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.
Weather Forecasting
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.
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