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  • Writer's pictureMark Hunt

June 6th - Tropical downpours and some interesting north vs. south DLI light data....


Well I think it is fair to say that the GFS prediction for a Bay of Biscay low pressure to give us a wet Platinum Jubilee Sunday proved to be very accurate ! That said, the band of heavy rain came through much earlier than predicted even a day before and it shows that rainfall and in particular summer continental rainfall remains one of the hardest nuts to crack in terms of forecasting accuracy. I've been using Dark Sky as a weather app lately to see how accurate some of the later forecasting weather apps are and I'll be doing a review in next week's blog. Meteoblue (my fav) predicted 31 mm for us so they weren't far out !

GFS output reproduced by kind courtesy of tropicaltidbits.com



General Weather Situation


At this time of year we often see the jet stream take a hike south which means cooler and unsettled weather follows in from The Atlantic and in addition it opens the way for Bay of Biscay low pressure systems to develop and influence the southern half of the U.K as we saw last weekend. I think it is actually the exception to see a high position jet stream in June which means hot and dry weather. The last time this occurred was in 2018. As you can see from the animated GIF above and the image I've edited, the position of the jet stream is looking to stay on the low side for the next 7-10 days or so and that means we will stay in an unsettled pattern I think for the time-being but with some slightly better temperatures than of late.


So for Monday we still have the legacy of the weekends low pressure affecting East Anglia and the north of England. So for many, it is a dull, cool start to the week with the exception of Scotland who have enjoyed some lovely weather of late and this will continue through Monday with temperatures up there in the low twenties again. Elsewhere Monday is going to be a dull, cool day with some showers over the south and south west of Ireland and across England / Wales as well but they should be light. Staying on the cool side with only 14-16°C likely. The wind will be north westerly and that will keep those temperatures down.


Tuesday sees a new low pressure system edge into Ireland from The Atlantic so showers over the north and north west of Ireland will quickly be followed by heavier rain into Kerry by lunchtime. This rain will move north and east across Ireland during the afternoon and evening. Across The Irish Sea we will see some showers for The South East initially but by and large a dry day for most of the U.K with some sunshine. The wind will slip round to the west and this will provide a welcome uplift to temperatures with 20°C likely for England and Wales. During the course of Tuesday evening, that westerly rain will push into The South West and move north and east overnight. Scotland will pick up more cloud cover , so a duller day here but still high teen sort of temperatures.


Onto Wednesday and overnight that band of rain has moved northwards across Ireland and the south of the U.K and by dawn will be straddled from East Anglia, across The Midlands through Wales to the north and north west of Ireland. This rain will move northwards into northern England and eventually the south of Scotland by Wednesday evening leaving behind a showery picture across the southern half of the U.K and Ireland. It'll be breezy with that westerly wind picking up but temperatures will stay in the high teens and possibly break into the twenties. A much cooler day for Scotland as the thicker cloud and rain is joined by a cool, easterly wind direction.


Thursday sees another band of rain courtesy of an Atlantic low pressure push into the south west of Ireland. This will move across the country through the day but may be more westerly-orientated this time with the east missing most of the rain. A drier day for the U.K in general but Scotland will see showers across the west from the off and later in the day will pick up heavier rain across the west and central areas. Wales and England look to be largely dry on Thursday, there will be some showers popping up but with that wind direction in the west, temperatures will remain in the high teens and perhaps nudge 20°C.


Closing out the week on Friday and we will pick up a ridge of high pressure across the south of England so that'll be mean some pleasant temperatures and sunshine. That high pressure ridge will keep low pressure from pushing into Ireland but instead it'll introduce some showers through the day and for Scotland rain in the afternoon to the west which will move into central areas later. For England and Wales, that westerly / south westerly wind will pick up strength, so it'll be a warm and windy day with plenty of sunshine and similar temperatures to earlier in the week. A high E.T day me thinks.


The outlook for the weekend is not great on Saturday for the north west of Ireland and England with plenty of rain around. Scotland will also see rain across the west and north west throughout the course of Saturday. England and Wales should be pretty pleasant, still with that strong wind present from the south west and a cloudy with spells of sunshine sort of day. Sunday looks better for most areas as the bulk of that rain departs but showers will still affect north western areas and the west of Scotland. Temperatures will remain in the high teens as the wind lessens on Sunday but swings round to the north. Across Scotland that thicker cloud base will mean mid-teen sort of temperatures are to be expected as low pressure sits close by.

