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.
Average (5.1C – 5.9C)
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.
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
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.
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.
Compiling a list of sunless, rainy days revealed some interesting spells of wet weather – the most miserable runs of June days in the capital since 1959.
First up was a three-day spell starting on June 25, 1974. Some 34.3mm of rain was recorded.
Next was a three-day spell starting on June 23, 1991. Some 26.3mm of rain was recorded.
Another three-day spell started on June 25, 1997. Some 36.2mm of rain was recorded.
Finally, and most recently, a two-day spell this month that began on June 17th. Some 28mm of rain was recorded.
The above spells all happened around the date of the ‘June monsoon’ singularity which has a probability of 77 per cent. Though the fact that these occurred 47 years, 30 years and 24 years ago shows that these extreme cases happen a lot less than three years in every four the singularity would suggest.
Comparing the current Northern Hemisphere pattern with 1974 suggests that while there’s just as much heat around at 850mb as there was 47 years ago, including an extreme heatwave over some Nordic countries, the air above Greenland appears colder.
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.
The mean temperature for winter 2017/18 is looking average overall with average precipitation. While that doesn’t sound exciting for anyone looking for colder weather and snow I think the figures mask frequent 3 or 4 day-long cold snaps from the Arctic interspersed with milder interludes from Atlantic incursions; typical characteristics of a pattern driven by the troposphere. For anything longer term we have to hope for a warming of the stratosphere, a sudden stratospheric warming over the Arctic, that downwells into the troposphere, reversing the general westerly circulation. We are overdue an ‘SSW’ event but, even if one were to happen, its effects wouldn’t be felt until much later in the winter.
Figures generated using QBO statistics in the run up to December were identical to the outcome of 5C. It is figures generated using ENSO statistics, however, that produced the best results considering December, January and February alone.
It would seem that the winter was most influenced by the ENSO variable up until February when the effects of the SSW were enough to overcome it?
An article by the late meteorologist and broadcaster Philip Eden a number of years ago considered many of these patterns and found that, to varying degrees of reliability, they provided a guide to what the weather would be like at any given time of the year.
Considering climate change I wondered how much these patterns could still be relied on. Using my own pressure, rainfall and ‘wind run’ data (the total amount of daily wind) going back to the start of 2013 I had a look at the singularities for January and February
January patterns at the beginning, middle and end of the month appear to be the most reliable. However, it is only the ‘mid-Jan settled’ period that is most reliable.
The early Feb settled spell occurs with very low probability: just 56 per cent. And this year the pressure, according to the GFS model, plotted below by WXCharts.eu, is predicted to be around 1040mb by February 2!
Looking at the results of the past 5 years it could be concluded that the patterns do still occur but because of the nature of the jet stream, which seems to meander far more readily than in the past, these stormy / quiet episodes are becoming shorter than they were in previous studies.
The knife-edge situation for snowfall across England today set me off wondering if there was a way to forecast snow locally to a given location.
Temperature, dew point and altitude are all crucial to forecasting snow, as is precipitation intensity that can lower the wet bulb temperature, the ‘rain turning to snow’ scenario. Less well known is the role air pressure plays in these events, such as the one on December 10th which caught many forecasters by surprise by its intensity.
While various models continually improve in their skill at warning us of impending rain / snow events that often cause chaos, their resolution can still struggle and especially when the event more or less becomes a nowcast.
In the International Standard Atmosphere (ISA) there is a 1 hPa difference for each 30 feet vertical change in height in the lower levels.
If we take a forecast pressure as 970 hPa, the difference between standard conditions (1000 hPa) and 970 hPa is thus: 30 hPa
30 hPa * 30 = 900ft height variation.
You then consider local altitude: in my case 18m (59ft)
So 59ft – 900ft = 841ft (256m)
A simple table, therefore, to consider air pressure is thus.
Looking at the system today the pressure rose quickly after the centre passed, leading to a 1hr (at best) window of snow falling. As the pressure rose, and the temperature picked up only slightly the snow turned back to sleet and then rain.
This month marks the 30th anniversary of the Great Storm. Some 18 people were killed as winds gusting to nearly 100mph affected London and the South East. Around 15 million trees were lost with Sevenoaks in Kent losing six of its seven historic trees.
The rapid development of ‘Low M’ took forecasters by surprise, the favoured outcome was for the low to move up through Brittany, remaining in or to the south of the English Channel.
I was living in a fairly sheltered corner of the London borough of Havering in 1987. I remember heavy rain just before midnight, around three hours before the storm reached its height, was heavy enough to send water trickling into my room, thanks to an overflowing roof valley. I thought it strange that Michael Fish hadn’t mentioned its severity in his lunchtime forecast.
