Fig. (1) The 500 hPa height field for a) 1200 UTC 24 June 2016 (WWA - BI =2.25), b) 1200 UTC 28 August 2016 (WWP - BI =2.07), c) 1200 UTC 4 October, 2016 (SCA - BI = 3.73), and d) 1200 UTC 24 February 2017 (SCP - BI = 5.02). The center point at this time is labelled with an H.