Graph explained 'Detailed rainfall outlook'
Understanding the 'Detailed rainfall outlook' page
The green and black lines
The green line on the graph shows accumulated weekly rainfall from either 1 January of the current year or over the last 9 months, depending on the option chosen for "Accumulated rainfall". Rainfall information for all sites is updated weekly. The right vertical grid line identifies the last rainfall observation, with the horizontal grid line indicating the accumulated rainfall over the chosen period.
The green line can be compared with the black percentile lines to gauge how accumulated rainfall over the chosen period compares with all records for the site over the same months of the year. If the green line is close to the 50% line, recent rainfall has been close to the 'middle' accumulated rainfall of all observations made at the site over the same number of months. If the green line is on the 10% line, only 10% of all records accumulated each week over the nominated period to the current week have been drier. If the green line is on the 90% line, only 10% of all records accumulated each week over the nominated period to the current week have been wetter.
The grey, red and pink shading
The edges of the grey and red (or pink) shading show the upper (90%) and lower (10%) range for accumulated rainfall for the next 3 months for individual years recorded at the site, assuming the rainfall for all historical years is projected from the current accumulated rainfall value. These lines are updated monthly. The grey shading represents all years, whereas the red shading represents those years with the same sea surface temperature phase at the time of year as the last current rainfall measurements.
Pink shading is used when the red and grey overlap. The red and pink shading may offer some insight into the rainfall that could be expected over the next few months if rainfall is related to sea surface temperatures.
Historical years in the same sea surface temperature phase as the last month of results are listed below the graph.
Recent monthly rainfall is compared with all site records.
The top row of the table shows the average rainfall (mm) for the month for all recordings at the site.
The middle row of the table shows the actual rainfall for each month of the period chosen.
The bottom row shows recent monthly rainfall as a percentile of all records. The number represents the percentage of years when historical rainfall records were below the rainfall actually recorded. For example, a value of 50 means the recent rainfall for the month was the same as the average historical rainfall with half the years in the past being drier and half the years being wetter. A value of 10 means that the recent monthly rainfall is equal to the 10th driest year in 100 years of records, whereas a value of 90 means the recent monthly rainfall is equal to the 90th driest year (or 10th wettest) year in 100 years of records.
What to do with the information
Use all three outlooks for rainfall, soil moisture index and pasture growth index to build knowledge of the likely impact of climate on pasture growth for the next 3 months.
Compare recent rainfall at your property to the selected weather station site.
- Analyse your records against the green line (accumulated rainfall) and monthly figures in the table.
- Regular analysis will increase knowledge of when and how much your rainfall varies from that of monitored weather sites.
Assess the outlook for rainfall by analysis of the grey, red and pink areas on the graph.
- Adjust the outlook for rainfall to reflect the observed difference between your property and the selected site.
- Use the adjusted outlook to improve understanding of the outlook for soil moisture index and pasture growth index.
Rainfall drives soil moisture and soil moisture drives pasture growth.
Temperature and radiation are also important seasonal variables but do not vary greatly from year to year.
Glossary of terms
Percentile: The percentage of years when historical rainfall records (or the simulated soil moisture index or pasture growth index) fall below the percentile number. For example, for rainfall, the 50% line is the median or 'middle' observation from all weekly records - half the recorded values are lower and half the recorded values are higher for any specific week of the year. The 10 driest recorded values for any specific week in 100 years of records would fall below the 10% line and the 90 driest recorded values for the week would fall below the 90% line (the 10 wettest records would be above the 90% line).
The percentile curves are lines joining individual weekly percentile values. The accumulated rainfall curves do not represent actual years. For example, the line through the 10 percentile accumulated rainfall is not a 1 in 10 year, but the succession of 1 in 10 weeks.
Accumulated rainfall: The total rainfall at the site either from 1 January or for the last 9 months depending on the option chosen.
Weeks: The day/month/year at the start of actual records is shown at the left of the x-axis. The numbers following represent day/month in subsequent months.
Similar sea surface temperatures: Rainfall outlook is assessed from sea surface temperature phase (1-9) determined by the temperatures of the Pacific and Indian oceans. Historical years with the same sea surface temperature phase for the same month are shown as the red shaded area and listed at the bottom of the graph.
Mean monthly rainfall: The mean rainfall (mm) for the month calculated from all records at the site.
Monthly rainfall: Rainfall (mm) recorded at the site over recent months.
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