Reading Weather Maps

Though most people are familiar with weather maps which are regularly shown on television during weather bulletins, only a select few are able to make sense out of them. In case you too would like to know what weather maps portray and wish to read them, then just come with us as we explore the subject in depth.

Weather maps are typically used to show detailed analysis of meteorological magnitudes at different planes of the atmosphere and to portray an outline of various atmospheric changes at a given instance in the atmosphere. They can be used to show wind movements, atmospheric pressure and gradients of temperature. In order to read a weather map accurately, you need to understand the general concepts, which are listed below.

Isobaric Analysis – Lines of equivalent average sea level pressure called isobars are drawn on a geographical map to achieve this. The innermost circular lines denote the “maxima” and “minima” where minima denotes areas with low-pressure and maxima denotes areas with high pressure. The highs are denoted by H’s and lows by L’s.

Isotach Analysis – These are the lines constructed on maps to depict equal wind speeds and are used to represent the rise and fall of wind speeds, i.e. Maxima and Minima. A minima will represent tropical cyclogenesis and a maxima will represents the position of jet streams at different atmospherical levels.

Isotherm Analysis – These are the lines constructed on maps to depict equal temperature. They are commonly drawn as continuous lines without breaks at a suitable interval of temperature. Isotherms are used to represent temperature gradients and are extremely useful in the determination of the type of precipitation.

Streamline Analysis – It is a method that is used to display wind motion in certain geographical areas with the help of a sequence of arrows drawn parallel to the direction of the wind. Low-pressure areas, commonly known as “cyclonic flows” are depicted by C’s and areas of high pressure, i.e. anticyclonic flows, are denoted by A’s.

Wind Plotting – Around 100 years ago, winds were depicted by using arrows, with feathers drawn on only one side representing a wind speed of 5 knots and on both sides, a wind speed of 10 knots. Today, the notation has changed and part of an arrow along with a little amount of wind barb represents a speed of 5 knots where as a full bar represents 10 knots.

Different kinds of weather maps are used in different kinds of scenarios. Two important kinds of weather maps are discussed below –

Surface Weather Maps – These weather maps are used in depicting positions of high as well as low pressure areas and also different kinds of synoptic scale schemes, for example frontal zones. Analysis of mesoscale boundaries like tropical cyclones, outflow boundaries as well as squall lines can also be accomplished using this particular weather map.

Aviation Maps – The aviation sector has their own customized weather maps. They include maps, which show the applications of Visual Flight Rules (VFR) and Instrument Flight Rules (IFR). Maps like weathering representation plots show the ceiling height, which is a level where half of the atmosphere is under thick cloud cover and also the nature of current weather. Ice hazards to flying are depicted by icing maps and maps related to aviation illustrate areas of high turbulence.

If you need to study weather maps in detail, a more comprehensive approach is required. A visit to the local meteorological department for valuable inputs is also recommended.