Posts Tagged ‘weather map’

USA Today has a weather map that is interesting. It has the fronts, the highs and lows, and the isobars, though it does not label or explain themĀ or give the barometric readings for them. At the top of the map, you will find that you have some other map options, such as satellite and radar views. But the view of fronts is the most helpful for our present purposes.

Of course the Jet Stream map is always interesting.

And the NOAA weather satellite map is more interesting that USA Today’s because you can get an animation over a 24 hour period.

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Chapter 10 of Eric Sloane’s Weather book explains the reading of a weather map. It’s one of those things that’s very jumbled and confusing when you first see it, but if you take the symbols one at a time, you can work it out and find it interesting.

  1. First, you see long curves with spikes on them, like the teeth of a saw. That’s the sharp edge of a cold front coming in, and the teeth point which way it is moving. Remember that a cold front isn’t necessarily “cold” as in freezing. It’s just colder than what’s already in place. It probably stormed along this line.
  2. Second, you see lines with scallops on them; they certainly look gentler than the cold front! This is the warm front, and again, the scallops show which way the air is moving; not as dramatic as the pointy teeth of a cold front, but the same idea. There may be low dull clouds here.
  3. Third, you may also see a line with points one way and scallops the other. Here, the warm and cold fronts have met and can’t go anywhere; they’re stuck for the moment. There may be low clouds and some wind. Sort of a useless wind that doesn’t take the weather anywhere…
  4. Fourth, you may see a line with points and scallops both pointing the same way. Here, a cold front has come up behind the warm front, and both are now moving together. Here there will be wind (like a cold front) and a long rain (like a warm front). It’s called an occluded front.

So that’s for the bold lines on the map. What about the big letter H and the big letter L?

  1. “H’ is for High, of course. It means a high barometer, and that means high pressure, which means dense air and no rain. When the air is dense, the water in it warms and evaporates.
  2. And “L” is for Low. When the barometer is low, the air is thin and water more readily condenses into rain and snow.
  3. Related to these two letters are some light lines that make concentric circles or beany shapes round about them. These lines are a connect-the-dots exercise, and the dots they connect are cities (or weather stations) where the air pressure is the same. As you move across these lines away from an “L”, the air pressure (the barometer) is rising. As you move across these lines outward from an “H”, the air pressure is falling. Simplified weather maps don’t use them, lest people be confused — but you won’t be!

Finally, there may be arrows on your map, and these tell the wind direction. The number of fletches on the arrows tell the strength of the wind.

If you take these items one at a time, you will soon find that the weather map is all sorted out and as readable as anything else written in a language that you know. I notice that many of the weather maps now in use are so careful to use pictures (of rain and snow) for example, that they only give information about “now” and no forecast or sense of direction at all. The announcer makes the forecast, not the map.

I guess they don’t think people can understand the symbols, and most can’t. But once you understand the symbols, there is actually more information in the symbols than in the pictures.

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