武汉市冬季大雪分析预报

The analysis and forecast of winter snowstorm in Wuhan

使用常规气象观测资料和数值预报产品,分析了1951—2005年冬季发生在武汉市的大雪过程,结果表明:武汉市冬季出现积雪深度大于5 cm的天气事件的概率大约为每年2 d,主要发生在1月,其次是2月;大气层结条件是产生降雪的关键,地面冷空气、中低层江南西南急流和中层西风带低槽是决定武汉市冬季大雪的3个主要天气系统,中低层江南西南急流的位置和强弱决定武汉市大雪的强度,地面冷空气的路径和强度决定武汉市的降温幅度;欧洲数值天气预报(EC)表现为:700hPa在25～30°N江南有≥16 m/s的西南低空急流,500 hPa明显东高西低,武汉与成都的高度差达到5 dagpm以上,850 hPa武汉站温度在0℃以下,700～850 hPa之间有逆温存在,地面上从蒙古或华北有1 045 hPa以上的冷高压,并且武汉站气压值有明显上升,达到1 025 hPa左右时,武汉市会出现大雪天气。

By using the 55 a data,the snowstorm in Wuhan during 1951—2005 were analyzed.The results suggested that the frequency of which snow depth is greater than 5 cm in Wuhan is about two days a year,mainly in January,the next were February and then December.Conditions of atmospheric stratification is the key to producing snow.The chief weather systems which contribute to the snowstorm were ground cold air,the lower and middle southwest jet in the south of Changjiang River and westerly trough of 500hPa.The southwest jet of 700 hPa in the south of Changjiang River is related to the intensity of snowstorm.The path and intensity of ground cold air affect the degree of temperature decrease.According to the numerical weather forecast（EC）,four requirements must be met for a snowstorm in Wuhan.Firstly,southwest jet in the south of Changjiang River is over 16m/s at 700 hPa.Secondly,the difference of geopotential height at 500 hPa between Wuhan and Chengdu is over 50 gpm.Thirdly,the temperature of Wuhan less then 0℃ in 850hPa temperature field,and a temperature inversion is present from 850 hPa to 700 hPa.Fourthly,there is cold high over 1045hPa from Mongolia or north of China and the pressure of Wuhan increased obviously to 1 025 hPa or so.