I was awoken around 3.30am by a loud crash. Looking out the window I saw two dustbins flying down the road. You could sense each gust building in strength – the next dislodged a roof tile, sending it crashing on to the family car. By this point my mum and sister had awoken, my sister swearing she could feel the whole house moving: Mum ordered us downstairs. By this point the power had gone off and we sat listening to a small battery-operated transistor radio. We listened to updates from BBC Radio London where, like most other people, nobody knew what the hell was going on. The storm continued and first light gradually revealed the damage in the garden – a couple of trees over and next-door’s shed on its side; nothing compared to the rest of the region. But the disruption meant I didn’t attend school that day.
The storm was obviously a weather nut’s dream, and following so close on the heels of the coldest January I can remember. John Hall, of Surrey, can remember the storm well: “I’m not normally a very heavy sleeper, but I somehow managed to sleep through the worst of it (in Cranleigh, then as now).
“It was still windy when I woke around 7 am, but presumably not nearly as much as it had been earlier. By some miracle we still had mains power, and it was only when I switched on the radio and there was no sign of Radio 4 that I realised that something was up. (I assume the transmitter must have been damaged.) I walked the half-mile to the centre of the village to get my morning paper and then to catch the bus to Guildford station for my journey to work.
“It was only then that I learnt from the newsagent that there were no papers and wouldn’t be any buses, as every road in and out of the village was blocked by fallen trees. So I went home, switched on the TV and learnt all about what had happened.”
Dave Cornwell, of Laindon, south Essex, said: “Quite exciting but scary for me at home in Laindon. I awoke probably around 3.00 am to the sound of a metal dustbin lid (remember those?) flying down the street.
“Things sounded pretty bad and my sixth sense told me this was no ordinary windy night. I got up and looked outside and there was stuff flying by and lots of strange noises. One was my plastic gutter blown down and banging against the side of the house. I can’t be certain of the timings but we awakened our two young daughters and took them downstairs as I was worried as they slept in a room with a flat roof dormer window and there was a tall brick chimney stack directly above it. I heard more crashing sounds which unfortunately turned out to be a couple of roof tiles landing on my car roof which was parked in the drive. Of course with no internet then I did what a lot of people did and tuned into the police FM radio network. This gave me a better realisation that it was serious as they were describing the carnage on the roads and all of the emergency calls they and the fire brigade were getting.
“At about 5.30am I ventured out into my driveway to see if there was any serious damage but the storm was still raging and I can honestly say I couldn’t stand up and was unable to keep my balance so went back indoors. I think the wind speed was probably over 100mph at this point being funneled down the side of the house which runs south-north.
“By 8.00 o’clock I was getting ready for work and although by then people were being advised to stay at home I worked in a fairly essential service so thought I would give it a try. I managed to get to East London but there was debris everywhere and I saw a car completely crushed by a one of many trees that were blocking some side roads.
“Another thing I noticed that evening was my south facing windows had a layer of salt on them which must have been blown in from the south coast 60 miles away. It was a sight I’ll never forget and to this day I don’t like strong winds (had a scary flight at Heathrow in a severe gale as well) and always get a nervous feeling if I hear the wind getting up. Probably the most dangerous weather I have experienced anywhere in my lifetime.”
Much has been written about the storm, a ‘once in 500 year event’, including this summary by the Met Office. There is also an excellent paper by Bob Prichard published in Weather. The synoptic charts below show how Low M develops from 1200 on the 15th to 1800 on the 16th.
Because of widespread power cuts many television viewers didn’t see this recording of ITV’s Good Morning Britain at the time of transmission. A round up of the immediate aftermath of the storm, including comments from Jack Scott, can be seen in this edition of Thames News.
The following Daily Weather Report was published by the London Weather Centre:
An intense, and almost certainly exceptional, depression crossed the coast of south Devon soon after midnight, moving quickly, and deepening rapidly, with a track across the Midlands and out towards the Humber Estuary, leaving the United Kingdom land area around 0700 hours.
Some very severe conditions due to storm force winds were generated around the southern and eastern flank of the low, with gusts from approximately 0200 hours well in excess of 70 knots, and reaching a peak in the period 0300 hours to 0700 hours, with gusts to 90 knots reported from Herstmonceux and St Catherine’s Point in the early hours, and similar value gusts from the Channel Islands. The very stormy conditions were accompanied by some heavy rain, this rain pushing into Scotland and parts of Northern Ireland after dawn.
Clearer weather, on westerly winds, swept across southern Britain, pushing the worst of the stormy winds away into the North Sea. During the afternoon the country settled down to a blustery westerly with some heavy and thundery showers developing in clusters, running especially into western and southern coastal regions and parts of southeast England.
