Subsidence inversions – the surface water vapour thief

Abstract A deep anticyclonic subsidence inversion reached near‐surface levels over southern England on 25 April 2026, resulting in relative humidity levels falling below 15% widely and sub‐10% in the Reading and Wokingham area. Such low levels in lowland England have very few historical precedents within the last century or more. Furthermore, careful analysis of the automatic weather station psychrometer records from the University of Reading Atmospheric Observatory on this occasion suggests that the relative humidity here may have fallen briefly below 6%.