【正文】 定的增厚，并向鋒的地面位置下降。最開始的云石薄而縹緲的卷云，緊接著是成片的卷層云和高層云。當高層云加厚開始下毛毛雨或者開始下大雨時，太陽就開始昏暗了。經(jīng)常會伸展到對流層大部分地區(qū)而且伴隨著連續(xù)性降水發(fā)生的云系通常叫做雨層云。當下降的雨水穿過冷空氣時經(jīng)過蒸發(fā)，迅速的達到飽和，也可能形成一片片的層云。
下滑鋒中的下沉暖空氣極大限制了中高層云的發(fā)展。鋒面云系主要是層積云，由于在冷暖空氣團中下沉逆溫的作用，云系的厚度受到了限制。降水通常是由雨滴的合并作用引起的小雨或毛毛雨，因為凍結(jié)高度比較多地傾向于在逆溫層之上，尤其是在夏季。
暖鋒過境時，風向發(fā)生轉(zhuǎn)變，溫度升高，氣壓下降。暖空氣中，降水是間歇性的或者無雨，薄的片狀層積云也可能斷裂開來。
因為大多數(shù)鋒在對流層的所有層次上或者說貫穿鋒的整個長度并不都是上滑鋒或者下滑鋒，所以要預報與暖鋒相聯(lián)系的雨帶的范圍是很復雜的。由于這個原因，雷達波越來越多的用來直接測定雨帶的精確范圍和雨量強度的差異。
這些研究表明，大多數(shù)降水的產(chǎn)生和分布是由寬達幾百公里，厚達幾公里的寬闊氣流所控制，這股氣流平行于地面冷鋒，位于地面冷鋒之前就是在冷鋒之前，在離地表約1Km之上隨著風速增大到2535m/s，這股氣流形成了低空急流。暖濕空氣在暖鋒上上升，在暖鋒前轉(zhuǎn)向東南方，同時與對流層中部分的氣流合并。這股氣流被稱之為“傳送帶”。（因為在中緯度傳輸大尺度的熱量和動量）。大范圍的對流潛在不穩(wěn)定是由與對流層中部潛在的干冷空氣在低層氣流上爬越作用而造成的。 不穩(wěn)定主要在形成的對流群即中尺度降水區(qū)的小尺度對流單體中釋放。這些中尺度降水區(qū)進一步排列進帶狀，大約50100Km寬。在暖鋒前，這條帶狀區(qū)域橫向平行于傳送帶上升區(qū)中的氣流，然而，在暖區(qū)中，則平行于冷鋒和低空急流。在某些情況下，對流單體和對流群在暖區(qū)中和暖鋒前進一步排列成帶狀。
暖鋒雨帶的降水經(jīng)常隨著來自上層云層“散布”的冰粒。據(jù)估計，大約2035%的降水來源于“催化劑”區(qū)，其余的來源于低層云系。一些對流單體和對流群天氣會通過地形影響而成，而且但大氣不穩(wěn)定時，這些影響會延伸到下風方向。
冷鋒冷鋒的天氣狀況同樣是多變的，它依賴于暖區(qū)氣團的穩(wěn)定性和相對于鋒區(qū)的垂直運動。經(jīng)典的冷鋒模式是上滑型的，導致在冷鋒上出現(xiàn)雨層云的概率更多。
伴隨下滑型鋒面的云系一般是層積云，降水較少。伴隨著上滑型冷鋒，通常會短暫的傾盆大雨，有時還會伴隨打雷。冷鋒的坡度大約是2176。，這意味著壞天氣的持續(xù)時間比暖鋒要短。冷鋒過境，風向急劇變化，氣壓開始上升，溫度下降。天空會突然放晴，有些情況下，甚至在地面冷鋒過境前就放晴了，雖然下滑鋒的變化總的來說要緩和得多。
1. 錮囚鋒錮囚鋒分為冷式和暖式。區(qū)別在于暖區(qū)前和暖區(qū)后的冷氣團的相對狀態(tài)。如果氣團比其后更冷，則為暖式錮囚鋒，相反，則成為冷式錮囚鋒。當冬季歐洲上空的低壓錮囚以及很冷的空氣影響大陸時，低壓前的空氣很可能是最冷的。
暖空氣楔形隆起的形狀是與層云區(qū)相聯(lián)系的，經(jīng)常會有降水。因此，在一些天氣圖上，它的位置會單獨標識，加拿大氣象學家稱之為高空暖舌。這一段的錮囚鋒和高空暖舌帶來與極地空氣團天氣相反的變化。
當極地槽和主要的極鋒相互作用，會產(chǎn)生不同的過程，會引起短暫的錮囚。極鋒的暖傳送帶上升到對流層上部的急流區(qū)形成層狀云帶，然而在低空極地槽傳送帶與之呈90度角，則在冷空氣前邊緣形成主要極鋒向極的對流云帶和降水區(qū)。
盡管鋒消代表鋒面存在的最后階段，但鋒消并不一定與錮囚聯(lián)系在一起。當臨近的氣團之間的差異不再存在時，消亡就發(fā)生了。這可能是由4個方面引起的：
一是由于它們在同一平面共同停滯；二是因為兩氣團的相同的速度平行的軌跡行動；三是因為它們緊接著以相同的速度沿著相同的軌跡運動；四是由于系統(tǒng)并入到與它本身具有同樣溫度的空氣中。注意表“原因”的幾種用法
1. since 因為 原因狀語從句
例 since the operator had more experience with mounting tape than a programmer, setup was reduced
鑒于操作員比程序員有更多的安裝磁盤的經(jīng)驗，所以（由操作員進行的）安裝時間減少了。
2. for 因為
例the output power can never equal the input power ,for there are always losses
輸出功率決不可能等于輸入功率，因為存在耗損。
3. by the fact that
：though 介詞，由于，因為
as a result of……
作為……結(jié)果 , 因為
例 the roughly 365day year is the result of the earth traveling around the sun in one period
365天左右約一年里地球圍繞太陽轉(zhuǎn)動一個周期的結(jié)果。
其他表原因的用法
1. because of , due to (由于),be the cause of (是……的原因), on account of (原因) 等等
例 in the cloudless night ground temperature decreases on account of the heat lost to the space
在無云夜間地面溫度由于其熱量散失到空間而下降。
…… 引導原因狀語從句
As no machine ever runs without some friction ,over ing the wastes work
因為沒有一臺機器可以無摩擦的運轉(zhuǎn)，所以克服摩擦力只是白費工夫。
that 因為（接從句）
In summer people feel stocking in that relative humidity is quite high.
view of 介詞后接名詞或代詞做賓語（后不能接that從句）必須加詞
