Severe weather to affect western France

12 08 2014

A spell of severe weather is expected to affect parts of France overnight and through Wednesday morning as an area of low pressure makes its way in from the Bay of Biscay.

The  area of low pressure highlighted in the satellite image above is expected to deepen and develop before affecting parts of France this evening and overnight.

Pressure chart for 1 am Wednesday 13 August

Pressure chart for 1 am Wednesday 13 August

Forecast rainfall for 1 am Wednesday 13 August

Forecast rainfall for 1 am Wednesday 13 August

 

 

 

This brings the risk of severe thunderstorms across western, then southern France overnight and during Wednesday morning. This will bring the potential for flash flooding and will give squally winds, with disruption to local infrastructure and to holiday makers in the region. Very strong winds and high seas are also likely for a time overnight along the western coastline of France. Meteo France currently has severe weather warnings in force.

 

This area of wind and rain should then move quickly across Switzerland and southern Germany during Wednesday afternoon.





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.





How often do we get tornadoes in the UK?

8 05 2012

Over the past few weeks there have been several reports of funnel clouds and tornadoes across the UK. So what are tornadoes and how do they form?

Tornadoes form when the weather is ‘unstable’ and showery. They are narrow, spinning columns of air that reach the ground from cumulonimbus (thunderstorm) clouds.  As they develop we often see funnel shaped clouds extending from the base of the cloud and it is only when these funnel clouds touch the ground that we get a tornado. If the funnel cloud touches down at sea we get a waterspout.

It is claimed that the UK gets more tornadoes per square kilometre than the USA, but not more tornadoes in total. On average, around 30 tornadoes are reported each year in the UK, although these are generally much weaker than their American counterparts. However, there have been a number of notable exceptions – such as the Birmingham tornado on July 28 2005 which left a significant trail of damage.

Most continents have regions with favourable conditions for tornado formation. The central and southern US states see the most violent tornadoes in the world due to a unique combination of geographical and meteorological circumstances. This region, from Nebraska to Texas and Oklahoma, has been named ‘tornado alley’. Here cold dry air moving south and east from the Rocky Mountains meets warm moist air from the Gulf of Mexico, giving perfect conditions for tornadoes to form, especially in late spring and summer.





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.





Heavy downpours across parts of the south-east

23 08 2011

As predicted, there have been heavy thundery downpours across south-east England and the London area this morning, with parts of Kent seeing 10mm of rain in one hour. Some areas of London also saw 5-10mm of rain across the morning.

The risk of heavy thundery showers continues into the afternoon. However, as is the nature of  showers, and as we saw in Bournemouth last week, some areas will have heavier bursts than others. Some parts of London, including Heathrow, have only had 1mm of rain so far this morning while Hampstead has had 9mm in an hour.





What is a ‘Spanish Plume’?

5 05 2011

There has been a lot of talk about warm weather expected across parts of England again this weekend.  Temperatures are forecast to reach the mid to high 20′s C on Friday and into the weekend, bringing the risk of thundery showers for some.  It has been reported that a ‘Spanish Plume’ is responsible for this. Here, Ewen McCallum, Met Office Chief Meteorologist explains what a ‘Spanish Plume’ is?

‘Spanish Plume’ is actually a rather catchy name for a rather complex meteorological phenomenon which leads to warm conditions and heavy showers or thunderstorms over parts of the UK and north-west Europe.

As the name suggests it is a plume of very warm air that pushes north from the Spanish plateau and reaches the British Isles on a southerly airflow.  Of course over the UK we are normally affected by much cooler Atlantic air as cold fronts encroach from the west. Now when these two air masses meet, the very warm ‘plume’ air is forced to rise vigorously over the cooler Atlantic air and as a result produces thunderstorms. Because these features can cover large areas the storms are often grouped together and can give widespread, heavy rainfall, often accompanied by hail.








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