Could a new June temperature record be set?

The weather has turned more changeable in recent days, with much of the UK seeing wet conditions at times. Despite that, rainfall amounts in the south have mostly remained very small. In the coming days an area of high pressure is expected to build, allowing exceptionally warm air to move northwards. The current June temperature record stands at 35.6°C (96°F), recorded at Southampton on June 28th, 1976. Could it be challenged?

Exceptionally warm air mass

During Friday, Saturday and Sunday, warm air will be spreading northwards across the UK. Temperatures are likely to peak in the low 30s°C in southern and central regions. Records are not expected to be challenged during this period.

By Monday things become more uncertain. An increasing number of computer model updates are showing a pulse of even warmer air moving up from southern Europe. Forecast values at about 1,500m above sea level are close to or even exceeding 20°C in a growing number of runs.

The reanalysis chart above, which shows the situation on 28th June 1976 when the existing record was set, has significantly lower values. They range from 10°C in northern Scotland to 16°C in southern England. The high surface temperatures at the time were likely due in a large part to heat building day by day over an extended period.

The forecast chart above shows 850hPa temperatures on Monday 30th June. In central and eastern England they are significantly higher than their 1976 equivalents. With that said there are important caveats:

1) The forecast is for almost 5 days ahead so the details will change as the time approaches

2) The main thrust of the heat will probably be just to the east of the UK, therefore it won't take much adjustment for it to miss completely

Nonetheless, as things stand there is the potential for a new June record.

How hot could it be?

Most computer models are showing temperatures peaking in the low to mid-30s°C. Therefore if a new record were to be set, it would probably only be a slight increase on the existing one. However, the UKV model, which the chart above was generated from, shows something even more notable.

On the forecast chart below London is toward the centre-right, with the Thames Estuary visible. On close inspection there are two grid points in western London showing 38°C. 

Why is that significant? Firstly, if correct ,it would smash the existing record. Secondly, there are official weather stations in that area, such as Kew Gardens, Northolt, St James’s Park and Heathrow. That means there's a greater chance of the highest temperatures occurring in a location where they could be officially recorded. This isn't always the case. 

Will there be a thundery breakdown?

As cooler air returns from the west there is a possibility of thunderstorms developing ahead of it in some areas. At this stage it's not possible to say how widespread the risk may be. Confidence in the longer-term outlook is also low, although there are indications that high pressure could begin building from the southwest fairly quickly. If that happens, a lot more dry weather would be likely, especially in the southern half of the UK. Temperatures would dip significantly, although it could still feel quite warm.

There are also indications of an amplified pattern developing, rather than a flat one. If that happens the weather we experience will depend on how the ridges and troughs become positioned. However, it would increase the possibility of another plume of heat spreading northwards across the UK, perhaps in the second week of July. If that happened, the first half of the meteorological summer would possibly also be challenging records.