Archives For October 2013

Three storms in three days (*though Midge arrives late Sunday/early Monday am to Reigate), let’s call them Mary, Mungo and Midge… three storms with different characteristics. The situation is so fast moving that computer models differ quite markedly over what’s going on, their track and how much rain these will bring and where any gales will blow. So keep watching forecasts and check our twitter feed for local “Nowcasting” updates. It will be down to the wire for how much rain we get. Nevertheless, expect an inclement three days with gales near coasts at times almost anywhere and up mountains in NW. Reigate and SE will by no means have a continuous wash-out and we will have good periods of dry, bright and breezy weather at times, particularly Sunday looks like this at the moment.  Ridges between LOWS will bring quieter periods, so it depends when these pass over your region.  So do check detailed forecasts as they come in. It’s also worth noting that these storms are not as powerful as StJude last week but, nevertheless, if you are planning recreational ascents of mountains in N England / Scotland or perhaps learning to sail off the SW coast you may wish to alter your plans 🙂

Here are some characteristics of each storm and what we can expect, especially focussed on SE and Reigate…

31-10-2013 18-34-28Mary: Friday: a relatively warm storm sweeps up from the SW with lots of rain attached. While the UKMO brings heavy rain across SE several other models move rain across the Channel and gales into N France. It could be a near-miss with this one.

  • Passes across S England Fri – fri night from SW
  • Heavy rain, gales over N France, but could reach UK south and Channel
  • relatively warmer air in UK South and SE; 13-14c max for Reigate
  • lower winds inland as centre of LOW overhead SE
  • lowest pressure 998mb but deepening as she goes east; getting windy much later Friday night and into Saturday for SE

31-10-2013 18-34-36Mungo: a beefier storm altogether…crosses UK West-East further north on Saturday bringing gales and rain to Northern England while the Scottish Highlands get significant snow and cold wind chill temps down to -12c on summits.

  • Passes S Scotland N England Sat pm deepening as it goes
  • lowest pressure 978mb and gales over N England
  • COLDER air, snow over Highlands
  • 12-13c max for Reigate, falling away to 8c in evening, feeling cooler in wind.
  • sweeps gales over Ireland, NW west coast UK and mountains; Reigate stays altogether more sheltered and could be an OK day Saturday, with showers later pm.

31-10-2013 18-34-04Finally, Midge looks like bringing possibly the heaviest rain of all three to the SE overnight Sunday-Monday with strong winds as well.

  • 989mb
  • could sweep lots of rain over SE
  • 8-10c for Reigate
  • gales in Channel

Total rainfall varies but the SE could see 30-40mm fall over the next three days, most falling with Midge who crosses SE Sun night into Monday early am. Blustery conditions and cooler temperatures can be expected, especially Saturday evening and windy into Sunday but that should stay mostly dry at least. Typically autumnal but the quick succession of storms is notable, especially as so many people will be out and about this weekend at bonfire parties.

SW and NW coastal areas areas will see high seas and big waves this weekend pounding the west coast, 3-5m waves in the Channel are possible for example.

31-10-2013 19-32-41

Mountain areas in the NW will also experience some wild conditions, with Cairngorms seeing windchill fall to less than -10c and heavy snow.

Cairngorm summit

Cairngorm summit

Reigate is as usual nice and sheltered from the worst but could see heavy rain and winds of 30mph on occasions.  Expect some very autumnal temps and a cool weekend, with possibly very heavy rain Sunday night into Monday.

p.s. Mary, Mungo and Midge was a children’s programme from 1960’s.

Friday update: looks like heavy rain will go thru N France, so S and SE can expect a damp day with rain am and more pm, possibly heavier pm.  But not the deluge forecast a day ago. This situation is changing rapidly so check back.

A fast moving situation and not certain of track yet but … heads up that TWIN STORMS are set to hit the UK this Friday and Saturday bringing peaks of further heavy rainfall and gales. The first storm has uncanny similarities to StJude but is a weaker affair… and a warmer and wet version of StJude which is set to bring a lot of rain and windy conditions to the south sometime on Friday, probably pm. Stress this is not as powerful as StJude. Wind speeds probably max 30mph in Reigate, so not damaging as modelled currently. This first storm will be shifting quickly SW-NE, arriving SW Friday am and leaving by midnight, clearing the country in less than 12 hours.

