March 23rd, 2026

Hi All,

As my last Spring of writing this blog, it doesn't surprise me that the issues that we face climatically and agronomically are just the same as when I first started writing over 15 years ago. Warm days and cold nights are probably the hardest to manage, especially if you are chasing growth to get surfaces back to where they need to be for the spring / summer. Cold nights are the handbrake to growth.

At the end of last week, I was over in Denmark to say goodbye to one of my relatives (last of the Copenhagen Amager old guard) at a funeral in northern Sjælland. Looking at the countryside, you could see how hard a winter it has been for Denmark, the grass was bleached a shade of dormancy brown and snowdrops were just emerging. A long way behind where we are over the water. As we visited our old seaside haunts in Sjælland, I was thrilled to see a White-tailed Sea Eagle overhead, my they are a big, big bird and a first for me !

I took a quick look at the cumulative GDD for a golf course just north of Denmark and noted they are at 11.6 total GDD for the year since Jan 1st (using a 6°C base), whereas we are at 129 ! By way of comparison we hit a cumulative GDD of 11 on the 19th of January.

On the subject of cold nights being a handbrake for growth....

If you look at the report above lifted from our Prodata Report software at The Oxfordshire (thanks Sean), You can see how the situation has rolled out in the last week. At the start of last week, we had some warm days and mild (ish) nights and consequently Growth Potential figures > 0.4 per day, a level commensurate with good growth. Fast forward to the end of last week and the weekend, although day time temperatures have remained in the low teens, night time temperatures have dropped to -2.8°C, just before dawn, with 3 frosts on the bounce.

And of course we have also been dry with no rain for over a week. In an entirely predictable scenario, the surface of the turf is drying down quickly and thoughts soon orientate towards the need for irrigation. For this particular location, in March so far they have had 17mm of rainfall, but 30mm of E.T, a net deficit. Now of course I fully appreciate other locations have an entirely opposite scenario, particularly down the south west of England, South Wales and some areas of Scotland. It won't be long though before we have the debate about irrigating during cold temperatures and the pluses and minuses. Hopefully though with some rain in the forecast this week, those thoughts can be put on the shelf for the time being.

Temperature ensemble for London courtesy of netweather.tv

From a weather perspective, the situation is not clear looking ahead with the GFS and ECMWF models profoundly disagreeing. You can see the lack of confidence when you run the temperature ensemble for this week for London. An ensemble is a multiple run of forecasts models with slightly different parameters to understand the 'robustness' of the forecast. The tighter the lines are together, the more confidence there is in the forecast, the more the lines are spread apart, the greater the variability in the forecast.

It might not be discernible but the forecast run shows significant variability 3-4 days out, in other words, not great when it comes to confidence in the current forecast.

ECMWF 10-day forecast courtesy of tropicaltidbits.com

With a recent sudden stratospheric warming event, there's always going to be some uncertainty introduced in the weather dynamics looking ahead and it is worth noting that the GFS long-term forecast features some significantly cold weather for the beginning of April for the U.K and Scandinavia. The ECMWF model doesn't show the same cold but it does show a highly-variable forecast.

This week will though feature two quite different weather features, the first some significant wind as a northern low pressure system passes by well north of Scotland. As we know, the wind around low pressure systems rotate anti-clockwise and with this low pressure being located in the far north, it means that the winds associated with that low pressure are both very cold and strong northerlies / north westerlies lurk on its trailing edge.

So for this week, Monday is a bit of a hiatus day, light winds and a cold, quiet start for most, warming up nicely in the south, but already those winds are beginning to ramp up in the north and rain is pushing into northern Scotland and north west Ireland.

Later today those stronger south westerly winds push in from the west and continue overnight to become a constant feature through Tuesday, accompanied by rain later in the day as a weak low pressure front moves through. As this low pressure front moves off into The North Sea, it's trailing edge will pull down strong (and cold) north westerly winds from early on Wednesday. In addition we will see a drop in the temperature and some blustery showers, some of them wintry in nature across elevation. Some cold and windy on Wednesday with plenty of showers across the north and west, but some reaching inland. As we move into Thursday, those winds calm down a little and move more northerly, so remaining cool with temperatures not likely to break double figures. Through Friday we will see a band of rain push down from the north west. This band of rain will move across The North Sea into Denmark for Saturday. Remaining cool and still with those winds in the north west for the first part of the weekend before temperatures begin to recover as a weak ridge of high pressure pushes in from the south west. Looking at the temperatures I think it's likely to be a pretty similar picture for Denmark this week, 9-10°C during the day, 2-3°C at night and some blustery showers thrown into the mix, some wintry in nature.

It is clear, winter hasn't quite released its grip on us yet, despite reports of an El Niño building in the Pacific. This may mark the beginning of a warming event that clearly our climate doesn't need. Interestingly for the U.K, most drought events occur during La Niña periods of Pacific cooling. Read about these two processes and how they can affect our weather here. On a day when the World Meteorological Organisation has stated that our planet's climate (not just the climate eh !!!) is more unbalanced than ever (read about it here), I wonder what will shake out for us this year climatically and how prepared we are ?

With the low confidence in the forecast currently, I won't waste too much time ruminating on next week's weather other than to say this. The ECMWF projection is for high pressure to establish through the week bringing at a guess a continuation of warm days and cold nights. The GFS shares this projection but they depart later in the week when the GFS points toward the development of a cold temperature trough event.

Earlier I discussed how cold nights are the handbrake to grass growth and to illustrate this I lifted a slide from one of my recent talks.

The two Growth-degree-day 'example days' are for a nice spring day when we have day time temperatures of 15°C, but 2 very different night time temperatures. One of 9°C and the other 0°C. Working through the GDD calculation above, you can see the mild night example delivers a GDD of 6, whereas the cold night's equivalent GDD is 1.5.

GDD is a scalar calculation, so for example a GDD of 1.5 represents very little growth, contrasted with a GDD of 6.0, which represents good spring growth.

So when someone asks why the greens aren't uniform or recovered from recent aeration, you can show them this slide and the weather forecast and hopefully they'll understand that it is night time temperatures that call the shots at this time of year, not those during the day.

All the best.

Mark Hunt