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.

Snow!

It’s been snowing in Potten End continuously for 5 or 6 hours now. Just measured the depth and it’s around 5.5cm.

Snow, Potten End, 2pm, 18th Jan 2013

Snow continuing to fall as I type. May update later.

2012 – The Wettest Year on Record?

While preparing an article for our local parish magazine reviewing the weather for 2012 and comparing it with other years, I’ve been digging through the database to get some interesting statistics.

Was 2012 the wettest year on (our) record ?

Yes! And by some margin!

We recorded a total of 821mm (32.3″) of rain in 2012. The previous high was 722mm (28.4″) in 2008 and it’s nearly double the lowest recorded amount of 430mm (16.9″) in 2006.

Though please bear in mind our records only go back to 2005 (which is a year for which we only have partial statistics and is therefore not included in the analysis).

These are the figures:

• 2006: 430mm
• 2007: 572mm
• 2008: 722mm
• 2009: 665mm
• 2010: 500mm
• 2011: 545mm
• 2012: 821mm

There’ll be a slightly more detailed analysis and more comparisons in the full article which will appear in print towards the end of January and on line on 1st Feb.

And more snippets of information may appear here as I dig around a bit more.

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.