Thunderstorms bring intense rainfall to parts of England

28 07 2014

This morning has seen some intense downpours across parts of south east England.

They developed across parts of East Anglia in the early hours of the morning, with further areas of heavy showers across Sussex, Surrey, Kent and the south of London following later.

The showers were very heavy in places with thunderstorms, hail, and torrential rain reported, giving high rainfall totals and localised flooding in some areas.

The high rainfall totals were caused by an area of low pressure and a plume of warm air that moved in from the near continent accompanied by light winds, meaning that the showers were slow moving.

Several spots have seen more than half of their average monthly rainfall for the whole of July in just one hour.

Below you can see some of the highest recorded hourly rainfall totals from Environment Agency rain gauges through the morning of Monday 28th July 2014:

Great Dunmow Essex 43 mm (4am to 5am)
Isfield Sussex 37 mm (8.30am to 9:30am)
Ardingly Sussex 35 mm (8.30am to 9:30am)
Santon Downham Suffolk 33mm (4am to 5am)
Weirwood Sussex 28 mm (9am to 10am)
Northolt London 20mm (7am to 8am)

 

The band of showery rain is now easing, but a yellow warning for rainfall remains in place for the south east of the UK as the risk of seeing some further isolated downpours remains.

In addition, the far south east of England could see further persistent and perhaps locally heavy rain later today and overnight, with parts of Kent and Sussex most at risk. Conditions across all areas should then improve through tomorrow.





Lightning strikes and heavy rain over the weekend

21 07 2014

Parts of the UK saw some very heavy downpours over the weekend, as thunderstorms caused disruption in some regions.

Westonbirt in Gloucestershire saw the most rain with 79mm over the weekend, more than its July full-month average of 59.3mm. Within that total, 34.2mm fell in just an hour Saturday afternoon – with some localised flash flooding as a result.

A rain gauge at Norwich airport saw the highest hourly-rainfall total, with 45.8mm falling between 3pm and 4pm on Sunday – this is close to its full month July average of 50.4mm.

Numerous other spots saw some high rainfall totals, particularly in eastern areas. Below you can see some of the highest recorded hourly and overall rainfall totals from the weekend.

It’s possible that some locations not included in the list saw heavy rain, but thundery downpours can be very localised – sometimes just a few hundred metres across.

This means that they can miss our rain gauge network, but you can explore rainfall totals from our Weather Observations Website (WOW) which has information supplied by observers all over the UK.

As we forecast on Friday, some locations avoided the storms altogether and saw prolonged fine weather over the weekend.

Nick Grahame, chief meteorologist at the Met Office, said: “The ‘Spanish Plume’ event we were forecasting led to some very intense thunderstorms over the weekend, with hourly and overall rainfall totals in line with our expectations.

“As we’d been highlighting in our forecasts, these storms can be very localised and that means some places avoided the storms altogether and saw a good deal of fine weather. It really highlights how events such as this can see some places with fairly severe impacts, while other places – sometimes quite nearby – can see no impacts at all.”

48-Hour Rainfall Totals from 2100HRS on 18 July to 2100HRS on 20 July 2014:

STATION LOCATION COUNTY RAINFALL (mm)
WESTONBIRT GLOUCESTERSHIRE 79
NORWICH AIRPORT NORFOLK 62.2
SHOEBURYNESS, LANDWICK ESSEX 48.6
PERSHORE COLLEGE HEREFORD & WORCESTER 45.6
PERSHORE HEREFORD & WORCESTER 39
ASTWOOD BANK HEREFORD & WORCESTER 35.6
KEELE STAFFORDSHIRE 32.4
ROCHDALE GREATER MANCHESTER 32
NEWPORT (SALOP) SHROPSHIRE 31
NOTTINGHAM, WATNALL NOTTINGHAMSHIRE 29.2

Highest hourly rainfall totals from the weekend:

DATE/TIME STATION LOCATION COUNTY RAINFALL (mm)
20/07/2014 15:00 NORWICH AIRPORT NORFOLK 45.8
19/07/2014 09:00 WESTONBIRT GLOUCESTERSHIRE 34.2
20/07/2014 17:00 MONKS WOOD CAMBRIDGESHIRE 22.8
19/07/2014 16:00 MARKET BOSWORTH LEICESTERSHIRE 15.8
19/07/2014 06:00 LIBANUS POWYS 15

This video shows the storms and lightning strikes as they developed over Spain and France and moved north across the UK.

