Understanding the Weather Map

CLIMATE, WEATHER,

WEATHER FRONTS,

AND THE WEATHER MAP

Weather is what conditions of the atmosphere are over a short period of time.

Climate is how the atmosphere "behaves" over long periods of time.

Weather forecasting is predicting what the weather will be like at a certain time in the near future, in a given location.

The weather map tells the distribution patterns of atmospheric pressure, wind, temperature and humidity at the different levels of the atmosphere. 

The Weather Symbols:

Air Pressure- This is the weight or pressure the air exerts on the ground and is measured in millibars.

An air mass is a large body of air that has similar temperature and moisture properties throughout.

A weather front is a boundary separating two masses of air of different densities, and is the main cause of different wheather conditions.

The 4 types of weather fronts:

Cold front- a front in which cold air is replacing warm air at the surface.

Some of the characteristics of cold fronts include the following:• The slope of a typical cold front is 1:100 (vertical to horizontal).• Cold fronts tend to move faster than all other types of fronts.• Cold fronts tend to be associated with the most violent weather

among all types of fronts.• Cold fronts tend to move the farthest while maintaining their

intensity.• Cold fronts tend to be associated with cirrus well ahead of the front,

strong thunderstorms along and ahead of the front, and a broad area of clouds immediately behind the front (although fast movingfronts may be mostly clear behind the front).

• Cold fronts can be associated with squall lines (a line of strong thunderstorms parallel to and ahead of the front).

• Cold fronts almost always are easier to locate on a weather map than are warm fronts, primarily because of the strength of the high pressure system to the north and west of the cold front compared to that north of a warm front.

•  • Cold fronts usually bring cooler weather, clearing skies, and a sharp

change in wind direction.

Warm front- a front in which warm air replaces cooler air at the surface.

Some of the characteristics of warm fronts include the following:• The slope of a typical warm front is 1:200 (more gentle than

cold fronts).• Warm fronts tend to move slowly.• Warm fronts are typically less violent than cold fronts.• Although they can trigger thunderstorms, warm fronts are

more likely to be associated with large regions of gentle ascent (stratiform clouds and light to moderate continuous rain).

• Warm fronts are usually preceded by cirrus first (1000 km ahead), then altostratus or altocumulus (500 km ahead), then stratus and possibly fog.

• Behind the warm front, skies are relatively clear (but change gradually).

• Warm fronts are associated with a frontal inversion(warm air overrunning cooler air).

Stationary front- a front that does not move or barely moves.

• Stationary front- a front that does not move or barely moves.

•  • Stationary fronts behave like warm fronts, but are more

quiescent.•  • Many times the winds on both sides of a stationary front

are parallel to the front.•  • Typically stationary fronts form when polar air masses

are modified significantly so as to lose their character (e.g., cold fronts which stall).

Occluded Front- forms when a faster cold front overtakes a warm front.

• Because cold fronts move faster than warm fronts, they can catch up to and overtake their related warm front. When they do, an occluded front is formed. 

• Occluded fronts are indicative of mature storm systems (i.e., those about to dissipate). 

• The most common type of occlusion in North America is called a cold-front occlusion and it occurs when the cold front forces itself under the warm front.The weather ahead of the cold occlusion is similar to that of a warm front while that along and behind the cold occlusion is similar to that of a cold front.

Note the three different kinds of front shown on the map - a cold front, a warm front and an occluded front.

Fronts occur where two different air masses meet. Warm fronts are formed when warm air rises over a mass of cold air. As theair lifts into

regions of lower pressure, it expands, cools and condenses the water vapour as wide, flat sheets of cloud.

Warm fronts are shown on synoptic charts by a solid line with semicircles pointing towards the colder air and in the direction of movement. On colouredweather maps, a warm front is drawn with a solid red line with red semicircles.

Cold fronts are usually associated with depressions. A cold front is thetransition zone where a cold air mass is replacing the warmer air mass. The cold air is following the warm air and gradually moves underneath the warmer air. When the warm air is pushed upwards it will rain heavily. Often more rain will fall in the few minutes the cold front passes than it will during the whole passage of a warm front. As the cold front passes, the clouds roll by and the air temperature is cooler.

Cold fronts are shown on synoptic charts by a solid line with triangles along the front pointing towards the warmer air and in the direction of movement. On coloured weather maps, a cold front is drawn with a solid blue line with blue triangles.

Occluded fronts occur at the point where a cold front takes over a warm front or the other way around. If a cold front undercuts a warm front it is known as a cold occlusion and if the cold front rises over the warm front it is called a warm occlusion. Occluded fronts bring changeable weather conditions.

On a synoptic chart occluded fronts are represented by semicircles and triangles positioned next to each other. The triangles are in blue and the semicircles are in red, or both are purple (mixing both red and blue colours together).

Isobars are lines on a weather map joining together places of equal atmospheric pressure. On the map the isobar marked 1004 represents an area of high pressure, while the isobar marked 976 represents an area of low pressure.

Example of a weather map:

EXERCISE A. Match the meanings with the correct symbols.

Write the letters on the spaces.a. Rain with sunny

intervals

b. Thunderstorm

c. Temperature (oC)

d. Wind and speed

direction

e. Sunny Interval

f. Sunshine

g. Rain

h. Fair weather cloud

interval

i. Dull weather cloud

j. Snow

EXERCISE B. Write the symbols to make a weather map. Use the description given.(Exercise should be printed on a paper for the students to write on.)

1.) Chiang Mai

- Fair weather

- temperature- 15 oC

2.) Udon Thani

- Dull weather

- temperature – 18 oC

3.) A cold front passes through

Doi Inthanon, Lampang,

Sukhothai, Nakhon Pathom

and Surat Thani

4.) Bangkok

- Rainy with sunny intervals

- Winds = 25, east

5.) Phuket

- Thunderstorm

- 21 oC