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5P’s Weather Terminology Handbook

All information sourced from the Australian Bureau of Meteorology http://reg.bom.gov.au/info/wwords/


Table of Contents Weather Terms ............................................................................................... 3 Time................................................................................................................ 4 Time of Day.................................................................................................. 4 Duration of Precipitation ............................................................................. 4 Dry .................................................................................................................. 5 Wet ................................................................................................................. 5 Showers or Thunderstorms.......................................................................... 5 Location of Showers or thunderstorms over an area ................................... 6 Likelihood of showers, rain or thunderstorms ............................................. 6 Rain or Showers Intensity ............................................................................ 6 Clouds ............................................................................................................. 7 Temperature ................................................................................................... 8 Wind ............................................................................................................... 9 Wind Direction............................................................................................. 9 Wind Speed ................................................................................................. 9


Weather Terms Precipitation: Any or all of the forms of water, whether liquid (e.g. rain, drizzle) or solid (e.g. hail, snow), that fall from a cloud or group of clouds and reach the ground. Showers: Usually begin and end suddenly. Relatively short-lived, but may last half an hour. Fall from cumulus clouds, often separated by blue sky. Showers may fall in patches rather than across the whole forecast area. Range in intensity from light to very heavy. Rain: In contrast to showers, rain is steadier and normally falls from stratiform (layer) cloud. Liquid water drops greater than 0.5 mm in diameter. Rain can range in intensity from light to very heavy. Drizzle: Fairly uniform precipitation composed exclusively of very small water droplets (less than 0.5 mm in diameter) very close to one another. Frost: Deposit of soft white ice crystals or frozen dew drops on objects near the ground; formed when surface temperature falls below freezing point. Fog: Suspension of very small water droplets in the air, reducing visibility at ground level to less than a kilometre. Mist: Similar to fog, but visibility remains more than a kilometre. Thunderstorms: Thunderstorms are one or more convective clouds in which electrical discharge can be seen as lightning and heard as thunder by a person on the earth's surface. A severe thunderstorm produces one or more of :* hail at the ground with diameter of 2 cm or more; * wind gusts at the ground of 90 km/h or more; * tornadoes; or * very heavy rain likely to cause flash flooding. Windy: A prolonged period of average wind speeds exceeding 40km/h during the day.


Time Time of Day Morning: Sunrise to noon or midnight to noon depending on context Afternoon: Noon to sunset Evening: Sunset to midnight Today: Until sunset Tomorrow: Midnight to midnight Tonight: Sunset to midnight Night, Overnight: Sunset to sunrise Day: Sunrise to sunset Day of the week (eg. Monday): Midnight to midnight Early: Until 2 hours after sunrise Late: From sunset (winter), from 2 hours before sunset (summer) Duration of Precipitation Brief: Short duration. Intermittent: Precipitation which ceases at times. Occasional: Precipitation which while not frequent, is recurrent. Frequent: Showers occurring regularly and often. Continuous: Precipitation which does not cease, or ceases only briefly. Periods of Rain: Rain is expected to fall most of the time, but there will be breaks.


Dry

Fine: No rain or other precipitation (hail, snow, etc). The use of fine is generally avoided in excessively cloudy, windy, foggy or dusty conditions. In particular, note that fine means the absence of rain or other precipitation such as hail or snow--not 'good' or 'pleasant' weather. Dry: Free from rain. Normally used when preceding weather has also been relatively dry, and dry weather is expected to continue for at least a day or so.

Wet Showers or Thunderstorms Shower or two: Not many, less than a few. Used to describe showers occurring infrequently. Few: Not many, amounting to a small number. Used to describe a small number of showers over a time period. Precipitation: Any or all of the forms of water, whether liquid (e.g. rain, drizzle) or solid (e.g. hail, snow), that fall from a cloud or group of clouds and reach the ground. Showers: Usually begin and end suddenly. Relatively short-lived, but may last half an hour. Often, but not always, separated by blue sky. Rain: In contrast to showers, rain is steadier and normally falls from stratiform (layer) cloud. Liquid water drops greater than 0.5 mm in diameter. Drizzle: Fairly uniform precipitation composed exclusively of very small water droplets (less than 0.5 mm in diameter) very close to one another. Dew: Deposit of water drops on objects at or near the ground, produced by condensation of water vapour from the surrounding air. Thunderstorms: Thunderstorms (commonly shortened to Storms) are one or more convective clouds in which electrical discharge can be seen as lightning and heard as thunder by a person on the earth's surface. Thundery rain: Rain with embedded thunderstorms.


