I know I am now going for a warmer and drier than normal July with some interruptions in between. I feel I need to emphasise that because I don’t want people to think I’m saying that July will be one big long heat wave because that’s not what I am saying. However, this is the first time the entire UK and Ireland is largely dried out and while the CFSv2 doesn’t showed a warmer than normal July for our part of the world, I think it’s area of above normal over Spain and France will transfer north once it sees the dry soils, it may turn cooler to the south thanks to a very wet spring and even recent weeks over France and Spain.

This spring has of course been cold with a dry start and wetter end but any rain over the last 2 weeks is all but gone from the top soils and any rain in the next 10-15 days, should be able to dry out with the next warm spell which I believe will arrive late June and could well commence July on a warm and dry note.

The setup is similar to 2003, 2005 and 2006 which saw cold waters surrounding the UK thanks to a cold but dry spring. The following summer were all warmer and drier than normal summer. I’m not talking regionally but NATIONALLY. The feedback from soil to atmosphere happens with large-scale dryness or wetness and certainly this year is very different to last when a large swath of the UK and Ireland was all but saturated.

I believe we may see the best July in at least 7 years. Bare in mind that since the turn of warm and dry to cool and VERY wet in 2006 to 2007, it’s stayed largely wet ever since. About time we got a break right?

In past posts I have stated that in warm AMO years, the UK can see an increase in summer rainfall and sure, it’s been terribly wet of late with flash flooding becoming a common occurrence widely, so why am I going for a warmer, drier summer when we still have a warm AMO.

I’ve always believed that the abrupt flip in our summer pattern from warm, dry to cool and wet (2006 was warm and dry, then it was record wet in 2007) was caused by the flip in the PDO from warm to cold in 2007 and ever since, it’s been generally wet as has the PDO been cold while the AMO remained warm. The increase in the imbalance has appeared to lead to increasingly wetter summers or at least the ‘flash flood’ events have appeared to become more extreme.

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The ENSO (El Nino Southern Oscillation) index can play a big role in breaking trends within a long term cycle. I.e, The UK saw record DRY winters in 2009-10 and 2010-11 due to the influence of LA NINA and with the transition to EL NINO in late March last year with a warming of the eastern equatorial Pacific, combined with the larger, longer term influence of the warm Atlantic, cold Pacific, the flood gates opened here last spring and this super wet pattern of course lasted much of the year. As the El Nino never really materialised, eventually this fed back to the atmosphere and we saw a drier second half to last winter and into early this year, precipitation distribution shifted. There is always a lag that must be considered between ocean and atmosphere.

I received a good question from a subscriber yesterday in which he asked why 1956 was the second wettest since 1912 (until 2012) and although the AMO (Atlantic Multidecadal Oscillation) remained warm till 1965, why up until the AMO turned cold, were summers less wet.

1956 was of course an extremely wet summer, just like 2012, only 2012 was even wetter but why? In 1956 the AMO was on it’s way down from a prolonged warm period while the PDO was on it’s way up from a prolonged cold period. That year saw a warm AMO and VERY cold PDO and the LA Nina was weakening. Last year likely beat 1956 because the AMO was at a peak while the PDO was very cold. The two extremes in ocean heat content, energy transfer to the atmosphere which enhanced the jet stream and with a stronger jet roaring across a very warm North Atlantic, allowed an injected of … moister air. Also the spring was unusually warm which heated waters surround the UK to well above normal. This would have increased the available moisture and so torrential, flooding rains was the result.

AMO

So, why did summers after 1956 turn less wet? It appears to me that the reason may have been that the PDO went mainly positive, along with the AMO. Warm the PDO and the imbalance is less and there’s less rainfall in the UK. The La Nina died and the ENSO went neutral.

One must consider ALL aspects and not just one or two. The Pacific is just as big of a driver, if not even more so than the Atlantic.

My reason way back for the warmer than normal summer this year is because the El Nino flat lined during last winter which shut down our excessive wet pattern and with a hint of La Nina coming on this summer, that to me hinted at drier than normal but a lot weighed on what happened this spring and although I never believed we would have anything like last year, a wet spring would have likely meant an average summer both in temperature and rainfall but a dry start to summer after a cold spring with cold waters surrounding, is pointing to DRIER and therefore WARMER than normal this year.

Summers will likely remain on the wet side until the PDO once again warms and the AMO cools again. Both oceans peaked last year in their warm and cold phases and the trigger was the ENSO going positive in a strongly cold phase of the PDO. While both remain cold and warm, the extremes aren’t there. The AMO isn’t AS warm and the PDO isn’t AS cold, plus the ENSO is all but neutral.

Areas of low pressure will be unusually strong over the North Atlantic but should weaken on approach to the UK thanks to the feedback of cooler than normal water temperatures surrounding the UK, plus pressures will be stronger also thanks to dry soil feedback.

PDO

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