Potten End Newsletter Article 17

This article originally appeared in the Potten End Newsletter, October 2014.

Potten End Weather

““Life is not about waiting for the storms to pass. 

It’s about learning how to dance in the rain.” 

― Vivian Greene

About a year ago I wrote a short article about lightning. Since then, after much research I found that I’d barely scraped the surface of the subject. Indeed, some of the results of research in to lightning had not been published when that article was written.

The science of lightning is called fulminology, and the fear of lightning is called astraphobia. Hopefully this article will spark (sorry) some interest in fulminology which may help reduce any astraphobia.

Lightning is not distributed evenly around the planet. About 70% of lightning occurs over land in the tropics where the temperature difference and lack of stability within the atmosphere is greatest.

There are three primary types of lightning that we’re all fairly familiar with: from a cloud to itself (intra-cloud or IC); from one cloud to another cloud (CC) and between a cloud and the ground (CG). IC and CC are more common types of lightning, but CG is the most studied and understood.

There are a number of more rare and elusive types of lightning that are all fascinating in their own right.

Invisible Lightning

Not all lightning is visible. Sometimes, extremely intense bursts of energy are produced high up in a thundercloud. These bursts of energy are called Terrestrial Gamma-ray Flashes or TGFs. These TGFs are millions of times more powerful than normal visible lightning. TGFs were first discovered in 1991 and only properly observed in 2009. Their precise relationship to visible lightning remains a subject of ongoing scientific study. Fortunately the gamma rays are directed out in to space and don’t pose any problems to people on the surface of the planet.

ELVES

ELVES appear above thunderstorms as a very brief dull flattened disk of dim light around 250 miles in diameter at an altitude of over 60 miles. They were first recorded from the space shuttle orbiter Discovery in 1990. ELVES is an amusingly tortuous acronym for Emissions of Light and Very Low Frequency Perturbations due to Electromagnetic Pulse Sources.

Sprites

Sprites are large scale electrical discharges that are red in colour and appear above a thundercloud at altitudes between 30 and 60 miles. Sprites were named after the rascally sprite Puck in William Shakespeare’s A Midsummer Night’s Dream.

Blue Jets

Blue Jets are a type of sprite that appear from the top of a thundercloud and project up to 25-30 miles above the earth in a conical shape. They were first recorded from a space shuttle orbiter Atlantis in October 1989 as it passed over Australia. They are far rarer than sprites and do not appear to be triggered by a lightning strike. By 2007, less than 100 images of Blue Jets existed, the majority of which came from a single thunderstorm.

October Expectations

September marked the beginning of the meteorological autumn and, barring an Indian Summer, we can expect to fully notice the autumnal weather in October with shorter days, longer nights and a distinct chill and dampness creeping in. On average we can expect to see daytime high temperatures between 7.5ºC and 15ºC though we have seen a high of 25.3ºC in 2011.

•••

I would like to dedicate this to the memory of friend and neighbour Peter Griffiths who  inspired and motivated me to write this series of articles on weather. He will be greatly missed.

Potten End Newsletter Article 16

This article originally appeared in the Potten End Newsletter, May 2014.

Potten End Weather

“Water and air,
the two essential fluids on which all life depends,
have become global garbage cans.”
― Jacques-Yves Cousteau

In early April much of the country experienced periods of very high levels of air pollution caused, in part, by Saharan dust.

Storms in the Sahara whipped up a large amount of sand and dust into the upper atmosphere. Saharan dust settling in the UK is nothing unusual and can happen several times a year. Winds of around 20mph are required to lift sand into the atmosphere, and the Sahara had been experiencing wind storms in excess of 40mph at the time.

Normally the sand and dust settles in the countries of Southern Europe. In April however, winds from the south and east combined the sand and dust with industrial pollution from Europe. Our weather at the time was stable and calm which meant that the pollution gathered over the UK and was not dispersed.

According to The Department for Environment, Food and Rural Affairs (Defra), certain areas reached 10 out of 10 – or “very high” – on its air cleanliness scale for a few days.

When levels reach 7 to 9 on Defra’s scale, adults and children with lung problems and adults with heart problems are advised to reduce exertion.

When pollution levels reach 10, the general population is told to “reduce physical exertion, particularly outdoors, especially if you experience symptoms such as sore eyes, cough or sore throat”.
The deposit of fine Saharan sand on cars and buildings was just one visible effect of the event. The air was visibly hazy with some reporting a distinctly blue tinge to it. This resulted in some incredible sunsets.

