Weather - Graph Description

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Temperature Graph

This shows the average daily minimum and maximum temperatures in each month. An average daily maximum temperature of around 20 Celsius is ideal for bushwalking with a full pack with tent, stove and food. The average daily minimum gives some idea of how cold it gets each night.

On the same graph is also shown the maximum recorded daily and minimum recorded daily temperatures. The width of the spread between these two extremes gives some indication of how variable the weather can be. Wide variations indicates that there can be very hot and very cold periods in the same month - a common event in some parts of Australia. Conversely, a more narrow spread indicates that the location has a maritime climate where the sea moderates the temperature and it is rarely high or low. While median values would give better indications of average conditions, they are not available.

It can be interesting to compare graphs for two nearby sites, one of the coast and one inland. The inland site will have more extremes and be both hotter and colder while the coastal sites show less variation.

Rainfall Graph

As the Bureau of Meteorology site explains - averages are not very good indicators of normal weather patterns, as they can be unduly effected by big storms and other rare events, like unusual dry periods. Hence the highest and lowest values are not used for rainfall as a bushwalker is very unlikely to experience these as they have only occurred once!

A better measure is the median value. The centre line indicates the average monthly median rainfall, half the time there will be less rain in that month and half the time there will be more. Most regions display a pronounced 'bell' curve, which shows that there are wet and dry seasons.

The same graph also shows the high 90% and low 10% median values. The 90% line indicates that for 90% of the time, rainfall be less than the value shown. The 10% line indicates that for 90% of the time the rainfall will be higher than the indicated value. While compiling this data, I plotted some graphs showing maximum and minimum recorded rainfall values. These turned out to be very misleading as they suggested that high rainfalls occur in every month - while storms do occur in every season, these could not be considered to be normal weather. Hence why I selected the median graphs - it matched what has been observed when out walking.

High 90% medians that are 3 or more times the median indicate that rainfall is highly variable - when it does rain it is sometimes extremely heavy. Such rains often result in flooding. Extremely low 10% median values also indicate that often it does not rain. Usually this graph is read in conjunction with the next one, which shows the percentage of days it rains each month.

Wet and Clear Days

The percentage of wet days gives some idea of how often it rains. Generally these are the days most bushwalkers would consider to be less attractive for walking. The percentage of clear days indicates how often there are no clouds in the sky at the time readings are taken - a perfect fine day. The remaining days in the month which result from the subtraction of these two values are the number of cloudy days for which there was no rain.

Near the coast most cloudy days would be normally be regarded as good walking days. In the mountains, up to half of the cloudy days would consist of fog and low cloud. While walking is generally OK, some cloudy days will have limited visibility as you walk in cloud and fog.


A final note - all these graphs indicate the long term trends and averages. Of course un-seasonal weather can occur at any time of the year. What the graphs give is some idea of what is normal and how often the unusual events occur. All the graphs have been colour coded from warm (red) to cooler weather (blue).

Source for most of the original weather data used for the graphs is the external site - Bureau of Meteorology, Australia. The Bureau retains copyright on the original data as presented on their web site. I have created my own interpretation by using graphing some of this data and merging it with other site observations for bushwalking areas. Corrections to temperatures for altitude and rainfall has been done for some areas.

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Photographs and text are copyright 1999-2015 John Chapman.
Last updated : December 8th 2015