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  • Writer's pictureMark Hunt

October 9th, 2023

Hi All,

As I drove back from an abortive weekend's Bass chasing session in Norfolk yesterday (big waves and coloured water) in my camper, I mused on the fact it was 22°C in the first week of October, with unprecedented warmth day and night.

I watched farmers preparing their fields with dust clouds rising up in the fading Norfolk sunshine. At the other end of the country, Scotland has just had a weekend of weather that defies belief from a rainfall perspective with over 7" of rain in some locations. On the weather stations I monitor, one of the Scottish units recorded 95.9mm in one day with a maximum rain rate of 47mm per hour, 160mm in 8 days. Unprecedented.

In general I don't talk much about climate change on this blog but it is hard to ignore this subject and comment on the weather with the experiences above and the type of statistics coming out of The Copernicus Climate Change Service (C3S) implemented by the European Centre for Medium Range Weather Forecasts (ECMWF), shown below.

Reproduced courtesy of Copernicus Climate Change Service / ECMWF

The graph above shows that the average temperature globally in September 2023 was nearly a degree higher than the average from 1991-2020, whereas previous years had hovered around the 0.3 - 0.4°C mark. I use that word again, unprecedented. With El Nino driving global heat I wonder what this winter has in store for us and indeed, next summer ?

Later in this blog I am going to look at our own situation for September using GDD as a unit of measure because it is relevant to growing 'things' as opposed to just using temperature. It also saves me a bunch of work :)

General Weather Situation - w/c 9th October, 2023

So we start the week pretty much as we did last week with a high pressure Omega blocking event in situ. It is this blocking pattern that has given us such a warm end to September and start of October.

So I guess the most relevant question is "How long will it last ?"

Well not for much longer as the position of the jet stream is dropping south as the high pressure declines and low pressure systems from the Atlantic look to push in.

Is this the last of the barmy / balmy weather ? Maybe not, as traditionally the end of October can coincide with very mild weather and there's a suggestion on the long-term GFS that we will see another warm high pressure towards the end of October.

So this week we will see transition from warm and muggy and mainly dry across central and southern areas to cooler, windier and more unsettled weather across all of the U.K and Ireland. Scotland and Northern Ireland as we know has already had a lot of rain and unfortunately there is more on the way. So Monday and Tuesday continue the warm and settled pattern for central and southern U.K, but for western Scotland, we will see heavier rain push in early on Tuesday morning. This rain will slowly drift south into The North West and later northern and western Wales. So 20-22°C across Ireland, England and Wales for Monday and Tuesday, 15-16°C for Scotland with heavy rain for north west Scotland.

Early on Wednesday morning, we see a horizontal band of rain enter into the southern half of Ireland, really from Dublin down. This horizontal band then pushes across The Irish Sea into mid / North Wales, with some very heavy rain for the latter, before pushing eastwards into the north of England and Midlands. During the course of Wednesday this band of rain sinks south and eastwards into central, southern areas, South Wales and The South West. As this band of rain sinks south, it'll pull much fresher air in behind it, so expect 12-14°C by Wednesday afternoon / evening with single figure temperatures at night. Quite a change !

Image courtesy of

It is quite an amazing weather feature because at one point this band of rain will stretch from Cornwall right across Europe and far into Russia !

It is a really slow-moving band of rain so overnight into Thursday it will bring rain, some of it very heavy in places along the south coast and finally, the south east of England. Away from this band of rain, it'll be cloudy, dull and feel much, much cooler than earlier in the week with 13-15°C typical. So a dry picture for most areas of the U.K & Ireland on Thursday away from that rain band across the far south of England.

It won't last though because by Thursday evening, another band of rain looks to push into The South West. This band of rain will feature some very heavy localised downpours on Thursday night into Friday and I expect the southern half of Ireland, Cork, Wexford to be in the firing line, along with The South West and South Wales. As it spreads north and east on Friday, that heavier rain will be a feature across The Midlands, Wales and north of England. Although it'll reach The Borders on Friday afternoon, it then sinks southwards into the north and north east of England, so Scotland will miss the brunt of this heavy rain. The rain won't be the only feature of Friday's weather, it'll be extremely windy and will feel much milder again with temperatures in the high teens (16-19°C) as the wind turns more southerly.

The outlook for the weekend is much drier but feeling considerably cooler as the wind swings round to the north west. So a largely dry weekend for all areas, except for some showers across the north west of Scotland and north west England on Saturday /Sunday. As mentioned above though, it'll truly feel like autumn has arrived with 12-13°C typical and maybe struggling to get into double figures across Scotland.

