Weather updates from site founder Brian Gaze that keep you in the know.
Despite the mixed start to July computer models are suggesting a change is on the way. That has led to speculation about the possibility of a heatwave and whether extreme temperatures could be recorded in the UK.
The GEFS ensemble plot below shows forecast temperatures at approximately 1500m above sea level for the next 16 days. The important thing to note is that most of the runs are above the thick black line which represents the 30 year average. It suggests there is a strong signal for warmer than average conditions, although temperature anomalies at this level don't always mirror those down at the surface.
A number of the runs show temperatures rising above 15C, especially later on. That is sometimes looked at as a rough benchmark for heatwave conditions. However, the dry ground and the fact that we are still relatively close to the summer solstice both mean that temperatures could well be approaching 30C at the surface even with a somewhat less warm air mass in place.
GEFS ensemble plot for London
The lower half of the plot shows forecast rain from all of the runs in the ensemble. The thing which jumps out is how dry it appears. There are very few rain spikes even at the very end of the run. Usually when looking more than two weeks ahead ensemble scatter ensures that there are at least some rather wet scenarios.
The UK Met Office defines a heatwave as:
"A UK heatwave threshold is met when a location records a period of at least three consecutive days with daily maximum temperatures meeting or exceeding the heatwave temperature threshold. The threshold varies by UK county."
The threshold ranges from 25C in much of the north and west to 28C in Greater London, the home counties, Cambridgeshire and Bedfordshire.
The highest temperature recorded in the UK is 38.7C at Cambridge University Botanic Gardens, on 25th July 2019. In recent decades temperatures of over 35C have been occurring more frequently in the UK. Therefore, if that trend continues it can only be a matter of time before 40C is recorded. However, the chance of it happening in any one year remains statistically low, but my view is it is increasing.
This year there has already been record breaking heat in parts of southern Europe. What that means for the UK is that if we end up with a Spanish Plume or "blowtorch" weather pattern, with high pressure centred over continental Europe and low pressure to the west or southwest of the UK, higher temperatures than would usually be expected could be expected.
In fact, a few recent computer model runs have hinted at that possibility. The chart above was generated using data from the Global Forecast System (GFS) which is one of the main weather computer models. It shows forecast maximum temperatures on 16th July reaching a record breaking 41C!
It's important to stress that the computer models are run many times each day and most updates do NOT support this outcome. Nonetheless, it perhaps indicates that 40C is now achievable in the UK due to the background warming that has taken place over recent decades.
Temperatures are set to rise and during the next couple of weeks at least there should be a lot of dry weather, especially in the southern half of the UK. In the north and particularly the north west it could remain more changeable.
There are indications that the heatwave criteria will be met in parts of the UK. Also, there is a chance of very high temperatures being recorded before the month ends. However, that is very uncertain and it depends on the pressure blocks aligning in a way which allows the anomalous warm in southern Europe to be funnelled northwards.
Open from 7am to 11pm. Off topic comments may result in your account being blocked.
Sign in with your TWO siteaccount
Recommended because it will give you access to extra features. Create your free TWO site account
Or authenticate with your Facebook or Google account.
For terms and conditions see Readers Comments on the Cookie and privacy policy page.
Hot and thundery summer?
Will the relentless rain relent for Easter?
Cheltenham Festival weather
A close to average spring?
Spring 2024 UK weather
Daily weather by email
14 day outlook
Monthly outlook
Seasonal outlook
Christmas weather
See the Model inventory for the full list of model charts and data