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IQ Weather Homeschool Extra: An Old Weather Forecasting Trick!

During the spring and summer months, as the air heats up, the chance for storms climbs. But how do you know if the air is hot enough to create thunderstorms? IQ Weather knows!

One tool that meteorologists use is the data that comes from weather balloons.  In fact, lesson number 23 in our weather course takes you on a field trip to a National Weather Service balloon launch so you can see where this information comes from!  We call the end product and upper air sounding!

Upper air soundings, give us a lot of information about the air overhead, including a variety of indices that we use to measure the risk for severe weather. The temperature and humidity profile is plotted on a graph called a Skew T.  Today, we are going to focus on two pieces of data that can, when tell you how hot the air must become for storms to develop, and whether or not that is likely.

The first bit of information on the sounding that we’ll focus on is called the MaxT, or forecast maximum temperature. At the time the sounding is taken, this gives us an estimate of the maximum forecast temperature of the air given the current circumstances in the area. Bear in mind that this number may change a bit during the day as the air mass changes, but it gives us a good starting point for figuring out how warm the air will become when heated up. The MaxT is expressed in degrees Fahrenheit.  On the sounding from Topeka (below) the MaxT is 70°. Look for the highlighted area beneath the graph for the MaxT.

The second number to look at is called the convective max temperature…or the ConvT. This number tells us at what temperature the air begins to rise on its own. In other words, when the temperature hits ConvT, convection, or rising air will start to develop and thunderstorms MAY form. There are a number of other things to consider, but once convective temperature is achieved, any moisture in the air could boil up into storms without any other assistance such as the presence of a cold front or upper air disturbance.  In the example from Dallas-Fort Worth (below) the ConvT is 86°. (see the highlighted section below the graph)

What do we do with these numbers?

There is an old forecasting trick that is very simple, but works well!

If the MaxT is lower than the ConvT, the air too stable for storm development. In other words, the air cannot get warm enough to reach convective temperature and updrafts will not be able to form…at least they will not be strong enough to overcome the warmer air aloft.  The air is then considered to be stable and storms are unlikely. The Dallas-Fort Worth (see the graph above) sounding is stable as the MaxT at 76° is lower than the ConvT at 86°!  No storms!

If, however, the MaxT is higher than the ConvT, then the air will be able to hit the convective temperature and start to form updrafts! In the Topeka sounding (see the graph above), the MaxT is 70° and the ConvT is 66°. That tells us that once the air climbs above 66°, which is likely based on this sounding, then updrafts may become strong enough to create billowing clouds and rain or storms!

Remember, as with anything in weather, conditions change during the day, but this old trick works well, particularly if you live near where the sounding was taken and if the sounding is fairly recent.

The soundings can be found at the Storm Prediction Center Website, and they are taken twice daily at over 100 locations around the United States!  When you click on a little star on the map of the location where you want to view a sounding, it will pop up! Try it out!

Happy storm forecasting!

IQ weather, homeschool weather, science at home information, learning how to forecast weather, thunderstorms, weather prediction tricks, upper air data, accu-weather


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