Weather Map Interpretation
Weather maps are issued everyday, providing a synoptic report. The weather report has a number of maps, each relating to a theme or two. The maps are full of symbols, indicating the weather conditions of the day. The maps are easy enough to interpret if you know what the symbols on them mean. The most important map is the map showing the distribution of pressure, by means of isobars, and letter symbols. Wind flow, wind speed and wind direction are all shown as well. Cloud cover - clear, fully covered or partially covered - is also shown. There are maps shown the distribution of temperature by means of isotherms. Rainfall or isohyetal map is also given indicating the distribution of rain and precipitation types.
In weather interpretation these maps are used to write a summary of weather conditions existing on a given day. It is possible to speak of weather changes over a short duration, two or three days, from the report given along with the weather maps.
Weather forecasting is a difficult activity. In tropical weather conditions, the prediction becomes even more difficult because of fast changing weather. Interpretation comes easy with practice and first interpretations are often not very good ones.
Atmosphere is the gaseous envelope of the earth in which all its flora and fauna survive. As weather is the statement of its physical conditions at an instant, its forecasting is of concern to one and all living over the earth. As such, since time immemorial weather forecasting was a subject of grave concern for the geographers and meteorologists. But, due to extremely complex nature of various physical processes of the atmosphere, which lead to weather, these endeavours have always been met with limited success.
Various methods were developed and used by meteorologists for weather forecasting. The most important methods in vogue currently are the conventional Synoptic, and Numerical Weather Prediction (NWP) methods. The former method is human subjective and the latter is objective and deterministic. Skill of these forecasts can be enhanced through use of GIS today by relating different features of the atmosphere and their proper visualization.
Conventional Synoptic Method: In this subjective method, conventional forecasting tools like, trend, persistence, climatology and analogue of weather systems are popularly employed. Each of these methods makes use of some basic assumptions for extrapolating the weather into the future. The forecaster blends these extrapolations with his own experience and the location specific weather quirks like topography and land-sea distributions.
None of these methods seems perfect, as the weather sometimes manifest differently, deviating considerably from the basic concepts on which these methods are founded. The inadequate human understanding of the various complex atmospheric processes leading to the weather development itself is one of the major problems associated with this method.
Numerical Weather Prediction (NWP) Method: To forecast weather, the NWP method makes use of numerical solutions (high speed super computers are generally required for this task) of complex system of mathematical equations or models representing both the physical and dynamical processes occurring in the atmosphere. These models are commonly known as Global Circulation Models (GCMs). In order to integrate the GCM forward in time, the model equations need initialization with precise knowledge of the current state or initial conditions of the atmosphere. To achieve this task, global observations of various atmospheric parameters, for example, temperature, wind speed and direction and humidity, made routinely at standard synoptic hours are usually assimilated into the model using a process known as Variation Analysis. The forecaster interprets these charts for weather forecasting at the locations of interest.
The National Centre for Medium Range Weather Forecasting (NCMRWF) was established in India under the Department of Science and Technology for issuing weather forecasts in the medium range of. 3 to 10 days in advance.