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Why this event became the perfect storm?

I believe meteorology and geography came together to create Britain’s Perfect rainstorm. Many people stated that, they had never seen rain like it. A 36-hour downpour from the southern Lake District to Ayrshire and an extreme torrent at Seathwaite Farm made for headline news across the UK and world. Britain has rewritten the weather history book by recording an impressive 12.4 inches of rain within a 24-hour period.

Both, worst hit areas (Cumbria and Dumfries and Galloway) are areas that both sit near or on a coast exposed to the full force of Atlantic depressions. They also are closer to the prevailing moist flow that is ushered in by low pressure circulation i.e. their not too far north or south for the main moisture plume that feeds into from the ocean. The convergence of both air aloft and at the surface and the mountainous topographical role in enhancing the precipitable effect over the Lakes made for the record to break. This storm remained off the British coast at all times and that’s why we didn’t see extremely high winds, worst were mainly restricted to the coasts and high ground, but what I do believe played a role was that of the sub-tropical jet which tends to be enhanced during El Nino years as well as a strongly positive Arctic Oscillation which at this time of year excellerates the ribbons of wind west to east across the mid-latitudes. The intensifying cold over the pole and the remnant warmth from summer, enhances storm formation on a strong zonal jet stream. The positive AO is one of the main reasons why we’re seeing a milder and stormier weather pattern..

A warm Atlantic Multidecadal Oscillation, positive Arctic Oscillation (which charges the frequency and intensity of Atlantic depressions in UK), an El Nino enhancement of the southern branch which adds heat and collects moisture in a long plume stretching over 1,000 miles from the subtropics to Britain and by adding heat adds moisture! These factors come together and bingo!

The warm, moist air flow collected from a warmer-than-normal Atlantic by the interaction between the Atlantic low and the southern jet aimed it’s plume of moisture rich air straight into the mountainous north of England and Southern Uplands of Scotland can force the southwest flow up the windward sides of these mountains and actually create more rain than what’s already in the clouds due to orographic cooling, condensing and the result is cloud formation and rain.. So the rains was forced the hit harder since the mountains acted like 200 buckets of water rather than 100, if you know what I mean.

The North Atlantic surface is currently warmer than normal, then cooler and then warmer. Far north (around Greenland) is warmer, then a below normal section between Newfoundland and Ireland and then warmer south of there. This is likely forcing a recent cycle to “wetter Atlantic depressions” and could explain what I see as a dramatic increase in rainfall in the UK since the warmth and dry summer of 2006.

This new rainfall record may have been caused by these key factors in Mark Vogan’s theory…

1) A global increase in water vapor to the atmosphere due to the cooling of Earth.

2) Warm Atlantic Multidecadal Oscillation, increases both frequency and energy for Atlantic depressions.

3) El Nino enhances southern branch jet stream, because of the sub-tropical origin, this increases amount of precipitation as heat contains more water.

4) All these factors came together with the low staying north and it’s circulation and southern branch connection hit directly into the hills of Cumbria and Dumfries and Galloway. Bringing as a result, devastating floods which wiped out roads, bridges and ruined many homes as well as killing a police officer.

The trend to an increase in flooding across Britain must also be blamed on an increase in urbanisation within flood plains. Many major population centers are situated along flat river vallleys which like places that get repeat wildfires, same will happen with flood plains which have flooded in the past and will be flooded again. Glasgow 2002, Boscastle of 2004, the vast floods of summer 2007, summer 2008 and summer 2009 as well as now have seen major floods. Major city flooding includes York, Carlisle.

It’s more the flat regions of the UK we need to worry about living in. Such places include, much of the Midlands where major industry is as well as the Solway flood plains or Solway flats as i like to call them due to the fact that when driving on the M6 past Carlisle, I always notice how flat that part of the country is.

We cannot blame global warming for these floods but more nature’s natural course.

