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How to Read a Weather Map

Charlie S Feb 8, 2019
A weather map can be defined as a map showing the important meteorological data in a definite area, at a specific time. Learn how to read and analyze the situation in a particular region.
Weather maps are used to explain and understand geographical concepts such as temperature, air pressure, humidity, rainfall, and cyclones. The department of meteorology publishes information related to weather in the print and electronic media, after detailed analysis of these maps.


Surface Weather Analysis

It indicates the low and high pressure regions, and also depicts different types of cyclonic scales.
A cyclonic scale is a thousand kilometer long horizontal scale. Severe thunderstorms and tropical cyclones are also studied using this method.

Aviation Maps

These are used to study visual and instrumental flight rules. They provide specific and accurate information about the cloud cover, current weather, and the ceiling height.
Ceiling height refers to the level, where 50% of the sky is occupied with clouds. These maps are used to ensure air traffic safety by giving prior information about bad weather.

Icing Maps

These are used to point out the locations, where flying can be dangerous because of icing.

Types of Weather Map Analysis

Isobaric lines denote lines of equal pressure, which are constructed in Isobaric analysis. Lines with the same speed of wind are drawn in Isotach analysis.
Isotherm analysis involves construction of lines with equal temperature called Isotherms. Streamline analysis consists of parallel orientation of groups of arrows to wind. Try to locate isotherms, isobars, and isotachs, while studying weather maps.

Tips For Reading Them

This activity is indeed very complicated. One should have a good understanding of all the related geographical terms. Learning the theory in detail, and then practically implementing it will need a lot of time.
Thus, you can go through the following details to quickly learn how to interpret weather maps. After studying these particulars, you will be able to tell how the weather would be, even if you don't have access to the respective reports.
Isobars are plain lines on these maps, joining areas with equal sea level pressure. They specify a lot about winds. Suppose a person is standing facing the wind. Then, according to the rule, the low pressure area will be on his left. Always remember that the wind flows clockwise around lows, and anticlockwise around highs in the Southern hemisphere.
In Northern hemisphere, it is vice versa. The red arrows denote the direction of the wind flow. The wind is stronger, if the isobars are close to each other. It always flows across isobars towards low pressure areas.
When isobars surround an area of high pressure, a high is created, which is represented by blue "H" on the map. A high is also called an anticyclone. In contrast, when they surround an area of low pressure, a low is created and is represented by red "L". Depression is the alternative term for a low.
Air mass is the flow of air originating from a particular location. The boundary line between two air masses is called a front; it is easy to locate it, as it clearly appears as a line with semicircles or triangles. Cold fronts are blue, while warm ones are red. Study both of them carefully.
Note the occluded fronts, which are a combination of warm and cold fronts. They are purple in color. Also, try to locate the stationary fronts; they symbolize the unchanged position of air masses.
The big black dots appearing in the map show the possibility of rain. Moderate rain is denoted by two small white dots, while continuous heavy rainfall is indicated by four black dots.

A triangle is used to represent showers of rain, while commas symbolize drizzle. If both the symbols are used together, it suggests mixed precipitation.
Snowflake symbols are used to denote possibility of snowfall; it will be heavy, if there are many flakes in the map.

A circle is used to denote cloud cover.

A trough (tongue-shaped structure) is formed, when isobars make a bend around a low.

A light fog is indicated by two dark lines, whereas three dark lines indicate heavy ice fog.
Wind intensity can be interpreted by observing the half and full lines. Half lines suggest the wind speed to be 5 knots, while from a full line, we conclude that it is 10 knots. To simplify the calculation, take the value of 1 knot as 1.15 miles per hour.
Nowadays, meteorologists use satellite weather maps to study cloud formation over sea and land. Live ones created by radars are also being used. Reading weather forecast is impossible without referring to complete maps; their ability to provide precise information about it has increased with the advancement in technology.