St. Jude Storm - 28th October 2013
This storm was an intense extratropical cyclone which battered parts of northern Europe from the 28th - 29th October 2013. The storm was unusually intense for the time of year, when trees are still in full leaf and more vunerable to strong winds. The southerly track of the storm across central/southern England was also significant and unusual because strong winds are rarer here, making these areas more vunerable to the effects of those winds. After causing significant damage and destruction in southern England during the early hours of the 28th October, the storm raced acrosss the North Sea, still strengthening and impacted Denmark. This was probably the worst hit country, and a low altitude gust of 121 mph was recorded in the south of the country. Wind gusts over the North Sea were likely around 20% higher than this, but the lack of observations over the sea meant that no higher wind speeds were recorded there. 
 
 
 
 
 
 
 
 
 
 
Infrared satellite image of the St. Jude Storm over England. A tip in the white cloud head band can be seen over southern England - this was a possibly a "sting jet". 
Credit: WeatherQuest
Unlike the Great Storm of 1987 before it, this storm was well predicted by the Met Office, allowing preparations to be made for the approaching high winds and heavy rain. This undoubtedly reduced the loss of life, injury and financial cost of the storm. The Met Office's forecast model first modelled the storm about a week before it made landfall. As time passed and confidence grew in the forecast, warnings for high wind and heavy rain were continually upgraded. Fortunately the track the storm eventually took did not change much from the most likely forecasted track. Unlike the Great Storm of 1987, the low did not track across southern England and London. Instead, it was a little further north, across the Midlands. Even so, the winds were still strongest on the southern flank, with storm force winds across much of southern England. Ultimately the storm was not as strong as the Great Storm of 1987 though.
 
     
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
The storm was born over the North Atlantic at a time when the conditions were perfect for the development of strong extratropical cyclones. The storm developed over the ocean, at a time of year when the sea surface temperatures are close to their warmest. What is more, they were 3-5°C warmer than the long-term average, providing ample moisture and latent heat to fuel the storm. Second, there was an exceptionally strong zonal jet stream blowing over the North Atlantic, with winds of around 240 mph. This means than the regions of rising motion at the jet entrance and exit were likely to be incredibly strong, creating a rapidly deepening area of low pressure at the surface. It also helped propel the storm forwards at speeds close to 50 mph. The strength of the jet stream was fueled by a strong temperature gradient at the surface due to northwesterly winds from a deep Icelandic Low and southwesterly winds from the remnants of ex-tropical storm Lorenzo. This input of warm, moist, tropical air helped the storm to rapidly deepen, or "bomb" - a deepening of the central pressure by at least 24 hPa in 24 hours, as significant amounts of latent heat were released into the storm. By the time it made landfall in Wales, it was a nasty area of low pressure - a "secondary low" situated on the southern flank of a much larger low to the north of Scotland.
 
'
    
 
  
Diagrams of the forecasted storm tracks of the storm several days prior to the event. Note that there was still some uncertainty about where the storm would head. A track with the low centred slightly further south would have been most damaging. 
Credit: Met Office
Surface pressure chart of the St. Jude Storm as it crossed the United Kingdom. The tight pressure gradient, with the associated strongest winds, can be seen on the southern flank of the low. 
Credit: Met Office
In the UK, hundreds of trees were blown over, and four people died as a result of falling trees. Around 660,000 homes were left without power, some for several days, as high winds blew down power pylons. The maximum gust in the UK was 99 mph, at the Needles in the Isle of White. Inland, the strongest winds were south of the M4, but were typically below 70 mph. They were strongest nearer to the coast, where the reduced friction over the ocean allows higher wind speeds. Waves reached 20 - 30 feet in the English Channel where ferry crossings were dangerous, eventually leading to the closure of the Port of Dover. Flights were also cancelled at Heathrow and Gatwick airports. The storm brought heavy rain to southern parts too, with a maximum of 54 mm falling in Cardiff. Overall, the storm caused about £1 billion in financial loss and damage in the UK.   
 
Was there a sting jet?
There are still uncertainties about whether this storm produced a sting jet. Sting jets are the region of strongest winds that any extratropical storm can typically produce, although they are thought to occur in just one third of all storms. The strong winds are produced at the rear of the storm and descend from the passing cloud head of the cyclone - hence why they are often referred to as "the sting in the tail". Rapid descent of air here is initiated by precipitation from the cloud head falling into dry air below and evaporatively cooling it. The air descends so rapidly that it can produce violent winds at the surface, where it spreads out rapidly. It is possible that the St Jude storm produced a sting jet, and the radar image of precipitation over the UK certainly seems to agree with this.  
 
 
A radar image of the precipitation associated with the storm. The curl of cloud can be easily seen (this radar image is at rougly the same time as the infrared satellite image at the top). 
From http://rgsweather.com/2013/10/29/st-jude-causes-and-impacts-of-the-october-storm-27-28-2013/  
Credit: Netweather
 
 
 
 
 
 
 
 
 
This curling cloud head moved northeast of London and eventually through East Anglia during the morning of the 28th October. There was a swathe of strong and damaging winds at smiliar times to the passage of the cloud head: however recent research has found there to be inconclusive evidence that a sting jet was present. The Great Storm of October 1987 produced a devistating sting jet which felled millions of trees along a very similar path, along with a gust of 122 mph in Gorleston, Norfolk. 
 
Credit must be given to the forecast models for accurately forecasting this event (and well in advance) over the UK. Other countries, such as Denmark, also had an extended warning of the storm thanks to the Met Office and other forecast models which picked up on the event. The storm was exceptional in terms of its strength and early season nature, but I think that the UK dodged a bullet, since it strengthened still further once passing into the North Sea. This has hopefully been a lesson to forecasters and emergency services on how to handle a situation of such severity in the future.