More warm weather this week – but what’s in store for the summer?

13 04 2015

This week is set to see some unseasonably warm weather for parts of the UK – with temperatures expected to climb to the low to mid-20s Celsius in the south on Tuesday and Wednesday.

Warm air flowing up from the south west will combine with high pressure, bringing settled conditions and sunny spells for many.

Warmest days of the year so far

This week’s above average temperatures follow on from a similar spell last week, which saw temperatures top out at 21.9C at St James’s Park in London on Friday.

This was the ‘warmest day of the year so far’, but It looks like Tuesday and Wednesday will top that – which is to be expected as we head through spring and edge closer to the start of summer.

Unfortunately, the weather we get in April doesn’t necessarily tell us anything about the kind of summer we can expect. We’re still in the midst of spring, so it’s far too early to say what the months of June, July and August may hold.

Summer ‘heatwave’ speculation

That hasn’t stopped speculation about heatwaves, the warmest summer ever and record temperatures in the media. Some stories cite our three month outlook for contingency planners as proof of the impending heatwave, but this is in no way an accurate reflection of what it shows.

The outlook shows probabilities attached to different scenarios for temperature and rainfall over the whole three-month period it covers. This is useful for those who use probabilities to plan ahead on longer-timescales, but not very useful for deciding where and when to go on your UK summer holiday, for example.

What does the longer outlook show?

Our current three month outlook does show that above average temperatures are more likely than below average temperatures for the April-June period. The outlook is essentially the scientific equivalent of factoring the odds on a horse race and, just like a horse race, the favourite doesn’t always win.

It’s also important to note that above average temperatures over a three-month period could come about in a variety of ways in terms of actual weather – we can still see warmer than average temperatures when it’s cloudy and wet, for example. Also, even in an above average three-months not all individual months would need to be above average.

This just reinforces the point that the contingency planners outlook doesn’t tell us what specific weather we are going to see at a specific location. For the best information on the weather ahead, people should use the Met Office’s 5-day weather forecast supplemented with our 30-day outlook.

By keeping up to date with the latest forecast, you’ll always have the most up-to-date and accurate view of the weather in store for the UK.





Air quality issues in the UK – what’s really going on?

19 03 2015

There has been some media coverage about air pollution issues in the UK today, so what’s really going on?

It is true to say that since Tuesday this week the UK has seen elevated levels of air pollution. This is mainly due to high pressure dominating over the country, which means a lack of wind and atmospheric circulation which would normally disperse pollution.

This allows pollution from things like cars and industry to build up in the lower atmosphere, affecting our air quality. This means much of the pollution we are seeing is due to home-grown sources, but with some contribution of pollution from the continent.

As you can see from the current air quality forecast on Defra’s air quality pages, whilst most areas of the country are seeing moderate or low levels of pollutants today, some areas are seeing high levels.

The situation is improving, however, with air quality levels expected to return to a normal level over the next couple of days.

Levels we have seen over the past few days and today are by no means unusual – we expect to see conditions similar to this several times a year.

The air pollution is also nowhere near record levels – in fact, we saw higher levels than this during a period of poor air quality at about the same time last year.

It’s also worth noting that the current air quality issues don’t fit any scientific definition of smog – which is a term which describes a mixture of smoke and fog.

There’s no fog around at the moment and smoke would only be a tiny fraction of any contribution to the poorer air quality we’re currently seeing.

The main effects of the current conditions will be felt by individuals with existing heart or respiratory conditions, who may experience increased symptoms. More health advice is available online on Defra’s air quality pages.

Throughout the next couple of days, the Met Office will continue to work closely with Defra, Public Health England and Public Health Wales to ensure they have the most up-to-date and accurate air quality forecasts in order to provide relevant advice to the public.





‘Super tides’, the weather and coastal flood risk

20 02 2015

UPDATED 27/02/2015 – this blog has been updated under the section ‘So what are ‘super tides” with the help of the National Oceanography Centre.

In this joint blog from the Environment Agency and the Met Office, we look at the issue of so-called ‘super tides’.

There has been a lot of media coverage about the potential impact of so-called ‘super tides’ which are due from today (Friday, 20 February) through to Monday.

So what are ‘super tides’?

Tides are governed by the gravitational pull of the moon and, to a lesser extent, the sun. Because the sun and moon go through different alignment, this affects the size of the tides.