Fortunately the event passed after a few days when wind and rain helped to disperse the pollution and remove the sand and dust from the air.

Recent studies suggest that air pollution can have wide-ranging effects on the weather. Parts of China and Asia have the highest levels of air pollution in the world and researchers have found that, especially during winter, these pollutants strengthen storms above the Pacific Ocean, which in turn feed into weather systems in other parts of the world.

The effects can be quite dramatic with the pollution causing thicker and taller clouds leading to heavier precipitation.

Potten End Newsletter Article 15

This article originally appeared in the Potten End Newsletter, April 2014.

Potten End Weather

Conquering the world on horseback is easy;
it is dismounting and governing that is hard.
– Genghis Khan

Recent reports suggest that Genghis Khan’s incredibly successful advance through Mongolia may have been helped by the mild, wet winters after a significant dry spell.

Scientists studying a 1,112 year tree ring record show that there was a fifteen year period of persistent moisture which was unprecedented in the previous 1,000 years.

This could have led to a rapid rate of growth of grassland which provided significant fodder for his war horses and favoured the formation of Mongol political and military power.

One other equally speculative consideration of a mild winter like the one we’ve just experienced is how insects, be they pest or delight, will fare. Common wisdom suggests that harsh winters decimate the insect population. But, to paraphrase a recent scientific study: “it depends”.

Insects relay on a huge number of strategies to survive the winter and it is more dependent on the availability of food than the actual minimum temperatures. It is thought that a mild winter can be more detrimental to the insect population than a harsh winter. During a mild winter, the hibernating insects may emerge earlier only to find that flowers have not developed sufficiently to provide them with enough food to sustain them and they will starve to death.

Soil moisture is another factor affecting insect survival. A damp mild winter may encourage the growth of fungal pathogens that kill insects. On the other hand, a dry winter may cause insects to dry out and die. Some insects are better than others at preventing water loss and may thrive in drier conditions.

Diseases, predators and parasites that have strong effects on insect populations are all affected by the weather in some way. And there is always the timing of reproduction when spring arrives and the local weather conditions at the time which will have more effect than any over-wintering issues the insects may have experienced.

So, as you can see, simply predicting insect populations from the type of winter we’ve experienced is about as straight forward and reliable as predicting the summer’s weather in March!

As I write this article, we’re experiencing some nice warm dry weather. It’s the first prolonged dry spell for England since the start of December. The aquifers and reservoirs are full to the brim (possibly the fullest they’ve ever been) and we’re almost certainly not going to experience a hosepipe ban this year and possibly next year which is good news for gardeners and car-washers alike.

Let’s hope the dry spell lasts long enough to enable those who have been flooded out to rebuild their lives and return to some sort of normality more quickly.

The temperature, wind, rain and many other weather measurements can be monitored live on the Potten End Weather web site.

Potten End Newsletter Article 14

This article originally appeared in the Potten End Newsletter, March 2014.

Potten End Weather

H:”What’s my temperature?”

L: “Wet and windy”

H: “That’s a barometer!”

– Laurel and Hardy

The country has been battered by fierce storms over the last few weeks. And as I write, despite it being a beautifully sunny day, there seems to be no end in sight. We have experienced the wettest December to January period since records began.

The latest theory is that our bad weather is a result of higher than normal temperatures in Indonesia and the tropical West Pacific. This has caused increased rainfall in that region and has caused major changes to the Pacific jet stream which, when linked to the unusually strong North Atlantic jet stream, has caused exceptionally bad weather both sides of the Atlantic.

As I have discussed before (Newsletter Article, October 2013), the highly variable nature of the British climate does not help when trying to link these extreme weather events with global warming. The Met Office say there is “… no definitive answer on the possible contribution of climate change to the recent storminess …”. They then go on to say that the increase in the intensity of daily rainfall rates is consistent with what is expected from a warming world.

Going back a few years in the Potten End Weather Archives, I’ve counted up the number of rain-free days we get in the months from November to February.

Rain Free Days

We can see that so far this year January and February have been exceptionally rainy with only a small number of days where rain has not fallen. It is difficult to find any other increasing or diminishing trend in the table. But the sample size is very small compared to the data that the Met Office works with.

When I started out saying there was “no end in sight” to the current poor weather, that really refers to the more accurate five-day weather forecast at the time of writing. The longer range forecasts show that while the weather may remain unsettled in to the middle of March, we should be expecting longer spells of drier weather with temperatures slightly above the seasonal average. Whether that will be enough to bring relief to the flooded areas of the UK remains to be seen. I sincerely hope it will.

