August 27th, 2024

Hi All,

Well my 1st blog for some time after I decided to take a bit of a summer sabbatical from my almost 15-year stint of Monday morning blogs. For a number of reasons, namely I wanted my Monday's back for the summer, I also felt with the unreliability of the GFS / ECMWF long-term (> 5-day) forecasts, my contribution wasn't useful / accurate and continuing that theme is one of relevance in terms of the content of my blog. In my past employment, I got to see a lot of turfgrass situations, in quite a few countries on a continual basis and that gave me plenty to discuss. Nowadays I see turf when I got out to install a weather station and so my content and its relevance is less turfgrass-orientated. So my apologies for not blogging and for not saying that I was taking a break.

I have spent my summer (mostly in a campervan) 'enjoying' our English and Welsh summer weather and being frustrated by the continuing inaccuracy of weather forecasts, both short and long-term and their effect on my walking, cycling and mostly of all, fishing :) That said, I have made the time count because Tempus Fugit and all that....

You only have to look at this week's weather for a great example of the current inaccuracy of our weather forecasts. Late last week, the news was full of a late August heatwave coming our way with temperatures due to hit > 30- 34°C this week. Looking at the forecast this week and that heatwave has 'disappeared' back to 'normal' end-of-August temperatures. Last year we had an early September heatwave with some very high temperatures and settled high pressure. Are we heading that way again I wonder ?

My time in a camper down in South Wales and North Norfolk has also highlighted to me how different the weather has been west-east this summer and particularly north west to east, with the rainfall pattern distributed really unevenly across the U.K & Ireland. The west and south west has had a pretty grim time of it rainfall-wise with The South West, Wales, The North West and west of Scotland in the firing line. The same is true for Ireland with the south west, west and north west coping heavy rain this summer whilst the south east and east has been significantly drier.

Of course if you read the somewhat, occasionally idiotic responses to Met Office weather tweets, it's all due to the global weather conspiracy that is cloud-seeding. As if anyone would want to make the recent U.K & Irish weather any crapper, I ask you ?

Nature has also been on the receiving end this year following our extremely wet winter and spring with insect numbers in particular noticeably affected. That said, the warm and dry August has really seen an uplift in late summer Butterfly and Dragonfly numbers. I saw my 1st British Swallowtail at Rutland Water and last week at Fineshades Wood, near Corby, an adult Slow Worm, which I initially thought was a snake, but it's actually a legless Lizard (and quite a big one by all accounts). I also saw a good number of Brown Lizards as well on the same walk, excellent to see some reptiles locally.

GFS outlook 1-7 days courtesy of tropicaltidbits.com

General Weather Situation - w/c 27-08-24

So with the current vagaries in the GFS forecasting in the back of my mind, I have split the output into the next 7 days (above) and then the more variable, liable-to-change, 7-10 days. The current weather scenario highlights the split in cooler, wetter weather affecting the west and north west vs. drier and warmer for the east and south east. That said as you can see from the output, we have a more general progression through this week to a stable, high pressure scenario across most areas, just not with the level of heat that was forecast this week.

So rainfall-wise, the current Netweather.tv output (10:00am Tuesday) kind of tells the story of the summer as you can see the orientation affecting the west of the U.K with the north west and west of Scotland picking up the worst of it. By the time it reaches central and eastern areas, it will be a shadow of itself with most of the rain fizzling out. That's the story of Tuesday with temperatures pretty normal for the time of year 16-22°C, accompanied by a strong south westerly wind (another feature of our summer I think). Wednesday sees a sort of re-run of Tuesday, with rain for the west of Ireland crossing the country through the day and also the west of Scotland. Through the day, we may also see some showers crop up across central areas culminating in some rain for East Anglia later on. As we move into Thursday, the whole weather picture begins to calm down as high pressure builds and stays put for the next 3-4 days or so. Now unlike the forecast from the daily tabloids, we won't be reaching into the heady heights of 30°C+, more like 20-22°C sort of territory, which personally I am very happy with.

Strangely for this time of year we will see the wind turn easterly / north easterly over that period and that's the reason why the temperatures won't be as originally projected (then the wind was supposed to be southerly). Wind direction it seems is another of the least-accurately forecasted parameters and to be fair it is extremely tricky because of local factors influencing the final outcome. That makes it hard to forecast (like rainfall). So we are well set for a nice end to the week and I for one will be grounding out some mile on the mountain bike in an effort to counteract too many Tebirkes Danish Pastry that I made recently !!!! (I love Danish baking when the weather is rubbish accompanied by strong coffee and Shed Seven !)

GFS outlook 6- 10 days courtesy of tropicaltidbits.com

Weather Outlook - 02-09-24

Perhap as an admission that forecasting any longer than 10 days is for la la land, the current GFS output has now dropped from a 14 to 10 day outlook. As it built today it highlighted the development of a continental low pressure across northern France and The Netherlands which threatens to start next week with some rainfall (may actually start Sunday pm) across the south and east of England joined by a front from The Atlantic that crosses Ireland at the same time. So Monday could be pretty unsettled for most areas and this theme will continue into Tuesday I think though more of the rain will become confined to the north west and west of the U.K. During Tuesday, high pressure looks to build south west of Ireland and this could usher warm weather into Ireland and the west, whilst low pressure comes to sit north and east of the U.K. So potentially (please note that well-advised caveat) a role reversal with the better weather to the west and cooler, more unsettled weather to the east. The potential (there's that word again!) emergence of a strengthening high pressure to the west will also vector the wind direction to a more northerly one, so I'd expect it to be cooler in the east as well, less so in the west. So warm and settled next week after an unsettled start, with the warmer weather in the west, but that northerly wind direction will mean it won't be a heatwave. That is how it looks currently.