The second storm is bigger and currently set to cross the UK further North and bring stronger gales across the South and SE, possibly gusting in excess of 40mph in Reigate and 50mph in exposed places nr coast; it will be wet but the wind is more likely to be the defining feature especially in the SE.  The Channel will likely see strong winds throughout this period.  Details are still emerging but twin storms, yet to be named, both deepen on their track across the country due to a lively jetstream. Once again, batten down those hatches, check the fence posts and tie down the trampolines!
More on this rapidly developing situation later as things emerge but prepare for a potential windy and wet fireworks on Friday and Saturday.  Watch forecasts.

She just won’t let up… enjoy the next few days of relative calm because the Atlantic is going to throw more storms at the UK Friday and through the weekend, so bonfire goers and organizers please check forecasts for details as they emerge!
For the SE and Reigate it is looking wet and windy with Friday being possibly very wet indeed in the SE with a weak Jude-like copy-cat appearing from the SW. By no means as strong as Jude, but it has uncanny similarities.  Saturday sees a monster appear to the NW. It has a deeper central pressure than Jude had when she left but, crucially, this one FILLS and weakens as she crosses the UK. Very tight isobars off shore will give NW UK a bashing on Saturday and the SE and E windy conditions on Sunday. Wind speeds will be less than Jude for us but still pretty blustery. These two storms may well pour cold water on bonfire night for many around the country.
Things still uncertain about this family of LOWS so check forecasts and details as they emerge.

30-10-2013 07-08-45

The popularly named St Jude storm (officially named Christian) of 27-28 October 2013 was the most severe to hit southern Britain for over a decade. Whilst it was less powerful than the 1987 Autumn storm, St Jude lived up to its forecasted strength and caused an estimated £1 billion worth of damage and losses across the southern half of the UK.  Here is a round up of  causes and some impacts of this severe mid-latitude storm.  Locally, @RGSweather covered the storm continuously overnight, providing updates and advisories on twitter as things developed minute by minute.  This is a summary of causes, what happened and what we have learned from this storm…

Causes

The “ingredients” for the birth of St Jude include…

1. A big warm soup:

A warm Atlantic Ocean, some 3-5c warmer than 30-year average, acted as a perfect birthing pool and nursery for StJude. The warm sea surface temperatures provided plenty of extra water-vapour, heat energy and lift ready for stirring up a potentially big storm.

Warmer than usual Atlantic

Warmer than usual Atlantic

2. Add some extreme pressure!

The North Atlantic Oscillation is a measure of the difference in pressure between Iceland and the Azores and it was in increasingly positive phase during the storm build-up.  Whilst this is more of a measure than a cause, a positive phase nevertheless indicates LOWER than average pressure over Iceland and higher pressure over the Azores, which usually indicates a strong zonal west to east flowing jetstream across the Atlantic and fast moving weather with the potential for plenty of low pressure systems from the west.  This rapid west-east flowing weather was a necessary ingredient in the set-up for St Jude.

29-10-2013 09-44-40

bubble bubble toil and trouble

bubble bubble toil and trouble

3. Throw in Mr Muscle

A very strong jetstream: blowing at 240mph across the Atlantic towards the UK acted as the main ingredient in the birth of storm St Jude. The jetstream directs weather on the ground.  The jet over the Atlantic in the days leading up to St Jude was extremely strong and blowing directly across UK latitudes. The jetstream is a product of the temperature and pressure contrast between cool Polar air to the north and warm Tropical air to the south.  The temperature difference between polar air and tropical air is particularly marked at this time of year: with the tropics still very warm, while the Polar ice sheets seeing a marked fall-off in temperatures with their attendant air masses.  This builds steep pressure gradients and a strong jet. The jet is also a key factor in creating and guiding LOW and HIGH pressure systems on the surface.  Like a dog on a lead, St Jude was dragged across the Atlantic by it’s angry owner, the jetstream. At times during the passage of the storm wind speeds above the Channel exceeded 180mph.