The wind, rain and many other weather measurements can be monitored live on the Potten End Weather web site.

Potten End Newsletter Article 13

The article from the December 2013/January 2014 Pottten End Newsletter can be found here in a slightly modified form.

Potten End Newsletter Article 12

This article originally appeared in the Potten End Newsletter, November 2013.

Potten End Weather

“October extinguished itself in a rush of howling winds and driving rain and November arrived, cold as frozen iron, with hard frosts every morning and icy drafts that bit at exposed hands and faces.”
― J.K. Rowling, Harry Potter and the Order of the Phoenix


After a calm, mild start, this October turned blustery, cold, and wet. At the time of writing we’ve yet to experience frost. I’m sure we’ll get some frost before October ends and we’ll definitely get it in November.

Forecasting frost more than a few days in advance is incredibly difficult due to the wide range of conditions that affect air temperature. For example, on cloudy nights the cloud can act like a duvet, trapping warmer air near the surface which makes it unlikely that frost will occur.

Did you know there are three types of frost that form in very different ways?

Air Frost

An air frost occurs when air which is at least one metre above the ground cools below the freezing point of water.

Ground Frost

When the surface temperature of the ground, trees, hedges or other objects falls below the freezing point of water, frost forms on the surface of these objects. Some surfaces are more prone to frost than others. For example, grass is more prone to frost than concrete or tarmac surfaces because concrete and tarmac hold on to heat more than grass.

It is possible for ground frost to occur even if the air temperature is above freezing. The ground and other objects radiate heat away at night and can cool significantly even in late spring and early summer. This is why gardeners need to be wary of frosts until at least the end of May and perhaps slightly beyond.

Hoar Frost

Hoar frost occurs when dew freezes. Hoar frost is either a ‘feathery’ or a plain white frost of a more globular form.

When the temperature of the surface is below freezing before dew forms, the ‘feathery’ variety of hoar frost is created on the surface.

When the temperature of the surface falls below zero after the dew forms, the dew droplets freeze and the white globular hoar frost is created.

November Expectations

November temperatures can vary as wildly as they can in October. In 2010 November had a record high of 17.7°C at the start of the month and a record low of -6.1°C at the end of the month. The average November temperature is around 7°C.

We’ve recorded an average of just over 80mm rain in past Novembers with a high of 148mm in 2009 and a low of 29mm in 2011 which precluded our 2012 drought.

Have fun sweeping and raking up the leaves … or just wait until the wind blows them over to your neighbour!

Potten End Newsletter Article 11

This article originally appeared in the Potten End Newsletter, October 2013.

Potten End Weather

“Don’t knock the weather. If it didn’t change once in a while, 
nine out of ten people couldn’t start a conversation.”
― Kim Hubbard


Weather Fronts

Weather fronts bring a change in the weather and are frequently mentioned in weather forecasts. But what are they?

Weather fronts mark the boundary between two air masses. When the two air masses have different properties; for example, one air mass may be warm and moist while the other might be cold and dry, they produce a reaction in the zone where they meet known as a front.

This reaction is the principal cause of significant weather like showers, thunder showers and related unstable weather. It is caused by air being lifted and condensing in to clouds by the movement of the cold front under the warmer moist air.

The two main types of front are a warm front and a cold front. On weather maps these appear as a line with semi-circles and a line with triangles respectively. The semi-circles and triangles indicate the direction in which the front is moving.

Cold fronts can produce sharper changes in weather and move up to twice as quickly as warm fronts, since cold air is denser than warm air and rapidly replaces the warm air preceding the boundary.

A warm front moves more slowly than the cold front which usually follows because cold air is denser and harder to remove from the Earth’s surface. This also forces temperature differences across warm fronts to be more significant. Rainfall gradually increases as the warm front approaches. Fog can also occur at the head of a warm front.

When a cold front catches up with a warm from, it produces an occluded front. Occluded means hidden. On weather maps this is shown a line with both semicircles and triangles. In an occluded front, warm air is lifted up from the surface, and therefore ‘hidden’. An occluded front can be thought of as having the characteristics of both warm and cold fronts.

In the UK our unique weather is a result of us being an island nation between a large ocean to the west of us, a large land mass to the east of us and our position north of the equator. This means we experience a large number of frontal systems and their associated weather. It is one of the reasons why it is only really possible to forecast up to five days ahead with any degree of confidence.

