March 10th, 2025
Beware the ides of March is an old saying dating back to the Roman times but it has since been adopted to mark some particularly gnarly weather events on or around the 15th of March. Out walking tentatively yesterday (I managed to tear my hamstring running recently and hate being inactive) from Oakham, Rutland on a beautiful day I noted this ominous cloud formation over the houses. I have spoken about it before and it is one of the most useful clouds for weather observers because it is a Mares Tail Cloud (Cirrus uncinus) and it usually marks a change in the weather to more unsettled conditions. It's also a directional cloud because it points towards the direction of winds high in the atmosphere. This one is pointing north east and that's precisely where the wind is swinging round after today following a week of balmy southerlies which pushed the air temperature close to 20°C. So a big temperature change is on the way this week with a 10°C change for the worse in day temperatures and a return to night frosts as well.
Apologies for the lack of a blog last week but I was on a 1,000 mile Scottish road trip (in my EV !) installing weather stations. Thanks to everyone I met up with for their hospitality along the way and for those naysayers when it comes EV's, it was a breeze with plenty of charging options along the route where needed. I reckon I could have got to Scotland with only 1 charging stop from Leicestershire with the only range anxiety more relevant to my bladder / coffee consumption than the car's battery 😀
Whilst the southern half of the U.K enjoyed beautiful sunny days and frosty starts, up there it was blowing a houlie and cooler (until I left and then the sun came out !).
Like us, nature has been enjoying this temporary emergence into spring with Brimstone butterflies prevalent, Sky Larks on the wing and the first migrant ChiffChaff's arriving to the woods of Rutland Water. There was a report of an early Osprey but it turned out to be a White-Tailed Eagle visiting Rutland Water (never seen one so it's on my bucket list !). I also noticed my Wagtails briefly departed the garden with the warming temperatures availing them of a more natural, insect-based diet as opposed to my suet sprinkles, but today they're back so maybe they know what's on the way !!!!
General Weather Situation - 10-03-25
Well the weather outlook is complicated for this week and next. A few week's ago I spoke about a Sudden Stratospheric Warming event possibly throwing a stick into the spokes of Spring and even now it looks like this is ongoing. There is a great explanation of SSW's on one of few science depts Trump and his tech bum chum haven't screwed up yet, the NAOO. Read it here
Now, as I have said before, SSW events don't always affect the weather lower down in the Troposphere, but when they do, they tend to result in the formation of blocking events across Europe and an easterly, colder wind flow, 7-14 days after they occur. if you look at the GFS animated GIF above, you can see how the winds are reversing from a southerly / westerly direction (usual path of jet stream winds) to north easterlies. With a SSW event occurring now, that could point to a cold end to March and beginning of April.
With such uncertainty in the forecast, I'll generalise rather than drill down into detail which may end up being inaccurate. So Monday night into Tuesday sees the temperature change as cold air pervades from the north east. This cold air will introduce some moisture into the equation on easterly-facing coasts of the U.K, Jutland and Ireland, particularly across the north east where in northern latitudes, those showers may be wintry. They'll be more of these showers in the first part of the week but they'll never be far away on eastern coasts all week really. That prevailing north east wind direction will mean they'll be a pronounced windchill this week so even though the day temperatures will be 6-8°C, the actual windchill temperature will be signficantly lower. It also means towards the end of the week we may see a return to night frosts as well as skies clear at night.
This is very much the weather pattern from Monday to Friday but as we approach the weekend, a blocking high pressure develops which will settle the weather down but it'll remain on the cold side with that north easterly wind in situ.
Weather Outlook - w/c 17-03-2025
Now bearing in mind my preamble about a SSW possibly influencing the weather, I would say the current GFS projection for next week will be subject to change. Currently it looks like we will see 2 low pressure systems cross the U.K & Ireland in the 1st part of the week (mid-week, next week for Denmark maybe !) so the first half of the week maybe wetter but it'll also be possibly milder as they flip the wind to a SW direction so we could see an uplift in temperature next week during the unsettled conditions (if they do occur) before high pressure once again comes into play later in the week to bring us cooler, more settled conditions but with a return to easterlies (potentially very cold over Denmark / Scandinavia). Like I say, this may well change but I wouldn't be surprised if we exit March on the back of cold easterlies.
