Well, here we go again. Summer has arrived and many of you are eager to hear my thoughts, strangely. Following on from last summer, which experienced the worst drought in Southern England since 1976 and the highest temperatures in likely centuries. There is some apprehension we will see similar again this summer, as with any British summer not famed for their predictability, one year can vary significantly from the next.
However, it's hard to ignore the run of summers since mid 2010s fierce heat spikes have become almost an annual occurrence.
Now enough of that, let's get into the forecast!
Summer Forecast 2023 headlines:
Overall, a warmer-than-average summer is highly favoured likely not as hot as 2022.
An unstable thundery summer featuring dry spells but also episodic intense showers and thunderstorms and occasional Atlantic influence. This summer I expect to see a low-pressure anomaly in Atlantic to our W/SW, it's more prevalent in El Nino summers as last seen in 2015, where strong El Nino conditions developed, it will try to progress east breaking down the heat in NW Europe. The west is likely to see the wettest conditions while the east is likely to maintain the hottest and driest weather for longest.
I consider it very unlikely we see 40C temperatures this summer, but temperatures above 35C are favoured by me, unlike recent years I expect humidity to be more of a feature, which would make the heat more unpleasant with sticky nights being a challenge.
Numerical Weather Prediction (NWP) Models
NWP computer models are used by forecasters and hobbyists to forecast weather in short and long timescales. Typically strong reliability is limited to 5-7 days out but with the help of teleconnections the "background signals". They commonly have more permanency and there are known patterns to our weather patterns in certain regimes. We can look beyond, sometimes weeks and even months ahead with some success. Of course day to day weather cannot be forecasted, but a broader feel for a season can be achieved. Some of the important teleconnections are the ENSO state (El Nino and La Nina); the MJO; the QBO; the Jet Stream; Stratospheric Weather; Sea Surface Temperatures; Sea Ice and Snow Cover extent. It's these telecommunications which are ultimately fed into NWP models and build these skilful forecasts.
The C3S seasonal forecast this blends and creates an average of top NWP models including ECMWF, UK Met Office and Meteo-France. The signal for this summer (June-August) is compelling. Warm summer. Above average temperatures are strongly favoured in Western Europe, there is a particularly strong signal for a hot weather in North Africa and Iberian peninsula, suggesting southerly flows will be capable of delivering very high temperatures to our shores with temperatures exceeding 35C.
There is an enhanced risk of above average rainfall across Southern Europe. Indeed, for a forecast which was initialised at start of May the anomalies have accurately identified the early summer pattern at least. As a whole though, across summer the wetter signal is not particularly strong, perhaps suggesting it will weaken as summer progresses.
A dry summer is not really favoured in UK/Northern Europe in contrast to last year's prediction, which was highly accurate identifying it to be very warm and dry, suggesting the risk of drought is lower this year, rainfall is favoured to be close to longterm average.
El Niño–Southern Oscillation (ENSO)
The El Nino/La Nina Southern Oscillation has a considerable influence on climate patterns across the world. Summer 2023 is expected to have El Nino conditions, this is a warm ocean phase, which results in higher global temperatures. Whereas, La Nina is the opposite, resulting in cooler global temperatures, I will stress last summer was a La Nina summer, yet it was record-breaking hot summer in UK and Europe. Not everywhere can be simultaneously hot or cold this is why global averages are not without scrutiny, and for tiny countries like ours compared to global field, the connection is not obvious and there is greater uncertainty.
It has been a rather long time since we last had a fully El Nino summer, the last was in 2015 which was last cooler than average summer in UK, and overall it was quite unsettled. In SE temperatures were near normal, but school holidays in August were a bit of a washout. While June was very dry. A varied summer, it is often remembered for its one-day heatwave at start of July which set a July record at the time despite much of month being cool especially in west.
A table of El Nino summers is provided below with SST data since 1950.
