Is our weather getting more stormy?

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Courtesy of the BBC

Now that we are getting into the stormy part of the year I thought that I would have a look back and see if the weather in the UK was getting more stormy in recent years. I don’t have access to climate statistics or any detailed anemograph records for the last 145 years, but I do have some thing that is probably a whole lot more useful in helping me to find the answer to that question a lot quicker, and that is the daily National Centers for Environmental Prediction [NCEP] reanalysis data back to 1871. Simply put, that is a grid of six hourly daily pressures values [MSLP] on either a 2° or 2.5° grid for the whole world. The Climate Research Unit [CRU] at the University of East Anglia [UEA] have done all the hard work really, because they used this reanalysis data to calculate daily statistics for the Objective Lamb Weather Type [LWT] series. Apart from producing a daily LWT, a by-product of these calculations is a Gale Intensity or Gale Index [GI] value. So there are a couple of caveats with anything that you find when using the LWT series, and those are that the GI is for a fixed place [55°N and 5°W]  in SW Scotland, and the GI is just for the 1200 UTC observation, so it’s a little basic. But the good thing is that the data series is long and easy to use. The first chart is of annual gale index values since 1871, and a s you can see from the linear trend the index is 6.9% higher now that it was at the start of the series.

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That 6.9% increase in the annual gale index since 1871 equates to an increase in 12.9 more days of gale in a year during that time. Incidentally the GI does not directly correspond to a wind speed in knots, so that a GI of 30 or more is equivalent to a gale (34-40 kts), a GI of 40 or more is equivalent to a severe gale (41-47 kts), and a GI of 50 or more is equivalent to a storm (>=48 kts).

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The anomaly chart below shows more clearly when the gale index began to increase, and as you can see it’s been mainly since around 1980 that it’s shown a concerted increase. 1990 for instance was a remarkably stormy year, but equally there have been occasional quiet years like 2010.

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If you look at the seasonal analysis through the year, all seasons show a similar ~7% increase in GI. This is the chart for Winter which shows an extra 5.8 gale days since 1871.

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So the short answer to the question that I posed in my title is, yes, that’s if the gale index in the objective LWT series is anything to go by. Why it’s getting stormier is another question, and one that I am not even going to try to answer!

 

Unprecedented early intense Scandinavian high?

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The maximum central pressure of the anticyclone over Scandinavia at midnight (5 October 2016) was 1051 hPa, which I thought was very high and unusual for early October, so I went delving into the synoptic charts for pentad 56 (2-6 October) with the aid of the objective Lamb Weather Types [LWT] from the University of East Anglia [UEA].  Below is a analysis of pentad 56 for 1871 to 2015 ranked on the highest pressure over the LWT area, and as you can see October 1945 tops the list.

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The 2nd of October 1945 was very anticyclonic, but the high was over central England and not Scandinavia and not intense enough, so much for the highest pressure.

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Courtesy of Wetterzentrale

If you do a secondary sort on the highest mean pressure to find the highest E’ly component in pentad 56 then the 2nd of October 1902 comes out top, and although quite similar (if you ignore the missing vigorous low near Iceland), the high is still not as intense as the that sits astride Norway and Sweden at present.

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Courtesy of Wetterzentrale

Then I checked out the fourth in the original list and I found a much better match, not perfect but close, again forget the vigorous low of 959 hPa nearing Iceland on last night’s midnight analysis. Interestingly it even has a similar cold-pool over the low countries even though the central pressure of the high in 1902 is still around 6 hPa lower than the 1051 hPa of 2016.

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Courtesy of Wetterzentrale

That’s about the best I can do in searching out an analog to match the current intense anticyclone over Scandinavia. Why do I look? Because the synoptic patterns in October have always been seen as some kind of guide to what the forthcoming winter may bring. And this, if you’re curious, is what the central England temperatures [CET] were like in the following winter of 1881-1882. Another cold December in the offing maybe?

daily-cet-winter-djf-1881-82

Tri weather data sets

A bit of a strange title I know, but I’ve recently written an application that displays climate data for the UK from three separate daily data sets for atmospheric circulation, temperature and precipitation, and hence the tri.

  • Daily Central England Temperature [CET]
  • Objective Lamb Weather Type [LWT]
  • UK regional precipitation series [HadUKP]

It’s not the first time I’ve merged weather data sets in a single application, but this is probably the first time I’ve managed to finish it and publish the results that it generates. The essential requirement of course is a source of regular daily weather data, and so the CET and LWT series were the ideal (and only) choice because they are both updated on a daily or weekly basis. The other daily weather set that fits was the HadUKP series that the Met Office maintain, but there are a couple of problems with this series, one being that is only updated on a monthly basis, and the other is that the series isn’t very long and only extends back to 1931, and not 1772 and 1861 as in the case of CET and LWT. The big plus for anyone interested in the climate of the British Isles is that you can explore the climate of a particular day, week, month or season very easily and quickly. Here is a screenshot of the application as it stands now:

LWT-CET-UKP application

LWT-CET-UKP application

Below are a few examples of some particular well-known periods and spells of weather from the past, starting with a look at last Autumn and Winter.

27 Sep 2015 - 20 Mar 2016

27 Sep 2015 – 20 Mar 2016

You can certainly see the lovely anticyclonic spell that we had in September 2015, and the record mild November and December that followed, in this six month overview. Next a four-month window and a look at the Winter of 1946-47, you can clearly see how the cold started with an anticyclonic spell in the second half of January 1947, with the snow following along at the start of February.

1 Dec 1946 - 23 Mar 1947

1 Dec 1946 – 23 Mar 1947

Here’s the summer of 1976 and the record warmth of late June and early July, notice also the preponderance of anticyclonic types up until the start of September, then the breakdown into more cyclonic weather and the rains that brought an end to the drought.

18 Apr 1976 - 17 Oct 1976

18 Apr 1976 – 17 Oct 1976

Here’s the great winter of 1962-63, in comparison to 1946-47 it’s clear that winter 1962-63 started much earlier (before Christmas) and finished earlier, but was also drier and more anticyclonic.

16 Dec 1962 - 24 Mar 1963

16 Dec 1962 – 24 Mar 1963

Improvements

I could maybe add an extra chart in the shape of a ‘barograph’ because I hold all the mean pressure points in the LWT data. I could present that as a scatter graph of all the 16 MSLP grid values for 12 UTC and then plot a moving average. I could also highlight with a star the named storms, but that would only work for the very latest years. I could also colour the precipitation bar chart blue to indicate snow rather than rain when the CET was less than 1 or 2 °C (I have in fact now implemented that idea as you can see if you look at the screenshot of the application!). I do plan to add functionality to show a grid of archived weather charts for the selected period from Wetterzentrale. The one element that I think it does miss is daily sunshine data, but there is no source that I know of for daily sunshine values for a region, let alone for a single station, so that’s a non-starter. I must say that this really is an excellent tool for any climatologist with an interest into the weather of the British Isles over the last 150 years or so.