Winter 2017/18 UK End-of-Season Report
As Spain, Britain went against the flow, having the past winter colder than average. The temperature was ~0.5°C below the average over England and Wales and ~1°C below the average over Scotland, compared to a climatology based on the most recent 10 years. January was the only month where there was a monthly averaged mild anomaly over a sizeable part of the UK (southern half of England and Wales), while February was a colder than average month over all parts, especially in the south.
The coldest weather of the winter came at the very end (and into early March), when a major sudden stratospheric warming in the polar stratosphere in mid-February triggered the development of intense high pressure over Scandinavia and the Arctic. This brought Siberian air rapidly south-westwards over the UK, with widespread snow and severe wind chill and frost.
Lows changed their tracks
A low-pressure track frequently displaced to the south of climatology resulted in a drier than normal winter over most of Scotland and northern England. We saw far fewer mild and wet spells sweeping across these areas than in a typical winter. Locations such as Cumbria and Lancashire, which have suffered severe and damaging flood events during several winters in the past decade did not have to endure these conditions this winter. Meanwhile, over southern and western areas of the UK, rainfall amounts were near or slightly above the normal, with most of the wet days occurring in December and January. February was a drier than normal month over all of the UK, but March was very wet, with more than twice the monthly rainfall falling in some southern areas.
The southerly displaced low-pressure track also resulted in a calmer than normal winter over Scotland and the far north of England. Nearly all of the deep low-pressure areas that crossed the UK between October and January produced their strongest winds over central and southern parts of England and Wales. From late January through to March, an increase in high pressure blocking weather patterns over northern Europe saw a distinct lack of strong and damaging wind storms over the UK.
The road salting crews were very busy last season, as there were plentiful nights of road surface temperature below zero and quite a lot of precipitation too.
Snow, snow, snow
Sunday December 10th, 2017 an area of low pressure moved eastwards across the far south of England. Just to its south, strong westerly winds, up to 70 mph (113 km/h), caused a few problems. However, the main issue was due to the heavy snow which fell on the northern side of the system, across parts of Wales and the Midlands. 10-20 cm of heavy, wet snow fell in just a few hours, which caused a lot of travel problems, despite the forecasts giving generally very good guidance. This was partly down to the intensity of the snow, as well as low traffic volume as it was a Sunday morning (so the salt doesn’t mix in so well with the snow). January 15th-18th 2018. A strong west to north-westerly flow brought frequent snow showers to Scotland and parts of northern England. 20-40 cm of snow fell in places, with drifting in the strong winds. Lightning was an additional hazard.
Siberian cold and …. snow
Late February into early March 2018: The Beast from the East. After a major Sudden Stratospheric Warming event in mid-February, a bitterly cold airflow from Siberia swept in from the east across northern Europe, including the UK. It was the coldest spell since December 2010, with some places having their coldest days since February 1991. Almost everywhere in the UK had snow, which was dry and powdery, and drifted a lot in the strong easterly winds. Storm ‘Emma’ (named by the Portuguese met. office) moved towards southern England and brought more widespread heavy snow (as opposed to the snow showers in the preceding days), especially to south-west England. Devon, a normally mild county, experienced drifts 3-4 metres deep. Additionally, slightly less cold air moved in for a time just above the ground, creating conditions favourable for freezing rain in parts of southern England. This added to the widespread travel problems.