In my search for some winter weather a tweet by Amy H Butler about dynamic final warmings piqued my interest.
According to the atmospheric scientist a winter where there was no major disruptions of the polar vortex (SSW) we are more likely to see a dynamic early final warming. A table published by Wiley shows the final warming dates.
So what could this mean for the weather in the London area? Considering all the above years with no SSW gives an average date of April 19th for a dynamic final warming.
I then looked at the TMax anomaly for those years for 60 days following a DFW and came up with the following graph.
The results suggest temperatures in April will be heading down in the final week for a cold end. The average to cool theme continues into May before temperatures lift in the final week for a warm end, with anomalies up to 5C above average. June, however, looks shocking with temperatures nearly 6C below average by the 16th.
This winter has so far been very similar in type to 1990. The dynamic final warming that year was among the latest in the list and led to a cool and dull June with anomalies in the second week nearly 7C below average!
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.
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.
A few years ago I devised a winter index to try to decipher how modern winters ranked against legendary seasons, such as 1947 and 1963.
With the media hyping conditions last week, which were severe in many parts of the country, it is very difficult for many to gauge just how conditions compare with previous winters.
My findings show that this winter so far stands 27th. It is possible that further snowfall that results in lying snow at 9am between now and April will boost the position higher though, given recent years, this would seem unlikely.
Last week’s cold spell, while containing some impressive statistics, is put into perspective when it is compared with other severe spells since 1960. A decent cold spell but no record breaker in the form of a 1962/63.
Perhaps it is the advent of social media, the plethora of constant updates of the latest feet-deep snowdrifts and instant tales of heroism in the face of icy adversity, that has made this cold spell seem far more severe than it actually was in the minds of many; February / March 2018 was the first truly social media-driven cold spell.
This week has the potential to see new temperature records set or matched as very cold air moves in off the continent.
Whilst amounts and location of snow are very difficult to estimate at more than 24hrs to 48hrs away there is no doubt that the incoming air is very cold indeed.
In the early hours of Wednesday one weather model is showing extremely cold air (496-504 DAM ie very low thickness) just off the coast of Scotland. In the last 60 years there have been only three occasions where air approaching this thickness (500 DAM and lower) has been recorded in the UK:
February 1st 1956: Hemsby, Norfolk
February 7th 1969 at Stornoway, Outer Hebrides January 12th 1987 at Hemsby.
With the deep cold air in place the potential for snowfall comes once the air starts to become unstable. East London, and much of the east coast, best falls come where convergence lines ‘streamers’ form.
If persistent, these ‘Christmas tree’ features are capable of producing snowfall accumulating at the rate of 5–7cm per hour in especially cold
outbreaks, albeit often very locally. The steep thermal contrast between the very cold air and the current warm anomaly in the North Sea could make any snowfall very heavy indeed.
Streamers during the cold spell of January 1987 saw 30cm fall widely with some up to 65cm in Kent and 45cm in south Essex. Parts of Cornwall saw up to 40cm.
During a cold spell in February 2009 thundersnow was recorded – the favoured spot this time being parts of Surrey which saw 30cm.
Personally the most snow I have recorded during a cold spell was in February 1991. A very deep cold pool, not unlike what is forecast this week, covered much of the south. in air approaching 500 DAM. Days and days of snow followed dumping knee-deep powder in my local park in suburban East London. Reported depths included 20cm at St James’ Park in the centre of London, and 38cm at Rettendon, Essex.
There is a very good paper on cold pools and snowfall here.
The models are showing another knife-edge situation for snow – similar to the ‘rain turning to snow’ event earlier this month. But there are a number of factors working against it this time round, at least for most of us who live between sea level and 30 metres.
The low level supply of air off the continent is much milder this time round. Hamburg and northern Germany on the 9th was some 5C colder than currently.
The air pressure, crucial to bringing that snow line down lower, is forecast to be around 10mb higher this time.
And even if we see settling the soil temps, after the recent mild spell, are still 5C – 10C down to 10cm…
There is much anticipation in meteorological circles about the possible track of a deep depression spinning up the west coast of Ireland early next week.
The National Hurricane Center in Miami, on the 12Z GM run, puts Ireland and south-west England in the firing line of Ophelia.
