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Quick interim storm summary graph with data from our Reigate weather station. Analysis and links to follow.  Below is a medley of images… analysis to be continued after festive season!  Meanwhile… hope you survived unscathed and Happy Christmas!

70mm total rainfall (manual rain gauge reading) now confirmed for Reigate during the storm 24hrs.

which was bigger, StJude or Caspar? (our name, not Dirk!) Caspar of course! Caspar goes on to Scotland today… 24 Dec

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Dramatic VIIRS sat pic from 24 Dec midday: note boiling clouds along Atlantic front

River Mole 3.45m above normal level: severe EA flood alert issued: the only one in the UK at the time.

Flanchford Bridge wall collapse

Reputedly, the first snow for over 100 years has fallen on the Sphinx but several photos on the web are actually of a model in Japan!  Anyhow, snow certainly fell across Cairo, N Egypt and even deeper snow has fallen over Israel, including Jerusalem and more widely across the Middle East and Turkey.  The upper air temperatures across Israel and Egypt are cold, of course, but only -2c or -3c at 850hPa which, in the UK is common and rarely produces snow for us… as a rule of thumb our 850hPa temps need to be at least -5c or lower to deliver much snow to the UK, especially the south away from hills.  So why did it snow on the Sphinx when the airmass was not really that cold?  BTW check this link for the sphinx in the snow pic

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Cold, but not like the UK!

Well, it looks like the snow in Israel and Egypt is what meteorologists call “Lake or Sea Effect snow” and is quite common near the Great Lakes in the USA and across Japan but of course rather more unusual in the warmer Middle East. A deep LOW pressure (Winter Storm Alexa) swept across to the north of Israel dragging in bitterly cold strong N winds across Egypt and Israel and the Middle East as a whole.  The air originated from further north over continental Asia, where winter temperatures are extremely cold. The strong wind has crossed the Med (still fairly warm of course) in a wide arc across the warm sea surface which has allowed a good deal of moisture to evaporate, adding humidity and instability to the air mass.  A temperature difference of at least 13c is required to produce the greatest evaporation and moisture input required to produce plenty of “sea or lake effect snow”. SST across the Med off Israel is currently over 20c and this air mass had a temp of -3c at 850hPa and around freezing at sea level.

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On hitting land the strong wind experiences friction and literally “piles up” against the coast causing convergence and uplift.  The uplift, especially pushed up over the heights of Israel, causes cooling in the frigid polar air and, eventually, precipitation in the form of snow. Ingredients for sea effect snow were therefore all met in this case:

  • deep polar air mass
  • strong winds
  • temperature difference between the water and the air at 850hPa must be at least 13c for significant lake/sea effect snow
  • hills near the sea to encourage uplift

More pics here

Elsewhere in the region, winter storm Alexa has caused flooding in the Gaza strip

The 2013 December 5-7 North Sea storm caused “the biggest UK storm surge for 60 years” (UK Environment Agency).  With associated gales across Scotland, coastal flooding in North Wales, Merseyside and the UK East coast, tidal river flooding in Hamburg, the closure of all major North Sea coastal surge barriers and disruptive snow further south in Europe, this storm system was arguably more powerful than StJude back in October.  Thankfully, this storm only killed 7 people across Northern Europe (

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Essentially a storm surge is a higher-than-normal sea surface caused by low air pressure coinciding with high tides which, when thrown into shallow coastlines by winds, can produce exceptional coastal flooding.  A surge can also include associated lower-than-normal water levels with off-shore winds pushing water away from the coast at low tide.

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This post outlines the factors that makes the North Sea so vulnerable to storm surges and, further down, there is a summary of some impacts and a quick resume of the successful responses to this hazard event with some useful links.  Finally, before we get too smug and chill out entirely about future storm surge hazard…will development land lapped-up on exposed coasts, for example in the Thames Gateway, increase our future vulnerability in the face of sea level rise and climate change?  Is it sensible to build in these locations?

Animation shows storm surge rolling round the coast and into the North Sea.


