November 27th, 2023

Hi All,

Went out on Saturday night after receiving a Red Aurora Alert on the Aurora Watch App but it was a bit hazy and the moon was up. Not just up, but accompanied by a beautiful halo (and a con trail in my picture !). Apparently, a halo around the moon is caused by reflections from ice crystals high up in the atmosphere and like the Cirrus clouds I have talked about before, these mark the leading edge of a warm, wet front.

So despite it being dry and cold, I knew we were due for some rain, 24 hours before it appeared. Clouds are such useful vectors of the weather and we can learn much from them. On Saturday and Sunday morning we had cracking frosts dropping down to -3.9°C just after dawn. On Sunday morning I could see mist and fog lying in the valleys, the cold air trapped by warmer air above. This morning as I type, it's raining and has been most of the night on and off. That Moon halo was an accurate predictor of the weather without need to reach for a Smartphone !

Last week, I wrote that I smelled Winter and this week we may well see our first snow showers, quite some change from 7-10 days ago, when temperatures were in the teens.

Nature has also provided us another clue recently that the weather was heading colder.

This beautiful winter visitor is a Waxwing, a Viking invader from Scandinavia. Waxwing come here along with Redwing and Fieldfare's to plunder our winter berry crop. Now most of the leaves have fallen, you can see how rich that is this autumn / winter. Waxwings travel in flocks and will descend on berry trees in retail parks, motorway service stations and gardens and are a delight to see. This year they are arriving in big numbers and that in itself is an indicator that harsh winter weather lies to the east of us.

The GIF above from tropicaltidbits.com does indeed show why Waxwings are arriving in numbers. A big chunk of cold air lying across Scandinavia and Russia. We can see another interesting feature. The jet stream (dark green band lying between warm and cold air) is no longer in a straight pattern denoting a strong jet stream wind. Rather it is now forming into peaks and troughs, synonomous with a weak jet stream and the potential formation of Omega Blocking Events. These are the same blocking events that can bring us summer heatwaves, warm, humid air in the autumn and sometimes (more rarely nowadays), cold air with snow.

So the scene is set.....

General Weather Situation - w/c 27-11-2023

So we start the week wet and unsettled with lots of cloud cover and probably the mildest temperatures of the week to boot before we drop colder and drier and then maybe some of the white stuff intervenes, though this is accompanied with a premium-sized caveat, as always 😉

So Monday is unsettled with plenty of rain overnight (6-12mm) across the southern half of the U.K, this is moving north and east and will fade into The North Sea later in the day, whilst Ireland sits dry for a change. Some of that rain may fall as sleet and snow over elevation further north. Winds will be from the north with temperatures in the 5-7°C range. It'll be a gloomy, instantly forgettable type of day.

Temperatures should keep up overnight as there should be plenty of cloud cover hanging around from that exiting warm front but that should be an end to the cloud for the time-being as Tuesday and Wednesday promise cold, bright and frosty conditions with temperatures peaking at 3-5°C during the day and dropping away at night towards the -1 to -3°C range dependent on location accompanied by a changeable wind that always tends to have a bit of northerly in it, be that north easterly or straight north.

The tricky part is the end of the week and whether we get a moisture incursion on Thursday night into Friday that may fall as snow. Last night it looked that way, this morning, typing this it is less likely. To me I would say the north east and east are most likely to see some showers slipping off The North Sea and these may well be wintry later on Thursday but I expect the synopsis to change. Ireland looks to have a dry, cold week with a risk of rain later in the week across Leinster I'd say, again more likely across the east of the country.

So Thursday into Friday presents the highest risk of snow but it'll be a changing forecast picture because snow is harder to forecast than rain and we know how inaccurately forecast that can be on ocassion.

So dry and pretty chilly is the majority of the forecast after this warm, unsettled front moves through. The outlook for the weekend sees a rain front push in from The Atlantic Saturday into Sunday, so the west of Ireland and south west of England / South Wales will see rain and slightly milder temperatures move in over the second half of Sunday accompanied by plenty of cloud. Further east I expect the dry conditions to persist through the weekend until the cloud and rain arrives later on Sunday accompanied by a south westerly / southerly wind.

Weather Outlook - w/c 04-12-2023

Tricky I'd say to pick a weather forecast over 5-7 days currently from the GFS but here goes.....

The wet front that is projected to push into the west over the course of Saturday / Sunday is the leading edge of an Atlantic low pressure system that will slowly edge eastwards into Monday so we can potentially expect a wet start to the week across the west, maybe drier across central, northern and eastern areas. Behind this reasonably weak low is a significant Atlantic low pressure set to dominate our weather from next Tue / Wed onwards, so the start of the week will be a calm interlude before this arrives. (if it indeed does)

If the GFS is accurate, we will see the wind switch to south westerly, pick up its strength significantly and then we will be in for a wet, windy, unsettled and potentially milder airstream for the foreseeable.

Big caveats attached to this forecast because it's been changing regularly with every update. This suggests low confidence / low probability.

Agronomic Notes

It's interesting isn't it, perspectives and all that....

