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.





Latest snow depths and wind speeds – 5 February

5 02 2013

As forecast, unsettled wintry conditions brought snow and strong winds to parts of the UK overnight and this morning.

Eskdalemuir saw the deepest snow, with 14 cm of snow recorded at 10 am this morning, while Aviemore recorded 12 cm.

Many areas also saw strong winds, with a gust of 78 mph recorded at Culdrose, Cornwall and 99 mph recorded at Cairngorm Summit.

Snow depths at 10 am 5 February

TIME SITE NAME AREA ELEVATION SNOW DEPTH ( CM)
10:00 ESKDALEMUIR DUMFRIESSHIRE 236 14
10:00 AVIEMORE INVERNESS-SHIRE 228 12
10:00 DRUMALBIN LANARKSHIRE 245 10
10:00 GLENANNE ARMAGH 161 9
10:00 TULLOCH BRIDGE INVERNESS-SHIRE 249 7
10:00 REDESDALE CAMP NORTHUMBERLAND 211 7
10:00 BALLYPATRICK FOREST ANTRIM 156 5
10:00 SPADEADAM CUMBRIA 285 5
10:00 THOMASTOWN FERMANAGH 72 3
10:00 BINGLEY WEST YORKSHIRE 262 2
10:00 ALBEMARLE NORTHUMBERLAND 142 2
10:00 WADDINGTON LINCOLNSHIRE 68 1
10:00 SHAWBURY SHROPSHIRE 72 1

Maximum gust speeds 5 February

TIME SITE NAME AREA ELEVATION MAX GUST SPEED (mph)
00:00 CULDROSE CORNWALL 76 78
04:00 SCILLY ST MARYS AIRPORT ISLES OF SCILLY 31 75
00:00 CHIVENOR DEVON 6 67
03:00 ISLE OF PORTLAND DORSET 52 66
04:00 JERSEY AIRPORT JERSEY 84 66
03:00 GUERNSEY AIRPORT GUERNSEY 101 64
00:00 CAMBORNE CORNWALL 86.85 62
02:00 SOUTHAMPTON, OCEANOGRAPHY CENTRE HAMPSHIRE 26 62
01:00 SOUTH UIST RANGE WESTERN ISLES 4 62
00:00 AVONMOUTH AVON 9 62
00:00 CARDINHAM, BODMIN CORNWALL 200 61
01:00 TIREE ARGYLL 9 60
03:00 WIGHT: ST CATHERINES POINT ISLE OF WIGHT 20 60
01:00 WIGHT: NEEDLES OLD BATTERY ISLE OF WIGHT 80 60
02:00 YEOVILTON SOMERSET 20 60
01:00 CAPEL CURIG GWYNEDD 216 59
01:00 ABERDARON GWYNEDD 95 59
04:00 ISLAY: PORT ELLEN ARGYLL 17 58
01:00 LERWICK SHETLAND 82 58
00:00 MUMBLES HEAD WEST GLAMORGAN 43 56
01:00 ODIHAM HAMPSHIRE 118 56

Maximum gust speeds – mountain sites

TIME SITE NAME AREA ELEVATION MAX GUST SPEED (mph)
09:00 CAIRNGORM SUMMIT INVERNESS-SHIRE 1237 99
07:00 CAIRNWELL ABERDEENSHIRE 928 86
08:00 AONACH MOR INVERNESS-SHIRE 1130 75
09:00 BEALACH NA BA ROSS & CROMARTY 773 67
04:00 GREAT DUN FELL CUMBRIA 847 56
10:00 GLEN OGLE PERTHSHIRE 564 54

Warnings for ice, snow and wind remain in place in some areas.





Overnight wind speeds – Wednesday 30 January

30 01 2013

Following Met Office amber weather warnings for wind in some parts of the UK yesterday, some high gust speeds were recorded late last night and into the early hours of the morning. The highest gust speed at lower levels was recorded at Fair Isle, Shetland which saw speeds of 86 mph this morning, while the highest gust recorded at a mountain site was 135 mph at Cairngorm Summit.

