利用NCEP再分析資料、地面和高空觀測資料、衛星和雷達資料等，對風暴系統在華北中部加強發展為颮線并產生地面大風的原因進行了分析。結果表明: ①2017年8月5日，在冷渦影響下，華北中高層有干空氣滲透，具有條件不穩定層結，11:00天津訂正探空CAPE高達3184 J〖DK〗·kg-1，且低層水汽充沛，有利于雷暴大風和濕對流的產生。②風暴出流邊界與華北中部地面輻合線合并，且東南部地面露點更高，是颮線系統在華北中南部強烈發展的重要原因。③高溫高濕環境使得風暴向南傳播，在西偏北的引導氣流作用下，最終風暴向南偏東方向移動。④北京探空0～6 km垂直風切變達到3.3 m〖DK〗·s-1〖DK〗·km-1，氣流在前側上升后側下沉，強垂直運動與強垂直風切變作用產生了強旋轉，使颮線系統初期具有中氣旋特征。⑤中層強輻合和風暴頂輻散產生強下沉氣流，地面最大風出現在中氣旋發展階段和冷池合并階段。
By using the NCEP reanalysis data, conventional ground and radiosonde observation, satellite and Doppler radar data, etc., the causes why the storm and ground wind strengthen in the central North China are analyzed in detail. The results show: (1) On 5 August 2017, under the influence of a cold vortex, there was dry air infiltration in the middle and upper levels and conditional instability in North China; at 11:00, according to the revised radiosonde data in Tianjin, the CAPE reached 3184 J kg-1 and the lower level water vapor was abundant, which contributed to the occurrence of thunderstorm gale and moist convection. (2) The merger of the storm outflow boundary and the ground convergence line in the central North China and the higher surface dewpoint temperature in the southeastern North China are important reasons for the strong development of the squall line system in central and southern China. (3) The high temperature and humidity environment made the storm spread southward, and under the guidance of the northwest airflow, the storm finally moved south by east. (4) At 08:00, according to Beijing radiosonde data, the vertical wind shear of 0 to 6 km reached 3.3 m s-1 km-1; the air flow rose in the front and sank in the back. Strong vertical motion and vertical wind shear produced strong rotation, which made the squall line system have the characteristics of mesocyclone in the early stage. (5) Strong convergence in the middle layer and divergence at the storm top produced violent downdrafts. The maximum wind on the ground occurred in the development stage of mesocyclones and the merging of cold pools.