Category Archives: weather pattern

The early March storms singularity

Storms in late February / early March occur in 88 per cent of years, according to Philip Eden’s study on singularities.

This year looks no different although the drop in air pressure looks like it will happen just in the nick of time.

The GFS op for the March 9th compared with the situation on the 2nd

A look at the past eight years shows the effects of the pattern are quite pronounced.

And a look nationwide reveals the following named storms occurred around this period.

Storm Jake, March 2, 2016

Storm Ewan, February 28, 2017

Storm Emma, March 1, 2018

Storm Karine, March 2, 2020

And going back further reveals a notable storm in the 19th century.

THE STORM OF MARCH 4, 1818

Early March often brings stormy weather, a singularity that has a probability of 88 per cent!

An example of just how long this singularity has been around can be found in the early 19th century

In his book The Climate of London Luke Howard mentions that the air pressure on March 4th was the lowest measured for some 37 years. The lowest point of 28.35 inches (960mb) is remarkable in that the lowest I’ve measured in Wanstead since 2012 was 969.8mb last December!

The storm brought devastation across a wide swath of southern England with loss of life on both land and sea.
Howard’s account of the storm mentions the barometer falling an inch in 15 hours with rain after dark with the wind “raging in violent gusts from SE and SW till past midnight when it abated after much thunder and lightning”.

His friend in Manchester, Dr William Henry, wrote a storm SW caused considerable damage, delaying the London mail in Macclesfield from 8pm until 3am on the 5th, the storm raging until 3am. The barometer fell to 28.2in (955mb) at Manchester.

Character of the period for the most part tempestuous with frequent rains the barometer running through a series of sharp depressions till near the close when it suddenly assumed the elevation of fair weather Almost all the showers from the first were more or less mingled with hail

Elsewhere in Britain public ledgers also reported the storm.

Yarmouth A most tremendous gale of wind from the S to the SE with rain came on about 8pm which continued with increasing violence all night and has done considerable damage to the shipping on this part of our coast.

Deal Last night it came on to blow a most tremendous gale from the south and continued nearly the whole of the night with unabated violence at midnight it blew a complete hurricane accompanied with thunder and lightning during which several vessels in docks suffered.

Portsmouth It blew a tremendous hurricane last night from S and SSE accompanied with the highest spring rides ever remembered.

Ryde One of the severest gales of wind that has been felt here for the last 37 years was experienced last night. It commenced about 4.30pm and continued with increased violence until past 11pm during which time the greater part of the pier and several houses were demolished. The supposed damage is estimated at between £4,000 and £5,000. No lives were lost nor any damage done to the shipping.

Dartmouth We experienced a perfect hurricane last night at SSE from 6pm to 10pm

Exmouth On the 4th instant between 7pm and 8pm we had a most tremendous gale of wind about SSE with dreadful rain thunder and lightning.

Falmouth At day light this morning the wind was from the WSW moderate. About 11am it strengthened to the S and from that to SSE and since that time until 10pm it has blown a hurricane with a heavy sea.

Penzance We had a very heavy gale here on Wednesday the 4th.

Milford On the 4th it blew a very heavy storm from SW to WNW.

Leicester Wednesday night was one of the most boisterous recollected for years past. Much damage has been sustained in this town and many parts of the county.

Hull At high water about 4.30pm the wind then blowing from the SW with moderate weather the tide flowed at the Old Dock Gates 18ft 6in. After the tide had fallen from 1 to 2in the dock gates closed as usual with the ebbing of the tide which then began again to flow to the height as near as can be calculated of four or five inches thereby opening the gates again and continued flowing. The tempestuous night of Wednesday ensued the wind blew a heavy gale still from the SW and at high water at 5am Thursday morning the tide was 14ft 1in being 4 feet 5 inches less than on the preceding evening although from the spring tides having put in the water ought according to the usual state of things to have flowed higher than on the Wednesday evening

Plymouth At the commencement of the winter a few large stones were placed by themselves on the top or finished part of the Breakwater to see if they would stand the winter gales they stood all but this last and this morning I found them washed from the top and lying on the North Slope There were three of them one of nine tons and the other two of five tons each they will be replaced as soon as possible for further trial Plymouth The effects of the late thunder storm of the 4th March on a fir tree belonging to W Langmead Esq at Elfordleigh in the neighbourhood of Plymouth are too singular to be omitted and perhaps the most extraordinary ones that ever occurred in this county on such an occasion The tree in question has been long admired for its size and noble proportions being more than 100 feet high and nearly 14 feet in girth but it exists no longer having been literally shivered to pieces by the electric fluid Some of the fragments lie 260 feet from the spot and others bestrew the ground in every direction presenting altogether a scene of desolated vegetation easier to be conceived than described.

London’s colder than average months

Last November was on the cold side prompting me to investigate whether we were about to record a third month in a row below average. December turned out to be mild and wet, the lack of snow especially stark in Scotland.

The findings of that study showed that any sustained period of colder than average months was more likely to happen during months of March, April and May, nothing unusual there, especially considering H.H Lamb’s weather types.

I decided to scrutinise further all the colder than average months in this area, considering the 1981-2010 average, back to 1981. This gave the below results.

neg anoms

The dataset covers 399 months, of which 200 were colder than average.

