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April 9, 2012

Weather Education Episode #6: Upper Air Weather Features

RedOrbit Meteorologist Joshua Kelly

In this lesson we are going to look at special features which are found on weather maps. The map we are going to look at is from 500mb. That is roughly about 18,000ft above the ground.

So to understand this map we need to go over the lines first. The solid black lines that are going from west-east are known as isoheights which are lines of equal height. At 500mb we label these lines using three digits. For example if you look over by Seattle WA, we see that the number is 540. This really tells us that the heights over Seattle are 5,400 meters. Why is this important? To understand that we need to look at the next area which is over Southern California where we see a number of 552, telling us that in Southern California the height is 5,520 meters. Meteorologist now know that we have a higher height over Southern California than we do over Seattle WA. This tells us that we have a upper air ridge sitting over the region. Also these heights are important to meteorologists as they can tell us about precipitation types. A rough guide that we can go by is that any number below 540 has a high chance of seeing frozen precipitation if there is moisture available in that region.

The next line that we will look at is the dashed red line, this is our isotherms which is another name for lines of equal temperatures. In our example above we see the 5 degree isotherm. This tells us that every place on the map south of that line has temperatures at 18,000ft that are at 5 degrees or warmer. The temps are always in degree C.  While places north of that have 18,000ft temps, that are below 5 degrees.

The third line we will go over is the solid red line that extends from Illinois to the Gulf of Mexico. This line is known as our trough. On weather maps this line will also be black, I used red to show the difference between a ridge and trough.  As you can see, the line extends from the lower height number of 528 down to the higher 552. This is a trough which is an indication of upwards vertical motion in that area of the map. This helps us to determine where we are going to have the potential to see precipitation.

The last line we see is the solid black line in the Western United States which is extending from 552 upwards to the 540 line as you can see its backwards of the trough. This also is used to help us determine where the weather is going to be nicer since a ridge serves as downwards vertical motion meaning our clouds will not be able to go upwards.

These maps are created every 12hrs and provide us very useful information to help us create our weather forecast. We get this information from the launching of weather balloons.  In the United States the majority of the weather balloons are released by the National Weather Service.