Abstract:

Based on the meteorological observation data and numerical forecast products of ECMWF, ECMWF_THIN, T639 and Ningxia WRF models, the performance and predictability of these models on the first snowfall process triggered by the low vortex and shear line in Ningxia from 30 October to 2 November 2015 were tested and analyzed. The results show that the more accurate prediction of the complex weather process accompanying with snowfall, strong wind, temperature decline, heavy fog, road icing and snow, etc, could be made in advance based on the forecasted results of models which the relative humidity was greater than 90% and the specific humidity was larger than 2 g·kg-1 on 700 hPa, the temperature on 850 hPa, 2 m and surface dropped below 0 ℃ and 1 ℃, respectively, the northerly winds on 200 hPa and 700 hPa were larger than 40 m·s-1 and 20 m·s-1, as well as the atmospheric stratification was stable. And the strong snowfall areas and snowfall intensity could be corrected effectively according to the high value areas of thick wet layer, moisture convergence and vertical ascending motion where the low vortex passed and overlap regions of heavy rain forecasted by the models. However, the elaborate predictions about the centre of strong snow, local strong snow when the snowfall decreased and regional strong fog were worse because the forecasters’ cognitive and correction capability to the consistency prediction errors of the models was limited.

Key words:  cold vortex snowfall, complex weather, predict bias, predictability

摘要：

利用常规高空、地面气象观测资料和ECMWF、ECMWF_THIN、T639及宁夏WRF数值预报模式产品，对2015年10月30日—11月2日宁夏首场冷涡降雪天气过程的数值模式预报性能及其相伴复杂天气的可预报性进行检验和分析。结果表明：依据700 hPa相对湿度≥90%和比湿≥2 g·kg-1、850 hPa温度迅速降至冰点以下、2 m和地面气温降至1 ℃以下、200 hPa和700 hPa偏北风速分别达40 m·s-1和20 m·s-1、雪后天气转为晴到少云、地面偏南风<4 m·s-1且相对湿度≥90%、大气层结稳定等模式预报结果，可提前对低涡和切变线引发的降雪、大风降温、雪后大雾以及积雪、道路结冰等复杂天气作出较为准确的预报。根据低涡所经区域的厚湿层、水汽辐合及垂直上升运动等大值区和各家模式预报较大降水的重叠区域对强降雪区域及强度进行有效订正，但由于预报员对各家模式一致性预报误差的认识和订正能力有限，使得对强降雪中心、降雪减弱时的局地强降雪以及区域大雾等天气精细化预报能力较差。

关键词: 冷涡降雪, 复杂天气, 预报偏差, 可预报性