July 7th, 2026

Hi All,

A short blog this week as I am busy sorting one house to move out of and another to move into. We have all been there but crumbs what a process it is.

As I type this blog we are heading into our 3rd heatwave of the summer with temperatures nudging into the low thirties for the 3rd time this year. Isn't it amazing how quickly our bodies adapt to temperature . Outside it is 20°C and it feels pleasantly cool. Yesterday, I ran and it was 27.5C and it felt a bit warm, but then my running is 'sporadic and a bit clown-like' (eh Steg ?) , so hey ho....

Reading a New Scientist article last night about our current climate, it stated that this type of heatwave is something we will have to get used to as our climate warms rapidly. It is of course nothing to do with a building Super El Niño, which probably won't be in situ till later in the year. Personally, I don't mind the heat despite being fair-skinned, I can deal with it fine, but the night temperatures are hard work for getting a good kip. That said I can't remember getting a good kip for the last, hmmm, 30 years or so !

On a nature note, I am seeing loads of Butterflies whilst out walking at Fineshades Wood, Corby, including a couple of very brief encounters with the elusive Purple Emperor. Those things are big and they get a shift on, so I haven't managed to get a photo yet but it's on my bucket list !

Now Butterflies are Poikilothermic, that is to say they cannot regulate their internal temperature. They, like a number of people who I have met along the way in my life are termed Poikilotherms or Cold-Blooded (My apologies in advance for such a sweeping generalisation but they were usually CFO's 😊 ). So when we have lots of sunshine and warmth, they benefit. (the Butterflies I mean). Poikilothermic is I think a great term to impress your friends down to pub, for example......"that ref is a bit of a poikilotherm" 😂)

It got me thinking, have we had more solar radiation this year than previous years because we are having more heatwaves ?

Of course the two don't necessarily follow because it can be hot and cloudy rather than hot and sunny. So, I extracted the monthly total solar radiation from the Davis weather station at our default location and graphed it out. Remembering that 2024 went down as a bit of a dull and cool summer. The results surprised me ;

The yearly totals from Jan 1st up to and including July 6th are ;

2024 - 23245 w/m2

2025 - 25,710 w/m2

2026 - 26,030 w/m2

Interesting, so that's a 12% increase y.t.d vs. 2024, but only 1.2% up on 2025.

You can see the uplift from March onwards through to April and May. Surprisingly, June 2024 came out higher for this location than June 2025 and June 2026, but then we must remember the first part of June 2026 was cool and wet, so that probably explains it. The figure for July is up to and including the 6th of the month in all years, so a big change there already me thinks. Great for everyone with solar panels and no I am not interested in how much money it has saved you (until I have my own ones fitted :) )

GFS & ECMWF image courtesy of tropicaltidbits.com

The backdrop for this heatwave is pretty similar to the last two with a plume of hot air extending up from Africa as we can see above, however there are subtle differences.

Firstly, the humidity will be lower this week, so we should be able to cope with it easier in terms of managing body heat by sweating (it is easier for sweat to evaporate and therefore cool the body if the humidity is lower).

Secondly, this one is windier as well I reckon, with lower humidity, which means E.T moisture loss will be even higher. Yesterday, for example we lost between 5.5-6.5mm in a day, which means applying 2.75 - 3.25mm of irrigation if you are working at a 50% E.T replacement rate. It also means your moisture readings first thing via a Pogo, Delta t, (delete where applicable) will change super-quickly because the moisture loss rate by evaporation and transpiration is so high.

Peak E.T loss at this location occurred from 14:00 through to 17:00, running at 0.7mm per hour and totalling 6.4mm for the day, a record I think. In other words a long time after you might have tested for soil moisture at the start of the day. That said with the majority using hand-watering to deal with the identified hot spots, I am guessing you are constantly monitoring those if time and staff resources allow.

Lastly, the models are pointing to the potential creation of a 'Cut Off' low pressure system (COL) down in The Bay of Biscay some time over the weekend and this could be important.

The significance of this in my view is that this type of isolated low pressure system has a profound effect on the position of the jet stream. I have noticed that when we see a COL form, they ultimately punch a hole in a stable, resident high pressure system as we have now and pull down cooler and sometimes more moist air. Let's see....

10-day GFS projection courtesy of tropicaltidbits.com

If you look at the GFS run above, you can see this process unfolding through next week and leading up to the following weekend. So sometime around the 20th / 21st of July we may (may!) see a significant change in our weather with cooler and potentially wetter weather coming into the weather picture. Now of course this isn't bolted or on dead cert. It is the weather, so a caveat-filled zone and especially with our current situation. Not all models agree it has to be said, but I will be tracking that COL to see how it shapes our coming weather.

Comparison of Ayr vs. Thame y.t.d - Prodata Reports

Now of course I keep talking about heat waves, but further north in this country we have had a much gloomier and wetter summer so far, especially across the west of Scotland.

Last month, many locations there had 100mm+ of rain as you can see from the above comparison from two locations, one near Ayr and the other our default Thame location. Not only is rainfall different, but so is the rainfall - E.T balance.

Ayr shows a soil moisture surplus of 183mm y.t.d vs. a soil moisture deficit of -149.8mm y.t.d at Thame. That is a 332mm difference !.

Looking across The North Sea to Denmark, as predicted they are the recipients of a cooler and wetter, north westerly airstream, but as with the last heatwave the pattern will repeat as that hot air plume will head eastwards into Scandinavia by mid-week, upping their temperatures considerably this week. Ireland will hang onto the distinctly un-Irish weather (but very welcome for sure I'd say) for a good while yet and potentially it could get substantially warmer according to the GFS. So the heatwave will continue here as well. All eyes will be on the middle / end of next week to see if that COL shapes our weather into something decidedly different or we stay on trend.

Agronomic Notes

So by now we are getting pretty used to dealing with this type of weather. We have had fair notice each time it has been on its way and therefore plenty of time to prepare.

To me it is all about 'treading the line'.

'Treading the line' between sustaining a healthy plant from a moisture and nutrient status perspective and creating too much growth, which then places demands for an increased water requirement on the grass plant. That coin also has a flipside, as too-weak a plant, low in nitrogen and potassium, is a fair target for disease and also plant parasitic nematodes at this time of year,. Anthracnose and Dollar Spot are the most likely plant pathogens to make an appearance during or shortly after heatwaves and especially if your grass plant is on its back foot so-to-speak.

Biostimulants, surfactants, light foliars, PGR's and pigments are your friend at such times

This week for example, we will record our 3rd Anthracnose trigger event of the summer which would suggest actual disease pressure will be significant this year if the basis of the model is correct. Let's see.

Short but sweet, enjoy walking the line, the sunshine and the abundance of Poikilotherms...

All the best.

Mark Hunt