Category Archives: Blizzards

Beast MkII or just a late March cold spell?

After the severe spell at the end of February that lasted into this month there’s lots of excitement / dread (*delete as appropriate) that the synoptic conditions that brought very cold air from our east is about to return.

The latest run on the GFS model shows that very cold air (-10C at 5,000ft) could be over us by next Sunday, with the ECM 12Z operational looking particular cold. ec

Snow this late in the year is very rare in the London area though, if the conditions are right, a blizzard is not impossible, as happened during the spring of 1952 when a two-day blizzard at the end of March brought drifts up to 6ft deep in the Chilterns.

Much more likely will be severe, possibly record breaking frosts. The coldest March night since 1959 across the London area occurred on the 3rd in 1965 with -7.4C recorded at Heathrow. Central London fell to -5C on the same night.

A look back at cold spells in March reveals that while snow was very scarce in London and the Home Counties it can be common on high ground from the Peak District northwards.

A history of March cold

1812: Luke Howard in The Climate of London noted that “great inclemency of the weather” on the 21st March disrupted mail deliveries between the north of Scotland and  Carlisle. The road between Appleby and Brough was impassable because of snow and between Sheffield and Manchester and Bradford and Halifax the snow had drifted from “two to three yards deep”.

Mail deliveries were also disrupted across South Wales.
In Plymouth a “a most tremendous gale from SW the whole of last night and this morning” brought flooding.
Howard’s account would confirm a classic battleground scenario of mild Atlantic air from the south pushing against cold Polar continental air in the north.
His own records from Stratford show a couple of cold days from the 16th, highs never lower than 2C, the coldest night on the 24th, being -4.4C. On the 20th he mentions snow in the morning followed by rain.
Wanstead mean: 4.9C (-2.8C) rainfall: 74.4mm (183%)

The following accounts of cold spells in March are recorded on the site London Weather.

1962: The first ‘spring’ month was colder than any month during the preceding winter. Frosty nights were much more frequent than normal, and sleet or snow fell on 10 days, although amounts were often trivial . On the 5th, the maximum temperature was only 2.2 C. Towards the end of the month, north to northeast winds were replaced by somewhat, cloudier milder, and moister south-westerlies. Atlantic fronts brought rain bands, and on the 29th nearly 10mm was measured.
Wanstead mean: 3.3C (-4.4C) rainfall: 36.5mm (90%) sun: 95.4hrs (88%)

1964: The first week of March was mostly cold with wintry showers and a fresh northeast wind. The temperature on the 7th only reached 2.3C. The second week was changeable and milder, and the high on the 13th was near 14C., but on the 15th, rain turned to sleet and gave a total of 26mm as cold air slowly encroached from the east. Nearly 15mm of rain fell on the 19th as milder air returned, but the rest of the month stayed mostly rather cold and changeable.
Wanstead mean: 4.9C (-2.8C) rainfall: 80.4mm (90%) sun: 63.5hrs (58%)

1969: The first week was mainly dry, and although dull and cold at first, it became fairly sunny and milder but with severe frosts. Overnight on the 6th/7th the minimum temperature was close to minus 8C. During the second week it became dull and wet, but after a cold start temperatures rose above average. Cold north-easterlies returned on the 16th with a high of only 3C., and cloudy, rather cold, and often wet, weather persisted until westerlies returned on the 29th.
Wanstead mean: 4.6C (-3.1C) rainfall: 53.2mm (131%) sun: 55.8hrs (51%)

1979: The first 12 days of March were changeable and windy with temperatures mostly above average. A wave depression formed on a cold front and produced 23mm of rain on the 13th, and as this depression became slow moving to the east of the country the rain turned to sleet and snow on the 14th, and continued into the 15th and 16th with highs near 3C. After mid month, the weather became less unsettled and milder, and the high on the 25th was near 15C.
Wanstead mean: 5.8C (-1.9C) rainfall: 96.5mm (237%) sun: 100.5hrs (92%)

1985: After a changeable start to the month, pressure built, and it became mostly dry, although often rather cloudy, with temperatures close to normal. On the 15th, showery rain turned to snow during the morning, and several cold and unsettled days followed. Sleet or snow fell on 5 days, and on the 21st the temperature failed to rise above 5C. Sharp frosts occurred, and although it then became less cold, the 26th was a miserable day with 11m of rain falling.
Wanstead mean: 5.9C (-1.8C) rainfall: 44.1mm (108%) sun: 100.5hrs (87.4%)

Advertisements

The most potent cold spells since 1960

With met models now coming into reliable range it now looks odds on that very cold air from the continent will be in place across most of the UK from early next week.

The big question is how long will the cold last and how much snow will fall? While the latter looks likely at some point once the air is in place it is impossible to pinpoint where and how much any given place will receive at this range.

Screen Shot 2018-02-22 at 09.01.04
The 00Z op run of the ECMWF model has the really cold air arriving at 00Z on Monday 26th.