Agronomic Notes

So in this blog I decided to have a look back at June - August (to date) to understand how this summer compared to last summer from a temperature, humidity, rainfall and Smith Kerns Dollar Spot Probability perspective. My gut feeling is that this summer has been cooler, wetter (in certain areas) and possibly more humid because there's been plenty of high temperature / humidity-related diseases kicking about. Plenty of Dollar Spot for one. The question in my mind though is are my gut feelings correct ?

The problem with answering that question is that we have of course lots of geographical variability in our weather across the U.K & Ireland and to crunch all that data takes a lot of time. In this blog I picked 2 locations where I have definitive weather station data from last summer and this one to compare. One is our default location at The Oxfordshire, a pretty representative location for central and eastern England and the other down near Bath, which I thought would describe the south west and have some connotations from a Welsh and Irish perspective.

I have graphed out the stats below for The Oxfordshire with from top to bottom, 2024 vs. 2023 - mean air temperature / mean relative humidity / mean daily rainfall and Smith Kerns Dollar Spot Probability.

Some features we can pick out here is the dismal month that was June 2024 with much lower air temperature than last year (Must be all those clouds from the seeding eh ?). We can also see some very specific high temperature spikes where the mean air temperature exceeded 20°C on 19th July, 31st July and 12th August. Those peaks exceeded what we saw last summer, however, the average daily mean temperature for June - August 2024 was 16.4°C vs. 16.7°C for the same period in 2023. So for this location, summer has been cooler overall but with some hotter peak temperatures vs. 2023. Cooler but hotter, clear eh ?

Humidity-wise, it isn't easy to pick out the differences and if we compare the mean humidity for summer 2024 vs. 2023, the figures are 81.3% vs. 81.7%. Practically the same then, so for this location it hasn't been a more humid summer but humid nonethless.

Next up is daily rainfall (in mm). No clear pattern there other than the fact that this summer there were 2 rainfall events which exceeded 20mm, whereas last summer there were none. Total rainfall-wise, the stats are 2024 -119.6mm vs. 2023 -110.4mm, so pretty similar.

Lastly, we have the Smith Kerns data 2024 vs. 2023. We can see for 2024 that the cool June temperatures kept the Smith Kerns values lower than last year, remembering that the equation works on an average temperature range of 10-35°C (read about the basis of the equation here). On the flipside we can see a period of sustained pressure at the end of July and also mid-August. Bearing in mind we are looking for levels > 20%, in my mind both summers represent high Dollar Spot disease pressure and because this summer we have had more daily mean temperature peaks, it is probably no surprise that some of the more exotic summer diseases (Grey Leaf Spot for one on sports pitches) have made an appearance.

We can also see a marked reduction in Smith Kerns since mid-August since the lower night temperatures kicked in.

Here is the data from the Bath location ;

Summarising the data from this location in summer 2024 vs. 2023, we see the following ;

Jun-Aug 2023 Jun-Aug 2024

Mean daily air temperature (°C) 16.2 15.5

Mean daily humidity (%) 83.5 83.4

Total rainfall (in mm) 286 183.4

So definitely cooler in the west, wetter than our central location but comparing summer 2024 vs. summer 2023, we can see less total rainfall.(bear in mind that summer 2023 was exceptionally wet in the south west of the U.K). Humidity-wise, practically identical.

Looking at the Smith Kerns data from the Bath location, we can see a similar pattern

to our Oxfordshire location, however the magnitude (severity) of the disease pressure is significantly higher. This makes sense because there's more rainfall and higher humidity in the south west than in a drier, central location. I have charted out the 2 locations above.

So in conclusion, my hunch was sort of correct and sort of not. Not a wetter summer for these two locations but I know of others where it has been much wetter so generalising is dangerous when it comes to weather data. Both summer's represent high disease pressure from a Dollar Spot perspective and of course humidity and temperature don't just encourage this disease, I'd add Microdochium, Red Thread, Fairy Rings and possibly Waitea to that list (the latter particularly after the last couple of 20mm+ downpours).

Now looking ahead we aren't out of the woods yet because in my mind September welcomes in longer nights and therefore potentially longer periods of leaf wetness. If the temperature stays up high enough, we can see some significant disease activity from Dollar Spot in the 1st half of the month. Taking the dew off mechanically or using a surfactant tips the balance back in your favour and dramatically reduces the severity of Dollar Spot disease pressure.

Ok, that's me for this week, I hope you found the blog interesting and above all, relevant to your situation. Drop me a line if you have the time to let me know either way. I accept constructive criticism but resent it according to my late father and he should know !!😊😊

All the best.

Mark Hunt