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  • Writer's pictureMark Hunt

March 6th, 2023

Hi All,


Well, the first blog of March and as I glance over at weather station read out, we are sitting at a toasty 9.5°C to mark the first day of meteorological spring. As you'll have no doubt seen on the news, this week's weather will feature a brief return to winter and for the south of England, the first significant rainfall since the middle of January, River level flow rates are down to summer levels and that is already having an effect on winter abstraction (thanks for the update Rob).


At the end of this week, we have a southerly-biased low pressure system heading our way and I think it will bring significant rain to the south of England. As you'll see from the rainfall and Growth potential summaries I will present later in the blog, rainfall levels particularly across the east of England are still under the amount of moisture evaporated by E.T during 2022.


Typically, locations across the east of England received 400mm or so rainfall last year, but around 600mm of E.T, so they went into 2023, -200mm (8 inches) down. Rainfall in January and February was crucial for bringing levels back to a standard point but it hasn't come. Maybe this year March will be the equaliser, rainfall-wise ?


So let's put some detail on what will be quite a variable week, weather-wise, compared to last week which was pretty humdrum.


General Weather Situation


That cold air is already making an impact across Scotland and during Monday it'll push south to affect more southern areas. I saw the BBC were reporting up to 200mm or 4" of snowfall for The Highlands and some areas of Scotland. Yes that's right, someone wasn't too good at their metric-imperial conversion. That's 8" in old money like.


So Monday sees moisture moving south from Scotland across the north of England and into the south. Already we have seen rain across the south and east of England overnight. Ireland will also see bands of rain pushing into Connacht and then moving south across the country during the day. Across Scotland and the north, these showers will turn increasingly wintry as that cold front pushes south. Monday though will hang onto some decent temperatures for the west and south with 9°C across Ireland, Wales and the southern half of the U.K, whilst the north sits at 6°C. This is because the wind will still be westerly on Monday but overnight it will swing northerly and that's when we will feel it.


So Tuesday sees us the wind turn northerly and switch that overnight rain to wintry showers. Some of these will extend south into The Midlands, Wales and the east of England. You could even see some wintry showers across the west / south west corner of Ireland. So Tuesday will dawn very cold with a northerly wind in situ but it'll be a pretty dry picture for all areas once that overnight moisture has moved south out of southern England. A dry but very cold day with a piercing northerly wind and skies clearing from the north. Typically temperatures will sit around 4°C for most areas with a windchill that will feel more like zero. Ouch !


With clearing skies, temperatures will head south quickly and so overnight into Wednesday we will have a very sharp frost and probably the coldest night of the year so far. Wednesday looks on face value like another very cold but mainly dry day with the only blot on the copybook, some rain pushing into The South West through the day. Winds will be light and predominantly from the north. Again 3-5°C, will be typical. As we reach the late afternoon, temperatures will drop sharply as we head towards another sharp frost. This will be markedly lower across Scotland and the north.


Thursday sees moisture begin to push into the south west of England and Ireland. As this moist air butts up against the cold front, it will turn to snow with rain behind the leading edge. Through the morning, that rain will move north and east into Wales and the west of England. Again it will turn to snow on its leading edge. Ireland will see this rain front fizzle out and be confined to the mid-west, whereas across The Irish Sea it will consolidate across the southern half of the U.K in the form of rain, sleet and snow. The latter more prevalent across the east and north of the front. Another bitterly cold day with 3-5°C likely, despite more in the way of sunshine for the north and Scotland. Winds will be light and from the north. They key will be where that moist air / cold air boundary forms and how much snow falls as a result.


Closing out the week on Friday, we see some heavy rain push into the west and north west of Ireland overnight. Again they'll be snow across the leading edge. The eastern edge of this rain front will extend across Wales and The Midlands with a mx of rain and wintry showers. That front will push into northern England by the rush hour. Meanwhile that heavier rain across Ireland will push into central and eastern areas, cross The Irish Sea into Wales and the western half of England. This rain will be heavy in nature. By midday it'll cover all of Ireland, England and Wales and extend up to The Borders with snow at its northern edge. So a wet day to end the week for sure.


The outlook for the weekend looks mixed currently and a bit cooler than I originally thought it might be. Saturday looks showery across the southern half of the U.K and Ireland, with some of that rain across England, heavy in nature. Further north, a cool day with some sunshine. Winds will be entirely changeable through the day dependent on your position reference to the low pressure. Overnight we see some heavy rain push into north west and Northern Ireland and this will move eastwards into The North West and southern Scotland. Again some of this rain will fall as snow over elevation. By midday, more rain, heavy in nature will push into the south west of Ireland and quickly push north and east across the country. This rain front will move quickly across The Irish Sea into The South West, Wales and western half of the U.K, with more rain and wintry showers across Scotland. By dusk, this rain will be across central and eastern areas of the U.K.


