November 22nd, 2021

Hi All,

A tad frosty out there today as winter finally begins at the end of November with the predicted decline in temperatures kicking in yesterday. We are still on track for some pretty gnarly weather at the end of the week / weekend so this cold spell looks like it’ll be round for awhile which is no bad thing as nature needs a reset. Soil temperatures are typically 4-4.5°C higher than normal for this time of year and that’s been driving worm activity but happily they’ll be taking a nosedive as we progress through this week to somewhere like ‘normal’.

Winter flowering plants are about 4 weeks ahead of themselves with the first flower buds visible on my Helleborus Orientalis, so a run of frosts and cold days will set everything back to where it should be. Mind you, there’s less than a month to the shortest day, tempus fugit and all that…..

General Weather Situation

So we start the week in a reasonably settled situation with Atlantic high pressure out to the west of the U.K and a continental low sitting to the east. As we felt yesterday, this will have the effect of squeezing the wind down between these two pressure systems in a northerly direction and this was the catalyst to the temperature drop. So the weather picture for Monday is pretty dry, bright and sunny after a frosty start for many. There’s a few showers drifting around across the south of Kent and out to The North East but otherwise we are settled. Temperatures will creep up from their currently low single figure status to around 6-8°C, but no higher and drop quickly once the sun sets behind the horizon at around 4 p.m. Winds will be light and from the north / north east.

After an overnight frost, a very similar weather picture for Tuesday. Overnight frosts, clear skies and a dry, settled winters day with light winds possibly swinging round slightly to the north / north west. Otherwise, a nice winters day.

Overnight into Wednesday and we see the first signs of change as low pressure begins to push down from the north west. This will introduce rain to the north west and Central Scotland first thing and to the north west of Ireland. This diagonal band of rain will drift southwards through the course of Wednesday moving across Ireland during the morning and pushing down into The Borders and Lake District later by midday. This rain front will push more cloud in front of it during Wednesday and bring rain to North, Mid- and South Wales for the second half of the day, taking its time to reach the latter. Despite a swing to a more westerly wind, the origin of that wind is in a cold frontal system so it’ll feel pretty cold on Wednesday with temperatures struggling up to 5-6°C.

Moving onto Thursday and that rain drifts down across The Midlands overnight and through the south of England. I don’t expect it to amount to much. Thursday sees a return to a dry, bright and frosty picture with clear skies kicking off the day and low single figure temperatures. And that’s the way it looks to stay through Thursday, sunny, bright and cold with a pronounced northerly wind with accompanying windchill pegging temperatures back to 5-6°C.

Closing out the week on Friday and if you remember from last week’s blog, this was Armageddon Day according to the Daily Mirror with -7°C forecast and blizzards for Scotland. Well it’ll be cold and wet but not like they forecast so they were probably 30% accurate two weeks out. About par for the course really. So Friday sees a band of heavy rain push into the north of Scotland early doors and this will quickly move south across all of Scotland and push into the west and north of Ireland during Friday morning’s rush hour. By midday this rain will be into the north of England and North Wales and be pushing southwards, so an unsettled end to the day for the southern half of the country. Ireland will it looks miss most of this rain after the initial wave on Friday morning.

If you look at the Meteoblue GIF for Friday 18:00, you can see wintry showers breaking out over Scotland with elevation getting a nice coating I’d suggest. You can see the orientation of the low pressure system with the lower end trailing across the south of England and the upper end pushing further rain and wintry showers down into Scotland and the north of Ireland. Some of these wintry showers will push southwards into The Lakes, across The Pennines and maybe into The Peak District overnight into Saturday. So Friday is a pretty manky day with a cold wind, lots of cloud and rain / wintry showers dependent on your location. Lot’s of cloud cover as well though it may brighten up for a time across the north between the rain fronts, but it’ll be temporary in nature.

So Saturday looks better for Ireland and Scotland with clearer skies and less risk of showers whereas the southern half of the U.K may see more in the way of showers as that low pressure system slips south. Sunday sees the boot on the other foot as rain pushes into Ireland early doors and across Scotland. Again some of this moisture will fall as snow across elevation. This band of moisture will cross The Irish Sea into Wales and northern England later on Sunday to give a pretty wet end to the day there. As this band of rain / wintry showers moves south on Sunday it’ll push into the north of England and The Midlands, so maybe a bit of a dusting there as well and further south overnight into Monday before it slinks out into The Channel. Sunny and bright then for England and Wales on Sunday before that moisture arrives, unsettled for Ireland and Scotland. 4-6°C likely with a cold westerly wind, veering northerly the further north you are.

Weather Outlook

Quite an impressive trough pattern when you look at it projected for the start of next week and that sets the tone really for what will be a chilly week, especially for the east of the U.K, as those cold winds rattle down some wintry showers and a pronounced windchill to boot. Now it is early to comment on the characteristics of winter but to see a cold air trough pattern at this time of year is what we would normally associate with a cold winter. If you remember back to 2010, we started what turned out to be a very cold winter at exactly the same time. This one isn’t the same and I  am not suggesting that, but it is the tendency for a cold air trough formation that has caught my interest.

