Anomalies of the past two months throw up some interesting singularities as we head into late summer and autumn – with a hint that we could be heading for a much colder than normal December.
Using stats from the past 60 days revealed the following years. Those most similar to the current ENSO situation are highlighted in bold.
The most negative month on average will be December.
In terms of rainfall those hoping for a deluge look likely to be disappointed, at least in the south-east, with a continuation of synoptic conditions that favour drier than average weather.
The best chance for a wetter than average month appears to be September though, given recent synoptics, this is likely more a result of trough disruption than any sustained period of Atlantic-driven fronts.
This winter is most likely to be on the colder side of average with near normal rainfall.
While the modelled prognosis for the first half of December looks unsettled with an Atlantic influence evolving from the current chilly NW’ly to a mild SW’ly, local analogues of the climate of London suggest the season could be a bit of a rollercoaster with spells of wet, windy and mild weather alternating with dry, calm and cold.
A large factor to consider this winter is the presence of a slight La Nina that is forecast to evolve cooler.
Given the uncertainties involved with the influence of ENSO I’ve decided to stick with analogues found in local data that stretches back to 1797.
Overall then the probabilities for the next 90 days are.
Mean
Probability
Rainfall
Probability
Mild (>5.9C)
14%
Wet (>178mm)
19%
Average (5.1C – 5.9C)
38%
Average (107-177mm)
62%
Cold (<5.1C)
48%
Dry (>107mm)
19%
The above table doesn’t reveal a great deal in that extremes can be hidden in a month or season that finishes broadly average. So I decided to look closer at the winters that were revealed in the analogues.
December
The first month, as already mentioned, looks like it will be on the mild side with possibly a notable storm off the Atlantic before things calm down over Christmas – the period between Boxing Day and New Year’s Eve possibly presenting the best chance of any lying snow in this region.
The below graphs are a smoothed representation of the years revealed in the analogues most similar to this autumn.
What is probably most interesting is that the analogues that shared a similar ENSO / La Nina index to this autumn tended to ‘turbo charge’ any yo-yoing in the weather type, be that super-mild or abnormal cold.
December probabilties for maxima: Mild: 48% Average: 19% Cold: 33%
And precipitation. Wet: 33% Average: 29% Dry: 38%
So, the month overall will be mild and slightly dry
January
The first month of 2022 probably represents this region’s best chance of lying snow this winter. A mild start perhaps with a falling off of temperatures in the final third of the month and a cold spell of a week or so. As with December the influence of La Nina could tend to boost the swings in the pattern.
January probabilties for maxima: Mild: 33% Average: 10% Cold: 57%
And precipitation. Wet: 19% Average: 43% Dry: 38%
Greatest chances for January, then, are cold with average precipitation.
February
The second month may see a slight return of the cold spell in January before temperatures recover for a mild and wet spell in the second half.
February probabilities for maxima. Mild: 33% Average: 15% Cold: 52%
And precipitation. Wet: 38% Average: 38% Dry: 24%
The stats suggest on the cold side overall with average to above average rainfall. Perhaps the depth of the cold skewing any very mild second half of the month?
The extremes that no-one can forecast
As well as the very mild winter of 1989/90 the analogues also revealed the very cold winter of 1978/79. There were others but their occurence makes the probability of a repeat at either extreme at less than 10 per cent.
The weather of late has been in stark contrast to the mostly dry, sunny (if a bit chilly) spring many enjoyed. Indeed the first half of June saw more of the same and, locally, was the warmest start to the first meteorological summer month since at least 1959.
My memory of summers years ago was that it was often hot and sunny but I also remember countless days of staring out the window for hours waiting for relentless rain to let up.
Looking back at sunshine stats to 1959 there has been over 4,400 days where no sun was recorded, roughly a one in five chance of a totally cloudy day.
Considering the months where the absence of sun is most noticed, May to October inclusive, the probability decreases to just under one in ten.
To decant these to ‘washout days’ I’ve only included those sunless days that were also ‘wet days’ where 1mm or more of rain was recorded. The probability further decreases to just under one in twenty.
All very interesting but were there more washout days decades ago or is the memory playing tricks?
Looking overall shows an increase since 2013. Out of all the months the most notable change has been August.
Spring in this neck of the woods was really mixed.
A chilly start to March became fairly benign before ending with the warmest March day locally since at least 1959.
April then turned much colder and drier; just 2.4mm of rain fell during the month – the driest April since 2007 and fourth driest in a local rainfall series back to 1797! Sunshine was abundant with over 200 hours. But clear skies at that time of year, with a polar continental airmass, often means air frost. And the ten recorded overnight was far higher than normal.
