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  • Writer's pictureMark Hunt

March 27th

Hi All,

Well in the blink of an eye it seems, March is nearly over. Last week we had the Spring Equinox which marks the point when the sun crosses the equator from the southern hemisphere to the northern hemisphere and our days stretch out significantly. As we know the weather doesn't read the calendar and so this week we will continue March's impression of February, that is to say, more significant rain is in the forecast. Thereafter it does look like our general weather pattern is changing. Tricky to say if its for the better but I am wondering if we are still seeing the effects of February's SSW event because the GFS longer-term is pointing towards a reversal of the normal flow of the jet stream. That doesn't normally bode well as easterlies are associated with this process. We will see.....

Nature is definitely on the move though regardless. Last week I saw 2 Osprey's return to my local fly fishing venue, Eyebrook reservoir. I also saw the first Sand Martins on the water on Saturday and there are reports of Swallows as well. Chiffchaff's are singing in the tree tops, another spring migrant, so whatever the ramifications of the weather, nature is ploughing on regardless.

Danish Sea Scurvy (Cochlearia danica) is now in flower along the edges of roads, dual carriageways and motorways. This plant is a prolific invader of bare soil and a halophyte (salt tolerant species) so you often see it colonising the area that has been affected by salt splash along the sides of the road.

I use it as a marker of a certain GDD figure so later I'll take a look at how we are progressing in this back-to-front year when February was warmer and drier than March at times..

General Weather Situation - w/c 27th March

If you look closely at the top animated GIF above, you can clearly see the change that takes place at the end of next weekend as the jet stream looks to split and reverse direction with weather systems moving more east-west than west-east as we would expect. This process is almost always associated with easterly winds which in April are seldom welcome from a turfgrass management perspective.

So we start the week with probably one of the driest days as the low pressure that gave us sunshine and blustery showers over the weekend has moved off east and the next one is out in The Atlantic. Dry but cool with a ground frost in places with light and changeable winds blowing initially from the north. With light winds, temperatures will pick up during the day to 10-11°C. So a pretty non-descript day with rain arriving late in the day to the south west of Ireland.

Tuesday sees the wind swing round to the south and pick up strength. This heralds the arrival of slightly milder air and rain. This rain arrives on Monday evening to the south west of Ireland and overnight it crosses Ireland and moves into the west of the U.K, pushing quickly across all areas and largely clearing Ireland as it does so. It'll clear from the south and west so the north and Borders will hang onto rain into dusk but further south we will see some dry periods in the afternoon as will Ireland, though the west will stay pretty murky. Despite the change in the wind, it'll remain on the cool side at 9-10°C.

Wednesday sees more rain arrive into the west / south west of Ireland and England. This rain will slowly cross Ireland through the day and across The Irish Sea, it'll move slowly north into The Midlands, northern England and eventually Scotland. As we approach dusk, we see heavier rain push into The South West and Wales, with Ireland clearing from the south and west. This band of heavy rain will move north and east across all areas overnight. Winds will be more south westerly and it'll feel a lot milder with temperatures pushing up towards the low to mid-teens.

Thursday will see that main rain push eastwards and clear the U.K by dawn leaving behind showers across western coasts of Ireland and the U.K. These westerly showers will begin to push inland through the course of the day to give a sunshine and showers day with a moderate south westerly wind and mild temperatures pushing up towards 15°C.

Friday is a BOB day (Bay of Biscay low pressure system) meaning a southerly-orientated low pressure system is due to swing into The South West in the early hours of Friday morning. By dawn it'll cover the southern half of the U.K with the north, Scotland and Ireland missing most of this rain. As we progress through Friday this low pressure moves very slowly eastwards clearing The South West during the afternoon. A slow-moving low pressure tends to me high rainfall totals. As we approach late afternoon, we will see rain across Ireland and this low push into Scotland with a very wet end to the day for eastern areas of the U.K. A little cooler on Friday as that wind swings round to the north west with 10-12°C typical.

The outlook for the weekend is changeable with sunshine and showers and feeling notably cooler for the 1st day of April. On Saturday, the east of the U.K will still see some showers but Ireland and the west will be largely dry save for some afternoon showers and a chillier north westerly wind. Sunday sees rain still affected areas with a slow-moving, narrow band of showers moving south and west into western areas during the afternoon. Some areas will be dry but it'll be cool and dull with that north westerly wind still in situ.