So next week looks to start cold and unsettled with plenty of rain and wintry showers for Monday and Thursday, pushed down on a north west wind so my gut feeling is that we are talking more rain than sleet and snow in this forecast. Around mid-week, next week, the wind changes more northerly and that will lessen the showers but drop the temperature with some night frosts. The weather picture looks to change again at the end of next week as a northerly low pressure nudges in heavy rain on westerly winds so I think we will move to some milder air, stronger winds and a sunshine and showers type outlook for the weekend after next.

Agronomic Notes

Soil temperature from 1st September, 2021 – Location – Great Dunmow

As you can see from the above chart, the soil temperature has stayed really high this autumn compared to previous ones. Normally around the beginning of November it takes a step down to 6.0 – 6.5°C sort of territory, but this year in early November it was 8.5°C at the beginning of the month and then began to climb again, reaching a peak of 13.9°C on the 11th of November !

There’s been only one year when we have seen similar to this and that was 2015, when we had an exceptionally long run of mild and wet weather which continued all the way through to January 2016 with no drop in the temperature at all. This autumn has been different and maybe it is a sign of things to come in that air and soil temperature will continue to stay high later and later into the year until we go through without a step down that will occur later and later.

It’s no surprise then that earthworms have remained active for a much longer period this year with the elevation in soil temperature much later in the season.

It’s been a bit of a dull one ?

With it being mild and all, it’s also been cloudy and that means less light has been reaching the grass plant.

I did a bit on DLI (Daily Light Interval) back in September when I was looking at the amount of light reaching the plant in a shaded environment.

You may remember this graphic indicating the respective light requirements of the different grass species we work with ?

So it is a kind of scale of grass species going from high light (and therefore high DLI) requirement on the left through to low DLI requirement on the right.

Reproduced courtesy of the USGA Record

For me I think there’s still some questions to be answered here, particularly on Browntop bentgrass’s DLI requirement vs. Poa annua for instance. I’d love to see some hard and fast data here substantiating the lower DLI requirement on Browntop vs. Creeping Bentgrass because if it’s true then this offers a much better over-seeding option in terms of out-competing Poa annua during the winter months of low daylight length.  That is because we know Poa annua has one of the lowest DLI requirements of any grass species (that we work with) and because of this it grows better in the winter, it grows better in the shade and it grows for longer across a year because it grows at light levels which other plants don’t. If for instance Creeping Bentgrass has a DLI requirement of 30 and Perennial Ryegrass of 14, then you can see how both grass species would begin to suffer as we go into the autumn / winter when you look at the graphic above showing daily DLI totals for this autumn from our Great Dunmow location ;

So you can see we are a long way from the comfort zone for Creeping Bentgrass and more surprisingly to me, for Perennial Ryegrass.

Surprising because you can see a good number of days in November and even going back to September when we failed to hit the optimum level for ryegrass growth in terms of its requirement for light, which then fuels energy production, which thens fuels growth.

As the days get shorter then we see two characteristics that contribute to this low daily DLI level regardless of the weather – Shorter days and lower light levels reaching the grass plant in general.

You can see this quite clearly when you compare the DLI per 15 minutes (reporting interval on this Davis Vantage Pro2) on the 21st November compared with the 25th of July. In July we see the DLI readings commence at 05:15 vs. 07:30 in November, they reach a peak value of 1.27 vs. 0.595 (so roughly 50% less light at peak DLI) and whereas in the summer DLI keeps going right through to 21:00, on the 21st of November, it finishes at 16:00 when the sun sets or pretty close to it. So give or take a few minutes we have 15 3/4hrs of light exposure on the July date  vs. 8 1/2 hrs for the November date.

All to be expected in some ways but I’m still surprised that some of our daily DLI levels have been so low. Interestingly today it has been a bright and sunny day so far and then DLI total up to 13:30 is 8.8, so maybe we will just reach a total DLI of 11.0 for the day, still well below the claimed sufficiency level for Perennial Ryegrass and way below that required for Creeping Bentgrass. Now of course it isn’t a cut-off, i.e below that the plant doesn’t photosynthesise efficiently, it is a question of the level of photosynthetic efficiency. I’ve seen for myself species of bentgrass looking healthy at barely double figure DLI’s, when they had a bright, sunny day in the middle of winter and looking a bit sad when it’s been dull, cloudy and wet.

When we look at the bigger picture of out-competing Poa annua in a shade environment or just in general, we can see we are likely to be on the back foot when DLI values start to head south (with the sunshine :)). Now what we need is a grass breeder to publish some good data on the DLI requirement differences between cultivars to make selection a whole lot easier.

Food for thought…

All the best.

Mark Hunt