The system hammering the British Isles over the past 48 hours is no ordinary one for September bringing major flooding across large swathes of Northern England crippling rail and road transport between Scotland and England combined with near hurricane-force winds which have torn down numerous trees, even powerlines up and down the east coast of Scotland with howlling 70 mph onshore winds blowing off the North Sea.

According to the BBC, more than 100 homes have been evacuated and hundreds more are on lockdown across the North of England as a stalled boundary supporting heavy, persistent rains for over 24 hours has huing overhead causing signficant flooding.

The main east coast railway line was submerged beneath flood waters in the Northeast of England as you can see below, significantly disrupting service.

Over 4 inches of Rain For Ravensworth, North Yorkshire!

Since Sunday when the system first began to make it’s presence felt from the south, upwards of 3-4 inches of rain has fallen since over Northern England with North Yorkshire being worst affected. An impressive 4.5 inches of rain has come down at Ravensworth. Parts of Northern Ireland has been hit badly too with over 3 inches falling around Belfast, nearly 4 inches at Killylane near Larne.

In Southeast of Scotland was worst affected by flooding rains with parts of Haddington submerged as the nearby river burst it’s banks but throughout the South there was a lot of rain in the past 24 hours. I drove from Dumfries to Stranraer this morning and there was a lot of standing water lying in lowlying areas.

Here was the scene in York city.

100 mph Winds Roar across Glenshee Ski Area, Brutal -11C Windchills in The Eastern Grampians!

Severe, northeasterly gales has brought major disruption to road, rail and ferry services throughout today with the Forth, Tay and Erskine bridges closed to high sided vehicles. The greatest impacts to Scotland’s road network eas in the east with countless reports of trees blocking roads with the worst affected areas from Dundee up to Peterhead. As many as 2,000 homes lost power.

Part of a roof on a new block of flats in Dundee was blown off.

Winds at the surface roared in off the North Sea at 70 mph while just a few thousand feet up, a 101 mph wind gust was recorded at Cairnwell Pass where Glenshee Ski Centre is located in the heart of Grampians. According to STV’s Sean Batty, wind chills during the overnight were registering a winter-like -11C in the eastern Grampians thanks to a cold NE wind drawing cooler air in from Norway.

Notable Wind Gusts

Inverbervie 73 mph

Peterhead 69 mph

Why So Stormy?

Since way back last week, this system was already on the radar and being closely monitored. In fact it was anticipated BEFORE it had even formed. During mid last week, models showed a storm forming off of once-Hurricane Nadine and tracking northwards up into the British Isles. Remember back to late last week and the chilly days and cold frosdty nights. A strong trough was sitting anchored over the British Isles and Ireland and this extended all the way down towards the sub-tropical Azores. A low formed off Nadine and this trough grabbed this surface storm, pulling it north but with these circumstances came concern for both rain and even wind.

The fact the system formed off of a fully-tropical system meant it had ‘tropical’ energy despite not actually being tropical, i.e, it is fully COLD CORE and baroclinically driven whereas Nadine was warm core and driven by different properties such as the warm waters.

The warm source region in which this system came from meant there was a greater chance of flooding rains simply because warmer air holds more moisture and drive that warm, moisture rich air under and into a much colder environment increases ‘lift’ and when there’s a large confliction between warm/moist, cool/dry, the environment is very supportive for major rainfall. It was said this morning on the BBC that the moisture in the skies above our heads was 6-7 miles deep. Worst of all was the fact this moisture rich boundary stalled and this lead to the high rainfall totals.

Another factor was that it formed at the base (bottom) of the very deep trough. The trough was a monster and it can been looked at as a giant pool of cold air aloft. This trough had particularly cold air suspended aloft. A warm, very moist environment within a system beneath meant the perfect environment for the low to deepen as well as draw up plenty of moisture. The storm deepening considerably due to the increasing cold atmospheric profile over the British Isles.

As this system pulled north with a tremendous upper support of a vigorous jet stream, the storm, as expected deepened continuously from near the Azores back last Friday all the way to the north of England this morning. Pressure started out near 1000mb and by early this morning, the centre was down to an impressive 973 mb according to the Met Office which is a late November/December depth.

So, the warmth and moisture of tropical origin, pushing north into an increasingly cold environment allowed this system to become quite the formidable beast packing the 70 mph low level winds and 100 mph mid-level winds. The slow crawl of the system over the past 36 hours from the Midlands to North of England allowed the prolonged 36 to 48 hour rains.

Tags: aberdeen sea foam september 2012, scotland storm september 2012, september storm strike scotland, uk september storm