Category Archives: London weather

Summer forecast 2017: average

The dry nature of spring this year has scuppered a large part of my usual method of trying to predict the summer season.

burning sunset

With El Nino forecast to be neutral I decided to once again rely on pattern matching of meteorological data from this area for March, April and May stretching back to 1797.

The mean for the spring season, the second warmest on record, was 11.9C with 88.6mm of rain and 430.3 hours of sunshine.

If you take into account all years that were within +/- 10 per cent of these figures, for rainfall some 12 ‘best fit’ years emerge. I normally go on to reduce the list further by considering mean temperature but, this year, no figures would remain!
The list of 12 summers, ranging from 1807 through to 2005, saw all manner of summers, including 1808 when early July heat gave way to fierce thunderstorms with hail the size of tennis balls recorded. Only one was a real corker, 1906, but most were fairly nondescript.

As an average this summer could be expressed as: Mean: 17.2C (just below average) Rainfall: 141mm (about average).

Or, expressed in probabilities, I concluded the following:

 

summer 2017 prob

From the above you could deduce that the next three months will be around average, with average rainfall.

To try to give some idea of what month will have the best weather I’ve broken down the summer into June, July and August probabilities.

Looking at June, considering the unsettled outlook after the weekend, I would guess that a few very warm, thundery spells are possible– though much of any precipitation will stay to our west.June 2017

On to July. After an average June I wonder if the ‘return of the westerlies’ will happen just in time to affect this month?

July 2017

 

The above chart would suggest that July will be classically average overall. Fine, not too hot spells, with occasional depressions bringing cooler weather and showers.

On to August. Apart from last year this month has been a real disappointment the previous few years. Looking at the probabilities would suggest that August will be the most disappointing month.

august2017

Looking at the above probabilities there seems a fair chance of something cooler than average.

There’s not really much to go on. I note the Met Office is going for ‘warmer than average’ but a look at their methodology and the coming season doesn’t look that exciting.

* Taking into account the fact that temperatures in London are up to 0.66C warmer than they were 100 years ago I have added 0.66C to mean temperatures before 1915.

** Obviously, in the event of a series of direct hits from thunderstorms, my rainfall estimate could be hopelessly short – a symptom of abundant solar energy at this time of year which creates a ‘noisy’ atmosphere compared with winter.

*** The 1981-2010 average mean for summer in this region is 17.6C, with 144.9mm of rain and 564 hours of sunshine

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What is happening to Wanstead Park’s lakes?

Lack of rainfall and a broken pump have been cited by City of London Corporation as the main reason for the shocking levels of the ponds through the park.

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The Ornamental Water by the Grotto is virtually dry. Images courtesy of Ralph Potter

The plight of the water courses has been well documented of late; a press release from the Corporation explains the catalogue of issues hampering efforts to address the problem. Closer scrutiny of these reasons, however, suggest that too much is being blamed on the weather.

A study of local rainfall back to 1981 suggests that though the ground water replenishing season (October 1st – April 24th) has been dry it is by no means out of the ordinary.

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As you can see from the graph the rainfall here has gone up and down like a yo-yo and 2016-17 is only the fourth driest period: 1991-92, 1995-96, 1996-97 and 2011-12 were drier.

The Corporation’s press release states: “2015-16 was a helpfully wet period for us…”

Wrong. 2015-16 was average. And if you consider annual rainfall 2015 saw 92 per cent of average rainfall recorded; 2016 was 93 per cent – placing 58th and 66th in driest years since 1797. Nothing out of the ordinary.

“2016-17 has, however, been an especially dry period with below average rainfall since Spring 2016.”

Wrong. See above detail. There have been three drier periods since 1981. And since March 2016, only half of the months have been notably dry, a period that included the third wettest June since 1797.

“January to March 2017 has seen roughly 50% less rainfall than average”

Wrong. January to March rainfall was 94% of the 1981-2010 average

April has been dry, and could be among the top 5 driest back to 1797, but it seems the Corporation are trying to blame nature instead of years of neglect on their part.

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The past months have seen much of Heronry Pond dry out. Image by Ralph Potter

 

The situation is in stark contrast to CoL’s other open space, Hampstead Heath, which has recently seen the completion of a £23m project to make safe the ponds there. CoL has deep pockets yet they have dithered for years over spending £25,000 to renovate the Coronation Bridge – and offer the people of Ilford a route into the park.
Figures released by CoL show it has only invested £1.23m in Wanstead Park over the last five years, compared with £50m spent in Hampstead Heath.

We are constantly told that problems in the park are ‘in hand’ yet progress on anything is painfully slow – and action to repair the pump has sadly come too late for much of the wildlife on Heronry Pond.

People from far and wide use Wanstead Park – they really deserve better!

