2013年1月20-21日山东出现了一次暴雪过程,此次过程具有冷空气弱、东西雨雪共存及存在两个强降水中心等特点,济南至淄博(鲁中的北部地区)的次暴雪中心为预报难点。为了探讨此类暴雪过程降水落区、强度和相态变化的物理机制,根据常规观测、NCEP/NCAR再分析逐6 h及多普勒天气雷达资料,采用基于构成要素的预报方法(Ingredients-based Methodology,IM),从动力抬升、水汽、降雪效率和相态等四个方面进行了分析。结果表明:(1)高层两个短波槽、低层切变线、地面华北锢囚锋和倒槽等天气系统相继共同作用造成了此次暴雪过程,其中500 hPa短波槽对降雪的阶段性表现最明显。(2)四个有利构成要素相叠加导致鲁中地区产生暴雪:中低层有西南和东南两支气流输送了充足的水汽;低层经向切变线和暖切变线造成了强上升运动;云中温度在-15～-14℃之间达到最佳降雪效率;低层温度低。(3)低层经向切变线对次降水中心的暴雪形成有重要作用,暴雪发生在经向切变线的右侧东南风减小的区域。(4)最强降雪发生在对流层中高层西南风和低层东南风强盛的时段。(5)对流层低层冷暖平流导致边界层内温度垂直变化出现差异,从而产生不同降水相态,其中1000 hPa至近地面的温度最为关键,尤其2 m气温在1℃左右时,更需综合分析925 hPa以下各层的温度;同时复杂下垫面对降水相态的影响也不容忽视。
The process of snowstorm responsible for complicated precipitation type and distribution from 20 to 21 January 2013 is examined using conventional observation,NCEP/NCAR and radar data by IM(Ingredients-Based Methodology).The results can be briefed as follows.To begin with cooperation of two high trough,low level shear,and surface front and reverse trough caused the snowstorm.In the second place,the snowstorm depended on four favorable ingredients,including plenty vapor from two southwestward and southeastward flows,strong vertical velocity by low level shear,optimal Precipitation efficiency with appropriate temperature (-15～-14℃) and low temperature.Meanwhile,low longitudinal shear attached importance on the second precipitation center.Besides,the heaviest snowfall occurred while southwest wind in mid-high level and southeast wind got most powerful.Last but not least,with regard to precipitation phase,because of difference of temperature advection in low troposphere,temperature in low level especially 1000hPa and surface is key factor.Temperature under 925 hPa must be analysized particularly when 2 m temperature is at about 1℃.And complex terrain can affect precipitation phase,too.
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