The overall picture shows that negative anomalies are becoming more and more rare, though with notable exceptions being March 2013, December 2010 and January 2010.

The only month that has showed any sort of consistent general decrease in negative anomaly is November.

*For good snowfall at this station needs a negative anomaly of 2C during the months of November, December, January and February.

Months of perpetual cold

It’s been a while since this region has seen a sustained colder than average period. Though the past few weeks have seen colder than normal weather we have to go back to the beginning of 2015 where at least three consecutive months were colder than the 1981-2010 average.

The spell, which coincided with winter, was unremarkable with just one day of lying snow. The season finished 55th out of 73 of the most recent winters,  the anomaly for the 90-day period was -0.3C. For deep, lasting snowfall events a monthly mean temperature must be at least 2C colder than average.

For anything ‘snow-worthy’ you have to go back seven years to a 10-month long colder than average spell that began in September 2012 and coincided with probably the last winter I can remember that had more than one cold spell with snow that lasted longer than a few days. The average mean for this spell was -1.3C.

The most potent cold period occurred during the winter of 1984/85, a winter where snow lay nearly a foot deep by the end of January and where seven ice days were recorded – these days we’re lucky to record just one ice day per winter! Only just behind was the 3-month period January to March 1987.

As with previous blogs I have devised a way of ranking these cold periods, by dividing the mean with the length in months. The first nine months of 1986 achieved the highest ranking, a period that included the 5th coldest February in this area since 1797.

rank

And in chronological order…

chron

cold month index

It is looking like the mean this November will finish below average, making it the second month in a row, something that hasn’t happened since March last year. Will December make it three in a row and a new addition to the list?

 

Two Paris heatwaves two centuries apart

In July 1808 Paris wilted in a heatwave. The average maximum for the 13-day spell that began on the 10th was 31°C, higher than a similar spell last month that saw the all-time record for the French capital broken.

The temperature at the peak of last month’s hot spell reached 42.6°C, some 6.4°C higher than the peak of the 1808 spell but, as the graph below shows, maxima fell back more quickly than 1808.

paris heat line

The more ‘pointed’ nature of maximum temperature during the spell last month backs up findings of the changing jet stream;  the wriggly nature amplifying the heat.

Tmin

mean

The average mean and minimum temperature of both spells showed a difference of just 0.2°C.

Since Paris recorded its hottest day ever there have been just two days where the temperature has exceeded 30°C.

paris july 1808
The values for the 1808 spell were listed in Luke Howard’s Climate of London.

The heat in Paris in 1808, like in 2019, was also felt in London. Luke Howard noted the following in The Climate of London.

“Very hot from July 12th to 19th. On the 12th a thermometer in perfect shade in a window in St James’s Park was 81.5 degrees at 3pm, and on the 13th at the same hour, 94 degrees. On the same day four men and seven women were killed by sunstroke in various parts of the Midland counties, and numerous coach and other horses were also killed. On the 15th a very violent and destructive thunderstorm in Gloucestershire, Monmouthshire, and surrounding counties.”

* Values for 2019 were taken from the station Montsouris.
** Though there is no way of knowing how accurate the 1808 values were previous studies have found that historic temperatures can be as much as 3°F too high.

Front loaded rainfall months

Since February most of this region’s rainfall has been falling during the first half of the month.

feb

February: 86%

march

March: 134%

april

April 28%

may

May (to 26th) 54%

With only one of these months wetter than average the long-term, rolling trend continues to head downwards.

rolling

Considering past rainfall patterns it can only be a matter of time before the graph heads upwards again. Looking further back at rainfall data to 1961 reveals the extremes were higher and that the jump from dry to wet can be sudden.

The wettest 12-month rolling period ended mid way through May 1975 with a total of 873mm. However, just 16 months later, at the end of the hot summer of 1976, the rolling 12-month average was just 302mm, that’s less than half of our average annual rainfall!

average rain

 

An erratic season for snow in the Alps

Earlier this winter there were many reports on how good snowfall had been in Austria. But on closer inspection it was clear that the weather pattern at that time only favoured certain resorts.

In contrast with last year the totals I’ve used in my cross section of the range don’t look that exciting; Bourg-St-Maurice, the jumping off point for Savoie resorts including Les Arcs and Val d’Isere, has recorded 96mm of precipitation this season, in stark contrast to the 433mm it recorded last season between Christmas Day and February 5th.

In Switzerland Arosa, a resort well placed to pick up snow from any direction, has recorded the same this season as last. Totals in Davos are well down on last season. Similarly San Bernardino has recorded about half the amount of precipitation than it did last season. Its location toward the southern side of the range has been sheltered from the prevailing winds this year. That said it did enjoy a big dump last week.

Going further south and east St Vallentin in Italy has recorded about a third what it did at this stage last season.

Mean temperatures overall are about 2C to 3C lower than they were last season.

snowmap update
30-day precipitation totals reveal that Bourg St Maurice recorded just 96mm, compared with last year’s 433mm while Obertauern in the east recorded 77mm, compared with 106mm the same period last year

 

A winter heatwave

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.

1998 2019

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feb 1998 maxes

 

 

Update on effects of the polar vortex split

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 Eastevents 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.

jan 2018 2019

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.anom jan 13th to 19th

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.

3 years compared

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.

A winter drought

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.

winter droughts

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.