I’ve just read a recent article in the weather and climate forum about severe winters and the enigmatic and elusive Scandinavian anticyclone. I could have used reanalysis data from NOAA, but decided instead to analyse the frequency of this particular weather feature with the help of the daily objective Lamb Weather Types from the UEA. It’s quite simple really, all you have to do is add up the occurrence of all days of a certain LWT, in this case these twelve types which I thought were the best associated with a blocked circulation and Scandinavian or Siberian anticyclone:
Then examine the LWT of each day in a Winter [DJF] and if it matches any of the types listed above add it to a total. At the end of each Winter, calculate the frequency by dividing the total by the number of days in the season and multiplying by a 100, then repeat the process for each Winter since 1871, before plotting the results as a scatter graph, with a 10 year centred average and linear trends (fig 1), and adding the results to a table of ranked frequencies in descending order (fig 2).
No big surprises really, all the old favourites are showing frequencies of 30% or more. 1962-63, 1946-47, 1978-79, 2009-10 & 1985-86. The interesting thing is the steady decrease in frequency of these combined types since 1871, they are down 4.3%. Even more striking is the decline of 11.4% since 1960! It’s no wonder that people of a certain age feel like someone’s shut the fridge door since their school days in the 1960’s.
I was just looking at the temperatures and precipitation in the UK for this last Winter (2016-17), and apart from being a comparatively dry Winter (especially December and January), it was also very mild (fig 1), in fact it was probably (in good old Carlsberg fashion) the driest and mildest since these particular records began back in 1910. Here’s the spread across all the various regions for this Winter (fig 2).
And just to see what a typical spread looks like in a cold Winter looks, here’s Winter 2009-10 (fig 3). As always email me if you see any discrepancies that you might see.
Yes, ‘split personality Winters’ is a bit of a weird title for a blog, but I couldn’t think of a better one at the time of writing this piece. What started me investigating, was just how the Winter of 1946-1947 suddenly transformed from being so mild in its first half, to be being so cold in its second. I wondered just how many more ‘split personality’ Winters (or seasons come to that) there have been down through the years. So I enlisted the support of the trusty daily CET series, which started in 1772, to see just how unique 1946-47 actually was as ‘split personality’ Winters go.
Here is a table of the meteorological winters [DJF] with second halves colder than their first halves (fig 1), and surprise, surprise 1946-47 is only joint eighth in the list. Top of the list is the Winter of 1854-55 (fig 4), the second half of which was 6.5°C colder than the first. The Winter of 1946-47 only managed a 3.9°C difference in temperature (fig 3), but thanks in part to the coldest February in the CET series back to 1659, and to the prodigious amounts of snow that came with it, it is burnt into the psyche of anyone interested in the weather and climate of the UK.
The temperature difference between the first and second half of Winter 1985-86 and 1941-42 was also greater than that of 1946-47, but neither were memorable. It’s understandable how we forget about weather events that occurred outside our own lifetimes and never directly experienced, I’m sure that the Winter of 1854-55 was talked about for the rest of the 19th century as being the winter of two halves, much in the same way as we talk about 1946-47.
I’ve overlaid, as usual, a moving average and a linear trend on the series of meteorological winters from 1772 to 2015 (fig 2), and it’s interesting to see how gradually the second half of winter has become colder than the first half over the past 244 years.
Because of the anticyclonic nature of this meteorological Winter with 58 days of it gone so far, the air frost count across the British isles is looking fairly respectable as you can see from figure 1. There is certainly a cold pole in central southern England due to the frosts of the last week, but there are still a number of stations holding out at zero air frosts so far this Winter.
An interesting chart plotting the total number of ice days (fig 2) across Europe so far this Winter, so if you think you that we’ve had a few hard frosts or even the odd ice day in the last week or so, have a look at further east and think again.
Of course, before someone points this out to me, ice days are when the temperature fails to rise above freezing over a 24 hour period, usually from 0900 to 0900. This chart is a count of days when the 06-18 maximum is less than 0°C, that’s because not all countries (including the UK & Ireland) report a 18-06 maximum along with their 18-06 minimum in their SYNOP reports, or an 06-18 minimum to accompany the 06-18 maximum come to that, so this will have to do. I won’t even bother trying to sort out the time zone issues a chart like this one (fig 2) that spans multiple time zones throws up.
Interestingly the French do report both a 12 hour maximum and a minimum in both their 06 and 18 UTC SYNOP observations, which is very sensible, they also report hourly rainfall totals which again I applaud them for, but I still won’t buy any French apples, not after they sank the Rainbow Warrior in 1985!
Winter 2016/17 is shaping up to be one of the most Anticyclonic on record. At the moment it’s joint third most anticyclonic in all ‘meteorological’ Winters back to 1871 (fig 1), using the daily Objective LWT from the UEA. It’s no wonder it’s been such a relatively dry Winter so far, and why there has been so many foggy days and frosty mornings. So despite the anticyclonicity we have seen very little in the way of easterly types (AE, ANE or ASE) so far this Winter (fig 2), although the circulation may have become blocked at times, it appears that the block may well have sat over or just to the east of the British Isles rather than over Scandinavia.
Here’s what the Autumn of 2016 (fig 3) and December 2016 (fig 4) looked like across Europe with regard to precipitation.
Of course this article will probably put the kiss of death on what’s left of the Winter as far as high pressure is concerned, and we will see non-stop gales right through February, but hold on, high pressure may still play a part in February’s weather according to the Met Office latest extended outlook (fig 5).
There are a lot of references to gales in the northwest in that forecast, the GFS seems to have other ideas about that for early next week though…
This solution is not supported at all by the ECMWF (fig 7), who seem to have problems labelling highs and lows at the moment…
But not to be outdone, they do manage to run a ferocious looking low up the English channel in ten days time (fig 8). I’ll be watching eagerly to see just how the Met Office do, and if any gales we do get in the next 30 days are indeed limited to the northwest.
I know this is a bit late for those of you that hold to ‘meteorological’ seasons, but for the traditionalists amongst us, publishing it on the 24th of December seems just about right. Tomorrow may bring the warmest Christmas day on record or it may not, and early in the New Year we might see a cold northerly outbreak, not that the North Pole is that cold at the moment and there is a distinct lack of ice in Barents sea. But despite all this there is everything still to play for in Winter 2016/17 – well that’s what I keep telling myself – and just to cheer you all up here is what happened in January 1947!
The blue stars are extreme low minimums and the red diamonds (todo: make the red diamond blue – Bah! humbug) are extreme low maximums that are still standing.
After a bad first month to their long-range weather forecast for Winter 2015/16 are things looking up for the boys at Exeter? I don’t usually put much credence in any GFS forecast frame beyond T+120 let alone T+240, so I may well be clutching at straws here, but the latest run does forecast a classic northerly for the 2nd of January. In the last 30 day outlook the Met Office did mention that there were signs of pressure building in mid Atlantic and northerly winds although there was “very little confidence attached to it“, perhaps this is what they were seeing, but until they release any of their NWP products we will never know.
And this is not just another flash in the pan (excuse yet another cliché), because the cold trough is still there three days later, so who knows this was just how January 1947 started.