El Nino summers >0.5C SST anomaly based on Oceanic Nino Index (3-month running mean (JJA) of ERSST.v5 SST anomalies in the Nino 3.4 region
1951 | Cool summer June-July rather dry but August wet near 100mm at Heathrow. |
1953 | Unremarkable summer cool for modern climate, drier than average. |
1957 | June warm for period 23.6C average max, dry and sunny. July-August unsettled and cloudy. |
1963 | Another quite cool summer lacking in heat drier than average, August cloudy. |
1965 | Cool summer average Tmax of 19.3C in July at Heathrow significantly below average. Rainfall bit above average. |
1969 | One of the better summers of 1960s, August though cloudy and unsettled. |
1972 | June exceptionally cool average Tmax 17.5C modern average is 21.6C. A dry summer in London but often cloudy. |
1982 | Near normal temperatures nothing overly warm, all summer months deficit in sunshine. Largely forgettable but remarkably thundery June some locations had 14 days of thunder in June alone. |
1987 | Poor summer and often cloudy. June disappointingly cool, very dull and wet the rest of summer did not redeem itself. |
1991 | June cool, dull and wet, however July and August performed strongly. |
1997 | A decent summer August was particularly warm with warm humid nights. Most thundery summer since 1982. |
2002 | OK but quite forgettable as was wider year. |
2004 | All 3 summer months had over 200 sun hours at Heathrow not a common occurrence. August warmest month a month of two halves Newton Aycliffe in County Durham saw 210mm wettest month on record. |
2009 | June best month much of summer unremarkable a quite thundery and wet July but not cool. Coldest winter since 1978/79 would follow. |
2015 | A fairly good summer in south of England but poor elsewhere with westerly airflow, start of July saw intense but very fleeting plume. Setting a new July temperature record of 36.7C at Heathrow, It wouldn't last July 2019 saw 38.7C a new temperature record in UK exceeding 38.5C in 2003 in Kent, and then on 19 July 2022 would smash it apart with 40.3C at Coningsby, Lincolnshire . August though disappointingly wet and cloudy. |
From list above of previous El Nino summers, it's notable to me that none of the greats are listed there, many of these summers lacked significant heat there is also a pattern for these summers to have best weather in June or July, only for August to deteriorate.
Although occasionally August provides hottest weather of the summer, but it is unstable. Also quite noticeable a few of these summers were memorable for thunderstorms. Some might argue it is just chance, but I noticed a tendency for our classic British summers to cluster together in neutral ENSO conditions. Including: 1976, 1983, 1990, 2003, 2006, 2018. To me it strikes to me as more than a coincidence, my theory when ENSO is rather inactive weather patterns globally become more static, and dry and warm patterns lock in. This summer El Nino conditions have formed and are expected to strengthen to moderate/strong status indeed this is also expected to be a similar intensity to 2015. I believe this suggests the summer will be more prone to being mixed up, with not one pattern dominating for too long unlike in 2022.
Atlantic Sea Surface Temperatures
May 2023 global sea surface temperatures were the highest on record, relevant for UK and of influence, the east Atlantic warmth from tropical Atlantic to UK are warmest on record. This suggests southwesterly flows are prevailing wind direction will be warmer than average. It also suggests more water vapour in the air, with the higher temperatures of ocean water this signals to me a humid summer. Potentially prone to heavy rainfall events, perhaps also more prone to torrential thundery downpours. I get the impression heatwaves this summer will be more unpleasant, less of the dry heat in recent years which has made things a bit more bearable.
Summer Forecast 2023 recap:
Overall, a warmer-than-average summer is highly favoured likely not as hot as 2022.
An unstable thundery summer featuring dry spells but also episodic intense showers and thunderstorms and occasional Atlantic influence.
High temperatures are likely but the risk of pushing 40C is very low.
A changeable summer but predominantly warm. Likelihood of drought low/moderate, driest in southeast but downpours could muddle the statistics.
Conclusion
I typically give a monthly breakdown to my forecasts but ultimately it's a pointless exercise. My aim is more to present a flavour, this is more likely to be successful, and I'd rather not spend more time on this, and instead enjoy the lovely weather we're having. After what seemed a very long spring. I would say though, I favour the best weather of summer, perhaps the most lengthy spells of settled weather in first half of summer in June and July.
It's difficult to see into August potentially the hottest weather of summer may occur with unpleasant, high humidity, but also featuring the most disturbed and changeable weather. I don't expect a repeat of last summer, but we must be vigilant to extreme weather, it seems nowadays through very little build-up or effort we see terrific heat. Looking at historical El Nino summers you can't help but feel underwhelmed for our summer prospects, but in the year 2023 the climate has changed quite significantly and what was familiar then is not familiar now.
Thanks for giving some of your time! As always I will be posting regular updates this summer and beyond on my Twitter page @TheSnowDreamer :)
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