The jet stream and why it’s too early to write-off summer

There have been one or two stories in the press today saying we’re in for another washout summer, which would rightly inspire collective misery across the country.

However, it’s a far too early to be writing off any chance of a decent summer season – after all, it doesn’t officially start (for us meteorologists) for more than two weeks (on 1 June).

It appears the news stories are borne out of the current position of the jet stream, a band of fast moving westerly winds high up in the atmosphere. But why is this important?

A quick Jet stream explainer

The jet stream tends to guide the generally wet and windy weather systems which come in off the Atlantic. So, if it’s over us or just to the south, we tend to get a lot of wet and windy weather – which is what we expect through winter.

If the jet is to the north of us, it guides that changeable weather to the north to give us more settled conditions – which is what we expect in the summer.

(You can read a bit more about the jet stream, how it impacted our weather last year, and any potential connections to climate change in a blog story we wrote last year).

What’s going on now?

Right now the jet stream is sitting to the south of the country and it is influencing the unsettled weather we are seeing at the moment.

Forecast chart showing position of the jet stream at midday on 13 May 2013

It’s fair to say that this is roughly the position it was in for extended periods during the exceptionally wet weather that we saw last year, particularly in June.

Crucially, however, the jet stream does move around quite a bit and it can change its track significantly in just a few days. So the current position of the jet stream does not mean that it’s stuck in that position.

Looking ahead

Much like our weather, it’s a huge challenge to predict the exact track of the jet stream more than five or six days ahead, so there’s still a great deal to play for in the outlook for our summer.

In short, it’s far too early to write-off summer 2013 based on the current position of the jet stream.

To get the best information on what to expect you can see the latest detailed forecasts out to 5-days on our website, as well as a general view of what we expect out to 30 days.

You can find out more about the jet stream in our YouTube video.

UK snow depths Saturday 26 January 2013

As forecast, further snow fell across central, northern and eastern parts of the UK yesterday and overnight. The latest snow depth observations as of 0800 this morning for the UK are below. Redesdale Camp in Northumbria has the highest snow depth so far this year with 33 cm recorded.

Location	Area	Depth (cm)
Redesdale Camp	Northumberland	33
Eskdalemuir	Dumfriesshire	30
Albemarle	Northumberland	25
Spadeadam	Cumbria	25
Aboyne	Aberdeenshire	20
Bingley	West Yorkshire	20
Little Rissington	Gloucestershire	18
Leek, Thorncliffe	Staffordshire	16
Nottingham, Watnall	Nottinghamshire	12
Leconfield	Humberside	11
Strathallan Airfield	Perthshire	11
Church Fenton	North Yorkshire	11
Wittering	Cambridgeshire	10
Sennybridge	Powys	10
Andrewsfield	Essex	10
Dyce	Aberdeenshire	9
Cranwell	Lincolnshire	9
Linton On Ouse	North Yorkshire	8
Wattisham	Suffolk	8
Scampton	Lincolnshire	8
Marham	Norfolk	7
Shap	Cumbria	7
Leeming	North Yorkshire	7
Boulmer	Northumberland	6
Shawbury	Shropshire	5
Waddington	Lincolnshire	5
Rostherne	Cheshire	4
Bridlington MRSC	Humberside	4
Hawarden Airport	Clwyd	3
Glasgow, Bishopton	Renfrewshire	3
Coningsby	Lincolnshire	3
Bedford	Bedfordshire	3
Coleshill	Warwickshire	3
Liscombe	Somerset	2
Dunkeswell Aerodrome	Devon	2
Drumalbin	Lanarkshire	2
Hereford, Credenhill	Hereford & Worcester	2
Prestwick, Gannet	Ayrshire	2
Odiham	Hampshire	1

As we continue through the weekend all of us will see a change to milder and unsettled conditions, with further rain, heavy at times pushing east across the UK later on Saturday and into Sunday. A yellow warning of heavy rain has been issued for parts of the UK overnight tonight

The change to milder weather will result in a combination of a thaw of lying snow and periods of rain which inevitably increases the risk of flooding in some areas. The Met Office and Environment Agency are monitoring the situation very closely and advise everyone to stay up to date with the latest weather forecasts, severe weather warnings, and flood warnings.

By thinking ahead we can all be better prepared for severe weather. Throughout the winter, the Met Office works with agencies across the UK to help keep the country safe, well and on the move.