May saw things warm up slightly but the month still finished a degree colder than average. Some 80mm of rain fell which is over one and a half times what we’d normally expect. The wettest May since 2007 – the month playing catch up on the total absence of April showers that bring the spring flowers! It was a dull month with only 126 hours of sunshine, 69 per cent of average – the dullest since 1990 was third dullest back to 1881.
In terms of flora and fauna the colder weather played havoc with the trees, bud burst coming much later than recent years. As I write this on June 6th some of the later budders like false acacia have only just come into full leaf. The birds, as they normally do, just seem to get on with it raising their young. I’m not sure what the food supply has been like but judging by the amount of healthy juvenile fledglings I’ve seen I would guess that it has been a good season so far?
Here’s the stats. March 8C (+0.3) 30.9mm (76%) 90.9 hours (84%)24.1C on 30th (a record that had stood since 1965) April 7.2C (-2.6) 2.4mm (5.5%) 202.6 hours (127%) 10 air frosts in April, much higher than normal May 12.1 (-1) 80mm (156%) 125.6hours (69%) Spring 2021: Mean : 9.1C (1.1C below average, coldest since 2013, 111th coldest) Rain : 113mm (84% of average, wettest since 2018, 150th wettest ) Sun : 425.4 hrs (94% of average, dullest for three years. 51st dullest) The average masked extremes.
Looking out the window on a cold and miserable June afternoon yesterday reminded me of similar such days during the Seventies and Eighties.
But the mind plays tricks and I wondered if these kind of days were that common in the past.
To weed out the also-rans qualifying days had to be sunless with an anomaly that was at least 4C cooler than the daily average and rainfall of at least 12mm.
This gave the following list.
So, in the last 60 years there have been only 12 days similar to June 10th 2019. That would give a probability of less than 1% (0.00743)
Looking elsewhere it would appear that there was much more rain to the north, south and west of Wanstead.
April 2019 was yet another dry month. Just under 12mm was recorded, that’s 28 per cent of average.
There has been rain around but the prevailing wind has not been conducive for great amounts to fall here. Last weekend, over a period of 5 days, just 0.9mm fall. Yet Capel Curig in Snowdonia, 200 miles northwest as the crow flies, recorded 130mm thanks to a NW’ly regime.
A look at rainfall in Wanstead back to July 2013 shows that of the 3,550mm recorded just 17 per cent has fallen when the wind was NW’ly.
Because of the topography of the area most of our rain falls when the wind is blowing between SE’ly and SW’ly, a total of 43 per cent.
A westerly is usually reliable for rainfall, however because this area is in the lee of high ground areas such as Hampstead westerlies have delivered just under 8 per cent of that 6-year total.
The above graphic shows maxima recorded in the month of April with shading to represent the anomaly of each day relative to the 1981-2010 average.
The last two years show the warm spells experienced in the second half of the month. The overall impression is that warming seems to have accelerated since 2011.
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.
The GFS has been churning out some very strange charts of late
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 the mean temperature of both October and September finishing 0.2C below average it is probably safe to say that the weather is in an average kind of mood.
Conditions during the first part of November look changeable, according to the Met Office’s 30-day forecast . After mid month, however, the agency says the forecast is uncertain.
Now that much of the UK has had its first frost any warm spell in November will, correctly, be called an Indian summer. A singularity called the St Martin’s Summer occurs in 66 per cent of years, occurring between 15th and 21st and peaking on the 18th.
And, as if by magic, the GFS model today has this chart for the 16th, an Atlantic ridge of high pressure with daytime temperatures about 6C to 8C above average. Though warm during the day I would imagine there being a risk of fog forming at night
Beyond that there could be a tendency for much more unsettled weather at the end of the month. The early December storms singularity occurs in 98 per cent of years, starting between November 24th and December 14th, often peaking on December 9th.
November, the last autumn month, can often surprise with its extremes, though it can also often be characterised by days of anticyclonic gloom. The warmest, coldest and wettest November conditions in London back to 1959 can be found here.
Although many parts of the UK have already recorded their first air frost this part of the capital, being so built up and close to the City, remains frost free.
Although many may think that frosts are getting later a look back through local statistics to 1959 shows these events are very random.
The scatter graph below illustrates this.
Taking out the winters of 1974/75 and 2002/03, which didn’t see frosts until February and January respectively, the scatter can be seen better here.
The median for the first frost is November 6th with an average minimum of -1.4C.
October frosts can be a precursor to a mild winter much in the same way that heavy October snowfall in the Alps has lead to an awful season. But there are exceptions, as happened in 2008/09.
* To record an air frost the temperature must fall to -0.1C or lower.
: 9.1C (1.1C below average, coldest since 2013, 111th coldest) Rain 
: 113mm (84% of average, wettest since 2018, 150th wettest ) Sun 
: 425.4 hrs (94% of average, dullest for three years. 51st dullest) The average masked extremes.
Wanstead Meteo 
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