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  • Writer's pictureMark Hunt

December 18th, 2023

Hi All,


Well, my last blog of 2023 as we lumber up to the Winter Solstice at the end of the week. This marks the shortest day and thereafter we slowly make the return journey to longer days and spring.


We have had some lovely sunset and sunrises of late, real beauties and a pleasure to behold.



Out walking around Rutland's Hambleton peninsular late in the afternoon, I experienced one such sunset and an additional treat. Passing through a copse I heard a Tawny Owl, so decided to try and call it in using my own version of their hooting calls. Below is a clipped video (sorry for the swear word half way through) where I ended up successfully calling in 3 Tawny Owls to within 50m. I was taught it as a youngster and perfected the art whilst sitting out in The Fens night fishing for Zander. It was a great way to pass the time between runs or sometimes nothing at all. Brill fun :)



Back to the weather and currently we are sitting under the protective shelter of high pressure as predicted last week with some drier weather and crucially, some drying winds over the weekend slowly correcting the weeks of unrelenting rain we have experienced. Late last week the forecast over the Christmas period changed so below is how we look up to and including Christmas Day.



General Weather Situation - w/c 18-12-23


So one of the features of this coming week will be the strong and at times blustery wind. This strong wind will continue right through to boxing day when it will relent for a short while. It will continue to be a strong westerly so that means a very mild airstream pushing through the Christmas period until we get to Christmas Eve when it'll pick up a touch of north in it and that'll drop the temperature significantly, with a chance of some of the white stuff up north.


We do have some rain around with a significant band moving across the south of Ireland overnight and pushing into the southern half of the U.K early tomorrow (Tuesday). This rain will affect Wales and England with northern England and Scotland missing the worst of it thankfully. Now this will probably be the heaviest rain to affect the Ireland, Wales and the southern half of the U.K this week, but Scotland will see persistent rain into the north and north west and this will filter down some showers into the north west / north of England on Wednesday and later in the week as well. The next tranche of significant rain arrives into Scotland on Friday and then moves south across Ireland, England and Wales on Saturday. This will clear by Sunday morning but it will leave behind some showers across the north west of Scotland and England and these could turn wintry over elevation.


Temperature-wise we will remain mild all week across Ireland, England and Wales with temperatures into double figures, 10-12°C typically during the day and remaining mild at night. Normally this would be a recipe for Microdochium activity but the strong wind will hopefully keep the leaf dry and that'll put a mocker on its progress. Scotland will be a couple of degrees down on this through the week with the heavier cloud cover and share of the rain.


Come Sunday and that's the change day with the temperature dropping off markedly into low single figures for Scotland during the day and 6-7°C for Ireland, Wales and England. As we approach Christmas Day, the winds will drop back and we will have a quieter state of affairs wind-wise through Christmas and Boxing Day (St Stephens Day) before a new low pressure system pushes in from the Atlantic.



Weather Outlook - w/c 25-12-23


As the GIF above from tropicaltidbits.com shows, next week starts with a cooler outlook particulary over Scotland and the north of England. The wind is north westerly and picking up some Arctic air, so I think snow showers for these areas could be a feature of Christmas Day. As we move through to Boxing Day / St Stephens, the wind will swing round to a milder south westerly trajectory as an Atlantic low pressure system moves in. This will bring rain and wintry showers to most areas on the 26th, pushed along by a strengthening north westerly wind. If anything that wind will become even stronger on the 27th, particularly over Scotland, Northern Ireland and the north west of England, together with significant rain, sleet and snow over elevation for these areas. Further south we will remain windy but probably miss the worst of the wet stuff. As that low passes through, its trailing edge will pull down some cooler winds on the 28th, but this looks a mainly dry day initially, so perhaps a good one to get out and work off some Christmas calories first thing :). Later that day, rain will push into Ireland from the south and cross The Irish Sea overnight to move into the southern half of the U.K. The Friday to Saturday on the run up to New Years Day looks very wet and windy with a milder south westerly airstream but as we approach the start of 2024, the wind turns northerly and much colder air pushes in for New Years Eve. It's a long way away but if this forecast holds, I wouldn't be surprised to see snow to lower elevations and some pretty gnarly windchill accompanying it. Watch this space.


