Looking At The Variables Which Can Determine A Particular UK Summer Pattern

When producing a seasonal forecast I like to look at several global and regional factors/players. They include the current and projected state of the ENSO index (El Nino Southern Oscillation index), global SST’s and particularly for summer, soil moisture content and rainfall distribution.

Of course I also like to look back at previous years which had a similar kind of winter and spring and what kind of summer followed.

Winter 2017-18 of course was relatively mild December and January for the UK and Ireland as well as Western Europe as a whole (locally cold in areas) but February and March turned much colder with February turning out coldest since 2010 while March was 3rd coldest in 30 years.

In today’s post I want to simply look back at previous summers which had cool February’s and March’s with a mix of drier and wetter than normal with a coincidence of a neutral ENSO with possible El Nino development mid and late summer into autumn.

The years which most noticeably stand out in recent years for cold end’s to winter and early spring are 2010 and 2013. Interestingly both these years had a similar ENSO status to what we have now and that’s neutral.

While rainfall and soil moisture can be important and have significant atmospheric feedback influences, it doesn’t tell the whole story. In fact surrounding SST’s may play a greater role in feedback to the atmosphere above.

Take last summer for example, following a warm but more importantly dry February, March and April which came off a record strong El Nino, the hose was suddenly turned on in later May and June and the summer turned out to be the UK’s 9th wettest. It was slightly milder than average. The heating of the surrounding UK waters beneath a mild and stable air mass for weeks, may have helped increase moisture levels in the air. There is a link between warmer water and lower pressure patterns and cooler waters feeding to an anticyclonic pattern. On the flip side, wetter springs don’t always suggest wet summers as you may have wet ground during the spring but cold surrounding waters which favours high pressure and dry.

Another factor is high and low solar. High solar combined with El Ninos can lead to very warm summers with a mix of both wet and dry. La Ninas can be cool and dry.


Indeed there are so many variables to consider. Right now we have a 50-50 wet and dry ground. By that I mean there’s wetter and drier than normal areas and leaning cooler than normal BUT let’s not forget the current sudden surge of summer which in all likelihood should push April warmer not cooler than normal, more so England and Wales but Scotland could hold onto cooler than normal. It looks drier through the last 10 days of April.

Here are the current global SST’s. Interesting to see the cold water dominating the North Atlantic and stretching from Cape Verde to northern Scandinavia. The very unsettled, cool and wet spring in an around Iberia has helped the cooling for sure.

Now this favours warmer, drier into the summer but waters have been known to quickly heat, especially under warm, stable air masses and as mentioned already, warmer than normal waters can support lower pressure. The good news for summer heat lovers is, these waters aren’t likely to go warm all of a sudden as the current heat won’t last and the outlook is still for cooler than normal into May.

Essentially what I would be looking for if I wanted a warm, dry summer would be cool surrounding waters, drying out of soils into May and a neutral ENSO.

Summer 2010 had a similar late winter, spring and neutral ENSO to 2018 but the big difference is warm not cold waters around the UK.

Credit: Met Office

The warm spring waters may have helped make for a larger area of wetter rather than drier than normal.

Credit: Met Office

Summer 2013 was the UK’s warmest since 2006 and though not exact, it appears to be the better match to this year than 2010. While waters were warm to the west, they were noticeably cool in the North Sea and like this year it was a cool spring following a cold February with a negative neutral ENSO.

Summer 2013 was indeed a very warm, dry summer, especially further north.

Credit: Met Office

Credit: Met Office

The current solar cycle is heading back into the tank and should have reached a minimum within the next couple of years.

CFSv2 temp and precip anomaly for May.

Credit: Tropical Tidbits

Credit: Tropical Tidbits

So, this is some of the thinking behind the fast approaching summer 2018 forecast. I shall give my conclusion on 1 May, 2018.

Follow us

Connect with Mark Vogan on social media to get notified about new posts and for the latest weather updates.

Subscribe via RSS Feed Connect on YouTube

Leave a Reply