So cold that the first of the daffodil in the Olympic Park has already opened.
We seem to be deep into a big chill at the moment, a run of at least ten days with temperatures dipping below zero at night and rising no higher than 5°C during the day. But how unusual is that?
I've dug back into my favourite meteorological archive, the NW3 weather station at Hampstead, and counted up the number of days it's got cold over successive winters. In particular I've counted...
• the number of days the temperature stayed below 5°C all day
• the number of days the temperature stayed below freezing all day
• the number of nights the temperature fell below freezing
n.b. I've counted every chilly day between one summer and the next, the earliest being in October and the latest in April.
n.b. Hampstead is 200ft above sea level so a bit cooler than central London, but also benefits from the heat island effect so a bit warmer than locations further out. Unless you live in Hampstead the data isn't going to reflect where you live. But what's really interesting is the variation and the underlying patterns, and they work relatively well wherever.
Winter
days staying below 5°C
days staying below 0°C
nights going below 0°C
2009/2010
49
0
39
2010/2011
41
5
38
2011/2012
17
0
19
2012/2013
50
2
41
2013/2014
1
0
5
2014/2015
17
0
15
2015/2016
8
0
10
2016/2017
14
0
20
2017/2018
25
3
30
2018/2019
13
0
13
2019/2020
0
0
6
2020/2021
30
0
25
2021/2022
7
0
14
2022/2023
?
?
?
The chilliest recent winters were 2009/2010, 2010/11 and 2012/13, each with over 40 chilly days and about 40 freezing nights. Even so there have only been 10 days since 2010 when the temperatures has failed to exceed freezing, and none at all in the last five years. There have also been some ridiculously mild winters, notably 2013/14 and the absolute outlier of 2019/20 when every day managed to stay the right side of 5°C. With energy prices at an all time high we could really do with another 2019/2020, but 2022/23 is already careering towards the centre of the distribution and we're not even halfway through December yet.
Now let's try looking month by month...
Month
days staying below 5°C
days staying below 0°C
nights going below 0°C
October
0
0
1
November
13
0
21
December
69
5
62
January
97
2
92
February
73
2
56
March
18
1
32
April
2
0
9
Adding up the figures for all 14 winters we see that January is generally the coldest month, as you might expect, with December and February roughly on a par. Meanwhile March is chillier than November and April is chillier than October because early spring tends to be colder than late autumn. The sun may be higher in the sky in spring but autumn benefits from summer's heat baked into the ground and that's all disappeared by midwinter.
Another way of looking at variation might be to consider the date of the first emerging daffodil in the Olympic Park. I can't claim that all these dates are bang on, but yet again 2019/2020 lays claim for the winter that barely happened.
• 15th December 2019
• 1st December 2020
• 12th December 2021
• 9th December 2022
n.b. we reckon these daffodils are Rijnveld’sEarly, a species predisposed to start flowering in December/January rather than the more usual February/March.
These figures prove nothing about climate change because annual variations in weather trump any underlying warming trend. 2022/23 is certainly getting off to a colder start than any winter since 2010/11, but several more weeks of potential chill or warmth remain so who knows how it'll end up. Fingers crossed we can take our gloves off soon.
