August 16th – 17th, 2021


My apologies but for some reason this blog didn’t get published yesterday when it was completed 🙁


Hi All,

Last week I briefly touched on the pronounced difficulty weather forecasters have with predicting summer rainfall amounts and occurrence.

I was reminded of this fact this weekend gone…..

So there I was on Saturday, fly fishing the beautiful Thornton reservoir near Leicester and as usual I was fishing dry flies (for the uninitiated, dry flies sit on or in the surface of the water and the Trout take them off the top, it is a highly visual affair). For this you need cloudy conditions because any brightness will send the Trout deeper as like all fish, trout have no eyelids to protect them from brightness. So around midday, after a good morning spell, I saw a few spots of rain on the surface of the water and thought to myself, that’s fine and dandy, plenty of cloud cover then…..2 1/2 hrs later as the persistent rain overwhelmed by clothing and lets just say I was soaked through to my base layers, I wondered would it ever stop ?

Pretty soon after it did so, the sun came out and that was that. Not forecast, not predicted, a line of showers morphed out of nowhere and sat over North Leicestershire depositing 8 mm or so. That said, the Swallows, Swifts and Martins had a field day as soon as the rain stopped because they know the midges take to the wing then and that’s dinner. The air was full of them for 15-20 minutes, splendid to hear them all chattering away to each other, parents to young and the like. It won’t be that long before they’re packing their bags for Africa, bless them, with the Swifts heading off first.

On the drive home, 20 miles or so down the road, the farmers combines were at full chat with dust clouds billowing off them, no rain here then 🙂

I’ve been looking at the GFS (as you’d expect every day) looking to see what side of the weather coin we are likely to be dealt in the coming weeks and very aware that in southern Europe they are getting hammered temperature-wise. Sicily recorded 48.8 °C last week (though the accuracy of this reading is debated) and as the heat plume moved westwards (yep against the pattern of the jet stream), Spain recorded 47.2°C. You can see the distribution of heat very clearly on this excellent output from Meteoblue.

Image courtesy of

Just think about that magnitude of temperature for a moment. When we hit high twenties, low thirties, for many the heat is excessive. Add another 15°C on top of that and you’ll be close to what we could experience. And our grass ?…cool season grasses just aren’t bred (or evolved) to deal with this magnitude of temperature and what about Poa annua ? A constituent of many a grass sward in the U.K & Ireland that effectively stops growing at 27-28°C, how will it react at 45°C + ?????…

It’s one of the reasons I’m glued to the GFS output because a heat plume of that magnitude would I believe be a game changer for our industry. Many of our golf courses are irrigated with very old systems and are short staffed (hand watering is time consuming) currently with holidays, Covid pinging and the general difficulty with attracting younger people into a profession that requires them to get out of bed early and sometimes (shock horror) work weekends. Sweeping generalisation time, but most of today’s youth see work as something to fit around their social life, rather than the other way round. T’is true. It isn’t much better in the clubhouse either with a minor exodus of Europeans due to Brexit / Covid and the fact that hospitality is seen as a riskier profession after the mass furloughing / redundancy of staff that it has experienced recently. Tricky times whichever side of the fence you’re on, greenkeeping or clubhouse….

So what’s the weather consensus, heat plume or low trough and will another BOB make an entrance to rain on everyone’s parade ?

Image courtesy of

General Weather Situation

So as you can see from the GFS output above the situation is delicately balanced with heat below us, heat across The Atlantic and a low pressure over The North Sea. This is having the effect of channeling the wind from the north west so that means a cool one for sure until it relents. It also means it’ll stream in showers from The North West / North Wales south and east across The Midlands and into East Anglia on a regular basis.

Onto Tuesday and overnight from Monday rain pushes into the north west of Scotland and this will move south and east across most of Scotland in the wee hours before moving into The Lakes and northern England for early Tuesday, clearing Scotland as it does so….This rain will sink south across the East Midlands, eastern England and the south east through Tuesday morning / lunchtime, fizzling away as it does so. Away from this rain band, it’ll be another dry, breezy and cool day on Tuesday with that north west wind in attendance again for Ireland and the U.K. So high teens is probably the best we can expect. They’ll be a repeat potential for showers to stream down from The North West through the day making western coasts a bit of  dull and drizzly affair.

