D
Barrier to obstruct water flow.
Practice of turning clocks ahead by 1 hour during the warmer months. Also known as 'summer time'. In Australia, daylight saving is observed in New South Wales, Victoria, South Australia, Tasmania, the Australian Capital Territory and Norfolk Island. Australia's Daylight Saving Time (DST) regions:
- Australian Eastern Daylight Time (AEDT) covers New South Wales except Broken Hill, Victoria, Tasmania, Australian Capital Territory
- Australian Central Daylight Time (ACDT) covers South Australia and Broken Hill
- Australian Western Daylight Time (AWDT) covers Western Australia
- Norfolk Island Daylight Time (NFDT) covers Norfolk Island.
Dividing any dataset into 10 equal parts creates deciles – each part is a decile. We use deciles to show where an element like rainfall is above or below average, compared to the long-term average. To create deciles:
- sort all values in the long-term record from lowest to highest
- divide the data into 10 equal-sized parts
- number the parts 1–10.
The lowest 10% of observations are in decile range 1 and the highest are in decile range 10. So, a monthly rainfall total in decile range 10 is in the top 10% of observed totals. It's higher than (at least) 90% of monthly observations over the long term.
Indicator of moisture in the atmosphere used by the agricultural industry to help with decisions about when to spray crops.
Tiny water droplets that form on objects at or near the ground. Dew is produced by condensation of water vapour from the surrounding air.
Measure of moisture in the air and the temperature to which air must cool for dew to form.
Where the sea or swell travels from and where the wind blows from. For example, a northerly swell comes from the north. A northerly wind blows from the north.
Shower or two: Not many, less than a few. Used to describe infrequent showers.
Few: Not many, amounting to a small number. Used to describe a small number of showers over a certain period.
Changes within the course of a day – for example, temperature changes.
We use this term to describe systematic changes that happen during the average day. For example, temperature normally has a diurnal variation. Usually it's warmer during the day and cooler at night.
When air flows out of a region.
Strong and sometimes damaging gust of wind that falls heavily from a thunderstorm. It then spreads out and can be felt some distance away from the storm.
Light rain of very small droplets, less than 0.5 mm in diameter, very close to each other.
For terms describing drizzle in forecasts, see Intensity of drizzle.
Prolonged, unusually dry period when there is not enough water to meet normal use needs.
Annual season in the tropics that brings heat, sunshine and dry weather. In northern Australia, the dry season is between May and September.
Air temperature measured by a thermometer exposed to the air but shielded from sunlight and rain. It’s taken in an instrument enclosure known as a Stevenson screen (white louvred box) raised 1.2 m above the ground.
Brief: Short duration
Intermittent: Stops at times
Occasional: Infrequent but recurrent
Frequent: Regularly and often
Continuous: Doesn't stop, or stops only briefly
Periods of rain: Rain is expected to fall most of the time, but there will be breaks
Small and rapidly rotating column of wind made visible by dust, dirt or debris within it. It usually occurs in arid or semi-arid areas. It is most likely to develop on clear, dry, hot afternoons when the sun warms the ground, heating the air above it and causing it to rise. Also called a willy-willy.
When strong wind picks up dust and dirt from the ground, raises it into the atmosphere and carries it over an extensive area. Dust storms can trigger health problems for some people and disrupt transport by limiting visibility.