Abstract: Based on the conventional observation, wind profiling radar, the Doppler radar and the NCEP reanalysis data, the causes of the two rain to snow processes in Liaoning Province and the predictability of the snowfall were analyzed comparatively from the perspective of the weather system, water vapor and thermal dynamical evolution. The results show that it took a long time to warm up with a short frontogenesis time, and the precipitation increased due to the near-ground front zone in the process Ⅰ. The front zone between the 925 hPa and 850 hPa level presented a vertical distribution and the snowfall ended after the frontal passage on the 850 hPa level. While there was a transient strong warming in the process Ⅱ, the cold air wedged into the low layer earlier and the warm and humid air slid up along the cold wedge. The duration of frontogenesis was long and there was no precipitation in the period of the near-ground frontal passage. The occurrence of the heavy snow was closely related to the middle level front zone and low level cold recurrent flow. The slow passage speed of the 850 hPa level front zone led to the persistent snowfall which stopped until the frontal passage on the 700 hPa level. Radar echo displayed that the height of the 0 ℃ layer bright band significantly reduced before the rain changing to sleet, and that height basically maintained during the sleet stage, but the 0 ℃ layer bright band disappeared during the snowfall stage. The effect of preceding warming and the daily temperature change owing to the systemic cooling needed to be concerned when correcting the numerical forecast, then the precipitation period should be determined according to the dynamical characteristics of the precipitation system, finally the snow volume was comprehensively corrected.

Key words: heavy snow, frontogenesis, wind profiling radar data

摘要： 应用常规观测、风廓线雷达、多普勒雷达及NCEP再分析资料，从影响系统、水汽、热动力演变等方面对辽宁2次雨转暴雪成因及降雪量可预报性进行对比分析。结果表明：过程Ⅰ回暖时间长，锋生时间短，近地面锋区影响期间降水增强，925～850 hPa锋区垂直分布，850 hPa锋区过境后强降雪结束；过程Ⅱ短暂强回暖，冷空气楔入低层早，暖湿空气沿冷垫上滑，锋生时间长，近地面锋区影响期间无降水，中层锋区与低层东北回流叠加时出现强降雪，850 hPa锋区过境缓慢，强降雪持续时间长，700 hPa锋区过境后强降雪结束。雷达回波特征显示，0 ℃层亮带高度在降水相态转变为雨夹雪前明显降低，雨夹雪阶段基本维持，降雪后0 ℃层亮带消失。对数值预报降雪量订正，首先关注前期回暖、气温日变化与系统性降温叠加作用，再根据不同类型降雪影响系统动力、水汽辐合等条件判断降水时段，综合订正降雪量。

关键词: 暴雪, 锋生, 风廓线雷达资料