The term “backloaded” has been often thrown around since the Autumn season with some forecasters forecasting a backloaded Winter for Winter 2018-19 (including us here at Metcast) but what actually classifies as a “backloaded Winter”?
The term “backloaded” on its own means to defer something to a latter date. However, we use such a term frequently to describe seasons in the UK along with other terms like “fully loaded”, “middle loaded” or “front-loaded”. There is no official definition for a backloaded Winter as it’s used mainly informally but it can generally be described as a Winter that gets colder as the season passes, so the coldest weather of the Winter would be in around February whilst the mildest conditions would be in December. An example of a backloaded Winter would be 1955-56 where December was really mild and much of January was too but February was a severe month with a bitter easterly spell at the start of the month that resulted in subzero daytime temperatures and heavy snowfalls to the UK.
Front-loaded is the opposite way round with the coldest conditions in December and the mildest conditions in February. An example of a front-loaded Winter was 2010-11 where December was exceptionally cold (the coldest since 1890 for the long-term Central England Temperature (CET) series and the second coldest since 1659) whilst February was very mild and at that point was the mildest since 1998.
Meanwhile, fully loaded Winters have colder than average weather rather evenly spread out through each of the Winter months. An example of a fully loaded Winter was 2009-10 where each of the Winter months were colder than average and this resulted in the coldest Winter for the UK since 1978-79.
The rarest case, middle loaded Winters have colder than average weather focused on specifically January with the other two months on the mild side.
With December 2018 being a very mild month, though pale in comparison to December 2015, and much of January 2019 continuing to be on the relatively mild side, some people are thinking that time is running out and the clocks are ticking on Winter. Yes they are but we have all of February to go before it’s meteorologically over and March also tends to be a wintry month more often than December. 2018-19 will certainly not be a front-loaded or fully loaded Winter but there’s one more option for cold weather and that is a backloaded Winter. How often do backloaded Winters occur and what are some examples? For this exercise, we’re going to be looking at Winters with December CETs of around 0.5°C or more above average and February CETs of around 0.5°C or more below average; both against their respective 1981-2010 averages for the CET. February must also be colder than January for this exercise. There’s many ways you could change this criteria for a backloaded Winter definition though.
Last year was arguably a backloaded Winter by some as February and March were the coldest months relative to average of the extended Winter season with two severe easterly spells occurring at the end of February/start of March and mid-March. This was not a straightforward backloaded Winter statistically and in terms of snow as January was relatively mild for most of the UK and the mildest month. December was close to average with a fairly snowy spell around mid-month. November was also wintry in nature for places. Using our unofficial definition, this is not classified as a backloaded Winter.
In the CET series back to 1851, we found 17 Winters that fit our criteria above for a backloaded Winter. These Winters were 1985-86, 1983-84, 1980-81, 1977-78, 1955-56, 1954-55, 1953-54, 1951-52, 1941-42, 1929-30, 1918-19, 1900-01, 1894-95, 1863-64, 1857-58, 1854-55 and 1852-53. Some of the more notable ones are highlighted below.
1985-86 is a bit of a strange one to appear here as November 1985 was quite cold with a lot of wintry weather and with a CET of 4.1°C, it was the coldest since 1925. December was very mild for the most part in contrast with the Foehn effect leading to an exceptional mild spell at the beginning including a max. of 17.7°C at Chivenor, Devon. The month ended wintry though with some potent cold weather to the north of the UK. January had a lot of cold zonality and was relatively chilly. February was severely cold and it contained the most easterly winds since 1947 with a CET of -1.1°C . It was the fourth coldest month of the 20th century (and last subzero CET month before December 2010) and the second coldest February of the 20th century only beaten by the outstanding February of 1947. Further wintry weather were to occur in Spring including the coldest April since 1922. A Winter of flips and flops without a doubt and not a straightforward backloaded Winter especially with the cold November.
1977-78 was a more clear cut backloaded Winter as both November and December were mild. January acted as a transition month with some bouts of wintry weather. February was the coldest since 1969 with a cold and snowy spell during mid-month culminating in the great West Country blizzard which was the worst since at least 1947 in these regions. Snow accumulations were between 30-40cm and drifts were as much as 8m in Exeter and Cardiff.
The trilogy of backloaded Winters from 1953-54 to 1955-56 all had mild Decembers and cold Februaries with mixed Januaries. The Februaries got more severe each time in terms of the depth of cold and snow. February 1956 was the fourth coldest February of the 20th century with a CET of -0.2°C. February 1955 stands out especially for the February record low of the 20th century and the coldest temperature for any month in the UK since February 1895 with -25.0°C at Braemar on the 23rd.
1894-95 was one of the coldest Winters on record. February 1895 was the coldest February on record before 1947 with a CET of -1.8°C. It was an exceptional month on the whole with lots of heavy snowfalls brought in by a very cold easterly wind. It was the last time there was going to be a subzero monthly CET until January 1940. The UK record low temperature for February was set at -27.2°C on the 11th at Braemar which would later be equalled twice in January 1982 and December 1995. Braemar recorded an air minimum of at least -20°C during 9 days in February 1895. January was a severe month too with a CET of 0.2°C. In contrast, December 1894 was relatively mild at a CET of 5.1°C.
2012-13 didn’t quite fit the criteria we set but most people would associate it as a backloaded Winter due to each month simultaneously getting colder and colder in terms of mean temperature up to March and March 2013 being the coldest month of the extended Winter season – the first time March was so since 1936-37.
There’s an analysis on some historical backloaded Winters using criteria we set for this exercise specifically. You can look at it in different ways and come up with different criteria to classify a backloaded Winter.
Will 2018-19 be a backloaded Winter? Certainly a possibility but it’s a case of wait and see. Could, could not. Nobody really knows.