The timing of the depression, coinciding with the 30th anniversary of the Great Storm, is remarkable and I wondered if there were other similar Atlantic storms through history.
A search through Martin Rowley’s excellent weather history site revealed that in October 1886, a small-scale but intense depression tracked ENE across central Ireland during the 15th, with lowest pressure estimated ~969mb.
Gales, at least up to Storm Force 10, were reported by most ships and some coastal stations across the southern part of the British Isles, with ENE’ly gales across Scotland (north of the depression track). The low then moved slowly ESE to central-southern England (perhaps deepening a little) on the morning of the 16th, allowing N’ly gales (at least Storm 10) to affect the Hebrides.
Many trees were blown down across Ireland, the English Midlands and counties along the English Channel. Damage also occurred to standing crops, and the high winds were accompanied by heavy rain, which brought river flooding to England, Wales and Ireland, delaying the harvest, which was already compromised by the wet/windy weather. Some bridges were swept away.
Five years earlier, on October 14-15, 1881, an exceptionally severe gale (Force 9-10, locally Force 11) caused extensive damage across the British Isles & areas adjacent to the North Sea, especially along the north-east coast of England & across the eastern parts of the English Midlands.
Some 108 ships were reported missing. Inland, this gale was considered a ‘great storm’ with extensive loss of timber, especially in Scotland. One particular tragedy involved the destruction of almost the entire fishing fleet from the port of Eyemouth in Berwickshire.
The morning (14th) had been fine with near-calm wind. Some 41 vessels, mostly big deep-sea boats sailed out. In the middle of the day, the wind fell light, and then the storm struck suddenly. Nineteen of the boats were lost and 129 men failed to return to port.
Widespread heavy rain and gales across the UK have made the start of summer feel very unseasonal. But the conditions, which follow an extended period of mostly dry weather, are very typical for early June.
The ‘NW European monsoon’ is one of the most reliable ‘singularities’ on the annual weather calendar. Though it sounds very unscientific that the atmosphere can remember how it behaved on a certain date in previous years much statistical work over the past 170 years highlight tendencies for unusual weather at particular times of the year. These tendencies were first identified by the German climatologist, A.Schmauss, in 1938.
While the pattern isn’t set in stone statistics show that the probability of the euro monsoon occurring between June 1st and 21st is 77 per cent.
24hr rainfall totals
Depression across the UK
One of the most notable inclement spells of weather in June happened during the D-Day landings in 1944.
0100 June 5 1944
12 June 6 2017
With the changes in ice at the North and South Poles, together with the massive positive temperature anomalies last winter, it would be thought logical that this would have some bearing on the general pattern this year. But polar ice is only one variable to consider when trying to predict the world’s climate.
November 2016 was the sunniest in a record going back to 1881. Some 91 hours were recorded, 156 per cent above average and a complete contrast to last November which was the dullest for 47 years.
The mean temperature for the month finished 6.4C, that’s 1.5C below the 1981-2010 average ; 4C cooler than last year and the coldest November since 2010. The warmest day occurred on the 15th with 15.9C recorded. The first air frosts of autumn were recorded. The lowest temperature occurred on the 29th when the spirit fell to -6.1C.
Rainfall was 135 per cent of average with 80.1mm recorded. The wettest day was on the 19th when 23.5mm of rain fell.
The sunniest days were on the 2nd, 13th and 25th when eight hours of sunshine were recorded.
Air frosts: 4, Ground frosts: 19
What has December got in store weatherwise? The models suggest the high pressure that has been anchored over us, bringing cold nights, will pull away to the continent. This will allow an ever milder but mostly dry source of air off the Atlantic through to mid month. Days will grow milder while frost and fog will feature less at night.
Beyond the grasp of the models my long range outlook method suggests an coldmonth is most likely at 43 per cent probability. Average comes in at 29 per cent probability while rather mild and rather cold are both 14 per cent probabilities.
Rainfall looks finely balanced. Wetter and dryer than average both come in at 43% probability while average is 14 per cent. Given the influence of high pressure at the beginning of the month I’m inclined to think it will be a drier than average month.
So, to sum up, we’re looking at a mean of 4.4C, rainfall: 55mm, sunshine: 39hrs.
