LAB 5 - Upper Air Maps

In this lab, we will learn about upper air plots and upper air maps. We will learn how to decode upper air plots and how to breifly analyze upper air maps.

Upper Air Stations

"Upper Air" is a term in meteorology which refers to any type of reading that is not on the surface. Rawindsonde balloons launched twice a day across the nation record meteorological information such as temperature, pressure, humidity and wind speed and direction, as they ascend into the atmosphere.

An upper level map is a map of all of the station's readings that were recorded at a given constant pressure. The most common upper level maps are the 850mb, 700mb, 500mb, 250mb, and 200mb. On the 850mb map, every station is reading a pressure of 850 millibars.

Upper Air Station Plots


(850 mb)

Temperature:
The value located in the upper left corner is the temperature in degrees Celsius. In this example, the reported temperature is 12 degrees.

Dew Point / Dew Point Depression:
The value located in the lower left corner is either the dew point or the dew point depression in degrees Celsius. The depression is the difference between the temperature and the dew point. If the dew point depression is being plotted, an "X" represents a dew point depression greater than 30 degrees Celcius.

Some maps, such as Unisys, plot the actual dew point temperature, not the depression on the map. Use a little common sense by looking at all of the plots to determine what is being plotted on your particluar map. If there are plots where the lower left number is higher than the upper left number (as in our example), then dew point depression is being plotted. (Because the dew point temperature can not be higher than the actual temperature.) We will use maps from the Oklahoma Weather Lab. They plot the dew point depression on their maps.

In this example, the reported dew point depression is 14 degrees Celcius. This means that the dew point temperature is 14 degrees less than the temperature (dew point temperature = -2 degrees Celsius, in our case).

Geopotential Height:
The value located in the upper right corner represents the geopotential height in meters (m). This is how high above the Earth (approximately) the instrument is when it records the given pressure. On some maps, this number is truncated for ease of use. Use the following table to decode geopotential heights. (Unfortunately, not all map makers use the same truncation. Figure out what system they are using before decoding)

Pressure

Rule

Example

850mb

Add 1000m

533 = 1,533m

500mb

Multiply by 10

591 = 5,910m

250mb

Multiply by 10 and
then add 10000m

098 = 10,980m


In this example, the geopotential height is 1533 m. (Note: 1m = 3.28ft)

Wind Barb:
The wind barb, as we learned before, indicates wind direction and wind speed. The same rules apply to upper air wind plot readings as they do for surface plot readings. In this example, there is a 50 knot wind coming from the East.

Upper Air Maps

The following two maps, from the Oklahoma Weather Lab, are upper air maps of 500mb and 250mb, respectively. On the 500mb map, notice how the winds parallel the lines of constant heights. On reason this is happening is because there is no longer any influence from the friction of the ground.



250 mb: The jet stream is the area of the highest winds (>50 knots). See if you can find the jet stream (there may be more than one) on the map.