How to Read a Weather Map

Weather maps are used to explain and understand geographical concepts like 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 weather maps.

Types of Weather Maps

Surface Weather Analysis
A Surface Weather Analysis is a weather map which indicates the low and high pressure regions. It 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 Surface Weather Analysis.

Aviation Maps
Aviation maps are used to study visual flight rules 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
The icing maps 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. Such lines 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 Weather Maps
Reading weather maps 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 will need a lot of time. So, 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 weather reports.

• Isobars are plain lines on weather maps joining areas with equal sea level pressure. Isobars tell us 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 wind flows clockwise around lows and anticlockwise around highs in the Southern hemisphere. In Northern hemisphere, it is vice-versa.
• The red arrows in weather maps denote the direction of the wind flow.
• The wind is stronger if the isobars are close to each other.
• Wind always flows across isobars towards low pressure areas.
• When isobars surround an area of high pressure, a High is created and is represented by blue "H" on the map.
• A High is also called an anticyclone.
• When isobars 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 a flow of air originating from a particular location.
• The boundary line between two air masses is called a front. It is easy to locate a front as it clearly appears as a line with semicircles or triangles.
• Cold fronts are blue while warm fronts are red.
• Study these fronts 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. Stationary fronts 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.
• Continuous heavy rainfall is indicated by four black dots.
• A triangle is used to represent showers of rain.
• Commas symbolize drizzle.
• If both the symbols are used together, it suggests mixed precipitation.
• Snowflake symbols are used to denote possibility of snowfall.
• Snowfall 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 wind speed is 10 knots. To simplify the calculation, take value of 1 knot to be 1.15 miles per hour.

Now-a days, meteorologists use satellite weather maps to study cloud formation over sea and land. Live weather maps created by radars are also being used. Reading weather forecast is impossible without referring to complete maps. The ability of weather maps to give precise information about weather has increased with the advancement in technology.