Across Scotland and northern England the skies remained cloudy, with outbreaks of mostly light rain, but troughs enhanced the showers in the northwest later in the evening with heavy rain. It was a rather cold day in most places, although the temperatures were near normal in the southeast.
The storm remains the most severe I have experienced in this part of the UK. The Burns’ Day storm in 1990 brought severe gale force winds in the London area but the low pressure was centred much further north.
July 2017 was the wettest since 1960. Some 92.3mm of rain were recorded which is 212 per cent of the 1981-2010 average.
Although the opening third of the month saw a continuation of the June heatwave temperatures gradually returned to normal values to leave the mean for the month at 19.2C, that’s 0.7C above average.
With all the rain sunshine totals were down. Some 167 hours were recorded, that’s 87% of average.
Though the rainfall total was impressive it is well short of the record of 164.2mm set in 1834, and is only 35th in the list going back to 1797.
Summary for July 2017
Mean (1 minute) 18.9
Mean (min+max) 19.2
Mean Minimum 14.7
Mean Maximum 23.7
Minimum 9.4 day 12
Maximum 30.5 day 07
Highest Minimum 18.3 day 06
Lowest Maximum 19.0 day 24
Air frosts 0
Total for month 92.3
Wettest day 30.8 day 11
High rain rate 56.4 day 29
Rain days 10
Dry days 21
Highest Gust 17.4 day 27
Average Speed 2.9
Wind Run 2163.5 miles
Gale days 0
Maximum 1024.2 day 16
Minimum 996.8 day 31
Total hours of sunshine 167
In terms of the rest of the summer a look at the ECMWF control run out to 10 days suggests an unsettled start to August with the jetstream centred right over the top of the UK. Things may improve as the Azores high attempts to exert more influence – so perhaps more in the way of sunshine than of late. In terms of heatwaves it is impossible to tell at this range.
1st: Cloudy but with sunny spells developing, these growing longer in length by evening.
2nd: Sunny with just a few light cumulus.
3rd: Sunny start though with plenty of cloud around, this tending to thicken after lunch with odd spot of rain.
4th: Sunny and very warm early then tended to cloud over before sun returned in the late afternoon and evening. Some very unstable low to mid level cloud.
5th: Sunny with just a few cirro-cumulus. Feeling very warm with cloud bubbling up in the evening, however forecast storms failed to materialise.
6th: Sunny with cirrus and dotted cumulus. This tended to thicken late morning though sun stayed out and became hot and humid.
7th: Sunny with lots of high-level cirrus and cumulus most of the day.
8th: Bright but mostly cloudy start, the cloud tending to vary through the day. Sunny after 4pm. Warm overnight.
9th: Bright but mostly cloudy start, the cloud tending to break and vary through the day.
10th: A mostly sunny morning and lunchtime until 2pm when it clouded over.
11th: Cloudy with some bright breaks at first. Cloud thickening with rain by noon, this falling sporadically before getting going after 5pm and stopping by 3am.
12th: Cloudy, damp and close start.
13th: Sunny with variable cloud until noon when there were just bright spells.
14th: Cloudy but with a few breaks around mid morning. Turning cloudy again before sunny spells in the evening.
15th: Cloudy with some sporadic rain as warm front blew through and close. Very limited brightness.
16th: Cloudy with some bright spells. Feeling warm and humid.
17th:Sunny with just a few cirrus drifting around. Feeling hot, cloud thickened from the west in the late afternoon.
18th: Sunny with variable cirrus and cirro cumulus through the day. Feeling very warm. Storms began building with supercell to west of London and over Chilterns.
19th: Cloudy, dull start and very humid with heavy mist – the cloud tended to lift to give sunny spells in the afternoon.
20th: Drizzle after shower before obs time, then showers through to 1pm.
21st: Cloudy start but with sunny spells developing. Clouded over in evening with intermittent heavy rain at 11pm and through the early hours.
22nd: Cloudy but with sunny intervals developing around noon. Heavy showers developing with thunder at 2.30pm and 3.07pm.
23rd: Bright with variable cloud
24th: Cloudy with light, showery rain from northerly airstream that originated in the Med.
25th: Cloudy with light rain just after obs time.
26th: Cloudy with occasionally rain. Feeling warm and a late clearance. Breezy and chilly overnight.
27th: Cloudy but bright and sunny spells developing. A very heavy shower at 1pm.
28th: Bright start but clouding over.
29th: Sunny start with cloud increasing after noon to leave overcast before patchy rain moved in. This falling more heavily at 5pm before clearing to further showers. More rain overnight before a strong squall arrived at 2.45am and lasted an hour with further bursts of rain through the night – two claps of thunder and lightening during squall.
30th: Sunny with variable cloud through the day. Very warm in the sunshine
31st: Sunny with variable cloud throughout the day.