Recent rainfall totals

Rain has continued to cause disruption across parts of the UK, with overnight rain adding to significant totals over the past few days.

The wettest place in the UK (and Scotland) since the heavy rainfall began on 19^th December to 6am this morning has been Tyndrum in Perthshire, with 155.0 mm of rain.

Cardinham near Bodmin, Cornwall, is the wettest place in England with 128.8 mm of rain and the wettest place in Wales has been Mumbles Head, West Glamorgan, with 107.0 mm of rain.

Ballypatrick Forest in Antrim has been the wettest place in Northern Ireland, with 89.0 mm of rain.

Some areas have exceeded their full-month December average since the 19^th – such as Plymouth, Devon, which has seen 128.8mm of rain compared to a December average of 118.8 mm.

Below is a table of the wettest places in the UK from 0000 HRS on 19th December to 0600 HRS today, 24th December. The final column shows the monthly average for December, clearly showing some places have exceeded their monthly totals:

SITE NAME	AREA	PRECIP AMOUNT(mm)	DEC AVG(mm)
TYNDRUM	PERTHSHIRE	155.0	300.9
CARDINHAM	CORNWALL	128.8	155.1
PLYMOUTH	DEVON	127.4	118.8
LISCOMBE	SOMERSET	125.2	171.2
OKEHAMPTON	DEVON	115.0	184.2
MUMBLES HEAD	WEST GLAMORGAN	107.0	110.3
TREDEGAR	GWENT	102.2	169.0
CARDIFF, BUTE PARK	SOUTH GLAMORGAN	97.0	125.3
SENNYBRIDGE NO 2	POWYS	96.2	179.5
ST ATHAN	SOUTH GLAMORGAN	93.2	122.4
DYCE	ABERDEENSHIRE	92.4	76.1
CARTERHOUSE	ROXBURGHSHIRE	92.4	132.0
CRAIBSTONE	ABERDEENSHIRE	92.0	79.8
BALLYPATRICK FOREST	ANTRIM	89.0	133.9

There is more unsettled weather to come this week, so for the latest information keep up to date with our forecasts and warnings.

Heavy rain brings over 100mm of rain to parts of Scotland – rainfall totals across the UK

There has been some very wet weather across much of the UK seeing well over an inch of rain in the last 24 hours. The wettest place in the UK, in the 48 hours to 6 am this morning is Tyndrum, Perthshire with 102.4 mm of rain, with 94.6 mm of this falling in the last 24 hours.

The wettest place in England was Cardinham, Cornwall with 62.8 mm, in Northern Ireland was Ballypatrick Forest, Antrim with 57.8 mm and in Wales it was Tredegar Park with 54.4 mm of rain.

Although there will continue to be some patchy outbreaks of rain across eastern parts of Scotland today, generally the rain will continue to ease leaving a drier day for many, before more heavy rain pushes into the southwest of England later this evening and across Scotland tomorrow morning.

48 hour UK Rainfall Totals 19 Dec 0600 am - 21 Dec 0600 am
Stations recording more than 40 mm

SITE NAME	AREA	PRECIP AMOUNT(mm)
TYNDRUM	PERTHSHIRE	102.4
CARTERHOUSE	ROXBURGHSHIRE	68.2
CARDINHAM, BODMIN	CORNWALL	62.8
SHAP	CUMBRIA	61.6
BALLYPATRICK FOREST	ANTRIM	57.8
PLYMOUTH, MOUNTBATTEN	DEVON	55.6
STRATHALLAN AIRFIELD	PERTHSHIRE	54.6
TREDEGAR, BRYN BACH PARK	GWENT	54.4
PATELEY BRIDGE, RAVENS NEST	NORTH YORKSHIRE	53.8
RAVENSWORTH	NORTH YORKSHIRE	53.4
BINGLEY	WEST YORKSHIRE	51.8
DUNDRENNAN	KIRKCUDBRIGHTSHIRE	50.8
THORNEY ISLAND	WEST SUSSEX	49.4
SHOREHAM AIRPORT	WEST SUSSEX	49.2
USK	MONMOUTHSHIRE	48.4
NOTTINGHAM, WATNALL	NOTTINGHAMSHIRE	48.4
CARDIFF, BUTE PARK	SOUTH GLAMORGAN	48.2
HURN	DORSET	47.8
MURLOUGH	DOWN	46.6
THREAVE	KIRKCUDBRIGHTSHIRE	45.8
WEST FREUGH	WIGTOWNSHIRE	45.6
LEUCHARS	FIFE	45
MUMBLES HEAD	WEST GLAMORGAN	45
CAPEL CURIG	GWYNEDD	44.8
RONALDSWAY	ISLE OF MAN	44
BRAMHAM	WEST YORKSHIRE	43.6
GLASGOW, BISHOPTON	RENFREWSHIRE	43
DISHFORTH AIRFIELD	NORTH YORKSHIRE	42.8
HAMPSTEAD	GREATER LONDON	41.4
SWANAGE	DORSET	41
CAMBORNE	CORNWALL	40.8
SENNYBRIDGE	POWYS	40.8
TRAWSGOED	DYFED	40.4

