Recent circulation indices

An abrupt start to autumn 2020 is evident in these six charts of various objective LWT circulation indices since the 7th of July 2020. Mean pressure has been falling away since the second week in September, with an increase in both cyclonic types and in cyclonic and northerly shear vorticity, which has introduced more unsettled weather and gradually lowering temperatures. The two storms in August are prominent in the gale index bar chart, but storm Alex passed unnoticed because the gale index is for the fixed location of 55N 5W in the objective LWT data from the UEA. From the look of the circulation types we are overdue an anticyclonic interlude, but the chances on average of such a spell diminish as we go through October as the chances of an cyclonic spell increase.

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