When the gravitational pull of the sun and moon combine, we see larger than average tides – known as spring tides. When the gravitational pulls offset each other, we get smaller tides known as neap tides. We see two periods of spring and neap tides roughly every month.

Yet some spring tides are higher than others. This is because tidal forces are stengthened if the moon is closest to Earth in its elliptical orbit (astronomers call this perigee). Tide forces are also enhanced when the sun and the moon are directly over the equater. For ths Sun this happens on or around 21 March or September (the equinoxes). Spring tides are always higher at this time of year. The moon’s orbit also takes it above and below the equator over a period of 27.2 days. Just as with the Sun, the tide generating forces are at their greatest when the moon is directly overhead at the equator.

Very large spring tides occur when these astronomical factors coincide. Approximately every 4.5 years the moon is closest to the Earth, and is also overhead at the equator, at either the March or September equinox.

In some places, these extreme tidal conditions can cause water levels to be 0.5m higher than a normal spring tide, but the weather can have a greater impact than even these largest of tides

What is the role of the weather in sea levels?

It’s important to realise that just because we are expecting big astronomical tides over the next few days, these won’t cause the highest sea levels we’ve seen – even in the last few years. That’s because the weather can have a much bigger impact on sea level than the 18-year tidal cycle.

Strong winds can pile up water on coastlines, and low pressure systems can also cause a localised rise in sea level. Typically the difference in water level caused by the weather can be between 20 and 30cm, but it can be much bigger.

On the 5th December 2013, for example, the weather created a storm surge that increased the water level by up to 2 metres. Although an estimated 2,800 properties flooded, more than 800,000 properties were protected from flooding thanks to more than 2,800 kilometres of flood schemes. The Environment Agency also provided 160,000 warnings to homes and businesses to give people vital time to prepare.

This highlights the importance of the Met Office and the Environment Agency working together to look at the combined impact of astronomical tides, wind, low pressure and waves on flood schemes to assess the potential impacts for communities around our coast.

Will we see coastal flooding this weekend?

Given the height of the tides there may be some localised flooding. Weather isn’t playing a large part in water levels over the next few days, although strong winds on Monday are likely to generate some large waves and push up sea levels slightly. This is nothing unusual for winter. You can see more about what weather to expect with the Met Office’s forecasts and severe weather warnings.

The Environment Agency and the Met Office are working together to closely monitor the situation, and the Environment Agency will issue flood alerts and warnings as required.

In the Humber Estuary, for example, we are expecting total water levels of between 4.20-4.39 metres – well below record levels of 5.22m.

John Curtin, Environment Agency’s Director of Incident Management and Resilience, said:  “We are monitoring the situation closely with the Met Office and will issue flood alerts and warnings as required.

“It’s possible we could see some large waves and spray and urge people to take care near coastal paths and promenades and not to drive through flood water.

“However, we can only get a warning to you if you’ve signed up to our free service. People can also see their flood risk and keep up to date with the latest situation on the GOV.UK website at https://www.gov.uk/check-if-youre-at-risk-of-flooding or follow @EnvAgency and #floodaware on Twitter for the latest flood updates.”

For those in Scotland, you can see flood updates for your area on the SEPA website here.

For those in Wales, you can see flood updates in English and Welsh on the Natural Resources Wales website here.

You can also see John explaining the Environment Agency’s flood warnings here:





One year on – A look back to last winter

17 02 2015

This weekend marked the one-year anniversary of the Valentine’s Day storm, which also marked the end of a particularly stormy three-month period. A new review article – ‘From months to minutes – exploring the value of high-resolution rainfall observation and prediction during the UK winter storms of 2013/2014’ – written by 16 Met Office co-authors reviews the accuracy of our forecasting and warning of severe weather during winter 2013-14, and assesses its performance.

The paper concludes that the “prolonged period of high impact weather experienced in the United Kingdom during the winter of 2013/14 was very well forecast by the operational tools available across space and time scales.”

Here Huw Lewis, the paper’s lead author, and Derrick Ryall, Head of the Public Weather Service, look at the extreme weather last year and the role of the Met Office in communicating severe weather through the National Severe Weather Warning Service.

Analysis chart 1200 GMT 26 January 2014

Analysis chart 1200 GMT 26 January 2014

Winter 2013/2014 in the United Kingdom was remarkable. The country was battered by at least 12 major winter storms over a three month period and was officially assessed as the stormiest period that the United Kingdom has experienced for at least 20 years.

