Characteristic analysis of different snow in the continuous heavy snow in North China

In this paper, using observed data, the characteristics of two different feature of one heavy snowfall in North China region from 25 to 27 February, 2011 are studied. Results show that the heavy snowfall can be divided into two stages. The snowfall happened in same background circulation, but showed two different characteristics. First, the affecting systems of two stages of snowfall are different: the first period of snowfall is caused by a deep westerly trough at high latitude with a ground front; the latter is caused by a wind shear line move to the north, as well as a shear line at 700hPa and 850hPa. Second, the formation mechanisms are different: the first period snowfall is due to the consistent warm and moist southerly jet in the low level move to north and intersection with cold air from the back area of the trough; the latter is due to the strong horizontal and vertical wind shear in the warm and moist air. Third, the moisture sources are different: Southwest jets at 700hPa and 850hPa in front of trough transport abundant moisture to the North China region in the first period snowfall; in the latter period, the southwest jet at 700hPa and southeast airflow blowing through the Bohai Sea at 850hPa converged together to provide plentiful vapor for snowfall.