Agronomic Notes


Plant Leaf Wetness & Disease Pressure


Last week / weekend passed with some notable mild nights and high humidity and I'd expect that Microdochium responded accordingly. This time of year, high pressure systems are a double-edged sword, yes they bring drier, more settled conditions but if the system vectors up mild, humid air from the south, they also bring heavy dews and elevated levels of disease pressure.



I have charted out some leaf wetness data from a Davis sensor hooked up to a 6820 Vantage Pro weather station. This sensor records a value between 0 (dry) and 15 (saturated) to mimic plant leaf wetness with a reading > 8.0 suggesting dew formation on the plant leaf. This is measured on the vertical axis in the graph below which shows leaf wetness levels over the last week. You can see as the wind increased during the weekend, the period of leaf wetness shortened and then reduced to zero.



Looking at the week ahead the wind will be with us right up to Christmas Day and so that might make it tricky from a spray window perspective, however it'll also aid in leaf dry down, even if we have some rain, so it is also a double-edged sword. The threat may come on the 26th and 28th December when the wind is projected to drop and we may then see dew formation and increased disease activity. Hopefully you'll have been able to get a preventative treatment down in readiness.



Light levels (Plant available that is.....)


I have touched on this subject before but it was brought back to me recently when I looked at the house plants in my living room. The back of my house is in shade and from the end of November to the end of February seldom sees sunlight. Every winter my houseplants look sad so this year I decided to give them an early Christmas present by purchasing a Gathera Indoor Plant Grow Light which provides plant-available radiation (PAR light), specifically within the range of 400-790 nm (blue, green, yellow, red light). It has a timer function and I run it for 3 hours a day.


Boy has it made a difference, even the notoriously tricky Poinsettia (Christmas Rose) is happy though that also has to do with only using rainwater to water it and a low boron soluble feed (they are very sensitive to Boron levels and require good levels of manganese, magnesium and zinc else they show intervenal chlorosis on their leaves).


So that got my mind thinking, with this autumn being so wet, have light levels been noticeably lower as obviously more rain = more cloud cover ?


I charted out daily DLI levels from a Apogee PAR light sensor in Central England and compared autumn 2022 with autumn / winter 2023 to date.


The results surprised me ;



Surprisingly (to me) the results show very similar light levels comparing 2023 with 2022.


One feature of these graphs that did intrigue me though was the noticeable dip once we got to the 20th of October. It ocurred in 2022 and 2023, so I don't think it is just a weather phenomenon.


More likely to do with the distance we are from the sun maybe ?


What it means agronomically is that once we get past this date we are seeing low levels of plant-available light radiation (PAR) on a daily basis. So if you are overseeding for example, you ought to think that past this date there will be very little plant-beneficial light for the newly-emerging seedling. This goes for Bentgrass and Ryegrass in particular.


The monthly totals of plant-available light radiation measured in mols per m2 are shown below, remembering that the total for Dec 2023 is for a part-month :) !


Not as much difference year on year as you might think though October '23 was noticeably lower than the previous year. If you just work out a rough daily average though, you get the gist of my argument regarding the drop off after the end of October.


A monthly total of 178.1 mols per m2 for November works out as 5.95 mols per m2 per day. Given that the sufficiency level for Lolium perenne is 11 mols per m2 per day and Agrostis stolonifera, 30 mols per m2 per day, November's average daily DLI reading is well below what is required for a healthy grass plant. I'll keep an eye on this and follow it through into 2024 to see when we reach an uplift.


All that remains for me to do is to wish you a peaceful Christmas and all the best for the coming year. Thanks to everyone who has taken the time to follow my weekly ramblings, submit data and / or send a comment. It is appreciated.


All the best.


Mark Hunt


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