So a tricky mix of rain and wintry showers over the weekend and some of that rain will be heavy. Winds will be moderate to light and eventually swing round to the south west and pick up in intensity.

Weather Outlook


So after a cold week with some heavy rain at the end of the week, what does next week have in store ?


So the GFS output for next Monday courtesy of tropicaltidbits.com shows that southerly-biased low pressure system just off the west of Scotland and this will push in strong south westerly winds and rain to start next week. It will feel milder as well due to the wind change. This mild interlude will be short-lived though because cooler air will sink south and the wind will swing more northerly mid-week. That low pressure will then bring rain across Monday and into Tuesday pushing down in bands from the Scotland and the north. The same across Ireland. Wednesday will be slightly drier, but still with plenty of showers across Ireland and the U.K and feeling slightly milder at 7-9°C as the wind swings round to the west. Thursday heralds the arrival of a new, Atlantic low pressure which introduces rain into Ireland overnight. So next week looks potentially like finishing with another low pressure system pushing across the southern half of the U.K to bring rain, some of it heavy to all areas. Scotland will pick up this rain too but looks drier from the weekend possibly.


One of the potential enduring features of the recent Sudden Stratospheric Warming is the shifting of the jet stream to a more southerly position. This has two key affects. Firstly, cooler air from the north will prevail keeping temperatures I think to below the March average and secondly, Atlantic low pressure systems will have no block in place to prevent them swinging over to affect our weather. So I'd say that puts the first half of March down as cool and unsettled I think.


Agronomic Notes


So first up I'll start this part of my blog with a look back at the start of this year from a GDD, G.P and rainfall perspective.

If you look first at the lower chart and the GDD totals for the respective years, we can see that 2022 came in as the warmest year we have recorded from a GDD perspective since we started doing this in 2005. It just pipped 2017.


The other feature you can see clearly on the bottom chart if you look at the GDD totals for March 2010, 2013 and 2018 is the relatively low GDD total. These were the years in the past when a SSW event influenced the weather. I wonder whether March 2023 will follow a similar pattern, I think it may well do.


For 2023, we look at the top graph and can see both January and February came in towards the upper end of past month GDD totals and this reflects the milder start to the year we experienced despite a run of colder weather in both months. A cumulative total of 69.9 GDD at the end of February is again towards the higher end vs. previous years but it wouldn't surprise me if it slipped back by the end of the month.


Growth Potential and Rainfall - U.K Locations

Looking at the top graph showing January and February's Growth Potential, we can see as expected it is very low with very little differentiation between north and south, east and west locations. This is to be expected since all of the U.K was under high pressure for a great part of January and February and so I'd expect growth levels to be very similar. In addition January and February are low growth months and so low figures numerically so variability is bound to be small between locations.


Rainfall-wise (bottom graph) it is a different story, though most locations showed the same pattern, that is to say, a very wet January (remembering that the rainfall was pretty much the first half of the month) and an extremely dry February. Those amounts put February 2023 in the record books for lack of rainfall, with I think some locations recording their driest February ever.


Again you can see how the rainfall pattern is very much orientated towards the south west of England and Scotland with very high January totals. When we have a strong Transatlantic jet stream, it is these locations that are in the firing line !!!


The flipside to this coin is that central and eastern locations are the driest and this is an emerging trend. They are last on the list when we get rain from the south west and the same when it comes up from the south.


Growth Potential and Rainfall - Irish Locations

It isn't often that I note more growth potential in Ireland than in the U.K for locations other than for the eternally mild and wet, Valentia !


For January and February, some Irish locations showed slightly higher Growth Potential than other locations, namely across Co. Meath, Wicklow and Co. Wexford on the east / south east coast of Ireland but also down the south west in Co. Kerry and Co. Clare.

We also saw the same rainfall pattern across Ireland as we did for the U.K, which makes sense because it was 'cloaked' under that high pressure system as well for much of February.


So a much drier February than January and particularly across the same counties that we noted higher G.P in, namely Meath, Wicklow and Wexford. As you'll maybe have noted on the forecast above, this will soon be 'a changing' as the roadblock to Atlantic low pressure systems has moved and unsettled weather is poised to push in from the end of this week and bring some heavy rainfall. It isn't often that I would write that some locations in Ireland need rain in early March but 2023 is one such year.


Agronomics


Well with a broadly similar weather pattern across Ireland and the U.K during February, it was probably pertinent that last week I devoted some time to cool temperature nutrition because that is definitely what is going to be required for the first half of March with a low-lying jet stream and that blend of cooler, more unsettled weather than we have experienced of late. Granular fertiliser should be poised for application this week if ground conditions allow and growth is required to tick things on. It won't be an earth shattering effect as I think daily G.P will be in the region of 0.1-0.3, dependent on location, but that is enough to pick up a bit of clip in the box and initiate recovery if that is required.


OK, that's it for this week, my head is spinning after crunching all of those figures !


Wrap up well....


Mark Hunt


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