R
The terms and definitions found in the glossary relate to the science of meteorology.
For descriptions and definitions of words used in the Bureau's forecasts and warnings, please refer to Weather Words.
- Rain
- Precipitation of liquid water drops greater than 0.5 mm in diameter. In contrast to showers, it is steadier and normally falls from stratiform (layer) cloud.
- Rain day
- A rain day occurs when a daily rainfall of at least 0.2 mm is recorded.
- Rainfall
- The total liquid product of precipitation or condensation from the atmosphere, as received and measured in a rain gauge.
- Rainfall, Chance of any rain
- The chance of any rain is included on the Bureau's town forecasts, and describes the likelihood of receiving a measurable amount of rain (at least 0.2mm) during the day at that location. For example, a forecast of 30% means that there is a 30% chance of experiencing any rainfall. However, there is also a 70% chance of no rainfall.
- Rainfall, Likely rainfall
- Likely rainfall is the amount with a 50% chance of occurring during the day. This element is displayed as a map on MetEye. It is also used as the lower value of the Possible Rainfall range in the Bureau's town forecasts.
- Rainfall, Possible higher rainfall
- Possible higher rainfall is the amount with a 25% chance of occurring during the day. Conversely, there is a 75% chance that this amount may not be reached. This element is displayed as a map on MetEye. It is also used as the higher value of the Possible Rainfall range in the Bureau's town forecasts.
- Rainfall, Possible rainfall range
- The possible rainfall amount is included on the Bureau's town forecasts, and describes the expected rainfall range for the day at that location. The rainfall range is a useful tool to highlight the variability of certain types of rainfall days. On showery/thunderstorm days, the possible rainfall range may be quite large (e.g. 5 to 30 mm). When steady rainfall is expected over a wide area, the range may be smaller (e.g. 10 to 15mm).
- Reference Climate Station (RCS)
- A climatological station, the data of which are intended for the purpose of determining climatic trends. This requires long periods (not less than thirty years) of homogeneous records, where human-influenced environmental changes have been and/or are expected to remain at a minimum. Ideally the records should be of sufficient length to enable the identification of secular (lasting for ages) changes of climate.
- Relative humidity
- Is a traditional indicator of the air's moisture content. It is the ratio of the amount of moisture actually in the air to the maximum amount of moisture which the air could hold at the same temperature. Relative humidity is normally expressed as a percentage and at saturation the relative humidity will be very close to 100%. The air can hold more moisture at higher temperatures, hence the relative humidity alone does not give an absolute measure of moisture content.
- Ridge
- A ridge is an elongated area of high pressure. It is indicated by rounded isobars extending outwards from an anticyclone and has associated with it a ridge line. The pressure at a point on the ridge is higher than at an adjacent point on either side of the line.
- Run-up
- The maximum height of the water onshore observed above a reference sea level. Run-up is usually measured at the horizontal inundation limit.