Onto mid-week and a sunnier and warmer day in prospect on Wednesday as a ridge of high pressure teases warmer air across the southern half of Ireland and the south west of England / Wales. That strong to moderate north westerly wind will keep those temperatures down to the low twenties though despite the sunnier conditions but pleasant enough nonetheless. Later on Wednesday evening we will see a sneaky low pressure push rain into the south west of Ireland and this will move some showers across Ireland and the south west of England overnight. By Thursday morning this band of light rain showers will be into the south west of England, Eastern Ireland and South Wales, consolidating into some heavier rainfall for North Wales through the afternoon / evening. So a cloudier day on Thursday but the wind will now be westwards so feeling pleasant all the same and likely more showers across western-facing coasts. This first band of showers was really an initial foray from this low pressure because by Thursday evening we will see another band of rain, heavier this time make landfall across the south and west of Ireland. Overnight this heavier rain will push up country with some really heavy stuff for the south and south west of Ireland by Friday morning.

Closing out the week on Friday then we will see this heavier rain across Ireland and the south west of England.  By mid-morning or so, it’ll be into Wales and the eastern half of Ireland pushing up into The Midlands and northern England later on Friday. At this stage (summer rain caveat invoked), if you drew a line from The Wash to The Isle of Wight, the area south of this looks to stay mainly dry but north of this and with rain pushing up into the north of Ireland, we look wetter for the 2nd half of Friday. By Friday evening this rain will be into southern Scotland and pushing northwards. With a south westerly wind now in situ, we keep those pleasant enough temperatures so high teens / low twenties away from the rain and a few degrees lower under the thicker cloud and rain band.

No surprises then that the outlook for the weekend looks hmmm… unsettled with low pressure sitting off the west coast of Ireland out in The Atlantic…….So if you look at the animated GIF above you can see that the low pressure is projected to cross the southern half of England over the course of the weekend and in so doing will introduce cloudier and cooler weather and a changing wind that will swing from westerly through to easterly !

So Saturday looks unsettled with bands of showers moving up from the south coast and into The Midlands and north of England later in the day. Ireland looks to have a dry first part of Saturday but some very heavy rain is expected to push in from the south through the second half of the day. I really feel for the farmers at this time of year trying to get their harvest in when constant rain and wind is working against them. Sunday sees more wind and rain pushing up from the south across Ireland and England, with the rain now extending up into Scotland. A pretty cool weekend as you’d expect with mid to high teens only.

Image courtesy of

Weather Outlook

Now then maybe, just maybe there’s some better news on the horizon for next week. I do hope so because I’m having a few days off to tour North Wales on the motorbike and visit the British MotoGP at Silverstone. North Wales when the sun is out is a beautiful place, when it’s peeing down,  err maybe not…

So next week looks a better prospect with high pressure keeping things fine and dandy with Ireland and Scotland picking up the best of the temperatures initially I’d say. Now we will have easterly winds for a good part of the U.K & Ireland, but I think we will still be talking low to mid-twenties sort of temperatures for most of the week. From mid-week, a low pressure on the continent may introduce some showers along the southern coastline of England, tricky to say at this stage, but I think England and Wales will pick up the better temperatures at the end of next week. For the U.K Bank Holiday weekend, things look delicately-balanced with a new low pressure sitting off the south west of England. This could introduce showers for Ireland and the south west at the end of next week / next weekend but it’s too early to say for sure. Hopefully it won’t trash The Bank Holiday and MotoGP !!!

I would add a large caveat that the 7 day onwards forecast is showing huge daily fluctuation currently and has been for the last month or so, meaning it could easily tip either way weather wise, peak or trough.

Agronomic Notes

Has it been a gloomy summer for the grass plant ?

I thought about this when someone said to me how dismal it’s been this summer with a pronounced lack of sunlight / sunshine.