The North Sea is particularly vulnerable to storm surges because of an unlucky combination of factors that come together to occasionally make the “perfect storm”.  Fortunately, not every North Sea storm produces a surge!  Remember that Tacloban in the Philippines was hit by an even bigger storm surge generated by Typhoon Haiyan due to similar forces and a funnel shaped bay.  Compare videos on this blog to see the difference between Tacloban and North Sea surges. So what comes together to produce the most significant storm surge hazards in the North Sea? There are at least 6 factors that combine to produce the biggest storm surges: here they are:

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1. Sea shape and low lying coastlines: The North Sea is particularly prone to dramatic storm surges because it is open to the North Atlantic and then tapers towards the south in a funnel shape. This funnel shape has the effect of allowing strong northerly winds to direct storm surges towards cities like London, Amsterdam and Hamburg and surrounding vulnerable low lying coastal areas including Norfolk, Lincolnshire, Essex, Kent and the Netherlands. Some of these areas are at or below sea level and require sea walls and dykes and barriers to protect them during storm surge events otherwise they will be flooded. The 1953 storm surge broke the rather primitive sea walls of the time and flooded large areas of Essex and even more of the Netherlands causing the worst European peace-time disaster since the war and killing 307 people in the UK and thousands in the Netherlands (see you tube documentaries below)


2. Sea depth/ bathymetry: the North Sea gets shallower towards the bays and wetlands towards the south.  These shallows have the effect of increasing the height of tides and surges as they are forced up over submerged shelves into narrowing bays.  This is possibly why Boston, Lincs and Hamburg suffered some of the worst flooding because surges were forced up bays and rivers.

3. Intense low air pressure: A 1 millibar reduction in air pressure allows sea level to rise by 10mm.  This effect can be replicated by sucking water up through a straw. The storm that crossed to the north of Scotland on 5 December had a central pressure of 976mb that deepened to 968mb over the North Sea. This is a similar central pressure to the storm that caused the 1953 storm surge that killed 307 people in the UK and 1800 people in the Netherlands.

4. Storm track: the LOW pressure has to track east over north of Scotland, which will drive a surge of water into the North Sea that is then pushed south by vigorous onshore Northerly winds into the low lying east coast of UK.  Ideally, the storm should deepen on its’ track across the North Sea, thus allowing northerly winds to gain in strength driving the surge and associated wind waves south.

LOW track

LOW track

5. High tides: high spring tides are the final requirement for the biggest surges.  Tides migrate as a bulge of water around the coast and, for the worst impacts, any surge travelling south down the North Sea must match the dome of the highest tide to produce the highest water levels in any one place. Since high tides occur twice a day it is quite likely that high elements of the surge will match a high tide level somewhere down the east coast.

6. Wind driven waves: Finally, surge and tide heights can be increased yet further by strong on-shore winds producing locally high wind driven waves that can over-top sea walls.

Warnings and impacts

The impacts of the 2013 storm surge included flooding in coastal towns on the east coast of the UK with perhaps worst hit being Boston in Lincolnshire. Houses on some vulnerable stretches of coasts such as Hemsby were washed into the sea as waves eroded sand dunes.  There was also significant flooding in Rhyll, North Wales and along the Merseyside coast at New Brighton (note: not Brighton!) where a Morrisons supermarket was flooded. The worst impacts on major populations and cities were avoided by the raising of the Thames Barrier to defend London and the closure of the flood gates on the Delta Scheme in the Netherlands.

The storm was modeled over a week prior to impact.  Initially GFS and UKMO models were seeing a cold surge as the main factor bringing possible snow across the UK but from about 6-7 days out it became increasingly obvious that the exact track and orientation of the LOW meant that powerful northerly winds and a possible storm surge were the greatest risk.  The UK Met Office, with Environment Agency, then started preparations for warning those at risk from flooding.  Most news channels were airing significant coverage from 24 hours out.


Significant flooding did occur along the East coast, notably in Scarborough in Yorks, Boston in Lincs and Hemsby in Norfolk. In Hemsby some vulnerable houses located on the sand dunes were washed into the sea. Bridges near the sea were shut for a time, like the Humber Bridge; and rail services in some eatern counties were disrupted for a time.  Power was cut to homes in Scotland due to high winds.  Hundreds of residents were evacuated prior to the floods in various locations but some claimed to have little warning.

The worst impacts were successfully controlled by the massively impressive engineering schemes built since the devastating 1953 floods.London has nearly 200 miles of flood walls and 8 barriers holding back the tidal Thames. The Thames Barrier was opened by the Queen in 1982.

The Eastern Scheldt storm barrier was closed for the first time since the 1970’s.  The Netherlands barriers are built to withstand a 1 in 10,000 year storm surge event so it is perhaps unsurprising that they easily saw off this event.  It is also noteworthy that the Dutch have great faith in their storm surge protection barriers.

These measures, along with warnings and on the ground assistance for places that were flooded, proved extremely effective.

Further useful links on 1953 and 2013 storm surges:

1953 storm surge: original newsreel and timewatch documentary

The sting in the tale?

London is sinking into clay and, along with the rest of the SE, it is tilting into the sea partly due to an epeirogenic / isostatic adjustment taking place since the glaciation released the north of the country from the burden of millions of tonnes of glacial ice causing positive isostatic rebound in the north and related subsidence in the south.