As the wet weather continues into the weekend we have issued a number of severe weather warnings. It is important people are weather aware by staying up to date with these during this period of unsettled weather. Amber warnings mean you need to be prepared for the weather and take steps to change your plans and protect you and your family or community from the impacts of the severe weather based on the forecast from the Met Office. We’d advise people in the areas affected to expect some disruption and take precautions if they are in an area at risk from heavy rain and flooding.

Stormy November weekend

As forecast, unsettled weather continues across the UK, with more heavy rain and strong winds expected to affect many areas at times through the weekend and into next week.

The Met Office and the Environment Agency are warning the public to be prepared for possible travel disruption and flooding as some areas see up to 60 mm on top of the rain that has already fallen over this week.

Eddy Carroll, Met Office Chief Forecaster, said: “The current very unsettled run of weather is set to continue with further spells of wet and windy weather expected across the country over the next few days.

“The southwest of England and parts of southeast Wales are expected to see the heaviest rain on Saturday with between 30 to 40 mm of rain in many parts and up to 60 mm of rain in some areas. Further rain moving in from the west on Sunday continues the risk for further flooding and travel disruption. We urge everyone to keep up to date with forecasts and warnings and be prepared for what the weather will bring.”

Along with the heavy rain strong winds may add to the potential for travel disruption, especially across southern Britain overnight Saturday into Sunday. Winds gusting to 50 or 60 mph are expected across southern counties of England overnight Saturday and into Sunday with severe gale or possibly storm force winds over the English Channel.

Rain spreading north across the UK Saturday 24 November 2012

John Curtin, Head of Incident Management at the Environment Agency, said: “We would urge people to continue to be prepared for flooding, sign up for Environment Agency flood warnings, keep up to date with the latest situation, and stay away from dangerous flood water.

“Our teams have been out around the clock over the last few days to minimise the risks and prepare for flooding and we are continuing to deploy teams across the country to keep communities safe.”

Looking a little further ahead the weather is expected to become drier and colder in most areas by the middle of next week, however overnight frost may then bring the risk of some icy roads after the recent rain.

The public can keep up to date with the latest forecasts and warnings for their area on our website and with forecasts on TV and radio during this unsettled spell. You can also be #weatheraware by following us on Twitter @metoffice

Rainfall totals update

The table below shows total rainfall from midnight on the 20th November until 7.00 am this morning. Some areas have had over 90 mm of rain over the last three days.

Location	Total (mm)
Exeter Airport	92
Tyndrum	91
Westonbirt	79.2
Shap	73.2
North Wyke	72
Usk	69.6
Filton	67.6
Libanus	67.6
Winchcombe	65.8
Capel Curig	65.6
Tredegar	64.4
Brize Norton	63.6
Skye: Lusa	63.4
Little Rissington	62.8
Liscombe	62.6
Yeovilton	60.8
Cardiff	60.8
Cluanie Inn	59.8

Further rainfall is expected over the weekend. Keep up to date with weather warnings from the Met Office and flood warnings from the Environment Agency.

Satellite and rainfall radar showing the weather from midnight Tuesday 21st November to the morning of the 23rd November.

Storm caused by most intense low to cross UK in September in 30 years

The low pressure system that has brought heavy rain, strong winds and flooding to the UK is the most intense to cross the UK in September for more than 30 years, with the lowest air pressure of 973mb being recorded on Tuesday morning.

