TWO Buzz

Weather news and views from Brian Gaze.

Could July serve a weather surprise

Cooler than average?

Posted 29th June, 15:52

Unsettled and cool weather is set to continue through the coming week. Will the heat return as we head towards the middle of July?

Month after month of warmth

At the moment the first half of July isn't looking particularly warm. In fact recent ensemble models have been suggesting slightly below average temperatures for much of the next 2 or 3 weeks. That suggests a cooler than average July is a possibility but it would be an unusual outcome.

This year is following the trend of recent ones where most months turn out to be warmer than the 30 year average. In fact the first 6 months of 2020 have all finished comfortably above the Central England Temperature (CET) average. UK Met Office data shows the following:

Month CET Anomaly
January 6.4 2.6
February 6.3 2.5
March 6.7 1.0
April 10.4 2.5
May 12.5 1.3
June 15.6* 1.5

 

*June is provisional but even the current cooler spell isn't likely to offset the earlier warmth

The London GEFS 06z plot below shows the forecast temperature spread for the next 16 days. This is generated by plotting the temperature forecast from each of the 20 runs in the model plus the control, mean and GFS operational.    

The things to note are:

1) There is good agreement for rather cool conditions until about July 5th

2) A number of runs suggest a brief warm up between July 5th and 7th but it is very uncertain

3) Coolish conditions are generally favoured between July 7th and 15th when the plot ends 



If this proved to be on the money we could well be entering the second half of July with the CET running below the 30 year average. I'm not hanging my hat on this outcome though for the reasons outlined above. Nonetheless, I will be watching very closely to see if signal for average to rather cool temperatures is maintained.

London GEFS 06z 2m temperature spread, init 29th June 2020

Rain outlook

Another key factor in the summer months is rainfall. Sunny conditions in July will usually deliver warm or very warm weather. Therefore, it is cloud and rain which are needed to suppress temperatures. 

The lower half of the London GEFS 06z plot below shows forecast rainfall. It certainly doesn't look like a washout but there is an ongoing moderate risk of showers or longer spells of rain. Plots for locations farther north and west are wetter as is often the case.  

London GEFS 06z, 850hPa temperatures and rain, init 29th June 2020

The ongoing risk of rain adds support to the possibility of the first half of July being cooler than the average.  

TL;DR

The outlook for the next few weeks is quite mixed. Computer models suggest there is at least a possibility of the first half of July being rather cool. The general pattern is fairly typical for the UK with the wettest conditions in the north west and the driest in the south east. However, there is a hint that low pressure areas and rather cool westerly winds will have the upper hand over all of the UK for much of the period.

Cooler than average months in the UK have been as rare as hen's teeth in recent times. However, there is at least a shred of evidence currently to suggest July may buck the trend.    

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