Ex Bertha more likely to miss UK

6 08 2014

7 August update: The latest update about the whether ex-Bertha will affect the UK can be found in our news release


Tropical Storm Bertha is currently off the north east coast of the US and is likely to become an ‘extra tropical storm’ on Thursday.

It’s then expected to track across the Atlantic – and while there are still a number of possible outcomes, it looks increasingly likely that the UK will miss any serious impacts from ‘ex Bertha’.

The Met Office has been assessing the likelihood of the UK seeing any effects from Bertha by using our own forecast model alongside models from other world-leading forecast centres.

Map shows likely storm track for ex Bertha by midday Sunday.

Map shows likely storm track for ex Bertha by midday Sunday.

At the moment the majority of forecasts from those models suggest ex Bertha will track to the south of the UK as a relatively weak low pressure system.

In fact it’s debatable whether this is even ex Bertha, as the storm declines to such an extent as it comes across the Atlantic that it fragments.

Some of the warm air which it drags across then leads to a new weak low which generates an area of heavy rain. This could move across northern France and possibly clip eastern parts of the UK on Sunday.

A much smaller number of model outcomes suggest ex Bertha will move across the UK as a more distinct feature which could bring some strong winds and heavy rain. Because these outcomes are in a minority, however, they are less likely.

While there remains a good deal of uncertainty about the weather on Sunday, it currently looks as if it will be fairly unsettled with some rain and breezy conditions – but nothing too unusual for the time of year.

It’s worth noting that it’s likely that the south east of England will see some heavy rain on Friday, which is not part of Bertha. You can see more about this on the Met Office’s severe weather warnings page.

We’ll be keeping an eye on the latest outlook for the weather over the next few days and the progress of ex Bertha to keep everyone up to date with the latest information.

Cold snap expected

3 12 2013

The UK is going to see a very short, sharp, cold snap.  From Wednesday night (4th Dec) into Thursday morning (5th Dec) Scotland, northern England and Northern Ireland will see some strong winds, while Scotland will see some wintry showers and snow.  However temperatures will return to normal as we head through the weekend, and be more in line with what should be expected for December.

A rapidly deepening Atlantic depression is expected to move in an easterly direction to the north of Scotland bringing westerly gales, with gusts of 60 to 70 mph extending southwards across northern and some central parts of the UK on Wednesday night and Thursday.  Northern Scotland could see gusts of 80mph, and potentially 90mph for a time.

Because of this the Met Office has issued a Yellow Severe Weather Warning for strong winds. The public should be aware of possible disruption to travel, especially across Scotland, parts of Northern Ireland and Northern England.

The winds are expected to veer northerly and bring the colder arctic air southwards across northern areas before easing into Friday. The winds could exacerbate high tides and may increase the risk of coastal flooding in the Northern and Western Isles and along the East Coast of England.

A Yellow warning for snow is also in place. It runs from 6am Thursday to 12 noon on Friday, covering the northern half of Scotland, snow showers are expected to be most frequent across the Northern Isles, the North Highlands and northern Aberdeenshire.  Low laying areas could see 2 – 5cms of snow and higher altitudes 10 – 20cms. In addition the strong winds could lead to some drifting of snow and possibly blizzard conditions on higher ground.  Icy conditions may also develop on some roads across Scotland on Thursday night and Friday morning.

This winter storm is not expected to be as powerful as those in January 2012 and December 2011

This is expected to be a short-lived cold snap, with temperatures quickly recovering to near normal over the weekend.

Our video explains what to do during a Yellow warning for wind. You can also download a weather warnings widget for your website.

What’s bringing the stormy weather to the UK?

24 09 2012

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.


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