Location of Showers or thunderstorms over an area Isolated: Showers which are well separated in space (ie. generally covering 10 to 25% of the area) during a given period. Local: Restricted to relatively small areas. Patchy: Usually associated with rain. Occurring irregularly over an area (ie. generally covering 10 to 25% of the area). Scattered: Irregularly distributed over an area (ie. generally covering 25 to 55% of the area). Showers which, while not widespread, can occur anywhere in an area. Implies a slightly greater incidence than isolated. Widespread: For rain: Occurring extensively throughout an area (ie. generally covering 25 to 55% of the area). For showers: Occurring extensively throughout an area (ie. generally covering over 55% of the area). Likelihood of showers, rain or thunderstorms Possible, Chance and Risk: These terms may be used interchangeably for location forecasts. Indicates that the weather element is expected to occur over the surrounding area, but due to the random nature of showers and thunderstorms, there is only a chance of that weather element occurring at the forecast location. Risk is generally associated with thunderstorms. Rain or Showers Intensity Light: Up to 2 mm per hour. Individual drops easily identified, puddles form slowly, small streams may flow in gutters. Moderate: 2.2 mm to 6 mm per hour. Rapidly forming puddles, down pipes flowing freely, some spray visible over hard surfaces. Heavy: 6.2 mm to 50mm mm per hour. Falls in sheets, misty spray over hard surfaces, may cause roaring noise on roof. Violent: Over 50mm mm per hour. Gutters and downpipes overflowing, spray to height of several centimetres over hard surfaces, may cause roaring noise on roof.


Clouds Clear: Free from cloud, fog, mist or dust haze. Sunny: Little chance of the sun being obscured by cloud. Cloud expected to cover approximately 0 to 15% of the sky for the majority of the day. (Note: High level cirrus clouds are often thin and wispy, allowing a considerable amount of sunlight to penetrate them, sufficient to produce shadows. In this case the day could be termed 'sunny' even though the sky may consist of cirrus cloud.) Mostly sunny: Predominantly more clear sky than cloud. Cloud expected to cover approximately 15 to 30% of the sky for the majority of the day. For example, during the day the sun would be obscured by cloud for short periods of time. Partly cloudy: Predominantly more clear sky than cloud. Cloud expected to cover approximately 30 to 65% of the sky for the majority of the day. For example, during the day the sun would be regularly obscured by cloud for short periods of time. Cloudy: Predominantly more cloud than clear sky. Cloud expected to cover approximately 65 to 100% of the sky for the majority of the day. For example, during the day the sun would be obscured by cloud for substantial periods of time. Overcast: Sky completely covered with cloud. Cloud expected to cover 100% of the sky for the majority of the day. Notes on terms used in cloud forecasts Forecasts of cloud cover normally give an average, if no significant variations are expected. A clear day, for example, may at some times see a few cloud patches. Forecasters expecting significant variations in cloud amount may use such terms as sunny periods, sunny breaks, cloudy periods, cloudy at times, mostly/mainly sunny, mostly/mainly cloudy. If expecting a major change in cloud cover, they usually indicate a distinct trend, e.g. becoming sunny or cloud increasing.


Temperature Used to describe the temperature at a time of year. The 33° S line runs through Sydney so we will use the North of 33°S descriptions. October - March: Maximum daytime temperature Coast and ranges Descriptive term Inland plains south of tropics Very hot more than 40 °C more than 37 °C Hot 35-39 °C 32-37 °C Warm 30-34 °C 27-31 °C Mild 25-29 °C 22-26 °C Cool 20-24 °C 16-21 °C Cold less than 20 °C less than 16 °C October - March: Minimum overnight temperature Descriptive term Hot Warm Mild Cool Cold

South of 33° S more than 22 °C 18-21 °C 15-17 °C 10-14 °C less than 10 °C

North of 33° S more than 25 °C 21-24 °C 18-20 °C 13-17 °C less than 13 °C

April - September: Maximum daytime temperature Descriptive term South of 33° S North of 33° S Warm more than 20 °C more than 25 °C Mild 16-20 °C 20-24 °C Cool 13-15 °C 15-19 °C Cold 10-12 °C 10-14 °C Very cold less than 10 °C less than 10 °C April - September: Minimum overnight temperature Descriptive Term Mild Cool Cold Very cold

South of 33° S more than 10 °C 5-9 °C 1-4 °C less than 1 °C

North of 33° S more than 15 °C 10-14 °C 5-9 °C less than 5 °C

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Wind Wind Direction Remember wind direction is where the wind is blowing from. Example a wind blowing from North to South would be a Northerly wind Wind Speed

Units in km/h Units in knots Description on Land Calm Light winds

0 19 km/h or less

0 10 knots or less

Moderate winds Fresh winds

20 - 29 km/h

11-16 knots

30 - 39 km/h

17-21 knots

Strong winds

40 - 50 km/h

22-27 knots

51 - 62 km/h

28-33 knots

63 - 75 km/h

34-40 knots

76 - 87 km/h

41-47 knots

Gale

Storm

88 - 102 km/h 48-55 knots

103-117 km/h 56-63 knots Hurricane

118 km/h or more

64 knots or more

Smoke rises vertically Wind felt on face; leaves rustle; ordinary vanes moved by wind. Raises dust and loose paper; small branches are moved. Small trees in leaf begin to sway; crested wavelets form on inland water Large branches in motion; whistling heard in telephone wires; umbrellas used with difficulty. Whole trees in motion; inconvenience felt when walking against wind. Twigs break off trees; progress generally impeded. Slight structural damage occurs -roofing dislodged; larger branches break off. Seldom experienced inland; trees uprooted; considerable structural damage. Very rarely experienced widespread damage


Weather Terminology  

Weather Words

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