In view of the importance of the platen to the weather and climate over broad areas, a scientific investigation was carried out a few years ago.Unit Three: Meteorological Forecasts第三課：氣象預報National Meteorological Services perform a variety of activities in order to provide weather forecasts. The principal ones are data collection, the preparation of basic analyses and prognostic charts atmosphere conditions for use by local weather offices,the preparation of shortand longterm forecasts for the public as well as special services for aviation, shipping , agricultural and other mercial and industrial users, and the issuance of severe weather warnings.

1. Data sources
The data required for forecasting and other services are provided by worldwide standard synoptic reports at 00, 06, 12, and 18 GMT, similar observations made hourly, particularly in support of national aviation requirements, upperair soundings (at 00 and 12 GMT),
satellite data and other specialized networks such as radar stations for severe weather . Under the World Weather Watch (WWW) program, synoptic reports are made at some 4,000 land stations and by 7,000 ships. There are about 700 stations making upperair soundings (temperature, pressure, humidity, and, wind).
These data are transmitted in code via teletype and radio links in regional or national centers and into the highspeed Global Telemunications System (GTS) connecting World Weather Centres in Melbourne, Moscow and Washington and eleven Regional Meteorological Centres for redistribution.
Some 157 states and territories cooperate in this activity under the aegis of the World Meteorological Organization (WMO).
Meteorological information has been collected operationally by satellites of the United States and USSR since 1965 and, more recently, by the European Space Agency, India and are two general categories of weather satellite:
polar orbiters providing global coverage twice per 24 hours in orbital strips over the poles and geosynchronous satellites, giving repetitive(30minute)coverage of almost one third of the earth’s surface in low middle latitudes.
Information on the atmosphere is collected as digital data or direct readout visible and infrared images of cloud cover and seasurface temperature, but also includes global temperature and moisture profiles through the atmosphere obtained from multichannel infrared and microwave sensors which receive radiation emitted from particular levels in the atmosphere.
Additionally, satellites have a data collection system(DCS) that relays data on numerous environmental variations from ground platforms or ocean buoys to processing centers。 GOES can also transmit processed satellite images in facsimile and the NOAA polar orbiters have an automatic picture transmission(APT) system that is utilized at 900 stations worldwide.

2．Forecasting
Modern forecasting did not bee possible until weather information could be rapidly collected，assembled and processed．
The first development came in the middle of the last century with the invention of telegraphy，which permitted immediate analysis of weather data by the drawing of synoptic charts．
These were first displayed in Britain at the great Exhibition of l851．Sequ