Severe weather around the world

26 11 2014

While the UK is currently experiencing relatively benign weather for the time of year, extreme conditions are expected in some other parts of the world.

Morocco and Spain

Last Saturday, Agadir in Morocco saw 90mm of rain fall in just 24 hours, which is around twice the monthly November average for the region of just 50mm. The subsequent flooding resulted in more than 30 fatalities.

Unfortunately, more severe weather is expected through Friday and into the weekend across Morocco, but particularly around the southwest of the country.

A combination of a deep area of low pressure, relatively warm sea temperatures and strong winds will bring heavy rainfall. 100-150mm of rain could fall across SW Morocco on Friday with further heavy rain likely on Saturday, and totals could be enhanced over higher ground. Conditions should improve into Sunday.

Through the weekend, the same area of low pressure is expected to bring very heavy rain across North East Spain. Rainfall totals for both days could reach 150-300mm, locally 400mm over higher ground, with a gradual improvement into start of next week.

Both areas could experience flooding and landslides from the intensity and duration of rainfall, as well as the rain that has already fallen in recent days.

Forecast Chart 1200 Sat 29 Nov 2014

Forecast Pressure Chart for Midday on Saturday 29th November

North East America

A rapidly deepening area of low pressure is bringing heavy rain and snowfall across parts of the Eastern Seaboard of North America, with the storm quickly moving northeast over the coming days.

The weather has been caused by an extreme temperature contrast between the warm weather of the Gulf Coast and the bitter cold across inland parts of North America.

While heavy rain is expected on the coast, snow is likely inland, mainly but not exclusively over higher ground. As tomorrow is Thanksgiving, this system poses a risk of travel disruption to what is normally one of the busiest holiday periods in the States. Over 4 inches of snow could fall over parts of the northeast, before the weather improves into the weekend.





Strong winds and heavy rain affect parts of the UK

6 10 2014

After an exceptionally dry September, the UK has seen its first bout of widespread heavy rain and strong winds so far this autumn. An area of low pressure centred close to Iceland has driven a cold front eastwards across Britain, bringing unsettled weather, particularly in the west.

Highest rainfall totals

Some of the highest rainfall totals are shown below (between 10pm (5th October) to 10am (6th October):

SITE NAME AREA RAINFALL (mm)
CAMBORNE CORNWALL 44.8
LLYNFRYNACH POWYS 43.8
SOUTH UIST WESTERN ISLES 41.4
CARDINHAM CORNWALL 40.2
KATESBRIDGE COUNTY DOWN 34.6

Strongest wind gusts

There have been some strong wind gusts in parts, particularly across exposed western areas. The highest gusts are below:

DATE/TIME SITE NAME AREA WIND GUST (MPH)
06/10/2014 03:00 SOUTH UIST RANGE WESTERN ISLES 84
06/10/2014 05:00 ALTNAHARRA NO 2 SUTHERLAND 78
06/10/2014 02:00 TIREE ARGYLL 77
06/10/2014 05:00 MACHRIHANISH ARGYLL 75
06/10/2014 01:00 MAGILLIGAN NO 2 LONDONDERRY 70

Earlier rainfall image across the UK:

Featured image

Weather outlook

The rain will continue to move east across the UK during the rest of today with drier conditions following for a time, before showers follow in places overnight. Although winds will tend to ease for most areas, further gales are expected across northeast Scotland through tomorrow. During this unsettled weather we’d encourage everyone to keep up to date with the latest forecasts and national severe weather warnings.





Turning even warmer for parts of Britain

15 09 2014

After a disappointingly cool and wet August, September has been largely fine, with plenty of warm sunshine for many areas.

This has been thanks to an area of high pressure centred across the UK, which generally brings us dry and sunny weather.

Through this week, the high pressure will slowly move towards Scandinavia, with low pressure moving north towards southern parts of Britain.

This will introduce some isolated but potentially heavy showers in place. Cloud from the North Sea will also keep some eastern areas of the UK cloudier and cooler.

