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Weather updates from site founder Brian Gaze that keep you in the know.

Weather for the second half of July

Published 14th July, 15:52

The record-breaking June has been followed by a much more unsettled and cooler July so far. Is there any sign of summer returning as we head through the rest of the month?

Pressure rising next week

There are indications of pressure building from the south next week. The GEFS chart below shows the Mean Surface Level Pressure forecasts for the next 16 days from all of the individual runs in the ensemble model.

In the short term pressure falls sharply to around 1000mB. That is associated with a deep area of low pressure which is bringing the unseasonably wet and windy weather today and into the weekend. However, pressure then rises and by July 18th it is around 1020mB. Through the last week of the month most of the runs show it starting to fall again.

Comparable plots for locations further north show a similar trend, albeit at lower levels due to high pressure being centred to the south of the UK.

The trend for higher pressure between July 17th and 24th suggests that there is a greater chance of dry periods, especially in the south. Beyond July 24th the downwards trend suggests the opposite may be the case, but by that point the spread of possible outcomes is wider and there is less confidence in how things will develop. Does other data support the same general trends?

Temperatures and rain amounts

The plot below shows the 850hPa (about 1500m above sea level) temperature and precipitation forecasts for the next 16 days from all of the GEFS runs. The temperature profile doesn't really change until towards the end when a few runs go much warmer. However, they are in a small minority and for most of the time the thick purple line, which represents the mean of all the runs, remains a little below the thick black line which is the 30 year average.

This suggests that hot conditions are unlikely, but I wouldn't discount the possibility of warm or very warm days in the south. Sea surface temperatures around the UK are much higher than normal and that will help to warm things up at the surface level. Also, we're heading through what is typically the warmest part of the year. In the north the chance of very warm days is lower. 

The precipitation forecasts suggest mostly dry conditions in the south early next week. Beyond that the number of rain spikes increases again, although it doesn't look like being a washout in the south. Comparable plots for locations further north show point to a wetter outlook.

Summary

There are signs of high pressure having more influence in the south at times during the rest of July. Nonetheless, most of the computer model runs are not showing it building strongly enough to become the dominant feature of the UK's weather. In fact, in the north low pressure probably keeps things more unsettled for much of the period, and even in the south the risk of showers or longer periods of rain doesn't go away. It looks very different to last year when a new UK record was set with temperatures on July 19th at 40.3C (104.5F). 

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