In terms of longevity latest data shows the spell could have real staying power though my experience with models over the years has shown that they can overcook the potential of a cold spell.

I’ve lost count of the number of times when excited enthusiasts proclaim that an incoming cold spell is going to last as least three weeks; the reality being that the intensity of the cold has gone after four or five days. Cold spells since 2008 often arrive as a ‘blob of cold air’ from the continent that eventually gets ‘warmed out’; it’s been a very long time since we had a cold spell that’s been fuelled by a continual feed of air off the continent.

Screen Shot 2018-02-22 at 09.02.23
By Saturday 00Z the really cold air aloft has gone. A typical 4-5 day event?

To illustrate my point I had a look back at every cold spell in this area of suburban east London since 1960. I weeded out the feeble efforts of the last few years by only considering spells where the maximum didn’t exceed 2.8C. The results spanned from the most recent cold spell of March 2013 to the mammoth 31-day Siberian blast that began on Boxing Day 1962.

In another blog I remarked how similar the recent pattern was to February 1962. This cold spell began on the 26th and lasted 9 days. Some 7cm of snow fell, this drifting in the wind, possibly making it seem worse with only 4 hours of sunshine which would have maintained any snow cover.

One of the snowiest cold spells happened in February 2009, eight days after an SSW event that lead to a polar vortex split. This four day spell saw a total of 26cm of snow fall.

February 1991 was even snowier, the intense cold lasting some 11 days.

Looking at other February cold spells a 7-day spell occurred in 1985 about a month after an SSW event.

Overall the median length was 5 days with an average of 6cm of snow and 8hrs of sunshine.

*A survey of winters ranked for temperature and snow can be found here.

spells

rank cold

 

1960

 

 

 

 

 

 

 

 

 

 

 

 

 

The March blizzard of 1952

Warm sunshine looks likely to bring London’s first 20°C this week but the weather 65 years ago couldn’t have been more different.

180029031952
This chart shows the Synoptic setup at 1800h on 29th, the peak of the blizzard with F5 – F6 easterly winds, courtesy of the Met Office

A cold easterly airflow on March 29th and 30th 1952 affecting the southern half of England brought heavy snow whipped into drifts up to 6ft deep in parts of the Chilterns.

According to the Royal Meteorological Society’s weather log the snow varied from 3 to 6 inches and reached 10 inches at Northolt.

Squally winds, which gusted to 60 mph, blocked 330 main roads across the south. In places the temperature on the 29th remained below freezing all day – the snowstorm was probably the worst to affect southern England in late March since 1916.

The wintry weather followed a dry and fairly non-descript winter and must have been quite a shock at the end of what had been a fairly mild March.

Bernard Burton, of Wokingham, has a clear recollection of the event: “I remember the day very well as the Oxford/Cambridge boat race was held that afternoon. I was 14 at the time, and my brother-in-law gave me a ticket for a place on a launch to watch the race.

“My home was in Tooting at the time, and I took the bus to Westminster pier to catch the launch. I recall sitting upstairs on the bus with a thick layer of snow covering the front facing windows, but the roads and pavements were mainly slushy.”

Bernard, who runs Wokingham Weather, added: “I then spent one of the most miserable afternoons I can recall. There was a ‘lounge’ on the boat, which was warm, but was also full of diesel fumes and was very noisy. I alternately stood outside on the deck until the cold got too much, or went below for warmth until the fumes got the better of me.

“I recall bleak views of London with snow on roofs, in a poor grey afternoon light, but I think it was mainly dry at that time, although there may have been slight sleety rain.

“The boat race itself was a close one, but the crowds that usually lined the banks of the river were absent, just a few hardy stragglers, and by the time of the race I had a headache, probably brought on by the fumes. For my part, I couldn’t wait to get back to Westminster and back home to thaw out.”

John Hall, who was three at the time, said: ” I, sadly, don’t have any memory of it at all. That’s in spite of the fact that we apparently moved house from Cranleigh to Effingham (about 15 miles away) on the day of the blizzard.

“According to my father it snowed all day but the following day – which he reckoned was the 1st of April – the weather was glorious and all the snow was gone by noon. I don’t think his memory is quite in accordance with the facts, but of course that’s common with memories of past weather.”

The snow didn’t last long. March 31st saw temps rise to 5C; much of the snow had melted in the strong spring sunshine by April 1st. By the 3rd an Atlantic ridge of high pressure had moved in, raising temperatures to over 10C.

kew
Stats for Kew suggest there was 21cm of level snow

1952 produced two more weather shocks. On August 15th and 16th over 220mm of rain fell on the hills above Lynmouth, Devon, leading to flash flooding of the village and the loss of 34 lives.

Months later, a large anticyclone during the last of five days of December produced the notorious ‘pea souper’ fog that contributed to the death of thousands of Londoners. This fog, initially freezing, became very dense and was directly responsible for the Clean Air Act enabled in 1956.

You can find an analysis of the unfolding pattern that produced the blizzard here. And here’s Xmetman’s take on the event.