The Application Of Numerical Forecast Product Interpretation In Summer Heavy Precipitation Forecast In Qinghai

Heavy rainfall forecast is a big challenge in weather forecasting.Qinghai is located in the northeast of the Tibetan plateau,which is affected by the plateau topography.The summer precipitation has the characteristics of sudden,local and large rainfall intensity,that is easy to cause secondary disasters such as floods and debris flow which are the most important meteorological disasters in Qinghai.In the past,only relying on the observation data to forecast heavy rainfall in Qinghai has certain limitations.With the diversification of numerical model forecast products and the improvement of resolution and accuracy,its important part in precipitation forecast is also gradually recognized.However,how to optimize the application of numerical forecast products in heavy rainfall forecasting,and to explore and verify more convenient and effective methods for the interpretation of numerical forecasting products in operational forecasting are still practical topics worthy of continuous exploration.Therefore,this paper makes a little attempt on the application and improvement of the model output statistical method in the short-term weather forecast in Qinghai.Firstly,the spatial distribution characteristics and precipitation intensity characteristics of the summer precipitation in Qinghai during the last 10 year was analyzed by the daily precipitation data.The results show that:(1)The spatial distribution of annual average precipitation in Qinghai is extremely uneven,showing the characteristics of the northern region is less than the southern,the western is less than the eastern,and a decreasing feature from the southeast to the northwest.The annual precipitation is mainly concentrated in summer,and the frequency of heavy rainfall is also the most.(2)The intensity of summer precipitation in Qinghai has obvious inhomogeneity.and the precipitation above 10 mm belongs to the heavy rainfall.Statistics show that although the number of occurrences of precipitation over 10 mm by 24 hours is small,it is still the main contributor to summer precipitation in Qinghai,indicating that the precipitation above 10 mm is a stronger type of summer precipitation in Qinghai,that is the main causes of secondary disasters such as flood and debris flow in Qinghai.(3)The precipitation concentration in Qinghai is between 0.6-0.7,indicating that the precipitation is more concentrated;The concentration period is about 210 °,indicating that the precipitation concentration occurs in summer.It shows that precipitation in Qinghai also has obvious heterogeneity in time distribution.The summer precipitation concentration shows that precipitation is more evenly distributed in summer months,relatively large concentration is mainly in the middle and late June,early July and mid-August,that confirms the tradition precipition mostly located in“early July and late August” in flood season.Based on the high resolution prediction field data of European Centre,two severe precipitations occurring in Qinghai were analyzed for the forecast application,and The "Ingredients method" was used to try to construct a new parameter with physical quantities with better prediction effect.The results show that:(1)The helicity,water vapor flux and vapor flux divergence calculated based on the numerical forecast products and the local forecast experiences have a good forecast application value in summer severe precitipation in Qinghai,each physical quantity has a good corresponding relationship between the occurrence and development of precipitation and the heavy rainfall center: The intensity of positive horizontal helicity on 500 hPa had a good indicator for the change of precipitation intensity,the intensity of negative horizontal helicity can give good indicator to the location of heavy rainfall center when it was stronger.In large value area of water vapor flux the stronger the water vapor convergence intensity,the stronger the precipitation intensity.(2)The new parameters based on “Ingredients method” displayed: The effect of precipitation prediction of new parameters is better than that of single physical quantity,the probability of heavy rainfall in large value area of new parameters is greater.(3)The technique for objective forecasting heavy rainfall constructed by“Ingredients method” has good application in the summer precipitation forecast in Qinghai.How to use numerical forecast products to track the evolution characteristics of physical quantities and mesoscale convective system is the key for predicting the time and place of the rainstorms and severe convective weather,and it needs to be further research.