Wrap up well for St Valentine’s Day – a good chance of snow!

By Roger Brugge

The days are getting longer, the nights are getting shorter, but the temperature keeps falling – and so does the snow. At least in the climatological statistics they do!

Looking at the date of occurrence of the lowest temperature of the year over the past 108 years in Reading (Figure 1) we find that the average date of the coldest night is 16 January (with the dates of 18 December to 14 February lying within one standard deviation of this date). The complete spread of dates is rather more than might be expected, from as early as 13 November (‑5.3 °C in 1921) to as late as 5 April (-3.3 °C in 1990).

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Figure 1. A histogram of the date (day of the year) of the lowest temperature each year from 1908 to 2015 in Reading.

The year 1921 had seen a lack of low temperatures during the first three months of the year (down to -3.1 °C in January, but then came three air frosts and three days with snowfall in mid‑April) while in 1990 there were four mornings with an air frost in April – a monthly total only surpassed that year by December (9 mornings).

Thus, in terms of the lowest temperature of the year, the first week of February (days 32-38) is beginning to show signs that the coldest night is past – but there can still be a sting in the tail of winter for gardeners.

What does the average daily temperature tell us? Defined as average of the highest and lowest temperatures of the day, the evolution of this by day during winter and spring is shown in Figure 2.

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Figure 2. Daily mean temperature in Reading averaged over 1981-2010, from 1 November to 30 April.

This shows a notable dip around mid-February, with the 14th being (on average) the coldest day of the winter, and the only day in the year when the mean minimum temperature in Reading falls below the critical 0°C mark. What does that say about St Valentine’s Day?

Moreover there is also a peak in the incidence of snowfall at this time of year – snow or sleet fell eight times in the 30 years 1981-2010 on 8 February, with seven occurrences on the 9th. Statistically, this makes 8 February the most like day of the year to experience snowfall in Reading while 9 February is as likely to see snowfall as 7 January. Perhaps not surprisingly, 9 February is the morning most likely of any during the year to have snow cover on the ground at 0900 GMT.

So don’t put those sledges back in the loft just yet!

And finally …

Interested in local weather? Come along and learn more at this week’s University Public Lecture, One hundred years years of Reading’s weather by Stephen Burt and Roger Brugge on 10 February 2016 at the University of Reading. This illustrated lecture tells the story of Reading’s weather over the past hundred years and more using a combination of archived logbooks, contemporary photographs and today’s sophisticated automatic weather measuring equipment. Pre-registration essential – booking details here.

 

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