The series of storms resulted in the wettest winter in almost 250 years (according to the England and Wales precipitation series from 1766), significantly wetter than the previous wettest winter in 1914/1915.

Snapshot of UK rain radar surface rainfall rate for 2200 GMT on 23 December 2013

Snapshot of UK rain radar surface rainfall rate for 2200 GMT on 23 December 2013

The extreme weather caused widespread flooding throughout Southern England and coastal damage – most notably in the South West and Norfolk coasts. The impact of the severe winter storms on individuals, businesses and the government were substantial, including several fatalities, widespread power cuts and damaged infrastructure.

Recent advances in forecasting, technology and the scientific developments in meteorology have been considerable. These developments and improvements in accuracy mean that a four-day weather forecast is as accurate as a one-day forecast was just thirty years ago. During the course of last winter, the Met Office was able to use these forecasts to warn of any severe weather well in advance. In the case of the St Jude’s Day storm at the end of October 2013 warnings went out to the Government and the public five days before the storm even existed.

rainfall

As the accuracy of weather forecasts has evolved, so has the communication of the potential impacts of severe weather. The National Severe Weather Warning Service enables more ‘weather decisions’ which in turn help to minimise the consequences of severe weather. The Met Office was at the heart of the government response to the storms, providing advice on weather impacts through the National Severe Weather Warning Service and Civil Contingency Advisors. The Met Office also worked very closely with both the national and regional media, who in turn played a key role in ensuring that the public were fully informed about the potential impacts of any up-coming weather.

In addition to the Public Weather Service, commercial partners and customers were also provided with detailed updates throughout the period in order for them to plan effectively for logistical issues. Together, these advanced warnings helped authorities, businesses and individuals to be better prepared to take mitigating actions.

Driving further improvements in accuracy and therefore reducing the lead time and increasing the detail of severe weather warnings is one of the Met Office’s key priorities . The ultimate aim is to improve the potential for users to plan preventative measures for severe weather events much further ahead. Underpinning all of these developments is a continuing programme of scientific research and access to enhanced supercomputing over the next few years.





Very strong winds recorded over northern parts of the UK

9 01 2015

As forecast by the Met Office, a powerful low pressure system passed to the north of the UK in the early hours of this morning bringing exceptionally strong winds in places.

Two low level stations recorded wind speeds of over 100mph, with the gust recorded at Stornoway being the joint strongest recorded at the site (the other gust at that speed was recorded on 12 February 1962).

While the winds have now dropped significantly, it will stay windy through today in many parts and gusts will increase in strength once again tonight as another low pressure system is set to affect northern parts of the country. You can see detail on this on our forecast and warnings pages.

Below are some of the maxiumum gust speeds recorded during the first storm, between 10pm last night and 9am this morning.

Date and time Station Area Speed (mph)
09/01/2015 03:00 STORNOWAY AIRPORT WESTERN ISLES 113
09/01/2015 03:00 LOCH GLASCARNOCH ROSS & CROMARTY 110
09/01/2015 04:00 ALTNAHARRA SUTHERLAND 97
09/01/2015 06:00 WICK AIRPORT CAITHNESS 93
09/01/2015 03:00 ALTBEA ROSS & CROMARTY 90
09/01/2015 01:00 EDINBURGH BLACKFORD HILL MID-LOTHIAN 90
09/01/2015 00:00 SOUTH UIST RANGE WESTERN ISLES 90
09/01/2015 05:00 KINBRACE SUTHERLAND 87
09/01/2015 01:00 SKYE WESTERN ISLES 86
09/01/2015 07:00 KIRKWALL ORKNEY 86

The strongest wind in England was at High Bradfield, in South Yorkshire, which saw a gust of 76 mph at 1am this morning.

In Wales, the strongest gust was at Aberdaron, Gwynedd, with 76mph at 11pm last night.

For Northern Ireland, the strongest was 70mph at Killowen, County Down, at 10pm last night.

Winds are almost always stronger at our high level weather stations (those that are sited at 500 metres of altitude or higher), which are also often very exposed.  For this reason the winds from those sites are unlikely to reflect what the vast majority of people are experiencing. Bearing that in mind, the strongest gusts from the high level sites are quoted below for reference:

Date and time Station Area Height (metres) Speed (mph)
09/01/2015 04:00 CAIRNGORM SUMMIT INVERNESS-SHIRE 1237 140
09/01/2015 00:00 AONACH MOR INVERNESS-SHIRE 1130 129
09/01/2015 04:00 BEALACH NA BA ROSS & CROMARTY 773 124
09/01/2015 05:00 GREAT DUN FELL CUMBRIA 847 107
09/01/2015 05:00 GLEN OGLE PERTHSHIRE 564 102




Extreme global weather

5 01 2015

The UK may be experiencing what looks likely to be a milder than average winter but other parts of the globe are struggling against some extreme weather conditions.

