March 24th, 2025

Hi All,

I saw this fantastic graphic (below) which illustrates nicely some of the key weather events that have effected us over the last 12 months. The graphic compares temperature, rainfall and sunshine for the last 12 months of 2024/2025 with the 1991-2020 anomaly.

It highlights the very few months that were warmer than the 1991-2020 anomaly (note how the north and Scotland were much warmer in May 2024 than further south), how many months were duller and how for many areas of the south and Wales, September 2024 was the wettest month of the year. (courtesy of a cut-off low pressure system)

Reproduced courtesy of The Met Office and https://weatherquest.co.uk

What it doesn't show is a gradual upward progression in temperature in line with the global increase and that's entirely because our weather and that of Ireland and parts of Europe are subject to the vagaries of the Sub-Polar jet stream. How the jet stream behaves dictates our weather and how it behaves isn't a constant.

When I post each week the GFS animated GIF for the next 7 - 14 days, you can see the path of the jet stream. It's at the boundary of the cold and warm air and is portrayed as a dark green line.

This spring we have seen a lethargic jet stream for many weeks. When it flows slowly, it creates peaks and troughs and many of these result in so-called blocking events. (read about them here). During blocking events in the spring, we often pick up a run of easterlies and I can see this happening again as we move from March into April (predicted a month ago after we recorded successive Sudden Stratospheric Warming events). Spring easterlies are hard work from a turf management perspective as they are often dry and cold.

That warmth triggered off some thunder storms this past weekend with markedly localised rainfall. I left home on Saturday afternoon with a light drizzle only to arrive at Rutland Water in a full-blown thunderstorm. As I started fishing into dusk, a cool air inversion event descended on the reservoir as cool air immediately above the water caused water vapour to condense into an eerie mist. At one point it gave the impression that the famous Normanton Church was floating just above the water. Beautiful. I fished into dark and encouragingly as I caught my quarry, I was surrounded by feeding Bats and hooting Owls, lovely. And people ask me why I go fishing...well I connect with nature in a way few people do and boy is it good for my mental wellbeing 😊

Weather radar from Netweather.tv Rainfall data -Davis Vantage Pro weather station - Northampton County G.C

Not so lovely (although I'd argue that it would have topped up some after a drier than usual spring) was the very localised storm event over The Midlands. It was exceptionally localised and carried with it some violent rain rates topping out at 145mm per hour and depositing nearly 30mm of rain. Less than 5 miles away, areas received 3-5mm. Now try and forecast that (and no one did accurately BTW)

So after a blast of spring, how are we looking for this week and next potentially ?

General Weather Situation - w/c 24-03-2025

So this week for Ireland, the U.K and Denmark, we have high pressure sitting below us so that is pulling westerly winds across the U.K and Ireland. Above us sits cooler and more unsettled air and so we will see a pattern of sunshine and showers for the first part of the week, with more in the way of showers for the north and north west of Ireland, Scotland, England and Denmark early in the week. England and Wales will pick up some warmth this week with temperatures up in the low to mid-teens, whereas for Ireland and Denmark, day time temperatures will only just break double figures. Importantly for all though we should all be free of ground frost meaning that last week's growth peak will continue (as forecast last week) into this week.

So, showery and unsettled across the NW, brighter for more central areas for the first part of the week. As we approach the end of the week, high pressure retreats south and cooler, more unsettled air pushes in for all of us. This will allow rain to push into Ireland and Scotland and the north of the U.K on Thursday pm, before pushing south into the southern half of the U.K (probably affecting Wales and The South West more) across The North Sea into Denmark on Friday morning. Potentially it may be a wet end to the week here. Cooler then as we get to the end of the week. The outlook for the weekend is a bit unsettled on Saturday, remaining cool but with plenty of sunshine, extending into a drier day on Sunday, but remaining cool.

Weather Outlook - w/c 31-03-2025

The outlook takes us into the 1st week of April and if you remember back to my early March blogs, I did suggest the possibility of a cooler, more easterly at this time. Well as we push into the last week of March we start the week with a continuation of that westerly airflow but high pressure is set to build and that will do two things. Firstly, it'll bring a more settled theme to the weather and secondly it'll swing in easterly winds from Tuesday. Before that we will see a low pressure system swing down from the north into Denmark, so here I think the start of next week will be windy, cool and wet before settling down weather-wise. So my prognosis for next week is dry, cool with temperatures in the 10-12°C range, cooler and a bit more unsettled for Denmark, slightly milder for Ireland. Night temperatures may drop low enough to return us to slight night frosts, particularly for Denmark. (Undskyld)

This high pressure looks like it is set to build into and past the 1st week of April, so that dry / cold but settled outlook looks set to stay with us for awhile.

Graph showing leaf wetness and air temperature - North London

Agronomic Notes

A bit of disease about....

That muggy period of weather on Saturday night into Sunday was significant enough for us to pick up some Microdochium activity as not only did we have a comparatively mild night, we also saw long periods of leaf wetness as recorded on the Davis leaf wetness sensor. This records from 0 (dry) to 15 (fully saturated) and you can see how it was maxed out from 16:00 on the 22nd March through to 08:00 the following morning.

The Prodata Report above recorded an average overnight temperature of 8.8°C, relative humidity of 94% and a total maximum leaf wetness duration (15 out of 15) of 810 minutes. Bearing in mind Microdochium nivale needs less than half that time to develop pathogenically and you can see why you might have noticed some activity.

Even the Smith Kerns model picked up from its customary zero status at this time of year (too cool to fit the model) to positive values on the 23rd and 24th.

Fortunately we have also picked up some nice growth during the same period and so we would hope that any activity would be superficial in nature and not affecting the crown of the grass plant leading to scarring.

This time last week we were sitting on 58.1 total GDD since Jan 1st, 2025, now we are at 82.9, so a good uplift in growth last week. This week it'll be cooler but I still expect us to accumulate more positive GDD leading to a projection that we should see out March 2025 at around the 100GDD total. Last year at the end of March we were at 192.8, so we will have had barely 50% of the growth this year till the end of March vs. last year. With that high pressure blocking event / easterly wind scenario likely for the 1st week of April, we will see minimal GDD I think in the 1st week, so that's why we have to have a 'use it or lose it' mentality to these short-lived growth peaks.

Poa annua seedheads - annual biotype

100GDD or thereabouts is the trigger point threshold for many to see the annual biotype of Poa annua initiate widespread seedhead production. Now I am fully aware you can find a seeding annual Poa annua biotype any month of the year in higher height of cut, but 100GDD will see this biotype of Poa annua (not the perennial) begin to seed on collars, approaches, clean up strips around greens. At the same time it'll take on that familiar pale hue to the leaves as energy is diverted towards the seedhead and away from general growth. No great shakes, but as a point of reference, we hit 100GDD cumulative last year on the 19th of February, that's how far we are behind this year.

As we know the truth is that for the U.K and Ireland, growth in the spring is a stop-start affair right through till the end of May. It isn't usually till then that night temperatures stabilise. It does make me smile when I keep seeing BBC Weather stats saying that the spring season is getting warmer every year (By spring they mean March, April and May), do you know I just don't buy it, so I am going to do some delving.

In the meantime, have a good week.

All the best.

Mark Hunt