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  • Writer's pictureMark Hunt

25th March, 2024

Hi All,


Well we are heading towards the start of April and unfortunately another week of unsettled weather and rain. (I am sorry)


That late Sudden Stratospheric Warming Event (SSW) that took place at the start of March is I think responsible for the current weather and the outlook. According to the Met Office, the SSW was the 3rd such event we have endured this winter and that is unique. Some winters there are none, sometimes one, occasionally two, but they have never measured three SSW events in the same winter period. You can read their information on it here


SSW events can potentially reverse the normal west-east wind direction of the jet stream and consequently are associated with easterly winds and more often than not, a more southerly position of the jet stream. The latter means that warm air associated with high pressure systems across southern Europe are unable to influence our weather. For that we require a more northerly jet stream position.



You may remember last week I discussed the large variation between the 2 forecasting models (GFS and ECMWF) and showed a projection for this week (27-03-24) from the GFS and ECMWF models. Well it looks like yet again the GFS model prediction is going to be more accurate, which is a pity as we could have done with a nice high pressure ridge :(

It isn't spot on as the likelihood now is for a more pronounced trough formation (see GFS image below) but they called a trough and ECMWF called a peak, so they are the most accurate.



GFS output is courtesy of tropicaltidbits.com


General Weather Information - 25-03-24


Above is the GFS output for 27-03-24 and it highlights one of the key features of a trough pattern in the jet stream - a low pressure system that does not move from west to east, but rather stays in situ above the U.K & Ireland for a number of days. This low pressure system will in fact stay to the west / south west of Ireland for over a week, whereas normally a system like this would push through in 12-18 hours, if the jet stream had a strong west-east flow. It hasn't, so it won't.


Now before you reach for the bottle, there is a positive side to this weather pattern formation and that is the wind direction. It'll be southerly pretty much all week and extending into the weekend before that low pressure drops to the south of Ireland and pulls easterlies into the weather picture. That wind direction means a couple of things, firstly the temperatures will not be as bad as they actually look from the GFS output and secondly, mild air means more potential for E.T. More E.T means more drying, something I will discuss this later in my blog.


So this week is essentially a forecast of two parts ;


From Monday to Friday, we see that resident low pressure system usher in rain from the south and south west northwards across the U.K & Ireland. We are already seeing this today with the bulk of the rain across the west, south west and north of the U.K. That rain will clear Ireland and central areas, leaving showers and heavier rain across Wales, Scotland and the north west of England. Central and eastern areas will slowly clear with rain moving northwards into northern England and Wales. Despite the south east wind direction it'll be a cool day with temperatures just breaking double figures.


With low pressure in charge this week, another benefit (definitely trying to approach this with a glass half full mentality) is cloud cover overnight which means less likelihood of frost. Indeed night temperatures looks pretty reasonable this week which is an added bonus because cold nights are as we all know, a handbrake to growth.


As we progress into Tuesday, that low pressure intensifies and centres itself off the coast of Galway, so really Tuesday through to Thursday is the period of the week when we see a succession of rain pushing into the south of the U.K & Ireland and then pushing northwards through England and Wales and up into Scotland. I would pick out Wednesday night into Thursday morning as potentially the wettest period of weather for the southern half of the U.K. During that period I think we will be 8-11°C day time temperatures and obviously pretty dull with limited sunshine. The best of this will be for southern and eastern areas once the rain has pushed through, the same goes for Ireland. It will also become increasingly windy as that low pressure passes close to the U.K, with Wednesday, Thursday and Friday, particularly windy from the south.


As that rain clears on Thursday, we should start to see temperatures pick up a little and on Friday, more in the way of drier conditions and sunshine. They'll still be rain around across western and southern coasts but it is a much better weather picture for Good Friday, at least for Ireland, Wales and the southern half of the U.K. During the afternoon, we will see showers bubble up across the north of England and south of Ireland particularly and these will push northwards into Scotland. It'll remain windy on Friday and the wind will swing around to SSW. There may be some showers around through Friday further south but the main rain event will have passed.


As we get to the Easter weekend we see a better picture for Easter Saturday and Sunday, not completely dry, still with some showers lingering but much more in the way of sunshine and temperatures will pick up into the low teens with 12-14°C likely. Winds will lighten and we will see longer periods of sunshine, particularly on Sunday. Monday sees a new band of rain push into the south of the U.K and move north, so likely to be wet for England and Wales initially before moving into northern England and Scotland later in the day. Ireland looks to miss this rain front.


So a wet picture initially before something drier, warmer and brighter for the weekend.




Weather Outlook - 01-04-24


Next week sees that low pressure system still sitting in the Bay of Biscay, so that means we aren't out of the woods yet in terms of drier weather. Monday, I have already spoken about, with a band of rain pushing north and sunnier, mild weather either side of it. Whilst that low prevents any milder air pushing in from The Atlantic, on Tuesday we see another low pressure nip in off the North Sea and this will bring rain to the south east, east of England, Wales and Ireland again accompanied by a southerly wind direction. That low will slip off on Wednesday so we will still see showers affecting the south east of England, but from later on Wednesday into Thursday, high pressure settles across the U.K. Maybe not for long as a new area of low pressure is projected to impose from the north for the weekend.


So a pretty mixed weather forecast and still no longer-term sign of better weather with a move of the jet stream to a more northerly position. Fingers crossed it'll show in next week's GFS.



Agronomic Notes


For this week's agronomic notes I thought I'd use a month-to-date agronomic report from our Prodata Reports Software Package as a basis for discussion. This software package takes data directly from a Davis weather station and converts it into summary format.


Whilst the forecast for this week is hardly encouraging, that I will admit, I would like to point to the fact that the days are getting longer and that means the potential for E.T levels to increase are also higher.


In the report above, you can see the story of the year so far in the cumulative E.T and rainfall data ;


Rainfall to date = 220.6 mm

E.T to date = 60.60 mm

Soil Moisture Surplus / Deficit = + 160 mm


Of late the days are extending noticeably. A month ago, we had 10 hours 29 mins of day length, today that figure is 12 hours 34 mins. That means more day light and therefore more drying time.



In February, 2024 this location in Central England recorded a total monthly E.T figure of 18.97 mm, with a highest E.T reading of 1.17 mm.



In March 2024, we are currently sitting at 28.88 mm to date total E.T, with a highest reading of 1.98 mm on the 23rd and 1.96 mm on the 24th.


So we are heading in the right direction with more moisture being evaporated per day than we were a month ago. That means that despite the unsettled forecast we now face before us, more of that rainfall will be evaporated as our drying potential increases. So despite the wet period forecast this week, the strong and reasonably mild, southerly winds will help in drying down the soil between the showers or longer periods of rain.


So don't despair.


Yes, it'll be a wet run up to The Bank Holiday, but it will be accompanied by drying winds and that potential to dry down the soil is only going one way at this time of year.


All the best.


Mark Hunt

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1 Comment


Simon Hunt
Simon Hunt
Mar 25

Question

In the current unsettled weather climate should you overseed greens on the surface and just let it germinate / get eaten by birds?


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