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4. Whisk up some bad parents!

So all the ingredients are ready, but no storm yet!? The mother of St Jude was a deep robust LOW south of Greenland.  This formidable storm produced hurricane force polar winds directed from the NW in the days before St Jude was even a twinkle in her eye.  The father was a weakening and slow moving tropical storm called Lorenzo.  He had spent the week meandering slowly in the Mid-Atlantic but Lorenzo, despite his old age. still arrived with plenty of hot air from the Tropics.  Their respective air masses collided in the mid-Atlantic some 1000 miles off the SW coast of the UK and, encouraged upwards by the jetstream, they produced their only child, St Jude!

baby bomb is born

baby bomb is born

5. Give it a stir!

Cyclogensis is the process of rapid growth of a baby storm in the mid-latitudes: due to converging warm and tropical air and, encouraged by the jetstream, air rapidly lifted off the surface and Jude’s central pressure, as predicted by the UKMO fell steeply.  This so-called meteorological BOMB exploded (or perhaps imploded, as air was dragged into the low pressure causing all that wind) formed a deep wave depression LOW that charged across S Wales and England in less than 12 hours.  It made a rapid exit from the UK via the Wash and then continued to deepen across the North Sea before smashing into Scandinavia. Arguably the storm did not deepen over the UK quite as spectacularly as some models forecast, but nevertheless, the track and winds were much as predicted and the storm went on to cause significant damage. The chart below shows the pressure falling at a NOAA weather buoy in the development zone of St Jude some 300 miles SW of Cornwall. Note the INCREASE in pressure before the sudden drop-off.  This is entirely in line with cyclogenesis: pressure builds ahead of rapidly developing warm fronts as isobars are buckled up ahead of the storm.  This is popularly known as the “calm before the storm” where winds die down before the maelstrom hits.  This was marked across the country on Sunday evening. At that stage people wondered “what storm?”.

27-10-2013 17-29-56

calm before storm

The satellite picture below of St Jude still in development phase shows the characteristic wave form kink of a rapidly developing storm.

6. Watch out for that sting in the tale!

More immediate “causes” of storm damage from StJude, making it extra-powerful, include the relatively newly discovered weather phenomenon called a stingjet wind.  These are isolated fierce gusts of wind experienced behind a departing deep area of low pressure, often behind a cold front. Oddly, they tend to occur as conditions more widely are improving. In very tight depressions descending air from the upper troposphere pushes gusts to the surface and, like a giant invisible hand, these can, in a careless whim, push down whole swathes of mature forest, take rooves off houses, rip down scaffolding, push over cranes, roll over double decker buses and blow trampolines clear out of your garden!  The sting in the tale is an appropriate analogy, as the curl of winds descending round from the NW of the departing LOW are frequently the last hurrah for these storms. **NOTE: Stingjet NOW confirmed!**

28-10-2013 06-27-15

The storm was perfectly forecast by the UKMO up to a week before the event.  It was always going to be hit-and-miss up to the last minute, not least with inevitable media-hype; but the consequences of playing this down would have been potentially disastrous.  Overall, it was well predicted and people were warned effectively days beforehand.  Whether they prepared effectively or took warnings seriously is another matter.

Below is a slide-show of synoptic charts showing the progress of the storm.  Note that the central region of LOW pressure experienced light winds like a hurricane “eye” (but not as extreme in contrast!). Below this is a brief list of impacts.

