August 9th

Hi All,

The walk around Rutland Water’s beautiful peninsular felt positively autumnal yesterday with cool winds, sunshine and some sharp showers thrown into the mix. I can’t remember seeing ripe Blackberries before at the end of July as I have done this year and my Japanese Anemones are in flower when it’s usually early September before they start. It certainly has been a strange year for plant growth, diseases and the like. This run of low pressure systems, some cool nights, heavy dews and warmth in the day is more like September / October than August. It’s no surprise then that this image of Dollar Spot (on a tee) popped into my WhatsApp inbox this morning before I’d even had time to make a mug of Costa Rica’s finest instant coffee in a vain effort to fire a reluctant brain into action on a Monday.

Clarireedia homeocarpa (a recent name change to keep the fungal geeks and Kate happy :)) is normally for me at the end of August / early September but that said, we often see what I call these ‘marker spots’ in the height of summer so I suppose it isn’t strange. I call them ‘marker spots’ because in my mind they’re laying down a marker that when we get consistent dews, longer nights (and therefore longer periods of plant leaf wetness) you’re likely to see a more aggressive outbreak, so it’s kind of marking your card. Fortunately we have some good strategic steps we can put in place. I for one am glad of the ‘heads up’ and wish some of the other turf diseases played the same way !

Well onto the weather and is the jet stream going to remain low and allow this succession of Atlantic low pressure systems to come in or does it lift and give us our own heat plume ?

I see Greece is in the firing line this week, exactly as the GFS output indicated (remember that purple heat plume in last week’s blog). I know you guys like your sun, sea and whatever but every week when we have late teens / early twenties and the odd rain shower at this time of year is bunce to me. We don’t want what they got frying our turf surfaces before the autumn, believe me.

Images courtesy of Tropical tidbits and Netweather extra

It’s interesting because Karl at Meteoblue said to me a long while ago that forecasting summer rainfall is a really tricky proposition and for sure when I look back at last week’s forecast and what we actually got rainfall-wise, it was nowhere close. Watching the Austrian MotoGP practice on Saturday they commented how Sunday’s race might not even go ahead because of the huge rainfall predicted for Sunday. In reality they got a shower early the next day and then nothing….summer rainfall forecasting is best left to waking up on the day, looking at what’s on the radar and then planning your day accordingly I think. It’s just so tricky…

General Weather Situation

So you can see from the GFS output above that we have low pressure in charge and that’s giving a fair smattering of showers and heavier rain across the south east / east of England but also across Wales, Ireland and Scotland. That said we always like a punt so today I expect the rain across the east and south east of the country to slowly move off into The North Sea, whereas the rain over Scotland will move south and westwards (top of the low pressure system) across Scotland and The Borders and that rain over Ireland will rotate south and east to cover the country. Those showers in the middle of the country will be slow moving across The Midlands through the day. Winds will be light to moderate (and hence the slow-moving rain systems) and I won’t bother telling you from what direction because it’ll depend where you are located on the low pressure system  (could be east, south, north or westerlies !!). Temperature-wise, high teens to low twenties, which in my books is just right thanks…

Onto Tuesday and a much nicer day with plenty of warm sunshine and temperatures in the low twenties as that low moves off into The North Sea and a ridge of high pressure pushes up. Some showers expected along a line across Central Scotland but other than that an easy forecast day. So a nice one after Monday’s downpours.

Wednesday sees a new Atlantic low pressure look to enter the weather picture stage left and this will push a rain front into the west of Ireland and western Scotland from just after dawn. This rain will move eastwards across Ireland during the morning, clearing the west as it does so but for Scotland, The Western Isles and west of Scotland, you look to be in for some heavy stuff. By the evening it’ll be into north west England and North Wales but lighter rain expected here. Further south and east of this we should have another really nice day, with plenty of sunshine, temperatures in the low twenties and a good drying wind from the south west pushing the E.T up. Cooler across Ireland and Scotland with temperatures in the high teens.

Onto Thursday with a hop, skip and a jump, meteorologically-speaking and overnight that rain has fizzled out to a band of showers affecting the west coast of the U.K, but another rain front is on its way courtesy of that low pressure system. This time though the strengthening high pressure across the south of the U.K will push this rain across the north of Ireland and into the west / north west of Scotland and away from the north of England. It’ll mean that the middle and south of Ireland should be relatively dry and really from the east of Scotland south should be pleasant enough. Cloudier because of the proximity of that low pressure system but still with temperatures in the low twenties. Some showers about on Thursday across Wales and the west of England but otherwise hunky dory like.

Closing out the week on Friday and we have a north-south divide with the north affected by that low pressure system, so cooler and unsettled and the south sitting under that ridge of high pressure, so warm and dry (ish). That said, the low pressure quickly moves off from Scotland so a wet start in the west will soon fizzle out to leave a drier, more overcast sort of day. Ireland, Wales and England look to stay dry with plenty of cloud around though. That strong westerly wind will keep temperatures around 20°C across the south and high teens elsewhere.

