Deep and crisp and even

Given the fact we had about a week of lying snow last month, and that I’ve already been asked ‘is that it for this winter?’, I thought some statistics on lying snow here in Reading might not go amiss.

We have complete day-to-day records of the dates with lying snow (defined as a coverage of at least 50 per cent over the ground at 0900 GMT) at the University going back to 1948 with the actual measured snow depth on all but 38 days back to 1951. Note that the observing site moved to the Whiteknights campus from the London Road area in 1968.

So how often does snow lie in Reading at 9 a.m.? Over the period 1981-2010 (our most recent 30-year climatological period) the figures (shown in blue) are as follows:

The climatology of lying snow days in Reading.

This recent period shows a decline in lying snow with respect to 1951-80 (red), while anyone who has only been in Reading for a few years will only be familiar with the green plotted bars – and may not realise how fortunate they are (assuming they are snow lovers!). My own daughters – now both at university – had many a winter in which their sledges remained in the garage. Unfortunately, across southern England this is about as good as it gets, unless you venture into the hills – see this chart from the Met Office’s current 1981-2010 averages webpages (http://www.metoffice.gov.uk/pub/data/weather/uk/climate/averages/maps/uk/8110_1km/SnowLying_Average_1981-2010_17.gif):

Met Office: UK-wide snow lying days each year.

So how much variation is there in the annual incidence of lying snow? The next figure gives the answer:

The variation of lying snow days in Reading, 1948-9 onwards.

Winters without lying snow occur roughly every nine years. Winters with ten days of lying snow occur quite frequently – once every 3.8 years on average although only twice from 1986 to 2008. Winters with 20 days of lying snow are rare (5 years in 64) while the winter of 1962-63 stands in a class of its own – having 54 mornings with 50% snow cover (with most of those on consecutive mornings in January and February). Recent winters do seem to indicate that lying snow has become more prevalent.

Of course ‘days with lying snow’ gives no indication of the snow depth and its persistence. One way to judge that is to follow the suggestion of Philip Eden and to note the cumulative snow depth during the season (the cumulative snowfall is very difficult to measure in the UK as often rain and snow fall within a short space of time and separating the one from the other requires keen and frequent observations).  The cumulative snow depth is simply the sum of all the 0900 GMT snow depths added together during the (autumn-) winter (-spring).

Cumulative winter snow depths in Reading, 1951-52.

Again, 1962-63 stands out – but 2009-10 also makes an appearance. This is due to the great depths of snow recorded that winter, for example

  • 11 cm on 22 December 2009 and 10 cm on 23 December 2009;
  • 27 cm on 6 January 2010, 26 cm on 7 January 2010 – decreasing slowly to 9 cm on 15 January before clearing the next day.

This 27 cm was the greatest snow depth at 9 a.m. in Reading since 31 cm on 3 January 1963 (this latter depth following depths of 28 cm and 27 cm on the previous two days) – and this depth in 1963 was the greatest any University of Reading observer had ever measured.

The other winter that stands out in this image is that of 1981-82 – that winter lying snow occurred from 8 December, on and off, to 17 January. (Even more memorable that winter was the cold – minimum temperatures of -14.5 °C on 14 January following on from -13.4 °C on 13 December, temperatures which helped the snow cover to persist.) The former temperature was the lowest air temperature ever recorded at the university’s climatological station.

So what about the remainder of the winter? – forecasts currently suggest a ‘slight’ cooling in the air temperature over the next couple of weeks and statistically February (March) sees lying snow in about one year in two (three). In February 1986 snow lay for 15 days in Reading having been virtually absent up that point. Thus we may yet see some more of the white stuff lying – in 2008 snow lay 6 cm deep as late as 6 April (the deepest April depth in Reading since before 1951)…

Snow cover of 6 April 2008.

…and some were not amused!

Written 6 February 2013.

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