Middle East

Heavy snow is expected to affect large parts of Turkey, Georgia, Armenia and SW Russia early this week. As the cold conditions spread east later in the week, strong to gale force winds and heavy snow are expected across more eastern parts of the Mediterranean.

This will lead to the Middle East seeing temperatures 10 or 15C below normal for the time of year. For example, overnight temperatures could fall to -10C in Syria by mid week, with daytime temperatures struggling to rise above freezing.

This is likely to have a significant impact on refugees and the humanitarian aid agencies in Turkey, Jordan, Lebanon, Syria and Iraq, with problems enhanced by the threat of frozen water supplies. Although overnight temperatures of -5 to -10C are expected, these values may well fall much lower if there is snow cover.

North America and Canada

Large areas of the USA and Canada are experiencing very cold conditions, with the threat of heavy snowfall across some parts over the coming days.

The eastward movement of a cold front over the weekend has dragged very cold air down from the arctic. Temperatures across parts of Canada have fallen to -30C, and widely across North America, daytime temperatures have ranged between 0 and -6C, with the bitterly cold conditions enhanced by strong winds.

As well as the low temperatures, some parts have seen heavy snowfall, such as the Pacific Northwest and areas to the east of the Great Lakes.

Further heavy snowfall is expected this week, particularly down-wind of the Great Lakes due to “lake effect” snow. This is caused when cold flows across relatively warm bodies of water such as the Great Lakes. The air rises in strong convective currents which creates clouds and heavy precipitation. In these very cold conditions, the moisture in the clouds will fall as snow.

Lake Superior (top left) and Michigan (centre) can be seen generating 'lake effect' snow. Provided by the SeaWiFS Project, NASA/Goddard Space Flight Center, and ORBIMAGE

Lake Superior (top left) and Michigan (centre) can be seen generating ‘lake effect’ snow. Provided by the SeaWiFS Project, NASA/Goddard Space Flight Center, and ORBIMAGE

The significance of this is highlighted by snowfall projections over the coming days. Lake Ontario, the easternmost of the Great Lakes with a surface area of 18,960 km2, is expected to bring narrow bands of heavy snow to areas east of the lake. These narrow bands could generate 2-3 feet of fresh snow over the next 24-36 hours causing significant disruption.

Whilst the freezing temperatures are expected to last throughout the week, temperatures may recover slightly through the weekend.

Will the US weather affect the UK?

The cold conditions will have the effect of strengthening the jet stream, which will move close to the UK over the coming days. This will bring unsettled conditions through this week, with spells of wet and windy weather, particularly across northwestern parts of the country. However, it will be mild, particularly towards the end of the working week when daytime temperatures could reach around 14C.

There is the potential for the remnants of this cold air to move eastwards across the Atlantic to affect the UK over the weekend. However, the airmass will become heavily modified by the Gulf Stream, and there is little risk of the extreme temperatures over North America affecting the UK.





2014: A year in weather

31 12 2014

2014 has been another year of eventful weather across the UK. Here we take a look at some of the year’s more notable aspects.

Temperature

The obvious headline from 2014 is that it will be the warmest year in our UK record dating back to 1910, knocking 2006 from its top spot.

Using figures up to 28 December then assuming average conditions for the last three days of the year, the expected mean temperature for the UK is 9.9 °C. This beats the previous record of 9.7 °C set in 2006 and means all the UK’s top eight warmest years have happened since 2002.

Despite the overall warmth, there were no record-breaking months – it’s just a case that 11 out of 12 months (August being the exception) were warmer than average. Although individual months were unremarkable, it was the persistence of the warmth that was unusual and together they add up to something record-breaking.

It’s also worth noting it’s set to be the warmest year on record in the Met Office’s Central England Temperature (CET) series, which dates all the way back to 1659. The mean temperature estimate for the year is 11.0 °C, which would just beat the record of 10.9 °C set in 2006.

Human influence on the climate is likely to have substantially increased the chance of breaking the UK and CET temperature records. Estimates from the Met Office suggest that it has become about ten times more likely for the UK record to be broken as a result of human influence on the climate.