October Expectations

October is a changeable month weather-wise. In the past, according to our records, we have seen temperatures as high as 25.3ºC (2011) and as low as  -1.7ºC (2008). On average we can expect to see temperatures between 7.5ºC and 15ºC. October can be a wet month with total rainfall between 20mm (2011) and 110mm (2006).

Potten End Newsletter Article 10

This article originally appeared in the Potten End Newsletter, September 2013.

Potten End Weather

“The reason lightning doesn’t strike twice in the same place 
is that the same place isn’t there the second time.” 
― Willie Tyler

At last, after a run of wash-out summers, we’ve finally had a summer worth talking about. July may not have been the hottest on record, but it was close. The Met Office put it in the top three on record. In Potten End it was the second hottest on record with a high of 34.9°C. In our records, the hottest July was in 2006 with a high of 35.2°C.

The long July heat wave was aided by a jet stream located to the north of the UK which kept a nice stable high pressure area over most of the UK.

Spectacular thunderstorms around the country marked the end of the heat wave. It’s quite common for storms like this to form at the end of a heat wave. Water vapour rising with the warm air forms water droplets which combine and turn to ice crystals as the air rises higher. The ice crystals fall as hail and pick up a negative electrical charge by rubbing against smaller positively charged ice crystals. This results in a negative charge forming at the base of the cloud and a positive charge forming at the top of the cloud. The negative charge is attracted to the surface of the earth and other clouds and objects. When the negative charge becomes too strong, lightning is discharged which balances the charge within the cloud.

Some interesting facts about lightning:

• On average, a lightning bolt lasts for about one 10,000th of a second.
• A lightning bolt contains enough energy to light a 100 Watt light bulb continuously for three months.
• Lightning speeds through the air at around 75 miles per second (around 270,000 miles per hour).
• Lightning is hotter than the surface of the sun reaching temperatures of around 30,000°C.

September Outlook

September marks the beginning of the meteorological autumn. We can obviously expect the temperatures to drop a little and the evenings will start to darken earlier. We can expect average temperatures of between 10.1°C and 19.6°C and a little more rain than August – typically around 30-50mm over the month.

Weather Online

Don’t forget that you can check on the weather in Potten End wherever you are by going to http://www.pottenend.org where there is also an archive of all previous articles, historical weather data and other interesting information.

You can also subscribe to the Potten End Weather Twitter feed at @pottenend. Live weather information is tweeted several times a day.

Please note that if you send twitter messages to @pottenend about local information or events, they can be re-tweeted to all of the Potten End Weather twitter followers.

Potten End Newsletter Article 9

This article originally appeared in the Potten End Newsletter, March 2013.

Potten End Weather

“Sunshine is delicious, rain is refreshing, wind braces us up, snow is exhilarating;
there is really no such thing as bad weather, only different kinds of good weather.”

― John Ruskin

The sun seems to have been particularly absent this winter. If we go through our records and add up the number of days where the temperature has been at or below 0ºC (an arbitrary but useful measure of a cold winter) then we find that, as this article goes to press, this winter (Dec 2012 to Feb 2013) is the fourth coldest. The top five coldest winters on our records are:

1. 2008/09:  47 days at or below 0°C
2. 2009/10:   45
3. 2010/11:    39
4. 2012/13:    38 (incomplete at time of writing)
5. 2011/12:    28

The remaining years on record average out at about 20 days below 0°C.

Solar Cycles and Their Effect on the Winter

The sun goes through regular cycles of activity in which sun spots, solar radiation and many other factors vary dramatically. These solar cycles have a duration of around 11 years and have been observed for hundreds of years.

Solar cycles were discovered in 1755 and we are now in cycle 24 which started in March 2012.
Recent research for the Met Office by Imperial College London and the University of Oxford suggests that the variability of ultraviolet radiation from the sun over the solar cycle may have a much larger effect on our climate than previously thought.

When the UV levels are low, unusually cold air forms high up over the tropics and is balanced by a more easterly flow of air over the mid-latitudes. This is a pattern that brings easterly winds and cold weather to northern Europe.

The opposite occurs when UV levels are high and westerly winds bring warmer air and milder winters.

Measurements of solar activity indicate that the minimum occurred around December 2008.

No coincidence then that this was the coldest winter we have recorded in Potten End.

This research won’t help with short term forecasts (measured in a small number of days) but it will probably help the Met Office improve seasonal forecasts for months and even years ahead.

