How will ex-Hurricane Cristobal affect the UK’s weather next week?

27 08 2014

The third tropical storm in the North Atlantic, Cristobal, has been making some headlines about its potential positive impact on us here in the UK – so what’s actually happening?

Cristobal is currently categorised as a hurricane and is currently between Bermuda and northeast Florida in the western Atlantic.

The storm is forecast to move north-east across the Atlantic over the coming days, changing to an ex-hurricane as it moves away from the warmer waters where it formed.

However, unlike ex-Hurricane Bertha which moved straight to the UK and brought strong winds and heavy rain to much of the British Isles, ex-Hurricane Cristobal is set on a very different track.

Instead it is forecast to move towards Iceland, staying well away from the UK as you can see from the forecast pressure chart below.

Forecast pressure chart for 1pm on Sunday 31 August shows ex-Cristobal heading towards Iceland.

Forecast pressure chart for 1pm on Sunday 31 August shows ex-Cristobal heading towards Iceland.

As Cristobal tracks to the north-west of the UK it could bring stronger winds across northwestern parts of Scotland for a time and there will also be some rain moving across the UK on Sunday into Monday.

It will have a longer lasting and more positive impact on our weather, however, as the track of the storm will result in an area of high pressure building further to the south and over the UK.

This high pressure will be maintained through next week as the jet stream moves to the north of the UK, bringing settled conditions across the country.

At this time of the year, high pressure generally brings dry and fine weather with some spells of sunshine, and that’s what we expect to see from around Tuesday next week.

With high pressure, daytime temperatures could reach the low to mid 20’s Celsius in places. This warmth will be especially noticeable following the cool conditions of late.

This spell of warm weather, however, doesn’t fit the definition of an Indian Summer – which you can read about on our website.





Statistics announce an average autumn

29 11 2013

Early statistics for autumn 2013 suggest it has been a fairly normal season overall with temperature, rainfall and sunshine amounts all quite close to the long-term average.

Our early season assessment for autumn (Sep-Nov) uses figures from 1 September to 27 November, then assumes average conditions for the final few days of November.

According to that estimate, the UK mean temperature for the season is currently 9.8 °C, just 0.4 °C above the long-term average.

UK rainfall over the same period was 331.7mm, which is about 96% of the long-term average. Sunshine is similarly close to average, with the UK’s 274.4 hours adding up to 97.3% of the long-term average.

As ever when looking over a season, there can be a lot of variation within the three months. For example, while September’s temperatures were average, October was well above average and November was slightly below – but overall they make a fairly average season.

Similarly with rainfall, the period from mid-October to mid-November was wet and unsettled, but the remainder of autumn has been generally on the dry side, so rainfall statistics are also unremarkable taken as a whole.

Autumn 2013 will most likely be remembered for featuring the St Jude’s Day storm, which was one of the most significant and disruptive storms to impact the UK in the past few years.

Full statistics for Autumn and November will be available on our climate pages later next week.

Early autumn statistics:

Mean Temperature Sunshine hours Rainfall  
Autumn Actual Diff from Avg Actual % of Avg Actual % of Avg
  degC degC hours % mm %
UK 9.8 0.4 267.0 97 331.7 96
England 10.7 0.4 294.9 97 268.2 108
Wales 10.4 0.6 242.9 88 434.7 97
Scotland 8.3 0.3 229.7 101 414.6 87
N Ireland 9.8 0.3 254.0 100 300.7 93




UK’s unsettled weather and the jet stream

21 10 2013

The UK is set to see unsettled weather throughout this week as heavy rain and windy conditions are expected to affect many areas, whilst temperatures will remain mild for the time of year.

We talk about the jet stream quite a bit in the UK because it has such a big influence on our weather, and this week is no exception as it’s playing a leading role in determining the unsettled outlook.

What is the jet stream?

The jet stream is a band of fast moving westerly winds high up in the atmosphere which circle around the pole in the northern hemisphere. It can feature winds of up to 200 knots (230 mph) or more, and these winds tend to guide wet and windy weather systems which come in off the Atlantic.

The jet moves around a fair bit and its position can have a big impact on weather here in the UK depending on where it is.

If the Jet is over the UK or just to the south, we tend to get a lot of wet and windy conditions as it brings weather systems straight to us. If the jet is to the north of us, it guides that changeable weather away to the north to leave the UK with more settled conditions.

What’s the jet stream doing now?

Unsurprisingly given the outlook for this week, the jet is positioned more or less directly over the UK – but it’s the detail of its track which is important.

As you can see from the picture below, the jet currently swoops south from western Canada – moving over the Atlantic before taking a sharp turn north to head over the UK.

Forecast chart showing  expected position of the jet stream at 1pm on Tuesday 22 October

Forecast chart showing expected position of the jet stream at 1pm on Tuesday 22 October

This means relatively cool air is being dragged south then over the Atlantic, where warmer seas heat the air from below. This causes the air to warm and rise – creating instability and generating cloud and rain.