Pressure chart at 6am on 25 September 2012

To find a similarly intense low pressure system that affected a wide part of the UK in September you need to go back to 1981, when pressures below 970mb were reported across central parts of the UK.

Like this week, this low pressure system brought unsettled weather as it crossed the British Isles – tracking east over the Isle of Man before heading north to Cumbria, Northumberland, eastern Scotland, Orkney and Shetland.

But what do we mean by ‘the most intense’? The intensity of a low pressure system is measured as the lowest pressure recorded at the centre of the system, as this gives an indication of how active it may be. This will relate to the rainfall amounts and wind strengths associated with it.

However, pressure is only one indicator of how much wind and rain there will be, so it is possible that other systems have resulted in stronger winds or heavier rain in some places than we have seen over the last few days.

Although the storm we have seen this week is certainly unusual in that it crossed central parts of the UK, some parts of the UK have seen pressure systems of this kind of intensity many times before at this time of year. In fact, Met Office records show some 31 occurrences of pressure below 975mb being observed in the UK in September, but the vast majority of these were confined to north and west Scotland, Northern Ireland or the far west of England.

For example a deep low affected the northwest of Scotland with pressure as low as 972mb as recently as 12 September 2011, whilst the Isles of Scilly and part of Cornwall saw pressure as low as 966mb on 7 September 1995. So, with regard to the system which has recently affected the UK, the key to what makes it remarkable is that it has tracked over a wide area of the UK rather than those areas which are more used to storms of this intensity.

What’s bringing the stormy weather to the UK?

The UK has seen some very wet and windy weather since the early hours of Sunday morning and that is set to continue in places for the next couple of days – but what has brought these disruptive conditions?

As is the norm, a low pressure which moved in from the Atlantic is to blame, bringing bands of heavy rain and strong winds (as you can see from the tightly packed isobars on the image below).

Forecast synoptic chart for 12:00 on Tuesday 25 September showing the low pressure over the UK.

Despite some reports to the contrary, this low is not what’s left of tropical storm Nadine, but is a completely separate entity – the remnants of Nadine are currently sitting close to the Azores far to the south of the UK.

Some warm tropical air dragged over by Nadine was sucked up into the low pressure, however, giving it some extra energy – essentially increasing its potential for strong winds and rain.

This isn’t unusual though, virtually every weather system we see will have had some input of sub-tropical air during its evolution.

There are two more notable features of this low pressure, however. Firstly, it has remained unusually active as it sits over the UK, leading to the strong winds and heavy rain.

This is due to the fact that, as the low pressure system moved north across the UK, it has also pulled in cooler polar air from the north.  This cold air has come up against the warm sub-tropical air, re-invigorating the depression and allowing it to continue to deepen over the UK.

Secondly this low pressure is lingering for longer than we would often see. The reason for this is down to the position of the jet stream, a narrow band of fast moving winds high up in the atmosphere which ‘steers’ weather systems.

Normally the jet stream runs fairly directly from east to west and pushes weather systems through quite quickly. Similar to earlier this year, the steering flow of the jet stream is currently in a meandering mood – looking much like a river, curving north and south as it heads west across the Atlantic (we call this a meridional flow, with the more linear west to east flow being called a zonal flow).

When it meanders, weather systems can get stuck in the ‘peaks and troughs’ it creates – so they get stalled in one spot rather than moving on. The below picture of the jet stream as at 12:00 today shows with the steering flow of the jet over France and the UK in the resulting trough.

The weather system will move on during the day on Wednesday, but that still means the UK will have had three days of unsettled weather.

Like our weather, the jet stream can change rapidly and it’s difficult to forecast precisely what it will do for more than a few days ahead – so there’s no reason to expect it to continue to behave in this way and there’s plenty still to play for in terms of our autumn weather.

The low pressure system that is affecting the UK is unusually deep for September, with the lowest air pressure recorded so far being 973mbs. To find a similarly intense low pressure system in September you need to go back to 1981, when pressures below 970mb were reported over a period of 24 hours. Like this week’s, this low pressure system brought unsettled weather as it crossed the British Isles – starting in the Isle of Man and tracking east and then north to cover Cumbria, Northumberland, eastern Scotland, Orkney and Shetland. There have been other times when pressures as low as 970mb were recorded in some parts of the British Isles in September, such as in the Isles of Scilly in 1995 and others across the far north or west of Scotland or Northern Ireland, however none were as widespread as the low that pushed across the UK in 1981.