So not a bad week really and something for the weekend maybe ‘BOB’ ?

Yes, our old friend The Bay of Biscay (BOB) will come into play late on Friday evening and this sneaky little low which hardly shows on the GFS output will push rain into the south west of Ireland late on Friday night. This rain will get a shift on so by Saturday morning it’ll have tracked north west across Ireland bringing some heavy rain here and across The Lakes, south west Scotland. Not a day to be walking up Goatfell me thinks….Some of this rain will work its way into Wales during Saturday and move north and east across the north of England. Draw a line from The Wash to The Severn and north of this is more likely to be wet and south of this drier, but cloudy, though still with temperatures in the low twenties. Some of those showers will work eastwards across The South West and southern half of the U.K later on Saturday. Sunday looks the better day of the weekend with some showers still across Scotland and the north and south east of England but otherwise dry and settled with temperatures in the high teens / low twenties.

Weather Outlook

So as we look to track into the 2nd half of August are we talking heat plume peak or cool and unsettled trough ????…….cue pause for a coffee refill……

Well it is fair to say that opinions are divided on this one between GFS and ECMWF. The former projects that this low pressure trough will continue to stay in place all next week flanked by two high pressure systems whereas the latter has a high pressure plume extended up across the U.K and Ireland and if anything building as we go through next week.

It is a tough one to call but I think if you look at the jet stream it appears to fragment next week and then ultimately lift higher so in my books that means the chances of high pressure pushing warmer, hotter weather for the 2nd half of August have to be higher. So my bet is for an unsettled start to next week but drying up and settling down with similar temperatures to this week. I think as the week goes on though temperatures will pick up into the low – mid-twenties. A bit of mystic Megging but I have a hunch that the last week of August will be a warm / hot one.

Agronomic Notes

So last week I did a quick look back at July 2021 using data from Sean at The Oxfordshire.

Now here’s a more in-depth look at other U.K and Irish locations in terms of G.P and Rainfall….

At first sight you’d be forgiven for saying that July 2021 was a good growing month and in some locations you would be correct in this assertion. A total monthly G.P of on average 28 across our locations out of a possible 31 (31 x 1.0 optimum daily G.P) means we had 90% of optimum growth through the month so temperature was certainly not a growth-limiting factor in July this year. Rainfall was though in some locations and as I explained last week, the fact that most of July’s rainfall came from BOB’s meant that the southern half of the U.K received more rainfall than the north. This is shown clearly on the data above with the two highest rainfall locations being Okehampton at 99mm for the month and Sevenoaks at 110.6mm. In fact Sevenoaks was twice as wet as our Scottish location in Fife, now that isn’t ‘normal’. With a north-south divide in terms of rainfall but reversed in terms of our usual expectations, Scotland had its own mini drought, more on that later….

So for Ireland the first thing that strikes you is the similarity between the U.K and Irelands total monthly G.P for July 2021 with most areas between 27-28 total G.P for the month, so on face value a good growth month. Like some areas of the U.K though, July 2021 had a warm, hot dry interlude that wasn’t interrupted by a BOB event. You can see some locations like Gorteeen and Dublin had some pretty hefty rainfall totals for the month but they bely the actual daily rainfall pattern.

So above we have a graph for 3 locations, each in the south east of their respective country (ish).

You can see they all shared a very dry period from the 13th of July through to the 24th, 25th, when the weather broke firstly in the south and later up country and in the west as an Atlantic low pressure joined the earlier BOB low pressure system. During this dry period, air temperatures were high in all areas ;

Monthly total data is one thing but when it comes to rainfall and particularly summer rainfall of the ‘hit and miss’ variety, total monthly rainfall data often masks some specific rain events be that a localised downpour or a prolonged period of drought. As an example, take the data from Northampton and compare it with my data from Market Harborough, two pretty close geographical locations. Northampton had 2 x the rainfall of Market Harborough for the month of July and that was solely down to two specific downpours of 17mm + on the 27th and 30th of July, both of which we missed Market Harborough, much to Rob’s amusement and my dismay  🙂

Looking at the lower graph, you can see that during the same period most locations had a period when they were dry for 7 days + and the air temperature was close to or exceeded the crucial 25°C limit for Anthracnose spore germination. Of course it won’t be an all or nothing event, they’ll be some spore germination under that temperature. So for some areas of Ireland, England, Wales and Scotland, the middle of July 2021 joined the beginning of June 2021 as a significant Anthracnose trigger event in terms of air temperature and of course plant stress. Thereafter both periods were followed by significant rainfall events associated of course with high humidity. In other words perfect conditions for this disease.

As I always use to say, ‘A’ is for Anthracnose and ‘A’ is for August’, so it doesn’t surprise me that I am starting to get reports of Anthracnose activity at the beginning of August.

It’ll certainly be interesting to see how the rest of the month pans out when it comes to disease activity and specifically Anthracnose.

All the best.

Mark Hunt