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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 = .

## Weather Maps

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## Presentation on theme: "Weather Maps"— Presentation transcript:

Slide1

Weather Maps

NGS

Slide2

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 =

stormy

weather coming

Rising Air Pressure =

fair

weather coming

no

change is coming

Slide3

Isobars

Isobars is a word that describe constant pressure.

Iso

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

Slide4

WEATHER MAPPING ACTIVITYSurface 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

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.

Slide5

WEATHER MAPPING ACTIVITYSurface Pressure

We

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

H

. Label the center of the low pressure with an

L

.

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.

Slide6

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.

Slide7

Winds

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.

Slide8

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.

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

Slide9

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

Slide10

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

Slide11

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

isodrosotherms

.

Isodrosotherms

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

dewpoint

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,

dewpoint

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.

Slide12

Pressure Changes

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

millibars

pressure change

.

Draw

the remaining

"positive" pressure change value(s) at two

millibars

intervals.

Using

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.

Slide13

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

millibars

or less.

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

millibars

or more.