The effect of the solar cycles should not be blamed on general global warming. Joanna Haigh, Professor of Atmospheric Physics at Imperial College London, says:

“Compared with the effect of man-made emissions over the last century, solar variations still have a very minor effect on long-term global climate trends, but this study shows they may have a detectable influence on winter climate.“

March Averages

It is said that March comes in like a lion but goes out like a lamb. These are March’s averages over the first and last week for all years on our records:

• Temperature: starts at 3.3ºC, ends at 8.2ºC.
• Daily rain: starts at 1.5mm, ends at 1.3mm.
• Peak rain rate: starts at 0.5mm/hr, ends at 2.9mm/hr.
• Wind gust: starts at 11.1mph, ends at 12.8mph.

Temperature and daily rain concur with the saying, peak rain rate and wind gusts would differ. Feel free to interpret them individually or all together at your leisure!

Hope you all have a great spring in spite of or because of the weather!

Potten End Newsletter Article 8

This article originally appeared in the Potten End Newsletter, January/February 2013.

Potten End Weather

Teacher: “What is a blizzard?”
Stanley: “A blizzard?! … A blizzard is the inside of a buzzard”.
– from the Laurel and Hardy film “Pardon Us”, 1931

A Review of 2012’s Weather

2012 was certainly a year to remember. Apart from the phenomenal Olympic Games when the weather really excelled itself along side our athletes, it felt like most of the year was more like the washout that accompanied the Diamond Jubilee weekend.

The Met Office say that 2012 was the second wettest in the UK on record (the wettest was 2000 by 6.6mm). In Potten End however, it was by far the wettest year on our records (though admittedly 2006 is our earliest complete year of data). I’m pretty sure we’re not going to see a hosepipe ban this year!

Potten End Rain Totals and Wettest Months

Temperatures

Last year may not have had record hot temperatures, but it made up for it with the coldest day on our records which was 11th February 2012 with a temperature of -9.5ºC.

The hottest temperature we have on record is 35.2ºC on 19th and 25th of July. The hottest in 2012 was 31.4ºC on 19th August

Wind

Another record breaker last year was the highest recorded windspeed. On 15th June a gust of 21.9mph was recorded. 2012 was also the windiest year we have on record with 8 days where wind speed was 15mph or more

Winter and Spring

Past performance is no guarantee, but from our records we note that: February and March have about 9 or 10 days of rain on average; The minimum average temperature in February and March is around 2ºC with maximum averages of around 8ºC for February and 11ºC for March.

Potten End Newsletter Article 7

This article originally appeared in the Potten End Newsletter, December 2012.

Potten End Weather

“A snowball in the face is surely the perfect beginning to a lasting friendship.”
― Markus Zusak, The Book Thief

We’re finally in to the winter season with this issue of the Newsletter, and there can be no more obvious subject than snow.

Snow is formed when moist air in the atmosphere is at a temperature of 2°C or less. The moisture in the air then freezes to form tiny ice crystals. These ice crystals collide, join together and form snowflakes. If enough of them join together, they become heavy enough to fall to the ground.

Surprisingly, the heaviest snow falls in the UK tend to occur when the temperature is between zero and 2°C. Above that temperature, the snowflakes melt and fall as sleet or rain.

Snowflakes that fall through dry, cool air will be small and powdery and they won’t stick together. This is the kind of snow that skiers prefer.

At slightly higher temperatures, snowflakes will melt around the edge and join together to form larger wetter flakes. This is the kind of snow that is perfect for making snowmen and snowballs because it sticks together easily.

In Potten End we get snow on average between 10 and 20 days each year, though much of this snow does not settle. Snow does settle and remain on the ground for around 5-10 days each year on average (statistics based on Met Office data from 1971 to 2000).

Fresh-fallen snow settles at a depth of roughly 12 to 1 of equivalent rain. This means, for example, that 30cm (or 1 foot) of snow depth is approximately equal to 2.5cm (or 1 inch) of rain.

Forecasts

It is very difficult to accurately forecast snow for the UK because the UK is positioned between the Atlantic Ocean and mainland Europe and because of the volatile weather patterns we experience.
This means it’s a very fine line between forecasting rain or snow.

White Christmas?

Most people think of a White Christmas as a beautiful white covering of snow falling on Christmas day. The official definition is significantly less romantic in that it involves the observation of a single flake of snow falling at a particular location at any time on 25th December. It’s even less romantic to think that that single flake of Christmas snow may be a part of a thoroughly unpleasant mixed shower of rain and snow. Pity the poor Met Office employee who has to stand outside in the freezing snow watching and waiting for that snowflake! To be honest, we’re pretty sure it doesn’t happen exactly like that!

The chances of this Christmas being White are currently being estimated at around 20% for the country south of Yorkshire/Lancashire. But there is a huge amount of uncertainty around this figure.

