The North Sea is very prone to the impacts of a storm surge for various reasons. Boulder clay, which was deposited by glaciers during the previous ice age, lies above ancient “harder rock”. It is easily eroded by the force applied onto it from the North Sea. During an average year the North Sea retreats by an average of 1 meter.
That fact is all too true for many home owners on the east coast, where much property is destroyed each year.
The normal, prevailing wind direction for the British Isles is west to east. Storms, when they arrive, have a classical west – east progression which is a signature for a zonal jet stream. This example of a pressure chart from the stormy spell during early January 2012 shows exactly that.
The isobars on the chart above are aligned in an although “wavy” fashion which is formed by the various troughs and ridges in the North Atlantic, show a general west to east alignment in the North Atlantic jet stream zone. This “usual” direction means that the North Sea doesn’t normally see a great deal of storm surge activity, with the brunt of the storm surge hitting the UK head on from a westerly direction, which has less of an impact due to the different rock types in situ here affecting how the land responds to the high wave energy. Although that being said, storm surges can funnel into bays in the west affecting some towns, such as Galaway in western Ireland and parts of Wales.
Compare the above pressure chart to the one below from the 1st of February 1953, from the North Sea flood event of 1953. There are 2 main differences which caused this particular storm to have more of an impact compared to “normal” storms as per the one above. The first is the pattern in the Atlantic, the NAO is negative, with low pressure situated close to the Azores islands and higher pressure towards Iceland, this indicates that the atmosphere is behaving in an “usual fashion”, in stead of allowing strong areas of low pressure like the one situated to the north east of the UK to pass from west to east across the UK in an “orderly” fashion, the increased heights (blocking) in the mid Atlantic squeezes the pressure gradient between the high and the low, leading to a “screaming” northerly wind to rush down the North Sea, thus creating an unprecedented storm surge.
The pressure chart from the 5th of December 2013 below shows a fairly similar scene, low pressure situated close to the Azores and high pressure making an attempt to ridge towards Iceland, “squeezing” the pressure gradient on the westerly side of the low where the northerlies are, and exaggerating the northerly element to the storm. This was the last notable, destructive North Sea storm surge. Due to a “funneling effect” as the wave energy passes between the land masses of the UK and the low countries, wave energy can increase towards the Netherlands and nearby areas, leading to a more severe storm surge. These areas are often affected at the same time as the east coast.
There is a developing “risk” that we need to keep an eye on for Sunday / Monday. A trough associated with a large cold pool / low pressure system over Europe is expected to dive south east over the North Sea on Sunday. The GFS is known for over-deepening lows in the North Atlantic, and other models such as the ICON.DWD are forecasting a weaker low pressure system – so the GFS solution needs to be treated with a large grain of salt. However I am watching this closely as the synoptic shown has similarities to the charts above, mid Atlantic ridge and long fetch northerly wind.
Moving on…. to that very special thing that we all want.. Snow.
This winter we have conflicting signals in the broad pattern. A westerly QBO is in theory correlated with a stronger Northern Hemisphere jet stream and as a result “milder, wetter” winters for the UK. However various other “drivers” such as solar minimum, a weak stratospheric vortex are working towards a colder winter. The result of that is both an active jet stream and a signal for blocking to develop. The result is that the blocking high “tries” to make attempts at becoming northern blocking and introducing colder air into the UK however it’s efforts are impeded by a strong polar jet stream. If the jet stream had been a little weaker this winter, I have no doubt that the blocking would have surged further north towards the “sweet spots” of Greenland, Iceland and Scandinavia to allow colder air to surge into the British Isles. However since retrogression (east to west movement of blocking) has struggled, the UK has been stuck directly under the blocking high and colder air has been sent into central and eastern Europe. These 2m temperature charts from Meteociel.fr show where the cold air is right now, and is fairly representative of the winter season so far.
Are there signs of a change? Whilst I’m sure you’ve heard of the sudden stratospheric warming and stratospheric split, these events only lead to cold conditions in the UK a handful of times, not always. Which makes forecasting cold and snow after them a tricky business. Forecasting more than 10 or so days ahead in the UK is a tricky, almost impossible business especially in the winter months. In the next week however, there’s pretty much no chance of prolonged cold and significant snowfall, a chilly northerly associated with the low discussed earlier for circa the 13th/14th will bring cold air to central and eastern areas and perhaps some wintry showers along the east coast, but nothing really significant or locked in, “fleeting”. Later next week temperatures will remain on the cool side for the north with the jet stream running a “little south” allowing for at times chilly incursions for the northern quarter (Scotland), however elsewhere temperatures wont be doing an awful lot.
After “writing off” the next week, it’s in the longer term outlook that there is potential. From around the 18th on wards, is our next “chance”, which is gaining momentum through various long range weather models and some shorter range ones to. I’d personally put the chances around 55-60% of something significantly colder developing around the final 12 to 14 days of the month (next weekend on wards), and yes if the cold verifies there would be a risk of snow. However until cold is within the reliable time frame of the computer models, this is only speculation. I think the dice may be loaded towards bringing in some more of those “fleeting” cold spells later this month. Since we are in the heart of winter and it takes less of an impressive synoptic to deliver snow, I’d expect those set ups discussed to deliver the risk of snow. Both a “mobile” westerly pattern and a tendency for a southerly tracking jet stream are influencing these thoughts.