Rainfall

It has also been a notably wet year, with the rainfall up to 28 December totalling 1290.0 mm. This ranks 2014 as the UK’s 5th wettest year in the records back to 1910 and it is only 5mm away from 4th placed 2008, so this year could step a notch higher when the final two days of the year are included.

The first two months of the year really set us on the path to this high rainfall total, as both January and February were the third wettest in the record. The winter of 2013/2014 was especially wet across south-east England and it was the wettest winter for the UK in a series from 1910, and in the England and Wales precipitation series from 1766.

May, August, October and November were also all wetter than average. August was especially wet in northern Scotland – here it was the wettest August in a series from 1910. The other months were mostly drier than average, with September being notably dry – in fact it was the driest month on record for the UK in a series from 1910 with just 22.1 mm of rain.

Weather through the months

The year started with two spells of very wet and stormy weather from mid-December to early January, and late January to mid-February, as one deep low pressure system followed another. These brought extremely strong winds and heavy rain to all parts of the country, with widespread disruption across the UK.

A number of factors contributed to the unusually stormy weather, particularly the influence of a powerful Atlantic Jet Stream. You can see more about these in a report written by the Met Office. You can also explore the evolution of this spell of weather in our climate events pages.

The start of spring saw the weather calm down – with March bringing some much-needed drier and more settled weather. The spring (March – April – May) was warmer than average, while rainfall for spring ended up very close to average, which helped the UK recover from its wettest winter on record.

June and July saw a good deal of dry and fine weather, with above average temperatures and sunshine hours combining with below average rainfall. Although there were no major heatwaves, these months made for one of the better periods of summer weather that we’ve seen in recent years; summer 2013 also brought plenty of fine, settled weather in contrast to summers 2007 to 2012.

August was more unsettled, however, with above average rainfall and it was the only month of the year with below average temperatures. On 10th August the remants of ex-hurricane Bertha brought heavy rain and some flooding to parts of north-east Scotland.

September then immediately turned the tables, being exceptionally dry with above average temperatures. However, October and November brought some more typically autumnal weather and the autumn (Sep-Oct-Nov) ended up being fairly average overall, although again it was notably mild and with a marked absence of frosts.

December has seen the coldest temperatures of the year so far for all parts of the UK, but the lowest values for the year remain unusually high compared to previous years. The month so far (using figures up to the 28th of the month) has also been milder than average overall, despite the late cold snap. Rainfall looks set to be around average, while sunshine amounts are well above the norm.

Some 2014 extremes:

Max temp – 32.3 °C at Gravesend, Kent on 18 July. This is fairly typical: during most years we would expect the temperature to reach the low 30s in a few locations.

Min temp – -9.0 °C at Cromdale, in Moray, Scotland on 27 December. By contrast, this is unusually mild. During most winters we would expect the temperature to fall below -10 °C, if not -15 °C, most likely in Highland Scotland.

Max wind gust – 109mph at the Needles Old Battery on the Isle of Wight on 14 February

Wettest day – 146.8 of rain at Ennerdale, Black Sail, Cumbria on 6 March 2014. The high fells of the English Lake District are climatologically one of the wettest parts of the UK.





White Christmas?

26 12 2014

Most people woke up yesterday to a green Christmas rather than a white one.

Snow was recorded at our observation site at Lerwick and some sleet was also recorded at Wick between 11am and 12pm, however for the rest of the UK it remained dry and clear throughout Christmas Day.

To find out what the forecast for your area is for the next five days visit our website: metoffice.gov.uk





Has there been a recent increase in UK weather records?

17 12 2014

There have been a striking number of temperature and rainfall records broken in recent years, according to an analysis by the Met Office which is published in the journal Weather.

The paper examines whether recent decades have seen an unusually high number of records broken in the UK. It looks at the number of records over time in the UK national statistics compiled by the Met Office’s National Climate Information Centre (NCIC).

Records were collated from long-running national and regional series of monthly, seasonal and annual temperature, rainfall, and sunshine.

The analysis counts records by decade and weights them according to their relative importance. More weight is given to national records compared to regions, and more weight to annual records compared to individual months.

The UK’s climate shows a large variability and this is bound to also be reflected in weather records. Even so, the analysis does reveal some interesting patterns.