In total the UK are saw 62,277 lightning strikes between 9am on Thursday 17 July and 9am on Monday 21 July 2014





Rain totals for 19th July 2014

20 07 2014

As forecast there were severe thunderstorms across the UK on the 19th July bringing heavy rain and gusty winds. See the tables below for the largest rain totals across the UK.  Gloucestershire recorded the highest rainfall with 66mm between 6am and 6pm yesterday, the counties monthly average rainfall is 60.6mm.

The Heat-health watch put in place in parts of southern and eastern England in conjunction with Public Health England has now been downgraded. Temperatures in parts of the area covered topped 28C during 19 July, see table below.

Today, 20 July, temperatures are expected to reach low to mid 20’s across central, south and south east of England, with London seeing around 27C.  Northern England will reach mid to high teens and Scotland and Northern Ireland mid to low teens.

More thundery downpours are expected to develop today over some eastern and central parts of the UK.  A yellow, be aware, weather warning for rain is in place for the areas likely to be affected. Not everywhere will see a storm but where they do occur, torrential downpours are possible with lightning, hail and strong gusts of wind. The areas most likely to be affected are across eastern and southeastern England.

Many places will have a good deal of fine and very warm weather this working week although there is the risk of some heavy showers in parts of the south and west later in the week.

 

UK MAX TEMPERATURE 19 JULY 2014
TIME SITE NAME AREA MAX TEMP (Celsius)
16:22 London St Jamess Park GREATER LONDON 28.5
15:13 Northolt GREATER LONDON 28.4
15:22 Heathrow GREATER LONDON 28.3
15:59 Santon Downham SUFFOLK 28.3
13:29 Gravesend, Broadness KENT 28.1
16:51 Cambridge NIAB CAMBRIDGESHIRE 27.7
15:49 Marham NORFOLK 27.7
13:55 Hampton W Wks GREATER LONDON 27.6
16:52 Writtle ESSEX 27.6
14:51 Frittenden KENT 27.5

 

 

12hr UK RAINFALL 19 JULY
SITE NAME AREA PRECIP. (MM)
WESTONBIRT GLOUCESTERSHIRE 66.0
PERSHORE COLLEGE HEREFORD & WORCESTER 36.4
PERSHORE HEREFORD & WORCESTER 30.8
NEWPORT (SALOP) SHROPSHIRE 29.4
KEELE STAFFORDSHIRE 28.2
ASTWOOD BANK HEREFORD & WORCESTER 27.6
NOTTINGHAM, WATNALL NOTTINGHAMSHIRE 26.0
LIBANUS POWYS 25.8
NANTWICH, REASEHEATH HALL CHESHIRE 22.6
MARKET BOSWORTH, BOSWORTH PARK LEICESTERSHIRE 22.6




With hot and humid weather could we see a ‘Spanish Plume’?

15 07 2014

Over the next few days increasingly warm and humid air moving up from the continent will see UK temperatures on the rise, with the warmest days of the year so far expected.

Temperatures in the south east of the country could climb to the low 30s Celsius by Friday, while other parts of England and Wales are likely to see temperatures in the mid to high 20s.

These very warm conditions will be accompanied by a close and humid feel in the air, which could make it feel quite uncomfortably warm in places – particularly during the nights.

While there is a good deal of dry and fine weather in the next few days, there is also the chance of seeing some heavy rain and thunderstorms as we go into the weekend.