Flood plains and reclaimed land exposed to storm surges are still being lapped up by hungry developers as places ripe for building, like the Thames Gateway in London.  But is it sensible to concentrate massive new urban development in low lying areas vulnerable to coastal flooding when we have sea level rise and climate change?

31-10-2013 18-34-28Mary arrives today over SE England. She is the first of our three “storms” with Mungo and Midge following hard on her high heels this weekend, although the lack of wind over the SE inland hardly makes her worthy of such a title, she could bring gales to the Channel though. Anyhow, for Reigate and SE today she will be damp, cloudy and dreary and largely windless today as the LOW passes directly over the SE tonight. Her main threat is rain, and whilst some models still don’t make anything of this, the UKMET certainly does, with 20-30mm falling quite widely across a narrow corner of the SE as mass uplift of air takes place within the core low central pressure. However, she is not a deep low and winds will be remarkably light inland.  Any heavy rain will fall this evening and overnight on wet ground and this could cause local flooding.  There is also a tiny risk of a thunderstorm overnight for Reigate embedded in the heaviest rain rolling up from the south.

Reigate can expect a dreary and damp day all day with poss heavy rain overnight causing potentially localised flooding by Saturday morning.
Winds get up markedly tomorrow Saturday as Mungo arrives. He, along with Midge overnight Sunday into Monday, will be more lively and ultimately drag in cooler air with Tmax temps by Monday not even reaching 9c for much of the country.

This is a temporary cool-off as warmer air arrives from the SW during next week. Remaining unsettled.

The UK is trapped in a “cold washing cycle” with no end in sight this week.  The meandering north-south flow of the jetstream mentioned earlier is partly to blame for fixing LOW pressure over the UK which simply is not budging. Our LOW is sandwiched between a HIGH to the west (Atlantic) and the east (Baltic) and is going nowhere for a while. Hence the heavy showers are set to continue and there is worse to come… starting tomorrow!
A deepening wave depression is set to form on the polar front and spin out from the Atlantic across SW, Central and Southern UK during Tuesday and Wednesday. Heavy rain, gusty winds, cool temperatures and even wet snow are predicted. The worst of this will be in the south west, Wales and parts of central southern England but Reigate and the SE will get continuous rain for 24 hours peaking in intensity overnight Tuesday into Wednesday. Once the fronts move away during Wednesday morning cool unstable north westerly winds and warming surface temperatures will create unstable conditions with a risk of heavy showers and thunderstorms through Wednesday and Thursday pm.
Rain is likely to arrive Reigate Tuesday during the morning and it won’t stop until sometime Wednesday am, to be replaced by heavy showers and a risk thunderstorms. Reigate could see >30mm of rain before the end of the week.
The weekend looks utterly dreadful, especially for the SE: LOW pressure swings close to the SE from the continent and this could bring heavy thundery showers close to Reigate for the weekend.

Throughout the convective weather later this week: points to watch out for are tremendous cumulonimbus clouds and even tornadic conditions with mamatus clouds and perhaps the odd funnel cloud?
Some models show a ridge of HIGH pressure building from the west next week – this is forecast to bring a decent end to May.

Classic short wave depression: the following synoptic charts show how the wave depression forms out of the polar front jet stream.  An innocent kink in the front is the first indication of lower pressure.  Thereafter the fronts become more pronounced, central pressure falls and the whole circulation moves across the UK. Note that, throughout this episode, the “mother low” to the north of Scotland barely moves.

p.s. “cold washing cycle” is not a meteorological term!

Reigate should prepare for 24 hours of rain, starting Saturday 6am and continuing pretty much non-stop until Sunday morning. Rainfall totals for Reigate could be over 20mm which will add to the 18mm we got on our wet Wednesday this week. Totals before Christmas set to hit the 60 or 70mm mark which, as predicted, approach the total rainfall received in Reigate during the whole of November!

Interestingly, during the heaviest rain tomorrow the cloud above Reigate will extend over 9000 metres in height! This is as thick as Mountain Everest is high (8848m).  In addition, temperatures will go from 12C at ground level (warm for December) to -50C at 9,000 metres.  Winds in Reigate will be around 20mph while at 9,000 metres they will be blowing at around 120mph.

River Mole Flood Alert!

November 25, 2012 — Leave a comment

River Levels are high in the River Mole and are expected to continue to rise and may come out of banks in places. We have had a largely dry Sunday morning, but further rain is forecast for this afternoon and overnight, this is likely to cause river levels to rise further. See environment agency website for more details.

Country-wide nearly 1000 homes have been flooded and 3 people have died.  The SW has been worst hit where many rivers have burst their banks in the current run of storms.