Application of severe convection weather conceptual model to forecast of an extreme gale event occurred in Jiangxi on 4 March 2018

Abstract

The severe convective weather potential forecast, especially classification forecast of more than 12 hours in future is still one of the most difficult problems in forecasting operation at present. Jiangxi province encountered an extremely thunderstorm gale event (hereinafter referred to as the "3·4" gale event) on 4 March 2018. Although a forecast for severe convective weathers like regional thunderstorm gale and hail was issued by Jiangxi Meteorological Observatory on 2 March 2018, it was underestimated for the extreme intensity and beginning time of influencing Jiangxi. Based on numerical prediction models like ECMWF and comparing with the severe convective concept model, we have made a rethink for real-time forecast ideas, experiences and shortages of the "3·4" gale event. The results are as follows. (1) The synoptic situation of the "3·4" gale event meets the concept severe convective model of low-level prior-trough warm advection forcing type in China; it occurs under eastward movement of low trough with large degree of meridionality at 500 hPa and dry and cold tongue in front of trough. There exists an abnormally strong southwest jet pulsating in the low-level, whose strengthen is mostly different from that of southwest jet in south China in the morning in general. In addition, the significantly strengthening of wet tongue in the low-level is in coherence with the synoptic situation at 500 hPa, which causes the configuration of dry and cold air in the high and warm and humid air in the low level. (2) When the wind direction or velocity convergence occurs in the ultra-lower-level jet after surface low pressure with a warm inverted trough develops intensively, surface convergence line forms in the warm sector, which is an important criterion for severe convection weather occurred in warm sector of inverted trough. (3) Several instability indices, such as the temperature difference (T850-500) between 850 hPa and 500 hPa and CAPE, are significantly strong; they are higher than their climatological mean. (4) There are three key points to better forecast the extreme disaster-causing thunderstorm gale events, i.e. completely understanding the concept model of severe convection prediction, accurately grasping the averaged and abnormal values of the meteorological elements, and carefully analyzing the southwest jet pulse apart from its diurnal variation.

Keywords

• thunderstorm gale
• concept model
• warm advection force
• abnormal instability index