My forecast last month was good: predicted mean 6.8C (result 6.4C). Rainfall: 55mm (result 80mm). Sunshine was way off, however – predicted total: 41hrs (result 91hrs)
I have also published a winter forecast covering the London area that you can find here.
1st: Cloudy and mild all day. Patchy drizzle at times.
2nd: Sunny, cold start after first ground frost of the autumn.
3rd: Sunny, cold start with cirrostratus and cumulus drifting around. Cloud thickened through the afternoon with some light rain around 9pm.
4th: Cloudy, dull start up to 11am. Rain pushed in and lasted for much of afternoon, clearing in evening.
5th: Cloudy, cold and damp start. Some brightness though with a cold wind.
6th: Sunny, cold start, tending to cloud in. Rain after 3pm. Feeling cold but too windy for a frost overnight.
7th: Sunny, cold and very breezy to start, the cloud tending to fill in through the day. Clearer overnight though too much cloud and occasional air prevented an air frost.
8th: Sunny and cold start. Cloud thickened during the day to bring rain after dark at 8pm that then fell through the night – the biggest fall since Brexit day.
9th: Light rain slowly clearing to cloud.
1oth: Cloudy start with light rain showers around 10.30am then cloudy. Some sunny intervals in the afternoon. Milder.
11th: Bright start with cloud decreasing through the morning to leave a pleasant and clear afternoon.
12th: Miserable and rainy to start, this lasting past 11.15am. Drizzle thereafter into 6pm.
13th: Sunny start though cloud tended to fill in through the day. Damp overnight with patchy drizzle.
14th: Cloudy and damp start with some breeze. Brief brightness at noon but patchy drizzle moved in around 4pm.
15th: Cloudy and miserable though very mild.
16th: Sunny start and very mild though cloud tended to fill in during the day making the sunshine milky.
17th: Bright, breezy start, the breeze increasing until a squall blew through at 2.40pm then sunny spells.
18th: Bright start with milky sunshine then tending to cloud over. Feeling cold.
19th: Bright sunshine though cold to start. Patchy altocumulus developed through the day, leaving it to become bright, the strength of the sun diminishing. Rain started around 6pm and fell through night with varying intensity.
20th: Dull and cloudy start with rain returning at 10am. Cloudy afternoon with rain returning late evening and through the night, some heavier bursts.
21st: Cloudy with showers past noon. Heavier showers moved in mid afternoon and fell into the evening.
22nd: Cloudy with a few very light showers around. Breezy.
23rd: Cloudy and breezy. Feeling mild.
24th: Cloudy and mostly dull with brief brightness at noon.
25th: Sunny with just a few cumulus around.
26th: Sunny start but low cloud blotted out the sun around midday then cloudy and cool.
27th: Cloudy and mild.
28th Sunny all day with just a few cumulus floating around.
29th: Sunny all day with frost persisting on grass in shade.
30th: Sunny and very frosty start. Frost persisting on the grass all day with a very cold start to the night. A veil of cloud crossed the region late evening, lifting the temperature above freezing, before clearing before dawn
Summer 2016 turned out to be a very decent season overall, the mean temperature of 18.7C (1.1C above average) made it the sixth warmest summer since 1797.
While it wasn’t quite up there with the hot summers of 1976 and 2003 it still produced some notable records. The stormy beginning to June effectively ended with the Brexit vote, a period of 24 hours that coincided with the highest daily rainfall this area has seen since at least 1959.
The multi-cell thunderstorm in the early hours of June 23rd produced 60.8mm of rainfall, nearly half of the month’s total which became the third wettest June in a record going back to 1797. The high rainfall was in complete contrast to July and August and helped skew the overall figure: 168.6mm is 114 per cent over average summer rainfall.
With so much rainfall overall sunshine was affected with only 451 hours recorded, just 80 per cent of what can be expected in an average summer.
July produced another record, this time the highest overnight minimum recorded since 1959. The minimum of 21.1C was recorded during the early hours of the 20th – coming hours after the hottest day of the year: 33.5C – the 14th hottest day on record.
The warm and very dry theme continued into the final month of summer with the warmest August for 12 years, the 10th warmest and 12th driest since 1797.
My summer forecast, when the monthly probabilities are considered, was broadly correct though I didn’t estimate correctly just how warm it would be.