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.
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.
With talk of an imminent statospheric sudden warming (SSW) I thought it would be interesting to have a look back at previous SSWs and see what precedents could be found.
December so far is showing similarities with 1984: mean maxima is within 0.3C of 1984 while rainfall is virtually the same at around 30mm!
During the winter of 1984-85 the polar vortex split on January 2nd, setting up that month to be among the coldest of the 20th century, on a par with 1979 and 1987. A more recent January that was just as cold was 2010.
Indeed, the winter of 1984-85 was among the snowiest of the past 70 years, ranking at number 5 in my survey of winters.
The GFS model is now within range of the big day on the 25th. From now until Christmas Eve I will be having a look to see what is on offer.
The first operational run suggests something of interest but please bear in mind there is a long way to go yet. While operational runs are often exciting, the below suggests a potent northerly with snow for many, the right hand average is much more realistic though admittedly boring.
My own guess at this stage is for something benign, a high of 6C with a low of 2C, perhaps some frost early or late on?
10th: Op run this morning is showing quiet weather. A high of 4C after overnight frost.
11th: Op run now shows a slack north-easterly and possible snow.
13th: An anticyclone to the north of Scotland continues to keep things seasonal on the op run this morning. The average again benign.
14th: More interest on today’s midnight run. The op shows a cold pattern. Frost early and late and a high of 2 or 3C. A chance of flurries. Even the average looks less mild!
15th: The interest of yesterday has faded. Not terribly mild but not cold either. Xmas morning starting chilly, 6C with rain in the evening, a warm sector bring the temp up to 10C in the evening. The average suggests something similar.
17th: All change again on the op run today with an Atlantic ridge with plenty of cloud. High 7C Low 4C. Gloomy. The Average less settled…
18th: The op this morning suggests the 25th will be something of a changover from the present regime to something more settled. The op chart suggests a temperature of 9C day and night though perhaps the reality may see some frost late on in the day.
20th: It’s looking quiet and calm.
21st: quiet and calm.
You can find out what every Christmas Day in London was like weatherwise here.