Whatever the weather, I wish you all a happy and peaceful Christmas!

Potten End Newsletter Article 6

This article originally appeared in the Potten End Newsletter, November 2012.

Potten End Weather

“For man, autumn is a time of harvest, of gathering together.
For nature, it is a time of sowing, of scattering abroad.”
— Edwin Way Teale

An Indian Summer

At the time of writing, the notoriously unreliable long range forecasts make mention of an Indian Summer. It’s a phrase often heard, but what does it mean and where did it come from?

An Indian Summer is a warm, calm spell of weather occurring in autumn, especially in October and November. The earliest recorded use of the phrase was in America in 1778 and it is thought to have been in wide use there before that time. It wasn’t in popular use in the UK until the 1950s.

The Indian part of the phrase refers to Native Americans living on the east coast who used to rely on the extended warm season to complete the harvest and increase their food stores for the winter.

A record high temperature of 29.4°C was recorded in the UK on 1st October 1985 in the town of March in Cambridgeshire during one Indian Summer giving rise to the favourite quiz question: “When was the October temperature record set in March?”.

Fog and Mist

Fog and mist is formed when a moist cool, stable air mass is trapped underneath a warm air mass. Water vapour condenses in to tiny water droplets which remain suspended in the air. The source of the water vapour is usually ground-based like a river, lake or just wet ground.

The difference between fog and mist is simply visibility. If you can see less than 1km then it is fog, otherwise it’s mist. There are more strict definitions and classifications for aviation purposes.

In 1952, a thick fog, which became smog due to airborne pollution, turned in to the worst pollution event in the history of the UK. It was a particularly severe phenomenon caused by a period of cold weather with a slow-moving high pressure zone and windless conditions that collected and contained air pollution from coal fires. It lasted from Friday 5th to Tuesday 9th December, caused huge disruption and is estimated to have killed more than 12,000 people in the aftermath. As a result of the tragic loss of life, the Clean Air Act of 1956 was passed.

Potten End Skies

With clear skies it will be a great year to see the Leonids meteorite shower this year. A young crescent moon will set shortly after sunset which means the skies will be nice and dark – perfect for meteor watching. The shower peaks between midnight and dawn on Saturday November 17th. You need to look to the East in the constellation of Leo and you can typically expect to see an average of 10-15 pale yellow and blue meteors an hour and perhaps as many as 40 an hour if you’re lucky.

November Expectations

Crunching the numbers in our weather database, we find an average Potten End November to have around 80mm of rain, with an average daily high temperature of around 10°C and an average daily low temperature of just above 4°C. The autumn rain has steadily diminished in recent years which is partly why we are short of water in the summer. Whatever happens, make sure you enjoy your autumn!

“It was one of those perfect English autumnal days
which occur more frequently in memory than in life.”
— P. D. James

Potten End Newsletter Article 5

This article originally appeared in the Potten End Newsletter, October 2012.

Potten End Weather

“Autumn is a second spring when every leaf is a flower.”
― Albert Camus

Autumn is upon us, it’s getting colder and the nights are drawing in. Long range ‘White Christmas’ forecasts are being published but at the moment these are more for entertainment value than serious contingency planning. If you’re interested, the chances of a white Christmas are currently 20% south of Yorkshire and Lancashire and 25% north of there.

The meteorological seasons are different to the commonly seen astronomical seasons which are based on the equinoxes and solstices. In 1780 the Societas Meteorologica Palatina, an early international organisation for meteorology, defined seasons as groupings of three whole months. As a result in the northern hemisphere autumn starts on 1st September, winter starts on 1st December, spring starts on 1st March and summer starts on 1st June.

Wind Chill

With the increasingly cold weather, we’ll start to hear about wind chill in the forecasts. More recently this has been referred to as the ‘Feels Like‘ temperature. It’s the apparent temperature felt by people (as well as other warm blooded creatures) during cold and windy conditions. It’s not just a rough figure guessed at by forecasters. There is a sophisticated formula used to calculate the ‘Feels Like’ temperature that takes into account  things like modern heat transfer theory, skin tissue resistance and, of course, wind speed at around 5 feet which is the average height of a human face. We use the formula to provide the ‘Feels Like’ temperature on our web page (www.pottenend.org). It’s only calculated for temperatures below 10°C.

