Month: June 2014

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Weather Station on Legs

June 28, 2014 | Uncategorized | No Comments

What if you wanted to know what the weather was going to be like in the near future, but didn’t have a cell phone? Or the internet? Or a television or a radio or newspaper?
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I’ll show you how to turn  yourself into a working  portable weather station! Your body is equipped  to gather all the data to make your own weather forecast.
You’ll need to know five pieces of information: Temperature, humidity, air pressure, wind direction, and wind speed.

  • Temperature: Activate you on-board your temperature sensor. Using your skin, and standing out of the sun, you can come pretty close to guessing the temperature of the air. Practice makes perfect, so check how warm or cool you feel against the actual air temperature and learn to calibrate your sensors.  After a while you can tell the difference between 80 degrees and 85 degrees, say, and that’s close enough for our purposes.
  • Humidity: You can use the same outer organ to judge the humidity, too. Your body cools itself by evaporation of sweat through the skin. When humidity is low, this works great, but as the air gets wetter,  the sweat won’t evaporate and you feel that “sticky” feeling.  How humid you feel is also tied in with how warm you feel, since humid air tricks your body into feeling warmer than it is. Again, you can learn to judge pretty closely by checking your senses against the actual humidity.
  • Air Pressure: Sorry, you body has very poor pressure sensors. Air pressure changes too slowly for our bodies to notice.  But if you know that high pressure makes clouds dissipate and low pressure encourages them to form, you can estimate the pressure using your visual sensors (peepers) and looking to see if it’s clear or cloudy.  Clear skies equal high pressure, cloudy is low, and partly cloudy is somewhere in between. That’s close enough for our purposes. What’s important about air pressure is not so much where it is right now, but how it is changing: falling, rising, or staying the same. We’ll figure that out using the wind direction.
  • Wind Direction: The wind direction might be the most important piece of info. It tells you where the weather is coming from and whether high or low pressure is approaching. You can feel the wind on your skin, and probably sense the direction it’s coming from, but  if the wind is too calm to tell, moisten a finger and hold it up to the air. The side facing the wind will feel cooler.  By the way, wind direction always refers to the direction FROM which the wind is blowing, i.e., a north wind blows from north to south.
  • Wind Speed: This one’s easy.  You can generally feel how strong the wind is on your skin, hear the wind in the trees, see flags and banners blowing. Again, it’s enough to know the general strength of the wind, and you can learn to predict this pretty closely. One note: The air layer from the ground up to about 200 feet travels more slowly than the air above, as it is slowed down by friction as it flows past forests and buildings and landscape features.

Okay, so now we know, perhaps, that it’s about eighty degrees, with high humidity, low pressure and a strong south wind. How do we do our forecast?
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This sketch shows how high pressure “bubbles” of air the size of continents go marching their way across the landscape. In the northern hemisphere they all flow from west to east, and in addition they spin with relation to the ground. That’s because the ground is essentially turning its way out from under the air as the earth rotates. The wind never catches up, so as the heavy high pressure air falls downward and outward from the High, it also spins, flowing clockwise around the High (counterclockwise in the southern hemisphere).
In between the mountains of high pressure, valleys of low pressure form. The air is rising, not falling, in the low pressure areas, as the air rotates in toward the center, spinning counterclockwise.
That’s the basic picture of weather in the mid-latitudes, with these Highs and Lows continually flowing west to east all the time. (The tropics are another story.) Highs bring clear skies and fair weather, and Lows can bring clouds, storms and cyclones. By figuring out where the Highs and Lows are right now, we can guess what’s coming our way in the next hours and days.
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So, once you’ve found the wind direction, stand with your back to the wind. Turn about 45 degrees to your right, and you will have your back to the wind high overhead, which flows in a different direction than wind near the ground (remember, it moves slower,  so it also spins less).
You’re now facing “downstream” of the wind at high altitude. Raise your arms, and your right arm will be now be pointing to the High pressure system. Your left arm points to the Low pressure.
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Now you can place yourself on the weather map. What’s to the west? Since Highs and Lows move generally from west to east, whatever it is to your west will be coming in your direction.
The anatomy of weather systems is more complex than I can cover here,  but a good way to familiarize yourself with them is by watching Weather Channel and other published weather maps, then comparing your local weather experience with your position on the weather pressure map.
IMG3The familiar red and blue lines of fronts,  the highs and lows, the way that storms form and move across the land,  will start to make sense after a while.
But in our case, what we know is that a low pressure system is drifting towards us to our north. The winds are high, so there’s a big difference between High and Low pressure to push the wind.  The means the low might be very low. Since the air’s coming from the south, that means warmer temperatures are coming, but bad weather might be coming too. The humidity is high, so there’s plenty of moisture to make storms. I think it might be a day to stay indoors.
Maybe I’ll put on the Weather Channel !