Improving picture as many start school holidays

After weeks of heavy rain across parts of the UK, conditions are set to improve for many areas this weekend.

More heavy showers will affect some parts during the rest of the week, but by Saturday most areas will see drier weather with any showers few and far between. Temperatures will reach the low 20s Celsius.

Sunday will see the improved weather continue for a large part of England and Wales, with mostly dry weather and bright or sunny spells expected. However, the north and west of the UK, can expect some rain – which will be heavy in places – with strong winds.

Drier weather for many, with rain where it’s needed

Martin Young, Chief Forecaster at the Met Office, said: “As we move towards the weekend we will see a return to a more normal summer weather pattern for the UK. This will bring dry and bright conditions to southern parts over the weekend, and some much needed rainfall to the far north west of Scotland – where it has been exceptionally dry.”

Jet stream returning to ‘normal’ position

There has been a lot of talk about the position of the jet stream in relation to the recent wet weather, with this narrow band of fast flowing winds having been much further south than we would expect at this time of year.

Over the next few days, the jet stream is expected to move to its more usual position to the north of the UK, guiding rain-bearing low pressure systems from the Atlantic away from the country. This is why we expect to see a move to more normal summer conditions, with the south and east seeing the best of any drier and brighter conditions.

The above picture shows the position of the jet stream on 18 July 2012.

The forecast for 23 July 2012 shows the jet stream much further to the north.

Looking to the Olympics

There is understandably a huge amount of interest in what the weather will be doing at the end of next week in time for the Opening Ceremony of the Olympic Games. However, it’s still a little early to give a detailed forecast for the Olympic Stadium for the big opening event.

Sandie Dawe, Chief Executive at VisitBritain said: “The weather is a peculiarly British obsession, our international visitors come all year round for our temperate climate and enjoy a dash of unpredictability. Sunshine will help to get us all in the party mood, as we show the warmth of our welcome and the British know how to host not just a great Games but a great party too. Come rain or shine – Britain is the place to be in 2012.”

As ever, we’ll be working round the clock to make sure everyone – from the UK public, to athletes, coaches, and the organisers of the Games – has the very latest picture of what the weather has in store. For the latest information, keep up to date with our online forecasts and warnings.

First half of July continues wet and gloomy theme

Provisional mid-month statistics from the Met Office show that, after an exceptionally wet and gloomy June, the first half of July has continued the disappointing theme.

Normally at the halfway stage of a month we’d expect sunshine and rainfall to be somewhere around 50% of the average for the whole month, but the figures show a very different story.

Looking at the UK, we’ve already had more than the average rainfall we’d expect for the entire month – with 71.8mm (103% of the 1971-2000 average) falling up to the 15^th of the month.

Within that there are some big variations, however. Northern Ireland and Scotland have seen close to normal levels of rain, with 35.9mm (49%) and 56.4mm (61%) respectively. England and Wales have seen much more relative to their monthly averages, with 81.2mm (150%) and 95.8mm (122%) respectively.

Looking in even more detail at Scotland, however, you can see bigger variations in rainfall patterns: Mid Lothianshire in south east Scotland has seen 105.8mm (167%) of rain, while the Western Isles in the far north west of Scotland have seen just 10mm (10%).

This illustrates how rainfall patterns have really bucked their usual trend, with the far north west – which is usually one of the wettest places in the UK – continuing to be one of the driest areas. This is partly due to the position of the jet stream, as discussed in previous articles.

Looking at sunshine, there is a more consistent pattern across the regions. The UK has seen 45.5 hours of sunshine, just 26% of the average for the whole month, so around half what we would normally expect to see by this time. So far, England, Wales, Scotland and Northern Ireland have all seen about a quarter to a third of their monthly quota – making for a very dull month thus far.

Temperatures have also been on the disappointing side – with the UK seeing an average temperature so far of 13.7 deg C, which is 1.1 deg C below the monthly average.

With figures only going up to the 15^th of the month, it is of course impossible to say how the month could finish overall. It’s certainly too early to say whether this month will be a record-breaker, as that will depend on how the second half of the month plays out.

While more rain is expected in parts of the UK today there will also be some dry and sunny weather too.  The good news is that the weekend is set to bring drier and brighter weather to many parts of England and Wales – while the far north west of Scotland is likely to see some much-needed rain.