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Impacts

28-10-2013 02-53-24

The highest winds were largely restricted to places south of the M4, excluding Wales which had 80mph+ winds in the run-up to the storm on Sunday but calmed down for a time overnight Monday as the centre of the LOW passed over the Severn Estuary and S Wales. Across S and SE England wind speeds were widely 40-60mph and 70-80mph+ on the south coast.  Remember that average wind speed across an area can seem surprisingly low during a storm.  The average wind speed across Reigate from 5-8am during the height of the storm was only 16mph! It is, of course, the random gusts that cause the most damage. The highest gust in Reigate was 48mph at 6:20am on Monday morning.  The highest official max gust was 99mph on the Needles, Isle of Wight, other notable wind speeds were Heathrow 70mph and 62mph at Redhill aerodrome.  Reigate, as predicted by @RGSweather, was spared the worst as our max wind gust was 48mph. Our location in Surrey is away from the coast and locally the town is low down in a vale with low wooded hills to the south, Priory Park, that shelters the town from S or SW gales such as the ones StJude produced during the worst of the storm.  More exposed parts of our local area certainly experienced higher wind speeds.  Rainfall was intense for a period of time and caused localised flooding. In Reigate 25mm of rain fell overnight, which is more than for the whole month of July or, August, in less than 10 hours!  St Jude crossed at night and only keen meteorologists were awake to see it go through.  If this had been a daytime storm, impacts listed below are likely to have been worse with more people getting out and about, or attempting to.

Here are some of the impacts from St Jude in the UK:

  • 3 people were killed by falling trees, 1 boy was very sadly swept out in rough seas on s coast in the lead-up to the storm
  • 147 flood alerts, 17 flood warnings issued by Environment Agency, including our own River Mole
  • In the English Channel and approaches there were 20-30 foot waves and storm force winds.
  • power cuts in SE across 270,000 homes, some for 2 days
  • 5 train companies cancelled all their trains in SE
  • 130 flights from Heathrow cancelled, delays at Gatwick
  • Port of Dover closed, horrifying stories of Channel ferry crossings
  • crane collapsed onto Cabinet office
  • Major bridges were shut in high winds including Severn Bridge and QE2.
  • Dungeness B nuclear powerstation had a power cut in 90mph winds and had to shut down both reactors
  • In Suffolk a double decker bus was rolled over by a gust of wind
  • Clacton pier helter skelter was blown down
  • 1000’s of trees blocked roads and caused travel delays and closures
  • other impacts across the SE here http://www.bbc.co.uk/news/uk-24699748
  • here http://www.bbc.co.uk/news/uk-24700611
  • and costs here (sorry, only one I could find 🙂 http://www.mirror.co.uk/news/uk-news/uk-weather-storm-st-jude-2651458

Emergency service response was predictably very effective in dealing with thousands of calls.  Public were advised not to call 999 for tree falls, and only call in real emergencies.

The storm went on to cause significant damage and some 15 people in total died across the UK, N France, Netherlands, Belgium, Germany and Scandinavia.  It deepened across the North Sea and became more intense with stronger winds, with 120mph reputedly being recorded in Denmark (http://en.wikipedia.org/wiki/St_Jude_storm)

So… hundreds of trees down, some scaffolding torn apart, helter-skelters blown away and some very unfortunate people killed out in the storm… plus £1billion lost through days off and travel chaos.  Inevitably, forecasters are stuck between over-blowing storms and under-playing them so as not to cause panic.  Personally, I think they got this spot on from the start, so congratulations UKMO! The fine balancing act between under-playing and exaggerating potentially serious events is not an enviable task for forecasters.  Despite being very powerful, computer forecast models were still flip-flopping 24 hours ahead with the exact track and severity of this storm.  It was an on-then-off affair right down to the line!  For the future it is worth raising awareness in the public that, despite computers producing forecasts (and who trusts them!?), predicting the weather is still based on the judgement of experts at the UKMO and elsewhere. (photo of clouds over Channel below left was taken by an airbus pilot on his way over Channel during storm). other resources for this storm:

http://www.theguardian.com/teacher-network/teacher-blog/2013/nov/03/st-jude-storm-extreme-weather-teaching-resources?CMP=twt_fd

http://www.independent.co.uk/news/uk/home-news/the-30m-supercomputer-that-helped-the-met-office-predict-st-judes-storm-8911510.html

Which was bigger, 87 or 2013? http://www.bbc.co.uk/news/uk-24708614

Finally, the old chestnut “was it a hurricane?”… Despite getting winds exceeding hurricane force ((74mph+) UK storms cannot be classified as hurricanes. Hurricanes are tropical weather phenomenon and do not form in the Mid-Atlantic at our latitude, neither do they ever get to the UK.  We may experience hurricane force winds in extreme low pressure systems which are confusingly also called cyclones, although they are NOT tropical cyclones!  At our location, on this side of the Atlantic and this far north, we have never experienced a true-hurricane.  Even the ’87 storm was not technically a hurricane despite having even stronger winds. We sometimes get “old” hurricanes impacting the UK but this is not the same, and neither St Jude nor 1987 were one of these characters. Handy pic below illustrates this nicely. Below this are a selection of photos posted on twitter mainly from our local area in E Surrey.

