. Do you know people who change their minds a lot? Who often seem to be repeating the ideas of the last person they were with? That’s the atmosphere all over. (You want to scream sometimes: “Make up your mind!” Does it help?)
At the Go Figure Academy of Sciences, weather experts describe this maddening characteristic in polite, five-dollar terms like instability and turbulence and chaos. Frankly, the word unbalanced comes to mind, if you get my drift.
As any weather forecaster can tell you, the atmosphere is unreliable — here today, gone tomorrow, as the saying goes, blowing hot and cold. You think you know it when you go to bed at night, and then, poof! — as soon as the Sun comes up, there’s a completely different character. This chapter is all about the things that make the atmosphere and its weather the way it is — so changeable.
I Don’t Like Your Latitude!
Don’t be too hard on the atmosphere. (After all, it’s the air you breathe. Without it, you’re sunk.) Imagine trying to live in a house where it’s always hot at one end and always cold at the other. That’s the situation the Earth’s atmosphere finds itself in. You don’t have to be an Eskimo or a Pacific Islander to figure out where the warm spots and the cold spots are, but it helps.
The low latitudes, around the Equator, get a lot of warm sunshine, and the high latitudes, around the poles, get very little. (Figure 3-1 shows the layout of the imaginary lines around the Earth called latitudes.) This temperature difference is no small matter. On the same day, it can reach 120 degrees below zero overnight in Antarctica and 120 degrees above zero in a subtropical desert. The atmosphere