Agronomic Notes
At first sight, starting my agronomic note with an image of my latest Rugbrød bake may seem slightly off the record turf management-wise, but hear me out.
It's my 3rd go at this wonderful Danish incarnation (there are many Scandinavian variants I might add) and along the way I have observed my results, thought through where I am not quite getting it right (proofing temperature was my issue), refined my approach and achieved a better result as a consequence.
Now isn't that what we do in turf management ?
A good turf manager should always be looking at his surfaces, his / her data, dove-tailing the two, refining the multiple approaches that constitute turf management, whether that's quality of cut, PGR usage or disease management (for the list is long) and then observing the results. We know it doesn't always go the way we think it should. I found this out in my many years of product development, sometimes the results for a new product I was developing didn't quite match my expectations, but I probably learnt the most from when things didn't work out the way I expected. Once you drill down and understand why, it can sometimes open up an entirely new way of thinking.
The other thing that baking bread and turf management have in common is if you go on the online forums, you can end up more confused than when you started !
Surface dry-down
This time of year we often see a debate on social media when surfaces begin to dry out, whether a light irrigation is a good or a bad thing (thanks Rob for the subject matter). Some people say that irrigating with cold water depresses the soil temperature and thereby slows down growth. I did some trials on this area in the past and found that though it actually did do that, the effect was only temporary for a matter of hours.
The bottom line to me takes me back to that bread baking analogy. If you observe a plant that shows the effects of desiccation (and let us remember this can come from either warm or cold temperatures), then that grass plant is moisture-limited, so worrying about temperature holding back growth is a bit of a misnomer because the plant's growth is already being restricted by moisture. Of course we all have moisture sensors nowadays but remember that the sensing field is different between different manufacturers (so comparing between 2 different sensors is inaccurate) and often in the spring we see the profile in the top 10-20mm dry out whereas below that it is still moist. That is a good way above most soil moisture probes sensing depth unless you have shorter probes fitted.
Drying out in the surface ?
Is this actually likely ?
Let's look at some data from Prodata Reports for our default location at The Oxfordshire.
Looking at the above report yields a number of valuable insights, particularly when we contrast moisture input from rainfall vs. moisture loss from evapotranspiration.
So month to date, the cumulative rainfall level is showing as 0.2mm vs. cumulative E.T of 15.32mm, so we have a soil moisture deficit for March currently at this site of -15.1mm. In those circumstances it is quite possible that the surface has dried down and would benefit from a very light irrigation cycle (couple of passes of the heads). That said, if the grass looks fine and dandy, then no need.
Stop - start Growth
Another interesting feature of last week's weather that is worth highlighting is the lack of growth in the early part of the week because of the penetrating ground frosts at night.
Look at the GDD and G.P data in the top spreadsheet and you can see how the daily G.P sat close to zero until the 6th of March even though before that daytime temperatures were in the low teens. The reason for the supressed G.P / GDD readings was that the night time temperatures dropping to -4.4°C on the 3rd March at this location.
We didn't see positive GDD and a daily G.P > 0.25 until when the night temperature was -0.8°C, but by then the daytime temperature was 17.1°C, high enough to offset the slight ground frost. Even when we were no longer getting ground frosts from the 7th March, the daily G.P was only at 0.50 (50% of optimum temperature) because the night's were still cool.
Spring growth is ALL about night time temperature, as I have said before, they are the handbrake to Spring growth.
So all of that nice Spring weather last week and over the weekend only added a sum total of 20GDD (using a 6°C base temperature), with a cumulative total of 57.8 for the year since Jan 1st.
Where were we last year on this exact date GDD-wise ?
We were at 119.9 GDD in 2024 vs. 57.8 GDD in 2025 on the 10th March. As a matter of interest we passed 57.8GDD in 2024 on the 6th of February, showing how warm a start to the year it was in 2024 vs. how cold a start to the year it has been in 2025.
OK, that's me for another week, I have a burgeoning in tray after last week's road trip, so I better get round to addressing it, but first a nice slice of Rugbrød with a boiled egg, time to get my diet back on track as well !!!!
All the best.
Mark Hunt
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