I thought for the agronomic component of this blog I'd take a look back at this autumn vs. last autumn from an air and soil temperature perspective using weather data from Sevenoaks, Kent. My gut feel was that we have had a much warmer autumn this year, commencing with the heatwave at the beginning of September and very warm temperatures at the beginning of October.

Well, the data says otherwise (so much for my gut feeling eh ?) and perhaps illustrates why recording data is key vs. a subjective opinion such as my own...

Here's a graph of air temperature from September - November 2022 vs. 2023 y.t.d ;

So you can see that the air temperature during the first part of the autumn in 2023 was indeed signficantly higher than 2022, with the beginning of September and October, key notables. The surprise for me was mid-month when we had 2 consecutive ground frosts and the mean temperature for the day plunged down into mid-single figures. Although it did recover, it then began a 'normal' descent towards typical temperatures for early November. You can then see the peaks of air temperature that provided us with some disease activity. The surprise for me was that once we got past the 20th of October, the air temperature was cooler in 2023 than 2022.

Agronomically the warmer air temperatures of early September and October brought with them high disease activity, particularly from Microdocium and Dollar Spot. Very high Growth Potential as well not surprisingly, so rapid growth and short longevity of fungicides, PGR's and nutrition applications. You'd have used some diesel or some watts keeping up for sure !

Come mid-October, we have been more true-to-type, with a slowing down of grass growth as both the daily G.P and daylength conspired against it and thankfully this extended the application longevity of the afore-mentioned treatments. If you look at the end of the graph you can see the air temperature has picked up today with the milder airstream and cloud cover, but it'll soon drop back down with the clearer skies and frost forecast for this week. So I think come the end of November 2023, our air temperature will pretty much mimic 2022. In a microcosm to me it looks like the early part of the autumn is the real change period temperature-wise but we eventually get to a point where the climate resets and normal service is resumed.

As a point of interest, up until and including the 27th of November, the total G.P for the month at this location is 6.43 vs. 9.52 for the same month last year. I think we will be lucky to finish the month with a total G.P of 7.0, so that's 20% less growth than last year potentially, as measured by Growth Potential.

Let's look at how the soil temperature 2023 vs. 2022 pans out ;

Well very much an autumn of two halves in 2023, with really warm soil temperatures extending right up to the middle of October when we had the first significant ground frosts. Up to then you'd have seen rapid germination of grass seed, be it that Lolium perenne or Agrostis species. Since that date, 2023 has tracked lower than 2022, soil temperature-wise, so that means slower germination and establishment. Interestingly, right at the end of the graph, you can see the soil temperature picking up today as the warmer rain increased the soil temperature. Again this will drop back pretty sharpish as the frosts kick in this week to a lower level than 2022.

Root development and the role of phosphorus

Growing good roots is I think one of the hardest things groundsman and greenkeepers have to do, with some many variables impacting.

For sure it is here where the physical properties of the soil come tothe fore, air-filled porosity, sand, silt, clay content, organic matter to name but a few. Persoanlly, I think nutrition plays a minor role in promoting root development.

Let me clarify that statement ;

For as long as I can remember, phosphorus has been linked to root development, with conventional preseed fertiliser analyses reflecting this. When you look at a grass plant, you are lucky to find 0.25-0.5% Phosphorus in the leaf tissue vs. 3.5 - 4.5% Nitrogen, so the suggestion is the plant can only utilise a small amount of this nutrient. When we look at a preseed or preturf scenario, we are applying a high amount of P to a newly-germinating plant with a minimal root system. It is incapable (IMHO) of utilising that large amount of P physiologically.

We also have to consider the status of 'unavailable phosphorus' in the soil.

When we test for phosphorus in a soil test, we are usually measuring plant-available P, but normally (not always, but normally) we have a 'reservoir' of plant-unavailable P in the soil bound to certain nutrients like calcium for example. This reservoir acts as a drip feed of phosphorus as it is converted by microbial activity. So the actual requirement for P-applications to managed-amenity turf is minimal, except of course if you're in a situation like a calcareous soil / sand (as most of Ireland is), where phosphorus is bound to calcium and rendered mostly unavailable, albeit for the drip feed I have mentioned.

So if we are chasing roots, we should concentrate on managing the physical properties of the soil first and foremost and maintaining adequate but not excessive nutrition, paying particular attention to nitrogen. Excess N will cause the plant to prioritise shoot development over root development, so-called nitrogen partitioning.

The reason this is relevant timing-wise is because of the fact that our air temperature is dropping down to a point when shoot growth will stop for most grass species. We are also rapidly heading towards the shortest day, so light availability is also a shoot growth-limiting factor. All this means the plant is potentially able to maximise root development so it is now when you hope that your soil physics are conducive to this.

The hard bit I know is the high rainfall of late has meant autumn aeration has been difficult to undertake and if the soil conditions aren't optimal you can end up doing more harm than good. So 'if' and I accept it is a big 'if' you are able to use the dry, cold period to aerate, you will definitely be helping root development, provided of course soil conditions are conducive.

OK, that's me for another week, wrap up well and enjoy the winter sunshine :)

All the best.

Mark Hunt