Temperature records:

  • Since 2000, there have been 10 times as many hot records as cold records.
  • Taking into account the weighting, the period since 2000 accounts for two-thirds of all hot records in a national series from 1910, but only 3% of cold-records.
  • The longer Central England Temperature (CET) series, which dates back to 1659, reveals a similar trend – with seven out of a possible 17 records set since 2000 but no record cold periods.
  • The increase in hot records and decrease in cold records seen in recent decades is consistent with the long-term climate change signal. Seven of the warmest years in the UK series from 1910 have occurred since 2000.

Rainfall records:

  • Since 2000 there have been almost 10 times as many wet records as dry records.
  • Taking into account the weighting, the period since 2000 accounts for 45% of all wet records in a national series from 1910, but only 2% of dry records.
  • Remarkably, period since 2010 accounts for more wet records than any other decade – even though this only a 5 year period. The most prominent wet records in this period were winter 2013/2014 and April, June and year 2012.
  • The longer England & Wales Precipitation (EWP) series, which dates back to 1766, shows a similar trend – with six out of a possible 17 records set since 2000, but no record dry periods.
  • The large number of recent wet records may be indicative of trends in underlying rainfall patterns. We would expect an increase in heavy rainfall with climate change and this is an area of active research within the Met Office Hadley Centre.

Sunshine records:

  • In contrast with the other measures, there are no clear trends apparent in the sunshine records.

Exactly why we have seen these records is an ongoing area of research. You can see some discussion points related to this theme in a Met Office research paper on the drivers and impacts of our seasonal weather.

You can explore the Met Office’s climate data for the UK on our climate pages.





A closer look at ‘weather bombs’

10 12 2014

With strong winds affecting parts of the country today, there has been a lot of talk about ‘weather bombs‘ – but what are they and what do they mean for our weather?

First of all, it’s important to stress the UK is not being ‘hit’ by a weather bomb – the track of the low pressure system is well to the north of the UK, on roughly the same latitude as Iceland. We’re feeling its influence remotely.

This means we are not getting the very strongest winds associated with this system, but far north-western parts of the UK are seeing winds in the 70-80mph range as forecast. Further south the winds are much less strong – so London, for example, is unlikely to see even gale force gusts and mean wind speeds will be much lower.

Another point is that the ‘bomb’ element, the rapid deepening of the low pressure as explained below, happened on Monday – and its now just like any other powerful Atlantic low. In fact, the weather we’ll experience today is nothing unusual for the time of year.

Chart showing a low pressure in the north-west Atlantic at midday on Monday 8 December.

Chart showing a low pressure in the north-west Atlantic at midday on Monday 8 December.

Chart shows the same system 24-hours later, with a 26 millibar fall in pressure.

Chart shows the same system 24-hours later, with a 26 millibar fall in pressure.

So what is a ‘weather bomb?’

A ‘weather bomb’ is more usually referred to as ‘explosive cyclogenesis’ and is a meteorological term describing the rapid fall in central pressure of a depression (or low pressure) – it has to fall by 24 millibars in 24 hours in our latitudes to meet the criterion.

In many ways a ‘bomb’ can be seen as simply a more powerful, more intense version of the kind of Atlantic low pressure systems that normally affect the UK.

Climatologically speaking, explosive cyclogenesis events, or bombs, tend to occur most frequently over sea near major warm ocean currents, for example over the North Atlantic Ocean near the Gulf Stream or over the Western Pacific Ocean near the Kuroshio Current.

An explosive cyclogenesis event in these regions would then tend to happen as a particularly intense jet stream (which is a narrow band of strong winds high up in the atmosphere) interacts with an existing, and often weak, low pressure lingering near one of these warm ocean currents.

In other words, as with so many things in meteorology, it is the coming together of multiple ingredients that allow a ‘bomb’ to develop.

How many ‘bombs’ a year – and what is the impact?

There are gaps in the global observational record, so it’s difficult to give a definitive number of how many ‘weather bombs’ are seen globally each year. However, recent estimates based on a twenty to thirty year dataset suggest there are somewhere between 45 and 65 explosive cyclogenesis events per year, with more ‘bombs’ occurring in the northern than southern hemisphere.

Of course, it’s important to realise that the definition of a ‘bomb’ is somewhat arbitrary and ‘just a number'; a depression deepening only slightly less than 24hPa in 24 hours will still be a powerful depression more than capable of producing severe weather.

Another important point is that the track a ‘bomb’ takes relative to the British Isles, and at what stage of its development it does so, are key to its impact on UK weather – in general the closer the ‘bomb’ tracks to the British Isles the more severe the weather.








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