We’ve reached September 1st and the official start to meteorological autumn but the calendar won’t reflect the weather pattern this week. In fact it’s going to look and feel a lot like mid-summer not only across the UK and Ireland but across the vast majority of Europe this week as high pressure builds and expands dramatically.

The only aspect resembling autumn and the true time of year will be the darker, even cooler nights.

You can get years when a particular pattern sets up and once established, it tends to hold for some time. There may be breaks periodically but the atmosphere often has that tendency to return to it’s earlier or initial state and for summer 2013, that’s warmth and sunshine. Similar was 2012 in terms of rainfall. The atmosphere just wanted to keep the rains going over the UK.

Interestingly since July 1, London has only seen two below normal temperature days and as for other cities including Madrid, Paris, Amsterdam all the way up to Stockholm, temperatures are well above normal since June.

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Eventually this setup will break.

This will will see a boundary which hugs western Ireland and Scotland which disturbances will run along bringing rain at times to parts of western Ireland and Scotland but a ‘stacked’ southwest flow pumping sub-tropical air up from the Azores will allow temperatures with or without sunshine to comfortably rise into the 20s. With sun and that will be across the bulk of Ireland, England, Wales and eastern Scotland, expect temperatures to shoot into the mid to upper 20s Tuesday through Thursday. I expect a peak of around 28C in London but head east across the North Sea and expect highs nearing or exceeding 30C for a couple of days in Paris, Brussels and Rotterdam, upwards of 26C in Copenhagen.

Of course the Denmark, Norway and Sweden will need to see some unsettled weather clear out first and that may take till nearer mid week but by mid to late week it looks terrific with plenty of hot sunshine.

Here’s the GFS surface temperature for Tuesday afternoon.

Wednesday afternoon

Below is the surface/precip as well as the 500mb charts off the ECMWF showing the ridge build in from the southwest and by late week, covering pretty much all of the continent. An upper low will bring cool, wet and windy weather to northeast Europe initially with messy conditions affecting Moscow but as the ridge builds and expands, this mess clears east.

48 hrs

48 hrs

Notice by 96 hours (below), the boundary begins to push into Ireland and Scotland bringing potentially heavy, thundery rains but in eastern and southern areas could heat further that through the first half of the week with stronger southwest winds. With this setup, we could see 25 or 26C even up in Aberdeenshire.

96 hrs

96 hrs

By late week, the front which has held largely to the west of the UK, will press east aenergy begins to pile and pressurise the positively tilted trough that’s deepening. A low will form at the bases of this trough and so more unsettled weather is expected to impact Ireland and much of the UK towards next weekend.

120 hrs

120 hrs

 

144 hrs

Notice the low forming as the trough drops towards Iberia while the ridge holds firm further east.

144 hrs

The southward streaming energy with too strong of a ridge to break further east and the return of stronger heights out over the Atlantic, means a CUT OFF low forms just west of Portugal but moisture wrapping around the low will make for heavy downpours and longer spells of rain widely, couple with gusty winds.

168 hrs

As the system winds up, heights rebuild to it’s north over France and the UK, trapping this feature underneath.

162 hrs

204 hrs

204 hrs

Eventually the model opens this back up and so an arm of heavy rain may swing back north across France and eventually into the southern UK.

Looking longer term. The NAO looks to hold largely positive but close to the neutral line through the first 20 days of the month but the CFSv2 ensemble shows both NAO and AO dipping into negative territory by the later half of the month which could suggest colder weather.

Until then and after a very warm front running 7 days. I believe the period between the 10-20th should be largely zonal or west to east.

That positive arctic oscillation means lower pressure and colder weather for the arctic and this means building of sea ice, not the continued melt like you would expect at this time of the year. Keep in mind the peak of the summer melt doesn’t arrive till generally the end of this month but with more extensive sea ice compared to recent years, which makes for a colder atmosphere, there shouldn’t be any more melting.

This could have significant effects on cold shots into the mid-latitudes later this autumn and particularly winter. Ultimately arctic air masses that come south, could be more powerful than in recent years because there’s a better environment for cold air production. Look out for when that AO and NAO tanks and I think it should given the SST profile in the north, the Pacific and most importantly for us here in Europe.. the Atlantic. When these oscillations do go into the tank, we could have some impressive and record breaking cold blasts.

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