Jet Stream

This past summer, the Jet Stream has played a huge part in making our weather foul or fabulous. Existence of the Jet Stream was hinted at after the 1883 eruption of the Krakatoa volcano. The plume of ash from the volcano was observed over several years and became known as the “equatorial smoke stream”. In the 1920s, a Japanese meteorologist observed the jet stream using weather balloons launched near Mount Fuji. It wasn’t until 1939 that the term Jet Stream was coined by German meteorologist Heinrich Seilkopf. The original German term was Strahlströmung (or Strahlstrom in modern German). The real understanding of the nature of Jet Streams came during World War II when transatlantic flyers noticed tail winds in excess of 100mph.

There are two jet streams per hemisphere. The subtropical and the polar. Occasionally they merge in to one. It is the polar jet stream that broadly defines our weather and depending on whether it moves further north or further south, the weather is warmer or colder. In general, if it moves north, then the UK has better, warmer weather. This year, and in 2007, the polar jet stream stayed mostly south for the summer which resulted in severe flooding.

Outlook

We’re expecting nothing unusual for October’s weather. A low pressure area will dominate, bringing rain and temperatures of around 14-17°C which is average or slightly above average. We may enjoy the odd bright spell, but not for long.

In the night sky we can expect to see a great show of Orionid meteors from October 20th to the 24th in the south east. There should be about 20 pale yellow and blue meteors an hour. The Orionid meteors are produced by dust from the tail of Halley’s comet.

Potten End Newsletter Article 4

This article originally appeared in the Potten End Newsletter, September 2012.

Potten End Skies

From Meteorology to Meteors and Beyond!

A slight change of course in this issue takes us from meteorology to meteors and beyond.
We’re lucky to have relatively dark skies in Potten End. Free from the pollution of excessive lights, the skies are dark enough to view lots of interesting celestial objects that town and city dwellers will sadly miss.

Meteors or shooting stars are not as rare as you might imagine. Spend half an hour looking up at a clear night sky and you’ll often see a couple in the corner of your eye. You have to be lucky to see them directly as they pass very rapidly. It’s a little late to see the Perseid meteor shower that peaks every year between the 9th and 14th of August but this year the skies were slightly overcast during the critical time so you haven’t missed much. In perfect conditions the Perseid meteor shower can be quite spectacular as it produces over 100 visible meteors an hour with colours ranging from pale yellow to orange and blue.

Meteors are caused by small particles of debris (ranging from dust to the size of a small pebble) burning up in the atmosphere between 75km and 100km above the Earth leaving a visible trail of hot gases and melted meteoroid particles. The Perseid meteor shower is caused by dust particles from the tail of the Swift-Tuttle comet entering Earth’s atmosphere at around 132,000 miles per second.
Regular meteor showers are named after the area in the sky from which they appear to originate. The Perseid meteors appear to radiate from the constellation in the North East named after the Greek hero Perseus, and have been regularly observed for at least 2,000 years with the first written observations made in 36 AD in the Far East.

The next meteor showers to look out for are:

• the Orionids from October 20th to the 24th which should produce about 20 pale yellow and blue meteors an hour.
• the Leonids from November 17th to the 18th which should produce about 40 pale yellow and blue meteors an hour.
• the Geminids from December 13th to the 14th which should produce about 60 multi-coloured meteors an hour.

September has a few interesting celestial events. The equinox (when night and day time are equal) occurs on 22nd September. The days start getting shorter from that point. The full moon closest to the equinox is called the Harvest Moon and that happens on September 30th. It’s called the Harvest Moon because the light from the full moon allowed farmers to work longer hours in the fields in the autumn.

The International Space Station (ISS) will be visible towards the end of September. You can hardly miss it as it is extremely bright and fast moving – quite different to a high flying jet plane or a satellite – but you’ll have to be up and about very early in the morning to see it.

I’m hoping for better weather and clearer night skies in the weeks ahead, but all long range forecasts continue to indicate unsettled weather for the foreseeable future. However it’s worth taking a long look at the night sky whenever you get the time. There’s always a chance of seeing something truly awe-inspiring.

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“Look up at the stars and not down at your feet”
Professor Stephen Hawking,
London Paralympic Opening Ceremony 2012.

Potten End Newsletter Article 3

This article originally appeared in the Potten End Newsletter, July 2012.

Potten End Weather

There are an enormous number of old wives tales and country sayings that relate to the weather. Some of them are complete hogwash, but many of them have a basis in scientific truth.

Perhaps the most common, “Red sky at night, shepherd’s delight. Red sky in the morning, shepherd’s warning” is older than you might think and even appears in the Bible (Matthew 16) from as early as 1395. Undoubtedly the saying originated significantly earlier than that.