So today I wanted to speak about light and particularly the part of the spectrum that the grass plant can utilise because not all light is useful to grass. Plants only utilise a proportion of the light spectrum falling on the leaf for photosynthesis in terms of specific wavelength. The spectrum of light that they absorb is known as Photosynthetically Active Radiation, which is a bit of a mouthful, so you’ll be happy to know it is abbreviated to PAR. The diagram below shows you the PAR light spectrum that stretches from blue light (400 nm) right up to far red light (>700 nm)

Reproduced for educational purposes only

Now a measure of how much PAR light falls per day is given by the Daily Light Interval (DLI), which is the total amount of PAR light that falls onto a m2 over a 24-hour period and is measured in mols of light per m2 per day. Now of course we don’t see any PAR light when its dark (!) so realistically the DLI is measured from sun rise to sun set and this of course varies throughout the year due to day length. It also varies depending on cloud cover. So a short winters day will have a much lower potential DLI than one measured in mid-summer (or more specifically around the summer solstice when the days are longest). But a cloudy summers day could potentially have the same DLI as a bright winters one.

Of course that assumes that we have full sunlight and no obstruction to the light reaching the grass plant (so no shade).

This is where things can get complicated but before we discuss shade effects lets look at some data for this summer.

At our research facility at Throws Farm, we have a really cute, PAR sensor snappily called the Apogee SQ 212 SS, which is hooked up to an EnviroMonitor node that in turn talks to a Davis Vantage Pro weather station over the cellular network (no wireless requirement means no hassle with your own I.T department !!!!).

It measures the amount of PAR light reaching the sensor every 15 minutes and then calculates the total over a 24-hour period (DLI).

If you look on the net there’s a great deal of information about the DLI requirements of specific grass species, well more like creeping bentgrass and bermudagrass actually because this is obviously very pertinent to the certain climatic areas in the States (and elsewhere), where people are converting from creeping bentgrass to bermudagrass for better heat tolerance and the like. The snag comes when you have shaded greens because bermudagrass has a higher DLI requirement than creeping bentgrass.

We have a similar issue here which I’ll talk about later and that relates to what grass species thrives best in a shaded environment and specifically with respect to over-seeding and sward conversion. Now there is precious little info on the DLI requirements for Poa annua (because I guess it is so dependent on the biotype you’re dealing with) and browntop bentgrass, though the latter is held to be much lower than its creeping bentgrass cousin. I’m not so sure myself if this is true….

Reproduced courtesy of the USGA Record for educational purposes only

I did find this excellent schematic in a USGA Record article called ‘Light the way to healthy putting greens’ which has some great content relating to the shade tolerance of different grass species but unfortunately it doesn’t indicate how this relates to DLI. (You can find it here)

If you look at the research you’ll see some articles mention that perennial ryegrass has a minimum DLI of 14 mols of PAR per m2 per day and Creeping Bentgrass, a minimum DLI of 30 mols of PAR per m2 per day.

So I dutifully downloaded the measured DLI using from our Apogee sensor and charted it per day from May this year up to the current day.

You will see that I’ve added the minimum DLI requirement for creeping bentgrass and perennial ryegrass as a guide.

Now a couple of pointers – Firstly the end of May and first part of June were characterised by some lovely warm and sunny weather and you can see this in the DLI data. In fact during this period the grass plant was getting more PAR light than it could actually utilise !

Around the middle of June, high pressure gave way to low pressure with unsettled and cloudy conditions with a lot of rain. You can see this very clearly in the DLI data with values on the 16th – 20th of June in particular barely reaching the minimum amount of light required for perennial ryegrass and nowhere near enough to sustain creeping bentgrass. Since then we have had alternating periods of good high pressure and low pressure and you can see this clearly from the DLI data. Although the DLI level has been sufficient for grasses like perennial ryegrass, there have been quite a few days when it has been insufficient for creeping bentgrass. Now of course this is a massive topic and I’m sure some WAG will point out that there’s a great deal of difference between the DLI requirements of different creeping bentgrass and probably ryegrass cultivars….well if that’s a fact, why don’t you publish their respective DLI requirements eh  ??? While you’re at it let’s see some hard and fast DLI data for browntop vs. creeping bentgrass because I’m intrigued. You’d have thought for stadium usage having a DLI requirement for a cultivar would be really useful in making the correct choice for overseeding / construction.

