When does Autumn start? Defining seasons

20 09 2012

Seasons are fundamental to how we understand the UK climate and the environment around us, but how do we define when they start and end?

In meteorological terms, it’s fairly simple – each season is a three month period. So, Summer is June, July and August; Autumn is September, October and November, and so on.

Of course, this is fairly arbitrary, but provides a consistent basis for the Met Office, as the holder of the UK’s national weather and climate records, to calculate long term averages and provide seasonal climate summaries from year to year.

Mike Kendon, of the Met Office National Climate Information Centre, said: “Defining seasons in this way means we can compare weather from one season or year to the next. It also has the advantage that each season is roughly the same length, neatly dividing the year into four quarters.

“Looking at longer timescales, our recently updated 30-year averages can show us how ‘normal’ seasons are changing over time, giving us clues about trends in the UK’s climate.”

Astronomical definitions of seasons also exist – using the Earth’s position relative to the Sun as the cue for separating one season from another via equinoxes and solstices.

So the Summer begins around the Summer Solstice, when daylight hours are at their longest (around 21 June), and ends around the Equinox, when days and nights are of equal length (around 21 September, on 22 September this year). Thus astronomical Autumn begins, continuing until the Winter Solstice, when daylight hours are at their shortest (around 21 December), and so on. Astronomical seasons therefore are about three weeks behind the meteorological ones.

One thing both methods have in common is that the dates are fixed by the calendar and don’t take into account what is actually happening in nature, which is after all how most of us understand the notion of seasons.

So comes the third method, which is based on phenology – the process of noting the signs of change in plant and animal behaviour.

In this distinction, Autumn may be deemed to have arrived at the first tinting of oak or beech trees, the appearance of ripe sloes or elderberries and the arrival of winter migrant birds such as redwings and fieldfares. Winter begins when native deciduous trees are bare, and so on.

For more than a decade The Woodland Trust has been using observations from thousands of members of the public to build a phenological record for the UK, called Nature’s Calendar. This builds on records going back over much longer periods of time.

It aims to give a comprehensive view of how nature defines the seasons in a record which takes into account how weather in individual years or longer term changes to climate may affect natural signs from one year to the next. As such it is a more fluid, natural definition of our seasons.

Dr Kate Lewthwaite, project manager for Nature’s Calendar for the Woodland Trust, said: “Taken individually the observations of what’s going on in nature provide only anecdotal evidence, but taken as a whole and analysed with temperature data, they offer a powerful insight into local and national impacts of environmental and climatic change.

“For example, our data shows that, on average, native trees are producing ripe fruit 18 days earlier than a decade ago, with a potential consequence being that animals’ food reserves could become depleted earlier in the winter. In contrast, leaf fall, indicating the end of the growing season, is often much later nowadays than in the past.”

Ultimately, however you choose to define them, it is weather and climate which govern the perception of the passing of seasons for plants and animals, including us humans.

So, like our weather, the exact timing of when we ‘feel’ one season is over and a new one has begun will always be liable to change. Whereas, in contrast, the meteorological seasons always remain fixed by calendar month.

Between the Met Office’s climate records and our forecasts up to a month ahead, you can stay up-to-date with what’s going on with the UK’s weather and climate.

Local Jubilee forecasts wherever you are with the Met Office iPhone and Android apps

1 06 2012

With the Jubilee weekend looking likely to see a typical mixture of British weather across the UK you can make sure you always have your latest local forecast to hand with our iPhone and Android apps.

Met Office iPhone and Android apps

The Met Office provides local forecasts for over 5,000 locations across the UK, so with events taking place up and down the country you will always have access to the latest weather forecast.

Latest figures from Comscore show the Met Office’s apps are one of the most accessed apps in the UK. Currently positioned at number 16 in the list, it is accessed more often than apps from Amazon and Groupon.

Since its re-launch in January, more than 2 million people have downloaded the iPhone app. The new Android app has been downloaded by over 340,000 people.

Sarah Weller, Marketing Manager at Mubaloo said: “The latest stats from Comscore highlight how the Met Office’s mobile channel has become a vital source of accurate and up to date weather forecasts for a huge number of people across the UK.”

