Thursday, November 29, 2012

Using Contrails To Predict The Weather

Mohave Rat recently had a post dealing with contrails, and I offered an explanation for them, hence this new post. I first learned how to read them from Larry Williams, an extraordinary outdoors man.

First, we need to define contrails. Contrails is short for condensation trails. They are those long or short lines behind the jet airplanes that appear in the sky. The condensation trails are formed by water vapor that condenses or turns into ice crystals depending on the air temperature of the jet's altitude. Armed with this knowledge, you can mostly predict the weather. It isn't 100% accurate, but reliable enough when backpacking on extended trips.

Air can contain no more than a certain maximum amount of water vapor at any given temperature. The higher the temperature of the air, the more water vapor it can hold. When it is cold enough and there is moisture in the air, the exhaust of a jet engine "seeds" the water vapor making contrails. Snow and raindrops are also formed around a speck of dirt, which explains why the car gets so dirty after a rainstorm. If the temperature of the air at which condensation takes place is above freezing, water droplets form. If it is below freezing, ice crystals form.

Some contrails are short and some are long. On days when the contrails are short there is little moisture (cold) in the air at high altitudes. When the contrails are long, there is more moisture in the air (warm) at that altitude. You can take note and notice the rate at which the contrail disappears to determine the amount of moisture in the atmosphere.

You can predict the weather by taking advantage of this information in the sky. If the contrails are short, and there are few or no clouds in the sky, then there is little moisture in the upper atmosphere. The chances are very good that the next twelve to twenty-four hours will be clear. If the contrails are long, the moisture content of the upper atmosphere sky is high and more clouds or even a storm is on the way.

You can take two viewing of the contrails in the day and extrapolate a more accurate weather prediction. Short contrails and a clear day in the morning, then long contrails and clear in the afternoon most likely means that it will be clouding up tomorrow. You get the idea.

You can also get an idea of the direction and speed of the upper atmosphere winds by watching the contrails.

 The planes most likely crossed from right to left, and the winds are blowing from bottom to top of the picture. I say most likely because the contrails are thicker on the left side, and it dissipates on the right side. The upper atmosphere winds are pushing the contrails towards the top of the picture as the bowing of the contrails suggest. The winds don't move in nice fronts like the weather maps show on tv.

Have fun with this knowledge, make some notes, predictions, and observe the results.

Oh, and that sprained ankle from a few years back is an excellent barometer too!

Keep Right On Prepping - K


  1. I'm keeping my aluminum foil helmet just the same. ha ha ha ha the rat

    1. I've got mine sitting in the kitchen cabinet ready to roll out of the tube.

  2. That is very interesting. I did not know that. Thanks for the post!

  3. The bowing of those contrails is mainly owed to the fact that they correspond to a holding pattern.