Analysis Of The Severe Cold-air Outbreak Snow Storm Event In Shandong Peninsula On 3～4 December 2005

A cold-air outbreak snowstorm event have occurred in Shandong Peninsula on 3～4 December 2005.This event resulted in tow precipitation centers which are Zhaoyuan and Rongcheng. The 24h precipitation from 20:00 LST 3 December to 20:00 LST 4 December is 11mm in Zhaoyuan and 27mm in Rongcheng,meanwhile the snowfall is about 35cm in wendeng.This snowstorm results in severe damage and loss to lifes and propenty.Using the radar datas and the routine observations as well as the results of simulation by PSU/UCAR mesoscale model-MM5, we analyze and research this severe cold-air outbreak snow storm event and dynamic diagnoses in order to get the synoptic situation and the distribution of the meteorological elements. Meanwhile we also study the formation mechanism, structure evolvement process and dynamic mechanism of the convective snowband in Shandong Peninsula, so that we can deeply understudy this kind of weather, and base for further research, and progress weather prediction and reduce weather damages.The observations and the results of simulation show that there are tow precipitation centers: Zhaoyuan and Rongcheng. The precipitation of Zhaoyuan centralizes on the time when the convective snowband just forms, but the time is short Because of weak coastal front over Penglai and Longkou,so the embranchment of the convective snowband is difficult to keep. From Yantai to Rongcheng, the rainfall is heave because of organization of the stable coastal front and supplement of heat energy and vapor from bohai sea as well as mesoscale vortex.The quasi-stationary convective snowband which forms 00:00 LST 4 December 2005 and propagates northwest-southeastward beyond yantai maritime space maintains approximately 12h.The structures of the snowband in a vertical cross section show that the height of snow band reach to 500hPa at yantai. From the wind field in vertical cross section we can get that the snowband forms over the convergence zone between a cold southerly land breeze and northwesterly winter monsoon, to which heat and moisture is supplied from relatively warm bohai sea in night of 3 December. A cold pool forms under the snowband. The diabatic cooling due to the sublimation of snow is responsible for the formation of the cold pool.The results indicate that snow storm event generated owing to the cooperation of the favorable synoptic circulation and both thermodynamic forcing caused by the warm Bohai-sea surface and dynamic forcing by the topography as well as kinetic energy supplying by upper air with high potential vorticity. The coastal front generated owing to the different temperature between bohai Sea and land and the ageostrophic wind, which brings an obvious increase of local snow fall and whose secondary circulation decide the distribution of snowfall. Meanwhile the weakened land breeze which formatted in night is significant for the formation and maintenance of the convective cloud band.