Characteristics of environmental parameters for classified severe convective weather in central area of Shandong Province

In this paper, 106 strong convective cases accompanied with instantaneous winds at or exceeding the scale 8 in the central region of Shandong Province in 16 years are classified into three types:Thunderstorm, hail thunderstorm and mixed type of heavy rainfall. Using conventional sounding data and ground observation data, distributions of several key environmental parameters and thresholds corresponding to the three types are discussed respectively by the form of box and whisker plots. Furthermore, significantly severe convection cases among the 106 cases, including significant thunderstorm and strong wind cases with instantaneous wind speed exceeding 25 m/s, significant hail cases with the diameter of hails equal to or larger than 20 mm, and significant short-term heavy rainfall cases with the intensity about 50 mm/h or above, are extracted to form a subset. Distributions and forecast thresholds for significantly severe convection cases mentioned above are discussed and compared with the corresponding key environmental parameters for the total cases. Finally, the triggering mechanism for the strong convective system is briefly described and discussed. Results suggest that the minimum threshold of temperature difference between 850 and 500 hPa is 25℃ for the development of thunderstorms, hail thunderstorms and mixed type of heavy rainfall, while their corresponding minimum thresholds of ground dew point temperature are 13, 16 and 24℃, the atmospheric precipitation thresholds are 20, 24 and 32 mm, the thresholds of CAPE are 300, 900 and 1300 J/kg, thresholds of 0-6 km wind vector difference are 12, 12.5 and 8 m/s, respectively. The distributions of ground dew point temperature, atmospheric precipitation and warm cloud thickness can be used to distinguish the above mentioned three types of strong convective weather, but it is difficult to distinguish thunderstorms and hail thunderstorms through the distributions of these key parameters. For the strong convective weather associated with hail, the appropriate melting layer height is 3.0-3.9 km. Compared with the three types of all strong convection cases, the conditional instability for significant thunderstorms, significant hail thunderstorms and significant mixed type of heavy rainfall significantly increases, which is reflected in the fact that the temperature difference between 850 and 500 hPa, the water vapor condition, and the CAPE all increase. Corresponding to the above mentioned three types, the minimum thresholds of CAPE are 1000, 1100 and 2000 J/kg, and the 0-6 km wind vector shears are 16, 12 and 11 m/s, respectively. The thresholds of vertical wind shear for significant thunderstorms and significant mixed type of heavy rainfall increase obviously. The above work forms a basis for the short-term forecast of strong convective weather. Combined with the climatological occurrence probability, a short-term forecasting system for classified strong convective weather can be established for regional meteorological stations by means of decision tree or fuzzy logic method.