In this issue of Weather

Abstract

I was secondary‐school age in January, 1987, when one of the coldest airmasses for decades overspread much of the UK. I have vivid recollections of fluffy powder‐snow, big drifts, and several days off school where we lived in Bracknell, Berkshire. We didn't even have the worst that this particular event threw at the UK: parts of East Anglia and Kent had continuous heavy snow, gale‐force winds, and midday temperatures close to −10°C! February 1991 brought another bitterly cold easterly flow. Many people will remember the infamous ‘Wrong kind of snow’ which was emblazoned across newspaper front pages after British Rail cited the fine powder snow as the prime reason for their fairly new Class 91 electric locomotives failing on the East Coast mainline. Having moved with my family to Devon by this stage, I was very disappointed to observe very little snow from this, although the harsh frost and strong winds froze everything solid. Major easterly outbreaks have, thus, made quite an impression on my meteorological memory, and I suspect many other readers will have had similar experiences. In more recent decades, a lot of attention has been focused on ‘teleconnections’—the notion of climate anomalies being related to each other over large distances, the most famous of these being the El Niño Southern Oscillation (ENSO). Such teleconnections, when used in conjunction with each other, and against historical analogues, can give some credible indicators about upcoming weeks, and even seasons. Of particular interest to cold weather fans is Sudden Stratospheric Warming (SSW). In essence, upward‐breaking synoptic‐scale waves from the troposphere can induce a strong warming in the lower stratosphere above the Arctic, occasionally leading to the breakdown of the polar vortex, the cold‐season cold pool which forms over the high latitudes. When such a breakdown occurs, it can ‘drip down’ easterly flow into the troposphere, and cause strong blocking anticyclones to develop at the higher latitudes, eventually leading, on occasion, to bitterly cold easterly winds across the UK. In late January and early February 2018, forecasters latched onto the fact that a major SSW and polar vortex breakdown was occurring, and thus were able to predict, with some confidence, that a much colder pattern was likely to emerge later in February and into at least the start of March. Sure enough, in late February easterly winds transported a significantly cold airmass across NW Europe, including the UK. This special issue of Weather gives a meteorological analysis of this cold spell by Katie Greening and Amy Hodgson on p. 79; then Eddy Graham and Jonathan Webb look at the very deep cold pool which overspread the UK between late February and early March on p. 85. There follow a number of observational papers which detail the effects of this very cold spell, including information about the various ice and snow related phenomena which accompanied it. On p. 92, Keith Fenwick looks at freezing precipitation in Devon; James Robbins and Philip Gill describe hair ...