Weather Outlook - w/c 16th October

As I mentioned above, the position of the jet stream is dropping this week and that means it is paving the way for more unsettled and cooler weather, more typical of October, rather than the weather we have as I sit and type this !

Compare this GIF courtesy of with the one for the start of this week above, some change I think you'll agree....

So next week looks to start cooler with temperatures more typical of this time of year but crucially dry for most areas with light winds. This looks to continue through Tuesday but then we will see the weather break down from the north with stronger winds and rain pushing into Scotland later on Tuesday. Across Ireland and Scotland the winds will begin to strengthen markedly on Tuesday night from the south west and this will also pull milder air into the southern half of the U.K, so windy and mild for mid-week, next week before it all goes down the pan with rain and gale force wind pushing into Ireland later on Wednesday and very rapidly spreading to all areas overnight into Thursday. So Thursday looks very wet and very windy for all areas. Friday will see more rain across Scotland, the north of England and the northern half of Ireland (mainly) but there is likely to be rain further south as well. So wet and windy is the theme for the second half of next week and cooler as well after a brief hiatus. Hang onto your hats......

Agronomic Notes

I have said before in this blog and during my educational talks, I think our changing weather / climate is unlikely to track in the same way alongside the Copernicus results / projections because we sit on the path of the sub-polar jet stream and we are an island rather than a continental landmass so our weather patterns tend to be shorter-lived. So rather than a continual increase in temperatures, we will see more variability with more extremes due to Omega and Diffluent blocking events, courtesy of a meandering jet stream.

What I thought I'd do this week is look at the long-term GDD data I have courtesy of the great source of data that is Sean Wilson @ The Oxfordshire who has provided me with weather stats since 2005 ! Cheers Seanicus !

So first up where did September 2023 come in GDD-wise ?

So we came in with a total monthly of 338, which is the highest September total since we started recording GDD, but only by a smidge from the previous record holder, 2006. That is 33% higher than last September, which incidentally featured some very cold weather in the third week with ground frost. There's that variability I was talking about !

So how is our GDD trend tracking for September vs. the average September GDD ?

Well what I have done is to take the 2005-2022 average GDD for September as a month (this incidentally came out as 259 GDD using a 6°C base temperature in the calculation) and compare each September since 2005 with this figure.

This is how the resulting chart came out ;

So what we see is the total lack of an incremental change as is present in the global average temperature data from Copernicus. This doesn't mean climate change is not affecting the U.K & Ireland, I believe it is but the scenario is different because of our position vs. the jet stream and the fact we are an island.

What is the relevance of this data to turf management ?

Well, firstly that as a facility you need to future proof yourselves for more weather extremes, whether that is heat, rainfall, heat / humidity combination or all of the above.

If you take September 2023, we finished on 338 GDD for our default location, which incidentally was higher than August's figure ! .

Well that is a lot of temperature and with rainfall as well, a lot of growth. So for PGR and fungicide applications for starters, it means less longevity and greater frequency. It also represented a high level of disease pressure from Microdochium, Dollar Spot and Plant Parasitic Nematodes. This scenario has carried over in October with the first half of the month continuing the mild, humid and muggy overnight trend.

More G.P = Less longevity

Take fungicides as an example. I have always worked on their longevity equating to a total Growth Potential figure of around 10, with the weaker formulations not even lasting that long. Our equivalent G.P figure for September was 26.04 from the same location, which means if you were applying fungicides every 10 G.P, you'd have made 2 applications in one month and would be well on the way through the 3rd (which incidentally would have run out 4 days into October !

So to provide control, that would be 3 fungicide applications in under 5 weeks. Now clearly that isn't feasible from a strategic rationale and budget perspective, but the fact is with the unseasonably warm September we have endured, growth levels have been off the scale and the longevity of fertilisers, dew suppressants and pesticides (PGR's and fungicides), has been dramatically shortened.

Although September brought high disease pressure, the high level of growth will have minimised some of the damage / effects of this disease peak thankfully.

There is of course a strong argument not to apply a fungicide until temperatures drop away and there is a promise of more longevity. I'd argue looking at the current weather forecast that disease pressure will drop off markedly from mid-week and you'd be better served keeping your powder dry on a fungicide till we see temperatures drop and can spot another disease peak coming. In the meantime, apply hardeners, minimise dew through high pressure periods and keep your eyes peeled for the next warm, humid, high pressure peak.

All the best.

Mark Hunt

Prodata weather systems

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