Now this sensor was measuring DLI data over in Essex. I’d be really interested to see data from Scotland (where of course they have much longer daylight hours in the summer than we do) and say, the west of Ireland.

It is a massive subject with so many variables. Some articles quote that morning light is better for the grass plant than afternoon light but that really depends on your localised situation.

Here’s a comparison of two days of data, one from the 10th of June (nice sunny weather) when Throws Farm received a DLI of 37.7 and one from the 25th of July (poor weather) when it received a DLI of 18.3. I’ve graphed out the DLI broken down over a 24-hour period for the two respective days….

On the 10th of June, PAR wavelength light was recorded from 04:30 am in the morning and increased nicely until 07:00 am when the skies clouded over (note the drop in DLI). These clouds burnt off around 10:00 am and the DLI started to increases again rising to a peak at 14:00 pm with really good DLI holding through till 15:30 pm before dropping back markedly.

On the 27th of July, the sun came up later in the morning so on this day we didn’t record any PAR until 05:45 am and we reached a peak at 11:15 am. The average amount of PAR light during a cloudy, unsettled day was only about 50% of a nice, bright sunny one, so not good for grass species that like plenty of PAR light.

Now of course at our research sight we have no shade effects with respect to the PAR sensor, but what if you have a green with trees around it like this ?

This picture was taken at 10:45 am last week on a putting green and as you can see the sun had not cleared the tree line. so even in the middle of summer, 5 1/2 hours of sunlight was lost to the grass on this particular green. I say ‘lost’ but of course when you stood on the green it wasn’t dark, it had dappled shade, but therein lies another problem.

To reach the grass on the surface of the green, the PAR light had first to circumvent the Oak leaves on these trees which will reflect some light back and also of course absorb their own requirement for PAR light in order to photosynthesise. So it’s a good bet that the light quality reaching the grass on this green was not only reduced because of the physical shading effect of the trees but it was also of much poorer quality in terms of what the grass could utilise because the Oak leaves got there first and absorbed their chunk of PAR.

So light quantity is an issue in shade but also light quality, with specifically PAR light quantity the key factor.

I did find one excellent article where some superintendents measured DLI levels on various putting greens in the Chicago district using equipment provided by Spectrum Technologies who do a number of great sensors for measuring DLI.

Reproduced for educational purposes only

It was really useful because it had a chart plotted that showed the relationship between DLI and Poa annua…this is the only documentation I could find. The article can be found here

Here’s a blow up of the specific graph…

Reproduced for educational purposes only

You can see that as the DLI level decreases along the horizontal axis, the % of Poa annua increases in general, so there is a negative correlation between Poa annua and DLI.

So if we take the green in the picture above shaded by Oak trees we can surmise that Poa annua will be the dominant species because it has a competitive advantage in low light conditions over any other grass species that can realistically be utilised on a golf green. I think this is because Poa annua will constantly adapt to its environment through the process of producing seed. Logically the offspring will have descended from a surviving parent. So the Poa annua that is most shade-tolerant will produce seed and pass on this specific adaptation to its offspring allowing them to out-compete other grasses. So if you are over-seeding a shaded green you ought to know this and from a success vs. cost perspective, I’d like to know the specific DLI requirement of one cultivar vs. another.

It also means that when we have a summer characterised by lower DLI levels, we are less likely to see species like bentgrass thrive. If you want to see some really good graphics on the effects of shade on this species, have a look at Mike Richardson’s excellent 2019 presentation at the GIS in San Diego ! You can find it here

I should also mention the good work done by our own Glenn Kirby from Syngenta UK in this useful article here

Hopefully that sheds some light on what is a big subject 🙂 (I know but I couldn’t resist it)

All the best for the coming week…

Mark Hunt