2024年1月引发雪崩的阿勒泰极端强降雪天气成因和预报分析

Analysis of the causes and forecast of the extremely heavy snowfall in Altay Area that triggered avalanches in January 2024

在北疆典型双阻型暖区暴雪天气环流形势稳定影响下,2024年1月6-12日新疆北部阿勒泰出现一次极端强降雪过程,多站突破历史同期极值,导致阿勒泰山区多处出现雪崩,本文基于国家站和区域气象观测站逐小时实况观测资料、ERA5再分析资料、区域模式(CMA-MESO、CMA-TYM)和全球模式(CMA-GFS、ECMWF)预报资料,对此次过程的降雪特征、环流形势、极端性成因及模式预报性能进行分析,结果表明:(1)强降雪过程呈持续时间长、累积降水量大、小时降水量多等极端性特征,根据环流形势演变和降雪特征,降雪过程可分为三个阶段。累积降水量分布呈平原地区向山区递增的特征,强降雪主要集中在第二、三阶段,以上两个阶段阿勒泰北部沿山地区和山区新增积雪大、小时积雪多、雪水比大,满足雪崩形成的关键气象条件。(2)此次过程500hPa强盛极锋锋区不断分裂短波系统先后东移影响阿勒泰,850-700hPa长时间维持暖式切变线,并伴随强暖锋锋生,强降雪发生在300hPa极锋急流出口辐散区、850hPa切变线以北至700hPa切变线附近区域。(3)第二、三阶段阿勒泰北部尤其是北部山区水汽条件异常偏强,叠加地形增幅作用,低层动力抬升作用异常强盛,并长时间维持,是造成极端强降雪的重要原因。(4)区域模式对强降雪预报好于全球模式,但对极端性预报能力仍有限。ECMWF极端预报指数预报产品(EFI)和国家气象中心集合平均异常天气预报产品(EMAF)在中期时效能较好地发现了极端天气信号,强化相关产品的应用,并结合模式定量预报结果作出调整,可进一步提升对极端天气事件的预报预警精细化服务效果。

Under the influence of the stable snowstorm circulation situation of the typical double-resistance type warm area in northern Xinjiang,an extremely heavy snowfall event occurred in Altay,from January 6 to 12,2024.Several meteorological stations broke the historical maximum records for the same period,resulting in avalanches in several places of the Altay Mountains.This event can be divided into three stages according to the evolution of circulation situation and snowfall characteristics.In this study,the snowfall characteristics,circulation situation,extreme causes,and model forecasting performance of the event were analyzed using the hourly observation data of national and regional meteorological stations,ERA5 reanalysis data,and CMA-GFS,CMA-MESO,CMA-TYM,ECMWF model forecast data.The results are as follows:(1)The event was characterized by several extreme features,such as long duration,large accumulated precipitation,and large hourly precipitation.The precipitation distribution was increasing from the plain areas to the mountain areas.The strong snowfall process mainly concentrated in the second and third stages.In these two stages,the increase in snow accumulation,large hourly snowfall,and high snow-to-water ratio in the mountainous areas along the northern Altay provided key meteorological conditions for the avalanches.(2)During this event,a strong polar front at 500 hPa continuously split short-wave systems,which successively moved eastward to affect Altay.The warm shear line at 850-700 hPa was maintained for a long time,accompanied by strong warm front frontogenesis.Heavy snowfall occurred in the divergence area at the exit of the polar front jet at 300 hPa,from the north of the shear line at 850 hPa to the regions near the shear line at 700 hPa.(3)In the second and third stages,the water vapor conditions in the north of Altay,especially in the northern mountains,were abnormally strong.With the effect of terrain amplification,the low-level dynamic uplift was exceptionally strong and maintained for a long time.These were the important reasons for the extremely heavy snowfall.(4)The regional model performed better than the global model in predicting heavy snowfall,but the capability to forecast extreme snowfall was still limited.ECMWF Extreme Forecast Index(EFI)forecast product and the Ensemble Average Abnormal Weather Forecast(EMAF)product were better at identifying extreme weather signals at medium-range lead time.It is suggested to strengthen the application of related products and make adjustments according to the quantitative forecast results of the model to further improve the precision service effect of forecasting and warning of extreme weather events.