Friday may see an area of thundery showers moving north east across parts of England and Wales.

Our meteorologists are also keeping a very close eye on the potential for more widespread thundery downpours on Saturday.

These could develop from what meteorologists call a ‘Spanish Plume’, which is a catchy name for a rather complex set of conditions.

It involves very warm and humid air moving up from the Spanish plateau to the UK. If this meets cooler air from the Atlantic, the warm air can be forced rapidly upwards to produce thunderstorms.

There are a number of ingredients that all have to come in to place for this to happen, however, so the risk of disruption from any heavy, thundery downpours is low for Saturday at the moment rather than a certainty. A yellow alert has been issued for this risk and will be updated in the coming days.

You can keep up to date with how this situation develops by checking our forecasts and warnings over the next few days.

Interestingly, the warm weather we’re expecting can be traced back to the jet stream, a narrow band of fast moving winds high up in the atmosphere which forms where cooler air from the polar region meets warmer air from the tropics.

The jet stream has dipped south over north eastern parts of the US, allowing cooler air to flood in over the area and bringing much lower temperatures than usual for this time of year.

New chart v1

Top image shows forecast jet stream at 1am Wednesday, with an obvious kink over the NE of the US. The bottom forecast image, for 1am on Saturday, shows a kink now over Spain, with warm air from that region flowing towards the UK.

This kink in the jet stream causes a knock-on effect which pushes the cooler air south across the Atlantic, which in turn pushes the warm humid air over the continent (around Spain) towards the UK later this week.

This provides yet further proof of the way in which all weather is connected, but there are no hard and fast rules as to how events in one part of the world will affect us here in the UK.





Saturday’s squally weather and reports of tornadoes

27 01 2014

On Saturday we saw a number of heavy rain showers group together in what’s known as a ‘squall line’ – a narrow band of thunderstorms, intense rain, hail, and frequent lightning accompanied by brief but very strong gusts of wind and possibly tornadoes.

Radar image showing the narrow band of showers moving across the UK.

Radar image showing the narrow band of showers moving across the UK.

This squall line swept across Wales and then moved south east across southern parts of England – bringing about 6mm of rain to places in a very short period of time with gusts of wind of around 60mph or more in places.

It  also had the characteristics of a cold front, with the temperature ahead of it being around 11°C, falling to 7°C once the squall line had passed.

There have been reports of possible weak tornadoes from some locations, however it’s hard to verify them without pictures or footage because these features are generally too small to be picked up by satellites or weather observation equipment.

It’s also worth noting that squally winds can often be mistaken for tornadoes because these gusts can be sudden and strong – potentially causing very localised damage.

You can see more information on tornadoes and how they form on our website.





Stormy weather in the Mediterranean

15 11 2013

The central and western Mediterranean will experience very unsettled conditions through the weekend and next week.

Very heavy rain is expected to affect the northeast of Spain, southern France, the Balearic Isles, Corsica, Sardinia, Italy and the Adriatic facing Balkan nations as the very unsettled conditions move slowly east through the region.

Rainfall totals could be as high as 250mm in places, with a risk of up to 200mm in 24 hours. The average rainfall for November in this region is between 50mm and 100mm.

The rain will be associated with thunderstorms which could also produce hailstorms, very strong gusty winds and the possibility of tornadoes in a few places.

Storms developing over the western Mediterranean

Storms developing over the western Mediterranean

In addition to the rain, very strong winds are expected through the central and western Mediterranean, with widespread gales and a risk of storm force winds for a time. This will lead to rough seas that could pose a threat to shipping in the region.

There is also the risk of strong or gale force southeasterly winds affecting the Adriatic during Tuesday and Wednesday next week. These strong winds, combined with very heavy rainfall across the Venice region over the next few days could bring the risk of flooding in Venice.