-Mark Vogan

Notable 24 hour rainfall totals in the UK, compiled by MeteoGroup UK:
* Seathwaite, Cumbria, November 19 2009 – 314mm*
* Martinstown, Dorset, July 18 1955 – 279.4mm
* Bruton (Sexey’s School), Somerset, June 28 1917 – 242.8mm
* Upwey (Friar Waddon), Dorset, July 18 1955 – 241.3mm
* Cannington, Somerset, August 16 1924 – 238.8mm
* Loch Sloy Main Adit, Strathclyde, January 17 1974 – 238.4mm
* Long Barrow, Devon, August 15 1952 – 228.6mm
* Upwey (Higher Well), Dorset, July 18 1955 – 228.6mm
* Bruton (King’s School), Somerset, June 28 1917 – 215.4mm
* Timberscombe, Somerset, June 28 1917 – 213.1mm
* Rhondda (Lluest Wen Reservoir), Glamorgan, November 11 1929 – 211.1mm
* Upwey (Elwell), Dorset, July 18 1955 – 211.1mm
* Kinlochquoich, Highland, October 11 1916 – 208.3mm
* Seathwaite, Cumbria, November 12 1897 – 204.0mm
* Camelford, Cornwall, July 8 1957 – 203.2mm
* Bruton (Pitcombe Vicarage), Somerset, June 28 1917 -200.7mm
* Wynford House, Dorset, July 18 1955 – 200.7mm
* Otterham, near Boscastle, August 16 2004 – 200.4mm
*Figure recorded by the Environment Agency

Interesting Information on the hamlet of Seathwaite, Cumbria, it’s wet history and also newly updated information which includes the recent record rainfall

Courtesy of Wikipedia

“Seathwaite is the wettest inhabited place in England and receives around 3,552 millimetres (140 in) of rain per year.[8][1] In September 1966, five inches of rain fell on Seathwaite and the surrounding fells in an hour, the resulting flood severely damaging the nearby Stockley Bridge, which lies 1200 metres south of the hamlet. Stockley Bridge is an ancient packhorse bridge which lies on the old route between Borrowdale and the Cumbrian coast. The bridge was widened in 1887 and had to be repaired after the 1966 storm.[9] On 19-20 November 2009 Seathwaite received 314.4 millimetres (12.38 in) of rain in a 24 hour period, a major contributer to the 2009 Cumbria and southwest Scotland floods. If confirmed this is a record for the amount of rain falling in any UK place within 24 hours.[10][11]“

Geography and Climate information for the Lake District

I have included this information as this will give you an understanding as to why we have seen such extreme rainfall in this part of Britain… Note it’s close proximity to the Irish Sea (coastal exposure) and geographical exposure i.e. mountainous terrain which encourages wet air masses to orogrpaphically lift up the windward slopes of the Lake District which INCREASES rainfall through evaporative cooling with height.

Courtesy of Wikipedia

Geography and Climate of Lake District

Geography: http://en.wikipedia.org/wiki/Lake_District

Climate “The Lake District’s location on the north west coast of England, coupled with its mountainous geography, makes it the dampest part of England. The UK Met Office reports average annual precipitation of more than 2,000 millimetres (80 in), but with very large local variation. Although the entire region receives above average rainfall, there is a wide disparity between the amount of rainfall in the western and eastern lakes. Lake District has relief rainfall. Seathwaite in Borrowdale is the wettest inhabited place in England with an average of 3,300 millimetres (130 in) of rain a year[1], while nearby Sprinkling Tarn is even wetter, recording over 5,000 millimetres (200 in) per year; by contrast, Keswick, at the end of Borrowdale receives 1,470 millimetres (60 in) per year, and Penrith (just outside the Lake District) only 870 millimetres (30 in). March to June tend to be the driest months, with October to January the wettest, but at low levels there is relatively little difference between months.”

Additional Information: http://www.metoffice.gov.uk/climate/uk/nw/

Thanks for reading.

-Mark

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