Weather Outlook - w/c 3rd April

So we start next week cool, dull but crucially dry I think with light easterly winds. The first part of next week looks like staying the same, cool, dull and with light easterly winds so I'm expecting temperatures to be in 8-10°C region and if we keep cloud cover, frost-free. As we approach the end of next week the winds look to swing more northerly and that'll pull down showers, some of them wintry I think for the eastern side of the U.K. So the run up to Easter weekend at this stage looks cool, dull and showery with a easterly / northerly / north westerly wind in situ. Thereafter is Mystic Meg territory but I think we remain largely dry before the next big Atlantic low pressure swings in with strong south westerly winds and better temperatures. Now I would say that the Easter outlook could well still change as projections are showing low probability but if I was a betting man I would still go for cooler and unsettled.

Agronomic Notes

At the beginning of this blog I eluded to the flowering of Danish Sea Scurvy on the edges of our highways and to a certain GDD figure. Well normally I see this plant flowering at around 100 cumulative GDD from January 1st using a 6°C base temperature) and that is exactly the case this year.

Predicting flowering was one of the main reasons Growth-Degree-Days came to be because in horticulture, growers wanted to phase their crops of flowering plants. No point in them all flowering at the same time as they'd have a glut to sell. They learned that by exposing their plants to a certain maximum and minimum temperature (and so GDD) they would flower predictably and so they could phase flowering by altering the temperature to alter the total GDD figure.

We only have one flowering plant to concern us most days and that is Poa annua, a prolific seeder depending on the biotype. The annual biotype is a coarser, clumpier plant with pale leaves and it produces a lot of seedheads. It is usually the first to invade bare soil so you tend to see more annual biotypes on areas of your greens that may thin out during the year (wear pathways, disease and drought-affected areas are typical). It will seed all year round but I tend to see it commence seeding in the spring around 130GDD counting from January 1st and using 6°C as a base temperature in the GDD calculation.

So whereabouts are with this year GDD-wise compared to 2022 ?

Well my hunch was that we were ahead after a mild start to the year in January and some mild interludes in what was a very dry February. On the 26th March, 2022, the cumulative GDD figure was 114, on the same date this year, it was 124, so we are ahead.

Below is the graph of cumulative GDD for 2023 vs. 2022 using our default location at The Oxfordshire, Thame.

So you can see how 2023 got out of the traps quickly in January and then the graph took on a flat characteristic. When a cumulative GDD graph is flat it effectively means no more GDD are being added on day to day so you can very quickly identify cool spells. Conversely when the graph is picking up consecutive daily GDD, it will show an incline.

To put this into practice, I have graphed out both years and highlighted growth days in green and non-growth days in blue (because it would be too cold for growth).

You can hopefully see quite clear differences between the two years and the block of cold weather during late February and March in 2023 most likely attributable to the SSW event that took place this year.

The interesting point will be to continue this graph on through April and see when we hit the point I normally associate with the commencement of the perennial Poa annua biotype seedhead flush - 180 cumulative GDD at this location. This point varies dependent on your dominant Poa biotype and of course your location, which is why you shouldn't look on Social Media and be influenced by what other people are doing whether that be applying PGR's or nutrition. Your site, your sward, your grass is location-specific.

In the above comparison I said we were slightly ahead in 2023 than 2022 from a cumulative GDD perspective but if you actually count the number of green days (growth) on both graphs, there was actually more in 2022 than 2023, so we can deduce that 2023 has given us less growth days but when they have occurred they have been warmer days than in 2022.

Smith Kerns Disease Probability Model

Warm enough of late to pick up some positive numbers from March 21st to 25th, using the Smith Kerns Dollar Spot Probability model. See below using data compiled on Prodata Reports from a Davis weather station at a golf club in the east of England. Not high enough yet to raise any alarm bells but one worth keeping an eye on.

OK that's me for another week.

Next week's blog sees us nudge into April and by then I should have a pretty good idea how Easter's weather is shaping up.

All the best.

Mark Hunt

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