There is a scientific explanation behind the saying. When the sun is close to the horizon both at dawn and dusk, the sunlight travels to us through more atmosphere than at other times of the day. The red light is able to travel a more direct course and reflects off clouds giving a red sunrise or sunset. Bluer light is more scattered and less of it is reflected from the clouds.

In the UK and in the northern hemisphere in general, weather predominantly comes from the west. If red light is reflected off the clouds in the morning then those clouds are probably headed our way bringing with them an increased chance of rain. And if we see red clouds at night, then the chances are that the clouds have already passed us and we’re in for a nice day tomorrow.

The Rain in June

“And when it rains on your parade, look up rather than down.
Without the rain, there would be no rainbow.”
G. K. Chesterton.

From the weather archives, the average rainfall for the month of June is 38.4mm. The last measurement for June before publication showed we had 128mm of rain (333% more than local average) and the indications were that more was on the way.

So why are we still in a drought according to our local water company? The reason is that Veolia Central take most of their water from underground. They say that “Following two years of very dry weather before April, our groundwater levels remain very low.”

Because most rainfall in the spring and summer is either absorbed by plants or is lost to evaporation, very little of the rain makes it to the aquifers. However, we’ve had exceptional rainfall recently and the good news currently is that the aquifers are starting to fill up. They are still at a “Notably low” level according to the Environment Agency, but at least that’s one level up from the “Exceptionally low” level that they were at a couple of weeks ago.

At least the garden isn’t suffering too much from the hosepipe ban at the moment.

Potten End Newsletter Article 2

A condensed version of this article originally appeared in a special commemorative edition of the Potten End Newsletter, June 2012. Also, there were some minor mathematical errors in the original article – they have been corrected here.

Potten End Weather

I’ve taken a bit of a departure from my planned series of articles to briefly write about the extraordinarily wet April we’ve just had.

Also, as this is a special commemorative issue of the Newsletter, I’ve been digging around in the weather archives of the Met Office and other sources to find out what the weather was like over 60 years ago.

The Wettest April on Record

The rain it raineth on the just
And also on the unjust fella;
But chiefly on the just, because
The unjust hath the just’s umbrella.
– Lord Bowen

The Met Office declared April 2012 the wettest since records began in 1910. And it certainly felt that way. In fact, our region of the UK received 237% more rain than the average April rainfall from 1971-2000.

How do our Potten End records compare to that? Well, we measured a total of 113mm of rain in April. This is the wettest April we have on record by quite some margin. Here are the rainfall totals for April in previous years:

• 2011: 8mm
• 2010: 12mm
• 2009: 20mm
• 2008: 45mm

And it rained every day from April 17th to the end of the month. The wettest day being Sunday 29th April with a total of 21mm falling that day.

Surprisingly, the sunshine amounts for April have not been far off the average.
Despite all that rain we’re still in drought conditions with a hosepipe ban because we still haven’t had enough rain in the east and south-east this year.

April has been in stark contrast to March, which was the fifth driest on record for the UK.

The Queen’s Weather

As this is the commemorative edition of the Newsletter, some have been wondering what the weather was like sixty years ago.

In February 1952 when Queen Elizabeth II was proclaimed Queen, the month started out mild and dry, but became grey and a little wet towards the end. It was the driest February compared to the surrounding years with only 11mm of rain that month. In February 1951, 121mm of rain was recorded.

In 1953, the month before the Coronation had been dry and warm with temperatures reaching nearly 32C in the week before the actual event. But the weather turned at the end of May and the day of the Coronation was decidedly cold, grey and wet. Though it did dry out in the afternoon, the high temperature was only 12C.

And This Year?

Because of the lead time in producing articles for the Newsletter, it is not possible to provide meaningful forecasts for the Queen’s Diamond Jubilee bank holiday. All long range forecasts tend to be very vague with a lot of wriggle room. Depending on where you look and how you interpret trends, the weather will always be some combination of hot, windy, wet, cold and dry.

As an example of just how variable long range forecasts can be, here are just some of the forecasts at the time of going to press:

There are indications that a high pressure zone will develop to the north of the UK which could mean a westerly or south-westerly flow will bring changeable conditions resulting in a ridge of high pressure which could bring some pleasant weather. On the other hand that could also mean that low pressure systems will be forced to take a more southerly track resulting in prolonged wet weather.
My favourite prediction is that the high pressure zone extends and moves south causing warm air to be pulled up from Africa or southern Europe. This gives rise to the effect known as the “Spanish Plume” heat wave. Olé!