27-10-2013 15-11-29

Lead-up to storm in Reigate on Sunday pm

Monday 28: note: If you have pictures of storm damage then please send them in, I’ll do an “aftermath” gallery and pull some local snaps together in due course.

Latest meteosat image from 15:00hrs today with added features of the storm moving towards UK this evening and overnight.

There are no trains tomorrow on Southern Railways, Network Rail and Gatwick Express until lines confirmed as safe.

Severn Bridge closed overnight from 3am.

Overground rail in London will close am.

Check details of flights from Heathrow and Gatwick as delays likely.

Below are some pics from today up Reigate Hill showing incoming squally showers on a gusty 30mph SW

WEATHER WARNING (but with a note that some models are downplaying this in latest runs 🙂

The explosive LOW arrives Sunday night on the back of the parent LOW moving across today.  There is a risk of significant disruption, albeit there is also a risk of NO disruption as the LOW trails further north or south and some model runs are downgrading the storm inland to 60mph max which is blowy but not as severe… in any case check forecasts regularly for updates. It’s a very tight little low so changes in track will make an enormous difference to your experience on the ground from “oh, is that all?” to something more akin to “OMG!”.  In any case, the advice is to avoid unnecessary travel if at all possible and expect disruption to all forms of transport due to high winds in the SE and heavy rain further north. The strongest winds are located in the southern part of England and Wales.

Here is an outline of what we can expect in the SE and Reigate in particular.

The relative overnight calm will continue through the small hours until after breakfast when winds will slowly pick up, with gusts over 30mph.  Bands of squally, sometimes heavy showers will pass over during the morning. More rain and gusty winds will continue through Sunday pm making it a miserable afternoon with temps barely exceeding 14c and feeling more like 9c.

The highest winds exceeding gusts of 50-60mph arrive in the SE and Reigate around midnight on Monday and the winds quickly increase thereafter.

High winds with gusts exceeding 50mph will be a feature of Monday morning from 0300hrs through to around lunchtime when they will die down quickly.

Heavy rain will arrive with the highest winds overnight but become lighter through Monday daylight hours.

A NASTY STING IN THE TAIL? RED LINE ON MAP SHOWS POTENTIAL FOR 90-100MPH SUDDEN GUSTS IN AREA AT RISK FROM STINGJET: UPDATE: the 99mph winds at Needles were an example of stingjet winds

THERE IS A RISK OF VERY STRONG DAMAGING GUSTS IN THE SE FROM 09:00hrs – 12:00hrs Monday, ESPECIALLY NEAR THE COAST AND IN THE FURTHEST SE CORNER i.e. Sussex and Kent; but everywhere below the red line on the map is especially at risk from this atmospheric phenomenon discovered after the 1987 storm and only observed and studied retrospectively a few times. A stingjet is a newly discovered feature which can develop in rapidly forming storms such as this.  It is when cool dry air sinks from high in the troposphere and can accelerate winds wrapping around the back of an intense LOW, in this case to potentially over 90mph inland and even 100mph+ gusts are a slight possibility over the coast.  There is a risk of such winds occuring anywhere along the coast of Southern England and inland towards the RED line drawn on the map above.  These gusts are like a giant fist from the sky and can flatten whole forests and take off rooves as they did in 1987.  if one occurs it will be one of the rare occasions when it has been modelled.  The characteristic tell-tale of a stingjet is a loop or hook in the wind field or water vapour satellite photo.  Weathermen will be keenly looking for real-time evidence of this throughout the storm.  A hook-like feature on the high resolution model from NMM seems to suggest a stingjet-like formation.  You can see the hook travelling along the zone of highest winds on the animation below (courtesy of NMM netweather). Read below to see what sensible precautions you should make tomorrow.  OK, so this is not a hurricane and is not anywhere near the force of Sandy or Katrina but hurricane force winds MIGHT be embedded within the maelstrom, so we ought to make sensible preparations to avoid unnecessary damage.

