What is a “White Christmas”?
For many people a White Christmas is a Christmas Day (25 December) with a ‘traditional’ look to the day – that is one with snow covering the ground. For those whose fancy a flutter at the bookmakers (although it is probably too late to get good odds now) a White Christmas is one when snow or sleet is observed during the 0000-2359 h day. This latter definition includes a wet and damp with a few flakes during a shower of sleet on a day when rain is the dominant form of precipitation. In fact William Hill are slightly more restrictive with their White Christmas betting rules which state they pay out only when ‘… one flake of snow will fall on Met office monitoring stations over the 24 hr period of the 25th of December’.
Weather on past Christmas days
Here at Reading weather observations are made at 0900 GMT (9 a.m. in the morning in winter) every day of the year and in this note we will examine the incidence of
- Snow/sleet falling at some time during the 24 hours beginning 0000 GMT [SF annotation below],
- Lying snow at 0900 GMT [SL annotation below], and
- A measurable depth of snow at 0900 GMT.
We currently have records for every Christmas back to 1917 (in 1916 there was almost certainly a fall of sleet/snow on Christmas Day) and these indicate the following years when one or more of the above events was noted on 25 December:
1925 [SF] – The 9 a.m. air temperature in a NE’ly wind was 0.8C (following a slight air frost) and this subsequently rose to 8.2C in the next 24 hours. Some light snow fell during the day but it then turned dull in Reading with light rain. Further north, snow lay for in both Manchester and Glasgow. The state of the ground is not known for this day in Reading although it is not thought that a 50% snow cover prevailed.
1927 [SF] – According to Robin Stirling (in “The Weather of Britain”) “A depression from the Atlantic moved from Ireland to the English Channel and then across France to the Mediterranean. It caused a great snowstorm in southern England. About 18 h on Christmas Day, rain in the south turned so heavy that roads were hopelessly blocked by midnight, and a train was snowbound between Alton and Winchester.” As the storm continued some 15 cm of snow fell in central London. In Reading the 25th began with an air temperature of 6.3C at 9 a.m. – then rising only to 6.8C before dropping to -0.4C the following night. There was moderate rain falling in an E’ly wind at 9 a.m.; the rain became heavy at times and turned to snow fell later in the day (9.9 mm of water equivalent precipitation fell in 24 hours) – although, again, snow depths were not reported at Reading. However, newspaper accounts report that locally, a considerable stretch of the Reading to Henley road was under five feet of snow by Boxing Day (26th). “The Berkshire weather book” by Currie et al. carries an interesting account of the Boxing Day blizzard in Berkshire and adjacent areas.
For intensity, extent,damage and disruption many would argue that this snowstorm was the most damaging since March 1891 and probably the most severe snowstorm of the twentieth century in the UK. South-east of a line from Norwich to Dorchester over 30 cm of snow fell (Eden, 2008, “Great British weather disasters”) with 60-75 cm over parts of the North Downs in Surrey and the Weald in Kent. A-roads were blocked for up to a week – minor roads for much longer. The snow was of a high water content and hundreds of kilometres of lines came down as a result.
1938 [SL] – The 25th dawned with a minimum temperature of -0.3C and lying snow (depth unknown, although it had been lying from the 21st) after several falls of snow that fell over several days back to the 18th and in which time the temperature had only reached 2.3C. The temperature rose to just 0.6C on the 25th; no snow fell on Christmas Day (which was dull and cold) – but did fall on the 26th. Across the local area it was more the cold that caused problems in the run up to Christmas – with many frozen pipes and a very large demand for paraffin for heating.
1956 [SF] – After a dull, cold start to the day, a SE’ly flow brought some snowfall during the 25th with the temperature rising from -1.4C to 1.8C. Some 5.3 mm of water-equivalent precipitation fell leading to about 5 cm of lying snow on the 26th at 9 a.m. (so almost all of this precipitation would have been snow). The snow was initially light and turned heavier later. Locally snow was ‘several inches [~10 cm] deep’ (Currie et al.) later on the 25th in parts of Berkshire.
1968 [SF, SL] – This was one of the few Christmas Days when the Reading weather observer had to contend with falling sleet and snow at the observation time. At 9 a.m. conditions were air temperature 0.6C (after a minimum of 0.1C), sky obscured by falling light rain and snow (there had been a spell of continuous snowfall early in the morning), with a NE wind of 2 kn, visibility of about 400 m and 8 cm of lying (but thawing) snow. The temperature rose to 2.8C later in the day as the clouds thinned out and just 0.3 mm of precipitation fell in the next 24 hours. As a depression moved ESE’wards across Cornwall some places were cut off by blizzards in N England.
1970 [SF, SL] – Christmas Day began with a minimum temperature of -3.9C and 1 cm of lying snow. The temperature rose later to 0.9C and snow fell during the day to give a depth of 5 cm the next morning. However, on the 25th itself the snow was in the form of a shower before noon – more persistent snow was to fall next morning. Despite the morning snow, some 3.5 h of bright sunshine was recorded – with only 2 oktas of cloud at 9 a.m.
1981 [SL] – There was a cold start to this Christmas morning – the temperature had risen from a minimum of -4.5C to -3.4C by 9 a.m., although the grass minimum temperature had been as low as -10.2C. The ground was frozen to a depth of just over 5 cm under 5 cm of lying snow. No snow fell during the day, which was dry and sunny with 4.5 h of bright sunshine. This was one of the snowiest December’s of the twentieth century – on the 12th the snow depth in Reading had been 18 cm.
1996 [SF] – By now many people had begun betting on the likelihood of a ‘White Christmas’ and this year brought a pay-out. In Reading, after a slight air frost, some snow fell – but not enough to give a 50% ground cover at 9 a.m. With 3.5 h of sunshine during the day any lying snow had melted by Boxing Day morning.
1999 [SF] – Another day when the bookmakers had to pay out – certainly snow fell in Reading but not enough to lie on a ground surface that was ‘moist’ after some 43 mm of rain in the preceding 72 hours. In Reading rain turned to snow around 11 a.m., only to turn back to rain after about ten minutes. It was a cloudy day with another 7.2 mm of precipitation being credited to the 25th. It was a windy day with a gust of 43 kn measured at the university.
2009 [SL] – After a minimum temperature of 0.9C it warmed up to reach 8.4C later, the warmth helping to reduce the 5 cm of complete ground cover of snow (this had persisted since the 18th, having caused some severe pre-Christmas disruption to Reading) to a broken cover of 2 cm depth by the morning of the 26th. No snow fell during Christmas Day, which brought some rain and some sunshine.
2010 [SL] – Again, there was no snowfall but lying snow existed at 9 a.m. to a depth of 2 cm. This lying snow remained rather broken in cover and helped the temperature to drop sharply into Boxing Day down to -6.5C in the screen and to -11.3C on the grass.
A White Christmas in 2012?
In summary then, in the past 95 years there have been seven Christmas Days with snow falling and six with snow lying in the morning (1968 and 1970 fall into both camps). So the likelihood of a White Christmas as the bookies judge it is about one in 13.6 – the last one was in 1999 so we are (maybe) due for one soon…
Those who would like to read about the incidence of a White Christmas elsewhere in the UK should start also read Martin Rowley’s account at http://booty.org.uk/booty.weather/metinfo/snxm_cat.htm .