7下Unit7AboutWeather

1、Forecasting Terms The following definitions of some common forecasting terms will help you extract the maximum information from forecasts.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 particula

2、r, 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 tContinue for at least a day or so.Cloud CoverClear: Free from clou

3、d, fog, mist or dust haze.Sunny: Little chance of the sun being obscured by cloud. (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 more than h

4、alf the sky may be covered in cirrus cloud.)Cloudy: Predominantly more cloud than clear sky. For example, during the day the sun would be obscured by cloud for substantial periods of time.Overcast: Sky completely covered with cloud.Forecasts of cloud cover normally give an average, if no significant

5、 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 majo

6、r change in cloud cover, they usually indicate a distinct trend, e.g. becoming sunny or cloud increasing.Temperature DescriptorsMaximum Temperature (Highest daytime temperature) - Summer/Winter Summer Descriptive term Inland plains Coast and ranges south of tropics Coastal tropics Very hot: more tha

7、n 40 C more than 37 C -Hot: 35-39 C 32-37 C 35-39 C Warm: 30-34 C 27-31 C Not used Mild: 25-29 C 22-26 C -Cool: 20-24 C 16-21 C -Cold: less than 20 C less than 16 C -Winter Descriptive term South of 33 S plus ranges North of 33 S except ranges and tropics Tropics Warm: more than 20 C more than 25 C

8、-Mild: 16-20 C 20-24 C -Cool: 13-15 C 15-19 C 20-25 C Cold: 10-12 C 10-14 C less than 20 C Very cold: less than 10 C less than 10 C -Minimum Temperature (Lowest overnight temperature) - Summer/WinterSummer Descriptive term South of 33 S plus ranges North of 33 S except ranges and tropics Tropics Hot

9、: more than 22 C more than 25 C -Warm: 18-21 C 21-24 C -Mild: 15-17 C 18-20 C -Cool: 10-14 C 13-17 C less than 20 C Cold: less than 10 C less than 13 C -Winter Descriptive Term South of 33 S plus ranges North of 33 S except ranges and coastal tropics Coastal Tropics Mild: more than 10 C more than 15

10、 C -Cool: 5-9 C 10-14 C 13-17 C Cold: 1-4 C 5-9 C less than 13 C Very cold: less than 1 C less than 5 C -NOTES:1. No international definitions have been laid down for the terms hot, warm, etc. The above table has therefore been developed in the Bureau to serve as a general guide only.2. In using the

11、 table, forecasters use their discretion and take account of factors such as incidence of cloud/sunshine, wind (chill factor), location and time of year.3. In some cases, terms such as warmer may be used to contrast the expected weather with the weather recently experienced.4. Mild need not be used

12、in the strict dictionary sense (calm, fine) when indicating its assigned temperature ranges. Nevertheless, mild is not used when the weather departs significantly from the dictionary definition e.g: gales or heavy rain.Description of PhenomenaFog: Suspension of very small water droplets in the air,

13、reducing visibility at ground level to less than a kilometre.Smog: Smog ( contraction for smoke fog) is a fog in which smoke or other forms of atmospheric pollutant have an important part in causing the fog to thicken, and have unpleasant and dangerous physiological effects.Mist: Similar to fog, but

14、 visibility remains more than a kilometre.Frost: Deposit of soft white ice crystals or frozen dew drops on objects near the ground; formed when surface temperature falls below freezing point.Precipitation: Any or all of the forms of water particles, whether liquid (e.g. rain, drizzle) or solid (e.g.

15、 hail, snow), that fall from a cloud or group of clouds and reach the ground. (See Drizzle, Rain)Drizzle: Fairly uniform precipitation composed exclusively of very small water droplets (less than 0.5 mm in diameter) very close to one another.Rain: Precipitation of liquid water drops greater than 0.5

16、 mm in diameter. In contrast to showers, it is steadier and normally falls from stratiform (layer) cloud.Showers: Usually begin and end suddenly. Relatively short-lived, but may last half an hour. Often, but not always, separated by blue sky.Blizzard: Violent and very cold wind which is laden with s

17、now, some part, at least, of which has been raised from snow covered ground.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 earths 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