It is 21 years ago this month that London and most of the southern half of the UK experienced a remarkably warm spell of weather during what had been a mild winter.
The spell, which saw the record warmest February day on the 13th (19.7C), satisfies the Met Office’s old criteria of a heatwave whereby the maximum temperature is 5C or more above average for five consecutive days.
While these spells are fairly common in summer they are very rare during a meteorological winter. During the last 60 years the only other periods to have experienced a heatwave in winter are December 1966 and 2015.
Weather charts for this week look remarkably similar though, according to the latest forecasts, values will be nothing like they were in 1998.
Since this was published this 2019 spell has satisfied the Met Office criteria. But the anomalies are not yet as impressive as 1998.
During a miserably cold and wet stroll around the golf course in Wanstead Park I happened upon the remains of Wanstead House – basically a deep excavation where the basement and kitchens once were.
As a freezing cold mixture of rain, sleet and snow fell, gradually thawing the remnants of last night’s snow, I wondered what the weather was like when this magnificent building last stood. Luke Howard’s entry in The Climate of London revealed that the weather on this day 200 years ago was remarkably similar.
Wanstead House around 1819 just before its destruction
February 1st 2019
As I stood and tried to imagine what the house must have looked like it occurred to me that 200 years is a mere blip in time in the history of the Earth. People come and go, buildings rise and fall but the weather goes on and on.
* There’s a fascinating extract on Wanstead from James Dugdale’s The New
British Traveller (1819) that you can find here.
** This video clip shows the site where Wanstead House once stood.
My winter forecast went a bit awry in December – I predicted a mean of +0.8C, the outcome was +1.7C. January has been much better, I predicted -1.2C, the outcome is -1.1C! Also… “And another cold spell end of January into the first week of February?”
For February I predicted a mean of -1.7C. The current pattern to continue and signs on the EC of a more robust cold spell with air supplied by a Scandinavian high?
More than three weeks have now past since the polar vortex split on January 1st.
London’s weather has turned colder and there’s even been a (small) fall of snow but the negative anomalies recorded so far are less than those experienced during the ‘Beast from the East‘ events last March.
In the graph below I have plotted the mean anomalies since the day of the PV split against the mean anomalies recorded from the day of the PV split in February 2018.
The effect this year is much less pronouced so far: over the last 24 days the average mean anomaly has been -0.7C, compared with -2.1C last February/ March.
The NOAA anomaly map for the week of January 13th-19th shows much of NW Europe has experienced a positive anomaly with any serious cold restricted to Norway and Sweden and Greece.
It has been mentioned that the variables with this SSW are very similar to 2004. Using the anomalies generated after the 2004 event resulted in the graphic below.
Taking it at face value would suggest that two more snow events could be possible at the beginning and middle of February – a cold but not severe pattern currently reflected in the models – but forget any repeat of last year’s Beast from the East.
Five years ago I blogged about the lack of snow at the midway point through winter. This winter there has been a similar total lack of snowfall though this time it is benign anticyclonic conditions that have characterised the past 45 days rather than the raging zonality of the winter of 2013/14 which ended completely snowless in this area.
A look at the statistics reveals that the midway point of winter is the mildest for 3 years and the 6th mildest since 1960. There has also been around half the rainfall that we had to this point in 2018. Sunshine is similar and below average.
Since December 1st, Wanstead has recorded just 7 air frosts – 5 fewer than last year. The coldest night was just -2.5C. The current mean temperature this winter to January 14th is 6.9C with rainfall 60.6mm.
Further scrutiny of stats for the Wanstead area reveal few years were similar to this winter. Using my method for finding patterns stretching back over 50 years to forecast this winter I picked out years that were +/- 10% of the 2018/19 rainfall total. From these I then weeded out the seasons where the mean was within +/- 10% of the this year. This gave a list of three winters with similar temperature and rainfall.
The other winters weren’t anything special with ‘snow lying’ days below the median for this area of six.
As I write there are signs that the weather is going to turn colder this week. Whether it will be cold enough for snow remains to be seen though the ECM model is hinting at a rise in pressure around Greenland. A situation that *could* be conducive for something colder long term.
In summary, the probability at this point of at least one fall of snow before the end of February could be put at 100 per cent. Whether it will be abundant or merely a dusting is impossible to tell.
Elsewhere in the UK it has been similarly lacking in snow. During a visit to Fort William at the weekend locals told me that there has been no significant snow since October / November and that even frosts were few and far between. The lifts around Nevis Range looked forlorn against a green backdrop. And it wasn’t until I got to the summit of Ben Nevis and Aonach Mor that I saw any of the white stuff.
Rain today (January 16th) is the first meaningful fall since before Christmas, putting an end to the 23-day long dry spell.
This meteorological drought, rare given that it spanned Christmas and New Year Storm singularities, these having 84 and 86 per cent probabilities respectively, was the 3rd equal longest winter drought.
The only other similar droughts in a list that dates back to 1887 were 19/12/2008 – 03/01/2009 and 17/12/1972 – 02/01/1973.
The last precipitation I recorded was from a weak occlusion that followed a cold front on the evening of December 23rd.
This synoptic set-up was followed by a build in air pressure that peaked on the morning of January 3rd; 1043.8mb was the highest reading in this area for at least 10 years and is the highest pressure I have measured.
A fuller version of London droughts in all seasons can be found here.
Weather models are continuing to struggle in the aftermath of the stratospheric sudden warming on January 1st. The GFS and ECMWF have flip-flopped: on one run decent northern blocking extends southward only for the dreaded European high to appear on the next.
Using a combination of QBO and ENSO data featured in my winter forecast and statistics from previous SSWs (including 2013 and 2018) achieved the following results shown in this graphic.
Although some days in the next week or so will be cold it is not until the 14th that conditions start to bite, the start of a week-long cold spell that will probably be more notable for cold than snowfall.
The rapid recovery in temperature would suggest that the Azores / European high making a return. With the MJO moving back and forth between phase 7 and 8, and looking at the behaviour of previous cold spells, this would make sense.
As for February, unless there are further SSWs to disrupt the polar vortex, and depending on its recovery, it is unlikely we will see a repeat of the winter of 1984/85 that I hinted at last month. The graphic below, however, would suggest another cold spell in the third week of February.
…And not a flake of snow. There’s been lots of talk about how an SSW will eventually usher in a cold January and February but it is by no means guaranteed.
The average maxima for this December will finish 10.2C, precisely the same as December 1985. Other Decembers that finished close to this average maximum are shown below.
As you can see apart from the middle of the month the temperatures are all over the place. And so are the conditions that followed in January and February.
A closer inspection of every year reveals that just three were very similar to 2018: 1974, 1986 and 1988.
Again, there’s plenty of spread. The 500mb reanalysis charts below show the situation of the northern hemisphere on December 31st of each year, including this year.
December 31st 1974
December 31st 1986
December 31st 1988
December 31st 2018
What followed in January 1975, 1987 and 1989?
January 1975 in this area was the warmest on record, back to 1797, while January 1989 was the 12th warmest. Conversely, January 1987 saw one of the coldest spells on record.
Perhaps it is fair to say that there is a 66 per cent chance of a very mild January, though you cannot discount the 34 per chance of another January 1987…