Five things you might not know about thunderstorms

20 03 2013

1. Lighting can strike twice. The empire state building in New York has been struck by lightning as many as 48 times in one day.
2. The average flash of lightning would light a 100 watt light bulb for three months.
3. Lightning can strike in volcanic ash clouds. Not much is known about volcanic lightning, but we’re using it to help track ash clouds.

Volcanic lightning

Volcanic lightning

4. Thunderstorms can trigger asthma. The Met Office has worked with the NHS and Asthma UK to try and understand why.
5. The most thundery part of the earth is the island of Java where the annual frequency of thunderstorms is about 220 days per year.





Evolution of Thursday’s thunderstorms

29 06 2012

A series of intense thunderstorms brought exceptionally severe weather across parts of the UK yesterday, causing flash flooding and disruption in many places.

As the storms tracked across the country our observation sites picked up some very heavy hourly rainfall totals, with Scampton in Lincolnshire seeing 28.4 mm falling in an hour.

Several other sites saw hourly totals in excess of 20 mm. This led to flash flooding of properties, roads, and landslides in places.

More than 111,000 lightning strokes were also detected across Europe, with more than 1,000 detected over the UK in a 5 minute period at the peak of activity yesterday.

Hail stones ‘the size of golf balls’ also caused damage in Leicestershire, according to media reports.

The storms were borne out of hot, humid air which had tracked up from the Azores far to the south in the Atlantic. This air mass tracked up on southerly winds, moving over Spain before reaching the UK.

As a result, much of the country saw warm and muggy conditions, with the temperature reaching 28.4 C at St James’s Park, Central London.

The heat and moisture in the air were enough to cause thunderstorms, but the really intense storms were formed as an Atlantic weather front moved in from the west.

As it ‘collided’ with the warm and humid air mass, air rapidly rose to create towering cumulonimbus storm clouds which were laden with water, and ripe for developing hail, thunder and lightning.

This led to several distinct lines of thunderstorms developing along the boundary where the two air masses met.

As shown in the radar sequences below, one line originated in the Cardiff area of south Wales in the early morning. This moved in an east-north-east direction across Worcestershire, Shropshire, the West Midlands and Leicestershire to clear Lincolnshire by late afternoon.

A second line of thunderstorms reached the Lancashire coast around late morning and moved in a NE direction to reach the Newcastle area later in the day, clearing the north east coast by late evening.

There were also torrential downpours across parts of Northern Ireland and western Scotland. Southern parts of England and Wales saw relatively little rain and periods of warm sunshine.





Why are we getting thunder and lightning?

11 04 2012

With the weather in April being distinctly showery so far, what exactly causes this changeable weather and why do some showers give thunder and lightning?

 

Thunderstorms are normally associated with convective clouds which form from rising air warmed by the Sun. At this time of year we have longer days and therefore more heat reaches the Earth’s surface giving a greater chance for convective clouds to form. The air is continuously moving within the cloud in a very disorderly fashion, allowing the cloud to grow and water droplets or ice crystals to form. Given enough time and growth, the cloud may develop into a Cumulonimbus cloud and give quite heavy bursts of rain or hail for short periods of time, and possibly thunder and lightning.

Hail forms when ice crystals or frozen raindrops within the cloud get thrown about with the rapidly circulating air. As they ascend they grow as water freezes on the surface of the droplet or crystal. Eventually the droplets will become too heavy to be supported by the updraughts of air and they fall to Earth as hail.

 As hail moves through the cloud it picks up a negative charge as it rubs against smaller positively charged ice crystals. A negative charge collects at the bottom of the cloud where the heavy hail collects, while the lighter ice crystals remain near the top of the cloud and create a positive charge. The negative charge is attracted to the Earth’s surface and other clouds and objects and when the attraction becomes too strong, the positive and negative charges come together, or discharge, to balance the difference in a flash of lightning. The rapid expansion and heating of air caused by lightning produces the accompanying loud clap of thunder.

