UK Braces For Unusually Deep 980mb Low Wednesday, Set To Bring Gales With Gusts to 60mph, Widespread 1-2 Inch Rain

Written by on August 14, 2012 in United Kingdom & Ireland with 0 Comments

Image courtesy of WeatherOnline


For days now the models have had a storm forming over the Bay of Biscay at the base of a deep trough. A lot of energy spilling into the trough is forcing rapid bundling and development. This tends to force a lot of heat and moisture into the system adding more energy which forces a steeper pressure fall. Over the next 24 hours, all models take this storm northward and in the process it deepens towards 980mb and should be positioned due west of Ireland by noon Wednesday.

If you notice with the upper level height field, the trough axis is just enough west which allows the system to drag a lot of heat and humidity north and east of the circulation which will increase the amount of rain it will dump once it’s front advances north over England and Wales through tomorrow. This overriding warmth and humidity the system is drawing north is of course keeping a fresh supply of warm, juicy air going throughout the UK with another muggy night in store and a temperature range of 14-19C. But more importantly, as well as increasing it’s moisture capacity, it also keeps a higher level of baroclinic contrast as cool air will be constantly drawn in on it’s north and west wide. This keeps the deepening process going well into tomorrow and the GFS along with European has a central pressure down at around 980mb tomorrow afternoon over Ireland. The difference between the GFS and ECMWF is that the GFS has the centre nearer the Irish Sea while the ECMWF is further west. The ECMWF idea would make for a worse situation for Ireland than the UK with worst rains and wind while the GFS idea has worst conditions over the UK (mainly England/Wales) and I must say I prefer the GFS idea.


I must say, going by what I’m seeing just now and have seen for several days now, I am concerned about just how much rain may fall over a 4-6 hour period from Cornwall to Cumbria starting late tonight into tomorrow morning.

While I expect a decent 1-2 inches of rain for most from Cornwall up through Somerset, Dorset across to Oxfordshire, Warwickshire east to Nottinghamshire. Within the region from Cornwall all the way to Cumbria, we should expect LOCALLY 2.5 to 3 inches and this could fall within a 4 hour period, causing inevitable flooding problems, very poor driving conditions with spray and standing surface water.

The reason for the biggest rains being over England and Wales isdue to the fact the low will be continuing to intensify and with that comes a tighter grip of air from outwith. The warmth and humidity will be getting sucked up from the Azores and so copious amounts of moisture come with that, acting as fuel for the system. The front sweeping northwards over England and Wales shall be at it’s most potent and so rains will be most intense in this region.

By the time we get into the afternoon, the band should be working into the North of England and by late afternoon and into the early evening, the heavy rains will spread across the Scottish Southern Uplands where orographic influence may enhance the rains here before entering the Lowlands and the main population belt of Scotland between Glasgow and Edinburgh.

All in all, Scotland should see a fairly decent Wednesday before the heavy rains begin to arrive from Cumbria and Northumberland later in the afternoon. With sunshine, temperatures could well climb to between 20-24C, especially from the Centralk Belt north as here, skies should stay sunniest for longest.


As for the winds aspect to this storm, we can expect a blustery day pretty much everywhere with winds increasing across the South and particularly Southwest of England and Wales this evening. By mid tomorrow morning as the low pushes north to the west, expect strong 15-25 mph winds throughout Southwest England and South Wales with gusts along the coast easily topping 50-60 mph. The exposed south coast of Ireland, Southwest England and South Wales coast could see some areas pick up gusts to 70 mph. Inland areas may see gusts between 30-45 mph with even areas further east towards London and East Anglia picking up gusts to 25 mph with 30 on the coast.

Into the afternoon and the core of strongest winds advances north with the centre of circulation. Winds should turn quite strong throughout Southern and Central Scotland by dinnertime onwards.

Thursday shall see a rather wet and windy day across Scotland but with the front spreading further from the core of the storm, so the front and it’s associated rain band weakens. Winds could still be quite gusty though.

Elsewhere, a much improved picture for hard hit England and Wales.


As we push towards Friday, a long, stretched out, southwest to northeast plume of moisture will take aim at the UK and this may bring a further substantial rain Friday through Saturday before true improvement arrives Sunday.

You can see the model showing this hosepipe of moisture streaming from the subtropics and pointing this diectly into the UK. This moisture flowing along a very warm and rich boundary always suggests potential for some pretty substantial rain totals, especially if this sits in places for a long duration.

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