diamond geezer

 Friday, December 29, 2017

As another year draws to a close, I thought I'd look back at what the weather's been like. Not because it's something we all want to reminisce over, but because I thought it'd be interesting to see what a full year's weather looks like.

The tables below show the weather for each day in 2017, grouped into categories and totted up by month. Yes, there are still three days to go, so I've used the forecast to predict the rest, and I'll come back later to update speculation with fact. You'll see I've blanked out the background of every empty cell, to make the pattern of the coloured data stand out more, and emboldened any tally that enters double figures.

This is data from a weather station in Hampstead, so won't perfectly reflect your experience, nor the national picture. But it does present an interesting picture of the year gone by, and who knew the weather wasn't really that bad?

Maximum daily temperature, Hampstead, 2017

30-35°C      51     
25-30°C    15384    
20-25°C   11815192261  
15-20°C  16151373523223 
10-15°C 51422125   181110
5-10°C 161021      1514
0-5°C 103        17

Yes, we did have a summer this year - there were six days when the maximum temperature in London topped thirty degrees, and another twenty when the temperature topped twenty-five. That doesn't sound like many, but with a hundred days making it past the 20°C mark there was plenty of short-sleeve weather to go around. The impressive month here was June, with maximum temperatures running three degrees above the long-term average, and a particularly sultry peak around the summer solstice. March was also around three degrees warmer than it should have been, indeed it was a mild spring overall, which is only fair following a coldish January. Around twenty days failed to reach 5°C, which is twice as many as last year, but temperatures never once remained below freezing all day (thanks to the inner London heat island effect).

Minimum daily temperature, Hampstead, 2017

15-20°C     291410    
10-15°C  4611320171919172 
5-10°C 692020161 211131011
0-5°C 121559     11613
-5-0°C 13         27

Minimum temperatures show a similar up and down pattern. Thirty-five days this summer had nights with temperatures exceeding 15°C, ideal for sitting outside, and the temperature pretty much never went below 10°C throughout the summer. March enjoyed more than its fair share of mild nights, relatively speaking. Meanwhile there were as many as twenty nights, mostly in January, when the temperature dropped below freezing - again anywhere outside central London will have had rather more.

Hours of sunshine, Hampstead, 2017

12-15hr    54732    
8-11hr 3 463768541 
5-7hr 6285857113694
2-4hr 3949948313866
0-1hr 117104244476105
0hr 81051533327416

We're not used to seeing actual sunshine data, more usually simplifying the weather to "gosh it's sunny" or "oh it's dull". This year we've enjoyed twenty days with over twelve hours of sunshine, all of them in the middle of the year because the sun's not above the horizon long enough at other times. Meanwhile one hundred and forty days saw only one hour of sunshine or less, with over sixty days having no sunshine at all. December has been the month with the greatest number of entirely overcast days, while February was the most uncharacteristically dull month. January turns out to have been the month which most exceeded seasonal expectations, indeed all those blue skies help explain how it managed to get so cold.

Daily rainfall, Hampstead, 2017

>20mm    1 11    
10-20mm2   22111 12
5-10mm322  13351 4

It doesn't rain that often in London, with two hundred and twenty days this year (the bottom row) completely dry. Even most of the wet days aren't that wet, with only forty days exceeding 5mm, and fifty days sprinkled with less than 1mm. The true downpour days have over 20mm of rain - that's pretty much relentless - and there are only three of those. February and September had the most wet days, but July turned out to be the wettest month, which may confirm your worst suspicions about the summer. Meanwhile April was by far the driest, with barely a splash in the Hampstead gauge. But rainfall is a notoriously erratic statistic, often varying wildly geographically, and one torrential outburst can outrank weeks of lighter precipitation.

Extreme weather, Hampstead, 2017

Fog 1 11     1  
Frost 13         26
Snow 22         1
Hail   11        
 Thunder         1   

Finally, still based on observations in Hampstead, a look at some of the more unusual meteorological conditions. Fog has been infrequent this year, with much clearer skies than last. Air frost was particularly prevalent in January, but London's outdoor plants were then unaffected until the last day of November. Of the five days of snow, only one in January and one a few weeks ago amounted to any more than a flurry. It only hailed in spring, and as for thunder, 2017 has been unusually rumble-free. But overall, as you'd expect, the weather has been fairly ordinary. Here's to more typically atypical weather in 2018.

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