April 2nd, 2024

Hi All,

Well, a topsy-turvy Easter, weather-wise and one where the forecast changed literally on a daily basis. We were due two nice days on the weekend and rain either side of them. We got low cloud in the form of Haar on Sunday, totally un-forecast and it gave us a dull , chilly and mizzly day, but then Easter Monday was a good one as the rain came through early.

We did have more rain though and as I continued my long distance (for me) bike training, I was not surprised to see that the River Welland under the Harringworth Viaduct had broken its banks yet again.

So we have endured another wet March, 100mm+ would be the norm rainfall-wise, having a brief, bleary-eyed glance through the stats this morning. Pretty much the same as March 2023 I'd say and a break in the cycle of cool, dry springs that have been in since the early 2000's. It wasn't so long ago that the expectation for March / April was a blocking high pressure system that gave us those tricky agronomic conditions of low rainfall, mild days and cold nights, with limited growth.

So why the change ?

Well undoubtedly the wet winter and spring (so far) we have endured is due to the position of the jet stream. It has been stubbornly sitting south of the U.K for longer than I can remember, with very few changes in this position. Sitting south it allows a succession of Atlantic low pressure systems to batter the U.K & Ireland, and batter they have. The thick blue line in the GIF above shows the position of the jet stream and the likelihood of Atlantic weather to dominate. So we know the reason, but not the cause and that's something that I intend to do some digging on. I have a feeling it is related to a Sudden Stratospheric Warming / El Niño interaction, but usually this results in high pressure blocking events and the typical cold, dry spring we have come to expect.

The other feature that you may note from the GFS image courtesy of tropicaltidbits.com is the unfortunate succession of low pressure systems that are sitting in this trough, I have numbered them for clarity and as you'll see, there's 3 of them. That sets the scene for the week ahead :(

General Weather Situation - 2nd April, 2024

So this week we will see a succession of low pressure systems push into the south west and south of Ireland / U.K. That process starts today with rain pushing into the south west of England / south east of Ireland this morning and then moving north and east across the U.K & Ireland. It will be quite slow-moving, so by Wednesday, it'll be sitting over the north of England and slowly edging northwards into Scotland through the day. The next low pressure system makes landfall on Wednesday evening into the south west of England and Ireland and again track north east overnight into Thursday, clearing eastwards through the morning. The next low pressure arrives on the heels of the previous one, so by Thursday evening, rain, some of it heavy will again be pushing into the south west / south of the U.K & Ireland. This low has heavier rainfall associated with it, is projected to track more across all of Ireland, Wales, the north west of England and Scotland. As it hits colder air over Scotland, it'll change to wintry showers over Scotland during Friday morning. As we go through Friday morning, this rain will clear eastwards to leave a drier, second part of the day.

In short, a wet week I am afraid, but as noted last week, we will have a drying wind in-between the rain fronts.

Indeed, the other feature of this week is the strong south westerly wind and therefore milder airstream. Temperatures are expected to increase through the week, with the warmest temperatures on Thursday / Friday. I expect 8-10°C at night for Ireland, England and Wales, pushing up to 14-17°C during the day. Scotland will be cooler initially with 2-3°C at night and 7-9°C during the day, though at the end of the week, those daytime temperatures will push into the low teens. So expect mild day and night temperatures and that means a nice bit of E.T. It is the difference I pointed to last week, the days are getting longer and E.T levels are building, so that means a quicker dry down from these wet interludes. As an example, Meteoblue are projecting 30mm of rain for Market Harborough this week, but also 14mm of E.T, so just under half of that rain will be evaporated.

Mild days and nights mean we will have good Growth Potential / GDD levels for the coming week, so that grass plant will be growing. No bad thing if you are chasing recovery maybe, but if your site is waterlogged and getting machinery out there to cut is hard work, then this growth is wholly unwelcome I am afraid.

So a wet week, with a strong south westerly wind in situ and some sunny intervals either side of those rain fronts, with pleasant temperatures. The outlook for the weekend looks similar with a wet start for Ireland and the west of the U.K on Saturday, before this rain clears northwards to leave behind a sunshine and showers scenario, with more showers likely across the west and north west. Those mild temperatures will remain as will the south westerly airstream.

Weather outlook - w/c 9th April, 2024

So after another week of successive low pressure systems, how is next week shaping up from a GFS-forecasting perspective ?