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You can view City of London Corporation’s press release here

 

March 2017: very mild and dry

The mean temperature in March 2017 was the mildest in a local record going back to 1797.march 2017

A complete absence of air frost was mirrored in the mean which finished 10.5C, 2.8C above average and 0.3C higher than the previous record set in 1997.

The record temperature was probably down to notably mild air masses through the month as the total sunshine hours were about average, 107.2 hours is 99% of the 1981-2010 average.

The warmest day occured on the 30th with a high of 21.6°C in Wanstead, the warmest March day for 5 years.

Rainfall was very sparse, just 21.3mm were recorded, that’s 52% of average – a pattern that seems to be becoming more frequent; four of the last six Marches have been notably dry.

Sunshine was average. Over 107.2 hours were recorded, 99% of what we can expect to see during an average March.

The wettest day occurred on the 22nd with 5.8mm.

Air frosts: 0, Ground frosts: 1

Here follows the full weather diary for March. To view full stats follow this link:http://1drv.ms/1kiTuzv

1st: Sunny start, the sky gradually filling in with light rain at 3pm and into the evening. A windy night.
2nd: Sunny and blustery start, clouding over with some light rain in afternoon / evening. Drier overnight before area of light rain moved in at 0730z.
3rd: Cloudy start with light rain late morning. Feeling cold.
4th: Cold and cloudy with brief showers in the afternoon and overnight.
5th: Light rain at 9am and during the morning, briefly clearing at 10.30am before heavy showers moved in through the afternoon. Some warm sunny intervals in between. Showers into the evening until 10pm.
6th: Sunny start with just a few clouds around.
7th: Bright start with decreasing cloud to leave sunny late morning. Variable cloud through the afternoon. Rain at 00.50 until 0144.
8th: Light rain between 9 and 11am then showery though mostly light. Mild.
9th Sunny start though tending to cloud in late afternoon. Feeling mild.
10th: Cloudy with a burst of light rain at 10.30am.
11th: Bright, hazy start and feeling mild. Very quiet weather – pleasant in the garden.
12th: Cloudy with drizzle early afternoon
13th: Sunny start with a few cirrus, cloud gradually increasing but staying mostly sunny.
14th: Cloudy, mild and boring start – boring and cloudy all day.
15th: Misty start, quickly clearing to leave a glorious sunny day and pleasant.
16th: Sunny and clear up to 12 noon, then haze and cumulus pushing in and gradually thickening up. Light drizzle between midnight and early hours as cold front pushed through.
17th: Sunny but hazy start, this haze thickening through the morning. Feeling noticeably colder with patchy drizzle – felt quite inclement in the evening.
18th: Bright and breezy start. Then mostly cloudy with odd patch of drizzle.
19th: Cloudy, breezy with odd drizzle patch. Sunny intervals late morning and into the afternoon before clouding over in evening. Moderate rain at 1am.
20th: Cloudy and breezy start. Heavy showers spreading in with brief stair rods at 3pm, then clear and much cooler overnight.
21st: Sunny with well scattered cumulus.
22nd: Cloudy, dull and feeling cold in the wind. Showery rain, this turning heavier into the evening and to 1am.
23rd: Cloudy and breezy, some sun mid afternoon which felt warm.
24th: Cloudy, chilly and windy morning.
25th: Sunny and clear but with bracing easterly wind – pleasant outside the wind in the sun.
26th: Sunny and much more pleasant than yesterday with lighter wind.
27th: Cloudy and cold to start, the cloud breaking to long sunny periods that led to a pleasant afternoon. Cloudier overnight with cloudy, chilly dawn.
28th: Sunny, gin clear start. Cloud began building after noon with sun becoming ever more scarce. Light rain late evening and overnight.
29th: Cloudy and mild
30th: Sunny, though hazy start with lots of alto cumulus
31st: Cloudy and dull with brief drizzle at 9.30am. Cloud slightly less heavy at noon.

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.

February 2017: mild, dry and dull

A cold spell that saw a thin temporary covering of snow wasn’t enough to stop February 2017 from finishing mild. The mean temperature of 6.9C was 1.6C above the 1981-2010 average, the mildest February for three years. feb

The 20th saw the warmest February day in 13 years recorded, the 17.5C reached was marginally cooler than the 17.9C recorded on February 4th 2004.

Rainfall of 31.5mm was 80% of average – the driest February for 4 years. It was a dull month, some 44.6 hours of sunshine were recorded, just 61% of average, the dullest for 5 years.

The wettest day occurred on the 26th with 9.2mm.

Air frosts: 2

Ground frosts: 8

Snow falling: 4

So what has March got in store weatherwise? My long range forecasting method suggests the most likely scenario to be something rather cold waverage to slightly below rainfall

My February outlook for temperature, rainfall and sunshine was poor again.

