Weather Maps
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Weather Maps

NGS. How Does Air Pressure Affect Weather?. How much the earth. ’. s atmosphere is pressing down on us. Measured with a . BAROMETER. If it . CHANGES. , then new weather is on the way:. Falling Air Pressure = .

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Weather Maps

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Weather Maps



How Does Air Pressure Affect Weather?

How much the earth

s atmosphere is pressing down on us

Measured with a


If it


, then new weather is on the way:

Falling Air Pressure =


weather coming

Rising Air Pressure =


weather coming

Steady Air Pressure =


change is coming



Isobars is a word that describe constant pressure.


is a prefix that means the same and bar is the prefix that means pressure, so ISOBARS are lines of CONSTANT PRESSURE!!!



We will be drawing ISOBARS to find areas of High Pressure and areas of Low Pressure.

Begin with the 1024 pressure over Salt Lake City, UT (the one that is boxed). Draw a line to the next 1024 value located to the northeast (upper right). Without lifting your pencil draw a line to the next 1024 value located to the south and then to the one located southwest, finally returning to the Salt Lake City value. Remember, isobars are smooth lines with few, if any, kinks.

Repeat this process for the next lowest

pressure reading, which is 1020.

Continue this process until you have completed the entire map of the United States.

Normally, each ISOBAR is named after the last two numbers of the pressure, so the 1024 isobar will be named 24.




can use these maps to identify areas of high pressure and areas of low pressure. Using your colored pencils, label the center of the high pressure with an


. Label the center of the low pressure with an



High pressure is normally associated with dry weather because the heat causes the water vapor to evaporate. Shade in yellow the states you’d expect to see clear skies.

Low pressure is normally associated with precipitation because the pressure causes temperatures to condensate and be cloudy. Shade in green the states you’d expect to see storms.


Winds = created from differences in air pressure

Moves from areas of HIGH to LOW pressureGreater the difference in pressure, the FASTER the wind blowsMeasured with wind vanes and anemometers or you can estimate with the Beaufort Wind ScaleWinds moves counterclockwise around a low pressure system and clockwise around a high pressure system.



On your surface pressure map, draw arrows that show the direction of the winds around the areas of high pressure and low pressure.

Now your surface pressure map is done. Hold on to it, and let’s work on the air temperature analysis.


Temperature Analysis

We can look at a weather map to analyze temperature trends. We will be doing a similar activity to find ISOTHERMS – or areas of warm or cool air masses. ISOTHERMS are lines connecting similar temperatures.

Draw ISOTHERMS throughout your map.

Shade in blue, the areas of lowest temperatures and shade in red the areas of highest temperatures.


Dew Point

=Temperature at which the air is saturated (100% relative humidity)Several events can occur when the dew point temp. is reached: 1. If dew point temp. is above freezing: a. water vapor condenses as liquid b. dew will form on surfaces


Dew Point

c. cloud droplets will form in air2. If dew point temp. is below freezing: a. water vapor condenses as a solid b. frost on surfaces c. snow (or hail) in the air


Dew Point Weather Mapping

Using a green colored pencil, draw lines connecting the same dew points (as we have done in the previous two exercises).

These lines that connect the same dew point temperatures are called




are used to identify surface moisture. The closer the temperature and


are together, the greater the moisture in the atmosphere. As the moisture increases so does the chance of rain. Also, since moist air is lighter than dry air, the greater the moisture, the easier for the moist air to lift into the atmosphere resulting in a better chance for thunderstorms. Typically,


70°F or greater have the potential energy needed to produce severe weather


Shade in the region where the dew point temperatures are above 70˚F.


Pressure Changes

Using a blue colored pencil, beginning at any +2 value, lightly draw lines connecting equal values of the +2


pressure change



the remaining

"positive" pressure change value(s) at two




red colored pencils lightly draw a line connecting equal pressure change values of less than zero (0). Finally, using black, draw a line connecting the zero (0) line.


Pressure Changes

Cold fronts are often located in areas where the pressure change is the greatest. The front represents the boundary of different air masses. Cold air is more dense than warm air so when a cold front pass your location, the pressure increases. We analyze for pressure change to look for these boundaries. We can also tell where high pressure and low pressure systems are moving by looking where the greatest change is occurring.

Shade, in red, the region where the surface pressure change is -2


or less.

Shade, in blue, the region where the surface pressure change is +2


or more.