PREPARATIONS:

  • secure anything that can blow around e.g. bird feeders, bins, toys
  • cut back any loose branches and trees: store these in a garage
  • check where your car is parked … avoid parking under suspect trees
  • check roof tiles and chimney pots
  • make sure your pets are safe overnight
  • clear loose and clogged drains and gutters
  • ensure all outside doors and windows are shut and secure
  • locate torches and check they WORK in case of power cuts
  • charge your phone in case of power cuts

 

The ingredients for our Monday storm are stirring in the Atlantic, as shown by the sat pic from today.
The Mother of LOW pressures south of Greenland is whipping up hurricane force winds and 50 foot waves in the Atlantic.
A warm plume of tropical air is being brought up by a weakening ex-tropical depression Lorenzo.
They meet at the polar front where an extremely powerful 240mph jetstream is due to lower surface pressure rapidly forming the storm which will cross UK on Monday.  The birth of our storm is called cyclogenesis: it is rapid and will cross the UK rapidly overnight Sunday to Monday.  It will continue to fall in pressure and intensify as it does so.  Conditions will be worst along the south coast and SE where wind gusts could reach 80mph, inland gusts of 60mph will decrease north of the M25. The beaufort scale below shows what these winds mean to you and your house. Sustained winds around Reigate will probably hover around 20-30mph, which are certainly not damaging. Gusts are a different matter and these could lift tiles, bring down branches or even weak trees ready to fall.  Loose fences and garden furniture not tied down may also blow about in gusts and cause additional damage.  Umbrellas will certainly be “difficult to use”, (I love this description!) which is, of course, a critical meteorological threshold occurring when winds exceed Force 6, 25mph. 

Birth of UK Monday storm

October 24, 2013 — 2 Comments

Quick pic on how our Sunday-Monday storm is born… more later! 

 

The potential for a major storm hitting the South of the UK on Monday remains. The exact track and intensity are still uncertain, varying from N France to Scotland and having varying impacts on the south of the UK, from very little to a lot, depending on the final track.  However, best to be forewarned! Several models show a vigorous LOW developing to the SW of the UK due to an extremely lively 180mph jetstreak or potential stingjet over the Channel. This has the effect of lifting air rapidly off the surface and lowering pressure rapidly.  A rapid lowering of pressure to produce a storm is sometimes called a “bomb” and is similar to the propagation of the October 1987 storm (not a hurricane!).
As it looks at the moment… the LOW will cross the UK from SW to NE and develop Force 10 SW gales in the Channel during Monday morning and, as it moves into the North Sea, stronger winds are possible up to Storm Force 11 with potential for extremely rough seas and 70-80mph winds.

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Inland winds will be less powerful but gusts could reach 50-60mph widely in the worst case scenario. All from the S or SW and, later on veering to the NW. Waves of 3-5metres in the Channel are possible and 10 metres in exposed waters.
Overnight Sunday and Monday morning seem the most likely periods of highest winds for the South. The systems moves away rapidly into the north sea and winds ameliorate to sunshine and showers.  Thereafter, the rest of the week continues to look unsettled with wind and rain.  One to watch definitely!

Watch the propagation of wave heights across the Atlantic as the mother LOW moves in during the early part of next week.

Storm track early next week remains uncertain on these runs. One to watch as things develop. It is fairly certain to be a cooler and unsettled start to the week but the extent of this will be determined by the exact track of the jetstream and the LOW it propagates.  There are signals of a HIGH developing midweek next week for a respite, at least.

Update: gales for UK coasts from Sat – Mon, significantly for Channel from am Monday gusting Force 10 potentially 60mph. 30mph+ inland.