Here follows the full weather diary for February. To view full stats follow this link:http://1drv.ms/1kiTuzv

1st: Cloudy with light rain late morning. Remaining cloudy into the afternoon and overnight with further light shower before obs time.

2nd: Cloudy and becoming breezy. Some intermittently light rain then cloudy. Broken cloud overnight.
3rd: Bright start with sunny spells developing – feeling warm in the sun. Cloud built up afternoon with rain at 4pm and 6pm. Rain at 8am.
4th: Light rain to start then bright spells late morning. Feeling chilly.
5th: Misty start and foggy out toward Epping. Some bright spells though mostly cold and cloudy. Broken cloud overnight with frozen dew at dawn.
6th: Sunny start with just a few wispy cirrus around. Clouding over after noon with rain in evening, heaviest at 8.45pm with bursts through the night. Min temp was at 9am yesterday.
7th: Cloudy, calm and damp start. Then clearing in afternoon for some mild sunny spells.
8th: Cloudy start and feeling really cold. Thick stratus cloud remained overnight – snow grains seen just before obs time.
9th: Cloudy and dull, snow grains seen. Mostly drizzle through the day.
10th: Dull and raw with occasional drizzle, sleet and snow grains falling all day and through the night – temporary dustings.
11th: Very light snow falling at 9am.
12th: Light snow at 9am with 1cm settling at Stanstead. Then cloudy and cold all day.
13th: Sunny start with sunny spells, clearance at noon.
14th: Cloudy start with complete clearance at noon.  Then variable cirro cumulus.
15th: Cloudy start and cloudy all day with some rain.
16th: Cloudy start breaking to sunny intervals afternoon.
17th: Cloudy start breaking to sunny spells at 10.30am, long sunny spells and mostly clear overnight.
18th: Cloudy start  with complete clearance after noon – cloudier spells overnight.
19th: Bright start but clouded over. Some drizzle at dusk.
20th: Cloudy start but sunny spells developing mid morning. Date record broken and warmest February day for 13 years.
21st: Cloudy and mild all day. Breeze picking up in the evening and into the night.
22nd: Cloudy and breezy start, the wind increasing through the day with occasional light drizzle. Some squally winds overnight.
23rd: Cloudy but with cold front clearance coming through at obs time – sunny spells thereafter but with squally winds – these increasing through the day with damage reported and trees down – a woman killed in Wolverhampton from flying debris.
24th: Sunny periods and feeling warm though shade felt cold. Early ground frost before cloud moved in – burst of rain in early hours.
25th: Cloudy and miserable with some rain in the late afternoon.
26th: Cloudy and miserable all day.
27th: Cloudy start but moderate to heavy prolonged showers moving in from 11pm. A miserable day with limited brightness.
28th: Sunny, gin clear start but with cirrus building frost west. Rain at 2.45pm, sporadic through the rest of the afternoon / evening.

No ice day for London

There was much talk yesterday about a lot of the south of the England recording an ‘ice day’. screen-shot-2017-01-27-at-12-31-17

In the London area most places missed out because the temperature rose briefly above freezing around dusk and also just before the 0900 observation today.

So although it felt brass monkeys out there it doesn’t count.

Ice days are when the temperature fails to rise above -0.1C over a 24 hour period, usually from 0900 to 0900. The confusion over yesterday’s ice day was caused by the fact that some stations release a 06-18 maximum reading – both Kenley and Shoebury stayed below zero in this time period.

Ice days in the Wanstead area are probably even rarer than decent snowfalls. Since 1959 there have been 81 ice days.
The last time the temperature failed to rise above 0.0C was January 20th 2013. The last time the temperature failed to rise above -0.1C (a true ice day) was January 6th 2010.

screen-shot-2017-01-27-at-12-01-35

screen-shot-2017-01-27-at-11-51-46
Over a dozen stations stayed below freezing for 24hrs to 09z on January 27th

Stephen Davenport’s synoptic analysis of the event is included below:

“[The cold conditions were] all thanks to this nicely (or not nicely, depending on your view) blocked situation. On Tuesday 24th a 500 hPa ridge started build northeastwards to the north of  a small upper low situated over France. By 12z on Wednesday 25th it had cut off to leave a classic-looking Rex block over western Europe:

Surface winds from the Continent started to bring colder air across as the temperature anomaly analysis for 12z Wed 25th shows, while milder southerlies continued across Ireland and Scotland, and brushed western Wales and SW England:

By 12z Thursday 26th the block was becoming more omega-like…

… and cold air continued to percolate north-westwards from the Continent farther across the British Isles:

There’s a certain beauty in the sinusoidal flow around a Rex block, I always think.”