Well, slowly that jet stream position is nudging northwards, but not sufficiently far enough north yet to give us consistent dry conditions.

Next week looks to start unsettled again I am afraid, with an intense low pressure system sitting close to Ireland. During Monday, this low pressure will funnel in strong winds and rain, first to Ireland and then later to the U.K. These very windy and wet conditions will continue through Tuesday, with that wind being gale force and likely the storm will gain a name as well. Through Wednesday, this storm will start to clear, but it will only be a brief interlude as more low pressure systems line up to push through. Towards the weekend, the wind will shift from south west to north west and that'll drop the mild temperatures somewhat. Not great I am afraid.

Agronomic Notes

GDD - March 2023 - Location - The Oxfordshire, Thame, U.K

So starting off a new month, we take a look back at the prior month from a potential growth (GDD) perspective using our default location.

the off-the-scale GDD figure for February, March 2024 is more 'normal' (whatever that is !) coming in with a total GDD of 78.6. That said, it still ranks as the joint 2nd warmest March as measured from a GDD perspective since we started tracking data back in 2005. Not surprisingly, the yearly total to date is the highest we have measured, even trumping the best growth spring of 2017. So from a potential growth perspective, we can't really complain about this year.

Rainfall though is another matter.

Here are some January - March 2024 vs. 2023 rainfall totals to give you a flavour of how wet it has been at the start of this year vs. last.

And of course we must remember, this is following a record breaking wet end to 2023.

Jan-Feb '24 vs. Jan-Feb '23 - U.K Locations - Rainfall  in mm
Location	Jan-Mar '23	Jan-Mar '24	Delta
Bristol	352.2	441.2	25%
Newport, Wales	314	410.4	31%
Guildford	209.0	274.4	31%
Sevenoaks	218.6	308.4	41%
Pinner	186.8	320.6	72%
Thame	158.4	257	62%
Milton Keynes	153.0	221.6	45%
Northampton	139.8	239.2	71%
Bury St Edmunds	125.6	210.4	68%
Scarborough	98.0	184.4	88%
Manchester	306.1	324.8	6%
Sunderland	103.2	145	41%
Glasgow	159.8	248	55%
Edinburgh	159.8	229.6	44%

Again we can see that some of the biggest changes, year-on-year, are across the central and south eastern parts of the U.K. That's not to say that the south west / Wales isn't wet, it is just that the increase for 2024 is less than other locations. So we see an extension of high rainfall totals from the south west across the south and south east. In general we are looking at another 100mm of rain in 2024 vs. the same period in 2023, that's 4 inches in old money.

What amazes me is that Pinner in north London is as wet as Manchester in 2024 !

As discussed last year, this is all to do with the orientation of the jet stream and the fact that the low pressure systems have also pushed up from the south rather than the majority coming in from the south west. I have noticed this trend for a good while now and I am wondering whether it is a permanent fixture of a modern day climate ?

Looking across The Irish Sea, the rainfall situation has some similarities ;

Jan-Feb '24 vs. Jan-Feb '23 - Irish Locations - Rainfall  in mm
Location	Jan-Mar '23	Jan-Mar'24	Delta
Dublin	177.1	212.6	20%
Claremorris	317.9	371.4	17%
Cork	361.2	425.1	18%
Gurteen	215.5	308.4	43%
Johnstown Castle	244.6	400.7	64%
Valentia	496.8	549.9	11%

The scenario with rainfall in Ireland shows smaller increases year-on-year for the majority of the locations, but still a lot of rainfall !

The exception to this are the Gurteen and Johnstown Castle locations, which are across the south and south east of the country. These have picked up some of the effect from those southerly-orientated low pressure systems and show large year-on-year increases.

Ireland as we know is a wetter climate in general than the U.K, but the rainfall pattern appears to have extended this winter / spring from the south west being the wettest area across to the south and south east. Exactly the same pattern / trend as for the southern half of the U.K. Hmmm, surely that isn't a coincidence.

So a much wetter and milder 1st quarter than we could reasonably expect. The problem is there is no visible end in sight to this run of weather. When it does come though, you can't help but think it'll be a total change, a switch off of the taps and within a short space of time we will be looking to the west again for rain. That grass plant has had an awful long time now with its roots in a wet soil, it must have exerted a change on the plant itself from a morphology perspective ?

Food for thought indeed....

All the best

Mark Hunt