The iPhone App includes 3 hourly forecasts out to 5 days ahead; UV forecast maps and information on the likelihood of rain. In addition to the iPhone, we also provide an App for Android phones and Smarter Weather for other smart phones.

Met Office in the Media – 31 May 2012

31 05 2012

There is a lot of interest in this weekend’s weather as the Jubilee celebrations draw near, so there has been plenty of coverage in the news about what’s in store.

Some articles have ended up wide of the mark, however, with one in particular claiming the weekend could be affected by Tropical Storm Beryl – which has already dissipated in the Atlantic and is no longer a tropical storm.

The Met Office forecasts the remnants of this storm to dissipate further as it moves across the Atlantic and not affect the UK’s weather.

So what conditions will we actually see over the Jubilee celebrations?

There’s a fairly complex weather picture developing for the UK, with high pressure to the north and low pressure systems moving into the south by Sunday.

Forecast pressure chart for midday on Saturday showing high pressures to the north and south of the UK, and two low pressure systems to the east and west.

This means the situation is finely balanced, but the Met Office expects a marked split in the weather from the southern half to the northern half of the UK.

Saturday is expected to be a largely fine and dry day for much of the UK. However, cloud and rain will never be far away from the south-west and here we expect it to turn increasingly cloudy with rain moving in during the second half of the day.

As we move into Sunday, the southern half of the UK will see rain – heavy at times – while the northern half once again sees the best of any dry and bright spells. It will, however, be much cooler than last weekend in all parts.

Looking forward to next week, the outlook is for variable weather conditions – with sunshine, showers, and occasional longer spells of rain. You can see a regularly updated forecast for Jubilee celebration events on our website.

After a spell of exceptionally warm and fine weather, it may be disappointing that this won’t last through to the Jubilee weekend. However, many parts of the UK will see some dry and bright spells at times.

It’s certainly not unusual to see some rain at this time of year, in fact the general weather picture is for some typically British weather.

Looking back at past weather on important events in the reign of Queen Elizabeth II, her Coronation Day on 2 June 1953 saw rain and relatively cool temperatures for the time of year – with a maximum temperature of around 12C. You can see what the weather was doing on other dates during her life and reign in our online infographic.

Definitely May-be an average month

30 05 2012

After a particularly cold and wet start, followed by a dry and exceptionally warm spell, May could be seen as anything but average.

However, the early monthly figures tell a different story – statistics from 1st to 28th of the month show temperature, rainfall and even sunshine are very close to normal.

This May is a stark example of why it’s difficult to judge a month at its halfway stage.

Up to the 15th the mean temperature for the UK was just 8.1 °C, 1.9 °C below the long-term (1971-2000) average.

Rainfall was running at 79% of the average too, well ahead for just halfway through the month, and sunshine was behind at just 41% of the average. This tells the story of a wet, gloomy and cold 15 days.

But around the 20th the UK’s weather changed its mood – giving way to a run of dry and fine weather, with some remarkably high temperatures.

This included a new maximum May temperature for Scotland – with 29.3 °C recorded in Achnagart, Highlands, on 25 May, beating the previous record of 29 °C set in 1992 at Edinburgh’s Royal Botanic Garden.

In all, it has been the longest warm spell in May since 1992.

This means that, as we draw near to the end of the month, the figures for May now look very different and spectacularly average.

Mean temperature for 1 to 28 May is 10.1 °C, just 0.1 °C above the long-term average. Sunshine is at 104% of the average with 192 hours, so a little above what we would expect, and rainfall is just below at 90% of the average, or 59.8mm.

Clearly these are early month figures and the statistics at the end of the month will change somewhat.

However, the story of this May so far illustrates perfectly just how variable the Great British weather can be. From being a very cold first half of the month, to record breaking temperatures in the second – even if statistically we have had an ‘average’ month, it has actually been a very interesting few weeks of weather.

You can see full summaires of the UK’s weather for every month going back to 2001 on the UK climate pages on our website. The full summary for May will be available a few days after the month has finished.

Climate figures for December 2010 and the year 2010

4 01 2011

There is widespread interest in the cold weather through December 2010 and what this means for UK climate statistics.

Following early statistics up to the 28th December  issued between Chrismas and New Year, the Met Office will issue provisional statistics that cover the whole of December and 2010 on Wednesday 05th January on the Met Office website.


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