 Thunder and lightning facts:

  • A bolt of lightning lasts on average for about one 10,000th of a second.
  • The average speed at which the lightning cuts through the air is 270,000 mph.
  • There are several types of lightning, the most common being “sheet lightning” in which the discharge of positive and negative charges occurs within the cloud.
  • The risk of being struck by lightning is minimal and ninety percent of lightning travels from cloud to cloud. Lightning takes the shortest and quickest route to the ground, usually via a high object standing alone.
  • The average annual frequency of lightning is less than 5 days in western coastal areas of the United Kingdom and over most of central and northern Scotland, and 15 to 20 days over the east Midlands and parts of southeast England

Get more facts from our thunderstorms fact sheet.

See lightning observations for the last three hours on our observations map.





Volcanic lightning could help monitor volcanic ash

11 12 2010
Volcanic material thrust high into the atmosph...

Volcanic lightning (Source: Wikipedia)

Met Office researchers have published new findings in ERL suggesting that the amount of lightning produced near a volcano each hour is roughly proportional to the plume height. They believe that the technique could ultimately be used to monitor volcanoes in remote locations or those that are obscured by rain.

To assess the number of lightning strokes the team used ATDnet, the UK Met Office‘s long-range lightning-location network, which has recently been updated.

“ATDnet is used to monitor thunderstorms over a vast area of the world extending from the US to China and the Arctic to the South Atlantic, centred over the UK,” siad Alec Bennett of the Met Office. “Lightning emits powerful electromagnetic pulses over a broad frequency range creating both the bright flash seen by an observer and the crackles on a nearby radio. The peak energy of this emission is found in the very low frequency (VLF) radio band at about 10 kHz, and it is this part of the spectrum that ATDnet uses to locate lightning, utilizing sensors positioned across Europe and beyond.”

The system has previously located lightning from volcanic plumes in southern Chile and earlier eruptions in Iceland. “The availability of quantitative observations of volcanic lightning is sparse, so our results are hoped to add new and detailed observational data to this research field,” said Bennett. “The eruption of Eyjafjallajökull in April–May 2010 provided an excellent opportunity for us to study both the performance of ATDnet after recent network upgrades and to use the lightning data to learn more about the relationship between volcanic activity and plume electrification, a process recognised for decades but still subject to ongoing scientific debate.”

Bennett and colleagues from the UK Met Office and Icelandic Meteorological Office found that plumes from Eyjafjallajökull that reached about 5 km above sea level generated lightning strong enough to be detected by ATDnet. Above this threshold, the rate of lightning production was approximately proportional to the plume height.

“Perhaps most importantly, it was found that this relationship did not exist all of the time, with some plumes higher than 5 km producing no lightning capable of being detected by ATDnet at all,” said Bennett. “This presents us with a unique case study whereby we have several days where a tall plume was not strongly electrified followed immediately by several days of strong electrification, enabling more research to be undertaken on the cause of vivid volcanic lightning displays.”

An eruption of Iceland’s Eyjafjallajökull volcano in late-March 2010 produced a large plume of ash and considerable disruption to flights across Europe.

The team used C-band radar data from the Icelandic Meteorological Office to quantify the plume height above the volcano. This allowed the scientists to combine detailed observations on lightning and plume height as well as modelled atmospheric parameters, such as wind speed, wind direction and ambient temperature. “With these data we can begin to quantify the effect of plume and atmospheric conditions on the generation of volcanic lightning,” said Bennett.

“By comparing the distance between the vent and lightning strokes it was also possible to gain evidence that a charging mechanism was present away from the vent, with many lightning strokes produced several kilometres downwind from the vent,” he added. “This finding suggests that two different charging mechanisms may be present in the plume, one immediately adjacent to the vent – producing numerous weak lightning strokes visible to an observer nearby but not strong enough to be detected by ATDnet – and a further strong charging mechanism operating within the plume, generating lightning with peak currents of at least 3 kA and detected by ATDnet.”








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