By the time weather systems reach they UK they have picked up a lot of rain and relatively warm air, bringing us the wet but mild conditions we are currently seeing.

What’s the weather outlook?

Currently unsettled weather looks set to impact the UK through the week, with heavy rain affecting many areas at times.

There may be more settled conditions on Thursday, and perhaps again on Saturday, but looking further ahead into the start of next week the outlook is for unsettled weather to continue.

You can stay up to date with what to expect with our detailed forecasts out to 5-days and our weather warnings, as well as a general view of what we expect out to 30 days.

You can find out more about the jet stream in our YouTube video.





What is an ‘Indian summer’?

2 09 2013

After a warm, dry, sunny summer, the fine weather is continuing this week with temperature expected to reach 28 to 29 °C in the southeast on Wednesday and Thursday.

Many media reports are calling this an ‘Indian summer’, however according to the Met Office’s Meteorological Glossary, it’s a little too early in the year. An Indian summer is defined as a warm, calm spell of weather occurring after the first frost in autumn, especially in October and November.

William R Deedler, Weather Historian at the United States National Weather Service, describes it as “any spell of warm, quiet, hazy weather that may occur in October or even early November”.

The origins of the term Indian summer are uncertain, but several writers suggest it may be have been based on the warm, hazy conditions in autumn when native American Indians chose to hunt. The earliest record of the use of the term is in America at the end of the 18th century. Although William R Deedler also refers to a reference by a French man, John de Crevecoeur, in 1778:

“Sometimes the rain is followed by an interval of calm and warmth which is called the Indian Summer; its characteristics are a tranquil atmosphere and general smokiness. Up to this epoch the approaches of winter are doubtful; it arrives about the middle of November, although snows and brief freezes often occur long before that date.”

The term was first used in the British Isles at the beginning of the 19th century, but there is no statistical evidence to show that such a warm spell tends to recur each year. The warmest recorded temperatures in the UK in October and November are 29.9 °C on 1 October 2011, in Kent, and 21.1 °C on 2 November 1938, in Essex and Suffolk.

For the latest weather forecast go to www.metoffice.gov.uk/weather





Sorry, no heatwave in sight

8 08 2013

An article on the front page of today’s Daily Express suggests that there is a new UK heat wave in the offing for next week and temperatures could soar into the 90s °F (32-37 °C).

This is not a forecast from the Met Office and, sadly for those who enjoy the heat, there’s no sign that we will see a return to the prolonged hot and sunny weather we saw in July.

In the Express, the article talks about high temperatures on the continent – up to 104 °F (40 °C). This may be the case in parts of continental Europe, but that doesn’t mean we’ll see temperatures like that in the UK or even a heat wave of any description. For that continental air to impact us, you’d need a very specific weather pattern and – looking at several of the world’s leading weather prediction models – there is no sign of that at the moment.

However, we do expect to see periods of decent, sunny weather over the next ten days or so (including today and tomorrow for some parts of the country). These will be mixed in with periods of more unsettled, wetter and windier weather. In fact, it looks like fairly typical mixed weather for the UK at this time of year.

In terms of temperatures, currently it looks like our highs will continue to be in the mid 20s °C – with the warmest weather being in south eastern parts of the country. Elsewhere temperatures are likely to peak in the high teens to low 20s °C.

You can see the outlook to the end of August and in to September on our website.





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.





What has brought the warm autumn weather to the UK?

27 09 2011

Over the next few days we are expecting a spell of very warm weather for this time of year across much of England and Wales and even parts of Scotland too. The reason why we are seeing this unseasonable warm spell is due to an area of high pressure which has developed across much of central Europe, centred on Germany and Poland.

This draws up very warm air from a long way south, from parts of France and Spain. That comes across a dry continent removing most of the moisture out of the air. As a result we see very little in the way of cloud with blue skies and plenty of sunshine. As a result the sunshine warms the ground and the ground warms the air so we see high temperatures for this time of the year.

In the video below Paul Gundersen, Met Office Chief Forecaster provides more details about this warm spell, how long it will last and whether this really is an ‘Indian Summer’.





Wet and windy weather signals the start of Autumn

6 09 2011

This week is forecast to be one of the windiest of the year, a typical beginning to autumn. Autumn is well known for its wet and windy weather stripping the colourful leaves from the trees.

One of the reasons behind the autumnal gales is at this time of year the earth is tilted so that the sun is over the equator. This means that the poles are cooling down whereas the sub tropics remain very warm, creating a massive temperature contrast over our half of the globe.

The deep areas of low pressure that you see on a weather map are caused by the differences in temperature between the cold pole to the north of the UK and the hot equator to the south. It is nature’s desire to even out these temperature differences and it is this that causes these vigorous systems to form, resulting in a lot of wind and rain.

So there is one benefit of the wet and windy week to come – without it, it would either be too hot or too cold.








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