What does summer 2021 have in store? The TWO summer forecast will be issued in late May but before then we will issue two updates taking a look at what the latest data is suggesting.
Summer cloudscape overlooking Berkhamsted, Hertfordshire
A range of seasonal models are available. However it is important to remember that their skill level (accuracy) for the UK is low.
The notable things at this stage are:
i) The output is mixed but most models favour close to or above average temperatures when taken over the 3 month summer period as a whole
ii) There isn't a clear signal for levels of rain
It is often the case that the rain signal is less well defined than the temperature one.
The anomalies in the table may not be telling the complete story. They are for the meteorological summer as a whole and there is a chance that extreme swings are cancelling each other out to an extent. For example, in recent summers there have been several intense bursts of heat despite rather mixed conditions dominating.
The state of the El Niño Southern Oscillation (ENSO) has significant impact on temperature and rainfall patterns around the globe. Nonetheless its link to the UK summer is thought to be weak.
Latest forecasts suggest there an 80% chance of ENSO neutral conditions through June and July. Therefore ENSO is not expected to favour a particular outcome.
Several forecasts for the 2021 Hurricane Season have been issued. They are suggesting above average levels of activity.
Colorado State University is predicting 17 named storms of which 8 become hurricanes.
Accuweather is predicting 16 to 20 named storms of which 7 to 10 become hurricanes.
The predictions possibly favour an increased chance of settled weather in the UK during the late summer.
Perhaps the defining characteristic of recent summers in the UK has been the increased frequency of hot spells. Maximum temperatures for recent years:
2020: 37.8C, 31st July, Heathrow, Middlesex
2019: 38.7C, 25th July, Cambridge Botanical Gardens
2018: 35.3C, 26th July, Fathersham, Kent
2017: 34,5C, 21st June, Heathrow, Middlesex
2016, 34.4C, 13th September, Gravesend, Kent (Note: This was in the meteorological autumn)
2015, 36.7, 1st July, Heathrow, Middlesex
The last time 30C wasn't reached in the UK was in 1993. In that year the top temperature recorded was 29.7C in East Bergholt, Suffolk. In more recent times, 2007 and 2008 brought 30.1C and 30.2C respectively.
Therefore, recent climatology favours hot spells. There has also been a tendency for months to be more likely to be above the Central England Temperature (CET) average than below it.
1) Seasonal models on balance suggest above average temperatures taken over the June, July and August period as a whole. There is not a clear rainfall signal.
2) ENSO neutral conditions are not expected to favour a particular outcome.
3) The latest 2021 Atlantic Hurricane season forecasts perhaps point to an increased chance of settled weather relative to the average in the late summer.
4) Recent climatology favours above average temperatures and an increased chance of hot spells.
At this stage a warmer than average summer is favoured. Lower confidence is attached to rainfall levels, but close to average is weakly favoured.
The next update will be issued in mid-May.
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Models include UK Met Office UKV and MOGREPS-G, ECMWF, NCEP GFS, Meteo France Arpege and Arome.