However, this low pressure will also drag in warm winds from the Mediterranean and France, causing a rise in temperatures across parts of the country.

Where we see cloud breaks and further sunshine through this week, we could see temperatures across parts of the south and west reach the mid 20s Celsius by day.

This is considerably warmer than the average of around 17C that we would normally expect across the UK for mid-September.

There has been some press interest about what effect Hurricane Edouard, currently in the Western Atlantic, will have on the UK’s weather.

It’s still early days, but computer models currently suggest the storm will move into the Mid Atlantic and then track south towards the Azores, well away from the UK.

This will mean that the British Isles will not be directly affected by the storm, and there is a hint that the largely fine weather will continue into the weekend to give us further settled weather.





Visible satellite image of triple lows over the UK

14 05 2013

This visible satellite and rainfall radar image shows the three areas of low pressure affecting the UK today.

satellite and rain 14 May 2013

We can see three low pressure areas showing up as swirls of cloud to the north of Scotland near Shetland, north of Northern Ireland and off south-west England. The centre of the lows show up as cloud free areas.

The low to the south west has developed quickly through today and will bring strong winds this evening to parts of Cornwall.

Keep up to date with forecasts and warnings for your local area on our website.





How did the ‘Great Storm’ of 1987 develop?

12 10 2012

From the trail of devastation left by the ‘Great Storm’ of 1987, it’s clear that it was an unusual event.

Analysis of the storm suggests there had been nothing like it since 1703 and that it was an event so rare you would only expect a storm of that magnitude once every 200 years.

That does need clarifying, however, as we have seen storms as powerful as that before and since then – but they have affected areas which are more used to stormy weather such as the far north of the UK (like the north coast of Scotland) and far South West (like the Isles of Scilly).

So what was truly unusual about this storm was that it affected the South and East of England – which had an important bearing on the impact of the storm.

But how did the storm develop?

Initial phases

Most Autumnal storms head in from the Atlantic to the west of the UK, but this storm developed over the Bay of Biscay to the south.

It started as particularly warm tropical air and very cold polar air collided, forcing the warm air to rise and creating an area of low pressure.

The big difference in temperature between the warm and cold air helped to cause rapid ascent and therefore particularly low pressure – at one point it measured 951mb over the English Channel.

Crucially, just to the west of the low, pressure rose rapidly (due to descending air), to leave a big differential in pressure. You can see the difference in pressure in the tightly packed isobars in the (hand-drawn) chart from the early hours of 16 October 1987, below.

Great Storm surface pressure chart

Surface pressure chart for the morning of 16 October 1987

The atmosphere naturally tries to even out this pressure imbalance with the air flowing from the high pressure towards the low pressure – what we feel as wind

Much like water flowing down a plughole, that air doesn’t rush in straight lines but spins around the centre of a low pressure until it reaches the middle due to the Coriolis effect.

The bigger the difference in pressure between the high and the low pressure, the faster the flow of air is – and in this case that big differential led to hurricane force winds.

A sting in the tail

We now know that the strength of the storm was boosted by a phenomenon known as the ‘Sting Jet’, where cold dry air descends into storms high in the atmosphere.

Rain or snow falling into this jet of air evaporates and cools the air further, adding more energy which translates into stronger winds. By the time this ‘sting in the tail’ reaches the ground it can produce winds of 100mph which are concentrated over a small area.

In 1987, no-one knew sting jets even existed, but now they are well understood and included in forecast models. The storm which affected Scotland in December 2011 was boosted by a sting jet, explaining the maximum gust speed of 164mph recorded on top of Cairngorm.

The combined impact

It’s clear that several factors came together to make this storm particularly ferocious, but it was the track of the storm which was perhaps most significant.

Arriving on the south coast of the UK, it tracked north and east over the course of several hours before reaching the Humber estuary at about 5.30am.

This path took in a large, built-up and very populated part of the UK which exacerbated the damage caused.








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