Last week was an interesting week from a forecasting perspective and once again it highlighted to me the frailty of long-term (7-10 day) weather forecasting.
Looking at the forecast for this coming weekend last Wednesday, (so 9-10 days away) we were on for a heatwave weekend and the hottest November temperatures, indeed The Met Office were even hinting at this. Then over last weekend, the forecast changed again, 180°, to suggest we would pick up an Arctic low pressure system which would give us snow showers over the first part of the weekend !!!
Couldn’t have been more different, from 20°C one minute to snow showers and a negative windchill the next. Now it has settled down to 8-10°C and a pretty typical November weekend. So don’t believe the hype when organisations / media look to predict beyond that critical 7-10 day window because in reality, the accuracy is lacking and they’re mostly talking out of their jacksey.
The photo above looking over Rutland Water’s South Arm kind of sums up this week’s weather after the mild temperatures and for some, a deluge on Saturday / Sunday. That is to say, some nice sunshine but always in the background will be a threat of showers 🙂
So without further ado, it is onto the weather, I have a crammers Monday so this will be a shortish blog…
General Weather Situation
As you can see from the GFS output above we have low pressure influencing our weather at the start of this week with some closely-packed isobars, so that means a windy week beckons.
Monday will see a pretty dry and mild start for the U.K on the whole, but for Ireland we have a rain front pushing in from The Atlantic which will make landfall in Kerry just in time for morning rush hour down in Waterville 🙂 This rain will move across Ireland during Monday morning reaching eastern counties of Ireland by lunchtime. Across The Irish Sea it will be dry, cloudy but with some breaks in the cloud especially across the east / south east of England, which is nice because we need a drying day there after the inch of rain or so that fell over the weekend. Through the afternoon that rain continues to affect the east of Ireland and crosses The Irish Sea to make landfall in The South West and West Wales. This rain is moving in on a south westerly wind which gives it a north easterly aspect so it’ll push into Wales, the north west of England and south west of Scotland by dusk and move across northern Britain through the course of Monday night. A strong south westerly wind so that means mild (ish) temperatures in the 9-11°C range and remaining dry for the east of England.
Overnight into Tuesday and that rain has cleared the U.K to leave showers behind on western coasts. The far north west of Ireland will see more rain and this will push into the north west of Scotland through Tuesday morning to give some heavy rain there. Through Tuesday morning we will see further showers over the south west / north west of Ireland and Wales / The South West but further east from this looks to have a dull, mild and windy morning. So showery across the south west / south / north west coasts of Ireland, wet across the west / north west of Scotland and remaining showery across Wales and the north west of England. Further inland we may see the odd shower but largely dry, mild and windy with a fresh to moderate south westerly wind in situ.
Wednesday sees a more consolidated rain front push into Ireland through the early hours so a wet start to the day there. This rain will also link up with the north west / west of Scotland to give a wet start to the weather there as well. As we go through the morning this rain front clears Ireland from the west but pushes into the west of the U.K and moves eastwards with showers reaching The Midlands and London area around lunchtime. So a sunshine and showers afternoon for Ireland after a wet start and remaining wet across the western half of the U.K through the afternoon with that rain pushing across Central Scotland and The North East later in the day. Some of those showers will reach the east and south east at dusk but will have lessened in intensity by then. Again a strong south westerly wind in situ keeping temperatures on the mild side, with 12-14°C, likely and maybe a degree or two down across areas affected by the heavier cloud and rain. As that rain clears away, it’ll leave behind it some clearing skies and a cooler night for some with temperatures down into single figures.
Thursday sees low pressure exit stage right and that means a drier day (but not totally dry) beckons and also a cooler one, courtesy of a change in the wind direction to north westerly. Some showers will plague the North Wales / Merseyside area through the morning but on the whole a dry day with sunshine and with a decreasing wind strength. Much cooler than of late though with that wind direction so expect 8-10°C. With lighter winds and clearing skies, temperatures will drop on Thursday night down into low single figures. Ireland will see the wind switch round again to a south westerly as a new rain front pushes in from The Atlantic around dusk on Thursday. This will push across Ireland through Thursday night into Friday morning.
No surprise then that Friday looks to be a more unsettled day with showers / heavy rain from the off across the south west of Ireland and the southern half of the U.K, really from The Humber south I’d say. Through the morning we will see some brighter spells of sunshine along the east coast of the U.K / Scotland whilst more rain pushes across Ireland and into the western half of the U.K. This band of rain moves eastwards across most areas through the latter part of Friday with some potentially heavy rain for the west / north west of Scotland to end the day. Lighter winds on Friday swinging in from the south but it won’t aid the temperatures as it’ll remain chilly, but typical of November temperatures with 7-9°C likely across the U.K, but milder across Ireland with temperatures in the low double figures.
The outlook for the weekend looks like 20°C temperatures with the odd snow shower…:)
And on a serious note, Saturday looks like being wet initially for Ireland and the north west of the U.K with a band of rain moving south and east through the day. The north and west side of that rain band will be cool and sunny once the rain has moved through but south and east of it will be cloudy and dull. That rain might not reach the south / south east until later in the day on Saturday so a dry if a little dull day beckons there. The wind strengthens on Saturday to a strong to moderate westerly and that’ll keep temperatures down to 9-11°C for most. Scotland looks to have a wet start, especially across the west, but this will improve through the morning to leave showers behind across the west later. Sunday sees lighter winds and a drier day for some but still with showers across the west coast of Ireland and Scotland. Some of those showers across Scotland will be wintry in nature on higher ground. A dry morning I think for England and Wales though we may see some showers across The North West and later some showers will move across Wales into western England later in the day. For many though a dry, cool day with some winter sunshine.