Max gust speed at lower level sites

Date/time Site name Area Elevation Max Gust Speed (mph)
30/01/2013 06:00 Fair Isle Shetland        57 86
30/01/2013 05:00 Lerwick Shetland        82 84
30/01/2013 07:00 Kirkwall    Orkney          26 82
30/01/2013 01:00 Loch Glascarnoch    Ross & Comarty 269 79
30/01/2013 01:00 Stornoway Airport Western Isles 15 78
30/01/2013 04:00 Wick Airport  Caithness    36 75
30/01/2013 00:00 South Uist Range   Western Isles 4 75
30/01/2013 00:00 Tain Range Ross & Cromarty 4 70
30/01/2013 05:00 Altnaharra Sutherland   81 68
30/01/2013 03:00 Wight: Needles Old Battery Isle Of Wight 80 68

Max gust speed recorded at mountain sites

Date/time Site name Area Elevation Max gust speed (mph)
30/01/2013 00:00 Cairngorm Summit Invernessshire 1237 135
30/01/2013 01:00 Aonach Mor Invernessshire 1130 110
30/01/2013 07:00 Cairnwell Aberdeenshire 928 105
30/01/2013 00:00 Bealach Na Ba Ross & Cromarty 773 101
30/01/2013 02:00 Glen Ogle        Perthshire 564 77

Warnings remain in place for wind in some areas, you can keep up to date with the latest severe weather warnings on our website.





The worst storm in years?

28 01 2013

Various articles in the news today said that the weather over the weekend was the worst storm to hit the UK in years, and that there is more to come this week. There was indeed a very deep area of low pressure in the Atlantic over the weekend. At its deepest, on Saturday 26 January, the central pressure of the depression was 932 millibars and it was sitting some 1,800 nautical miles west of the UK. It came closest to the UK during the day yesterday with a central pressure of 950 millibars but was still around 600 nautical miles to the north west of Scotland.

Satellite image from 26 January 2013

Satellite image from 26 January 2013

To put this into context, the storm that affected the UK on 3 January 2012 had a central pressure of 953 millibars but was centred right on the west coast of Scotland and brought winds in excess of 80 mph to the Central Belt and a gust of over 100 mph in Edinburgh. Property was damaged, as well as trees, and there was disruption on the road network and with ferry crossings. Power supplies were also affected significantly.

The storm in January 2012 was therefore much more disruptive and severe than any wet and windy weather we have seen so far this year.

Much of the recent severe weather has been attributed to the phrase “Weather Bomb”, which is not a perfect meteorological term but is defined as an intense low pressure system with a central pressure that falls 24 millibars in a 24-hour period. This happened to the depression over the Atlantic during the weekend but as it was miles away from the UK its impacts were minimal. A better description can be more directly linked to the meteorological phenomena known as rapid cyclogenesis. This is where dry air from the stratosphere flows into an area of low pressure. This causes air within the depression to rise very quickly and increases its rotation, which in turn deepens the pressure and creates a more vigorous storm.





Latest rainfall totals and wind speeds

26 11 2012

Below are the latest rainfall totals from 6.00 pm Sunday night until 6.00 am this morning.

Location Amount (mm)
Mona        27.8
Blencathra              27.4
Capel Curig    26
Valley         25.4
St Bees Head    20.8
Keswick  19
Ronaldsway 18.4
Blackpool 18.2
Rochdale   18
Aberdaron        17.4

The highest rainfall totals are now futher north, however as the table below shows, areas in the south west have seen the most rainfall overall. This is in addition to the rainfall totals from the 20th – 23rd November, where some areas saw in excess of 90 mm of rain.

Rainfall totals from midnight 24th November until 6.00 am this morning:

Location Total (mm)
Plymouth, Mountbatten                72
Scilly: St Marys Airport             66.6
Cardinham, Bodmin                    66.2
Dunkeswell Aerodrome                 60.8
Camborne                             59.6
Exeter Airport                       55.6
Fylingdales                          51.8
Culdrose                             49
Capel Curig                 49
North Wyke                           48.2

This video shows the rainfall from this period with satellite and rainfall radar imagery.

There were also some strong gusts of wind last night:

Location Max gust (mph)
Berry Head                 62
Wight: Needles Old Battery 59
Plymouth, Mountbatten      49
Isle Of Portland           48
Scilly: St Marys Airport   48
North Wyke                 45
Warcop Range               45
Langdon Bay                44
Solent                     44
Cardinham, Bodmin          44

Severe weather warnings are still in place for further rainfall today. Keep up to date with warnings and flood warnings from the Environment Agency.





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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