With the return of more seasonal temperatures February 2019’s heatwave already seems like a distant memory.
Looking back at the stats for this area the past eight days have seen an average anomaly of 7.7C, beating the previous eight-day long warm spell of December 2015, which returned a mean anomaly of 7C. That spell was quickly followed six-day long warm spell that had a mean anomaly of 6.6C. There appears no chance of the heat returning any time soon.
Wanstead missed out on breaking the February high temperature record. While Kew Gardens recorded a high of 21.2C, the local area reached just 18.7C, falling short of the record of 19.7C set in 1998.
The erratic onset of spring in some years often presents that problem of what to wear every morning. During the current warm spell I’ve seen all manner of attire on the school run; everything from T-shirt and shorts to full winter regalia topped off with hat and gloves.
The position of the sun is now bringing in to range the season when the gap in temperature between day and night can be at its greatest.
On Saturday (23/2), virtually unbroken sunshine and ‘thick’ air saw the temperature in Wanstead peak at 16.1C before clear conditions overnight saw the minimum plunge to just 0.2C. The gap of 15.9C represents the fourth highest diurnal temperature range for February in this area back to 1959.
Looking at the year as a whole the greatest range is 20.8C with the months of May and June the most likely to see the condition.
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.
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.