A bit of a west-east split next week as a column of high pressure protects the eastern side of the U.K, whilst low pressure buffets Ireland and the west. So Monday looks to start cool, dry and reasonably quiet on all fronts with little in the way of rain around. Maybe misty / foggy with light winds. As we go into Tuesday, low pressure pushes rain across Ireland but as the low butts up against the high, it’ll move this rain north and east into the north of England / Scotland later on Tuesday, so the south and east will likely stay dry. Wednesday sees this pattern continue but a more determined low pressure pushes in on Thursday and that’ll make progress eastwards bringing rain into Wales, England and Scotland during the day. A brief hiatus on Friday with cooler and settled conditions for all before an intense low pressure pushes in from The Atlantic to bring very strong winds and rain next weekend if projections stay on track.
I know we / I talk about this alot but…
Last week represented some of the most sustained disease pressure we have seen so far this autumn with November representing in reality a much higher disease pressure month than October. Although Ireland and the west shared this higher pressure there was actually a west-east split due to the presence of a continental high pressure over Europe and a low pressure pushing in from The Atlantic. The GFS output for 11th November (when the disease was at its height) across central and eastern U.K shows this split nicely…
So when you look at disease intensity from 7th November last week, you get some quite different outputs depending on whether you are located in the west, centrally or in the east. (I don’t have a location for Scotland in order to generate data at this point in time but hope to remedy that soon enough). I am also very aware that having worked farming in Scotland from Dumfries to north of The Black Isle as a ‘wet behind the ears ag seed rep’, you’d probably need 5 to accurately describe it and my budget just doesn’t stretch that far for Davis weather stations !!!!!!!
So here’s our projected disease pressure for w/c 7th November up until yesterday for sheltered locations (so it is a worst case scenario) and just look at the difference in terms of periods of intensity between locations…As a rough rule of thumb, anything above 60% is likely to correlate with visible symptoms.
You can tell when the disease pressure is high because last week we saw mycelium on domestic lawns and on approaches, tees and fairways, so the forecasting shown above was accurate 🙂 or 🙁
I also saw the now very familiar dynamic of active disease on areas well under fungicide control. The image below from a site in Essex is an area of Poa / bent turf that was at G.P = 5.0 in terms of the cumulative G.P since a fungicide was applied. (If you like working in GDD that would be roughly 55-60 estimated total GDD since a fungicide was applied using a 6°C base temperature)
So you can see multiple areas affected by Microdochium nivale but in reality I would say most of this will not end up with deep scarring and here’s the reason why.
Firstly, consider the fungicide / disease dynamic going on in the above picture by looking at the disease triangle graphic below…We have a susceptible host (poa annua mainly but not exclusively), a pathogen present and a very favourable environment, that of high air temperatures and almost continual dew formation on some days last week. In other words every box is ticked in terms of favouring disease development by the turfgrass pathogen, in this case, Microdochium nivale. So this means if you already had existing disease scars present in the turf at the beginning of last week, there is / was every likelihood that these showed new activity around the periphery.
We also have two other dynamics that impact on this situation ;
Now the fungicide actives we have available to us currently are not curative, that is to say they don’t work late into the cycle of disease development and so once you have active disease they will not eradicate it. What they are doing is slowing down the reproductive capacity of the disease. So on the one hand you have climatic conditions driving disease development and on the other you have the fungicide slowing its growth potential. Now when we see disease pressure like we saw in some locations last week, the balance is tipped very much in favour of the disease vs. the fungicide, so even though the turf has been treated, you can still see disease developing but not at the rate it would have done without a fungicide application. Now some of you might blame the ‘inadequacy’ of the latest fungicide technologies to resolve this situation but in my view you’d be wrong. Cast your mind back over the last 10 years and I reckon I can remember this happening when we had Iprodione, Propiconazole, Chlorothalonil and the like. Maybe it happened less often, but happen it definitely did, so don’t point the finger at the fungicide on its own.
Of course there’s a flipside to the ‘climatic conditions favouring pathogen growth’ coin and it is the fact some of the same conditions that favour pathogen growth also favour grass growth, i.e air temperature for one.
Looking at the stats for November 1 – 15th, 2020 from the same location as the picture was taken from above, we can see that we also had very good grass growth conditions during the same period that the disease was developing.
Anything around 0.35 – 0.4 daily G.P represents good grass growth for the autumn / winter / spring and in the image above we can see that is was equalled or exceeded on 10 of the first 15 days of November. So in other words the grass was growing out the disease as fast as it was developing or nearly as fast maybe. This is when we enter into the ‘applying a PGR later into the year on greens’ debate. The ‘pro’ side of the debate will probably claim that you see more longevity if you regulate grass growth later in the season from applications made to the turf be they non pesticidal or pesticidal. The ‘cons’ side would state that by regulating the turf you are increasing the severity of damage because you aren’t growing the disease out. I think I sit in the ‘cons’ side on this one because I believe Mother Nature is in most instances a pretty effective PGR be that summer stress-related or growing out disease scarring.
It is an interesting debate for sure and as always I’d be interested in your experiences from a disease control / PGR perspective, good or bad.
To finish on a positive slant it looks like the stronger wind strength and cooler night temperatures from mid-week onwards will drop disease pressure back significantly so this should enable your fungicidal control to kick back in again as the balance redresses.
OK, that’s me for another lockdown week, all the best to you working away in this current situation. Stay safe and healthy.