Weather Outlook


Above is the projected GFS output for next Monday, 13th June and as you can see, that ridge of high pressure across the U.K has been replaced by a cooler, low pressure trough. So it should come as no surprise then that next week will I think continue to be a sunshine and showers type of week with rain across the U.K & Ireland especially on Monday, Tuesday and Wednesday. As we get to the second half of the week there's a suggestion that high pressure may assert itself which would be good as I'm off on my hols. That said, 10 days is a long time away from a forecasting perspective so we will see. Temperature-wise ? Probably a continuation of the high teens with cooler temperatures further north and west, recovering as we get to the second part of the week.


Agronomic Notes


So as usual at the start of one month we take a look back at the previous one.


GDD Stats - May 2022 - The Oxfordshire



So May 2022 checked out with a total monthly GDD of 220.2 which puts it towards the top end of May GDD totals since we started monitoring them back in 2005. (4th warmest). I see the Met Office have May 2022 down as the 5th warmest on record and point to higher than average minimum night temperatures as the stand out in May's stats. As we know, GDD is calculated from the minimum and maximum air temperatures and so this correlates well with the Met Office's findings.


A cumulative GDD y.t.d of 442.3 again is towards the top end of our stats when compared to previous years and a long way ahead of last year which if you remember was handicapped by the very cold and dry April we endured.


So a good growing month from a temperature perspective, but did we get the rain ?


U.K locations - Growth Potential and Rainfall - May 2022


Let's look at our other locations around the U.K and compare Growth Potential and Rainfall stats ;

From a Growth Potential perspective, May 2022 was a pretty good growth month, certainly south of the Scottish border anyway. The average monthly G.P across our data set of locations was 20.8 out of a theoretical maximum of 31 (31 days in May x optimum daily G.P of 1.0). That works out as 70% of optimum growth so we can see that it was a good month for growth and certainly we can't hide behind any excuses in terms of temperature.

Rainfall was a different perspective though because some areas (like us here in Market Harborough) got torrential downpours on the 19th / 20th of May, whilst other areas missed these completely. The month was characterised by some very heavy downpours but not excessive daily or monthly rainfall totals.


Here's some rainfall stats for May 2022 from Milton Keynes and they highlight this very well.


The blue columns are the daily rainfall and you can see the highest totals (wettest day) were on the 7th and 23rd of May at just over 7 mm. Nothing to shout about there as 7 mm is a wet day but not a very wet day. When you look at how this rain fell though by adding in the rain rate (shown as a red line and measured in mm per hour), you can see the nature of this rainfall was quite violent. In terms of rain rate we saw 221.6 mm per hour on the 7th, 217.4 mm per hour on the 23rd and 140.4 mm per hour on the 26th. So that's close to 10 inches per hour rain rate on the 7th, which is equivalent to a tropical downpour. Fortunately they didn't last long but would have washed out bunkers and puddled up surfaces for sure. To the greenkeeper and groundsman, gardener and farmer, rain rate is an ever increasingly important parameter.


Irish locations - Growth Potential and Rainfall - May 2022


Let's look at some Irish stats to complete the picture ;

From a Growth Potential perspective, May 2022 was a pretty good month in Ireland and also a really consistent one geographically with very similar totals whether across the west, north, east or south. Quite remarkable consistency really. Aside from Valentia which we know will be ahead of the crowd because it picks up milder air during the winter, every other location is very similar. Where the difference lay in May across Ireland was in rainfall.

Although May 2022 will go down as a dry month across Ireland, there was significant variability in terms of rainfall with totals varying between 19.8 mm and 85.0 mm. The east coast tended to be drier and areas like Cork and Killiney were particularly dry.


When you look at the UK and Irish rainfall totals they are pretty similar, a little wetter across the west of course but it means that despite the good temperatures, some areas of turf lagged behind growth-wise because they were moisture-limited for some periods of the month. Since these areas are typically un-irrigated fairways, pitches, semi rough and rough, this really isn't a negative as it means growth was nicely curtailed and we didn't see huge amounts of clippings and extra resource required to keep on top of it.


So to summarise, May 2022 was a good growth month, dry in some areas but characterised by some short torrential downpours.


Looking ahead....


With a low-lying jet stream and alternating periods of low pressure and high pressure ridges, we look to continue the theme of good temperatures and consistent moisture availability as we head towards the middle of June. This means a continuation of PGR usage to keep those Poa / Bent fine turf areas in check and consistent nutrition to maintain plant health and surfaces. With that combination of rainfall and then a bit of temperature, the level and frequency of nutrition and PGR applications will be key.


Daily Light Interval (DLI) Comparison - Central England vs. Central Scotland


As we head toward summer I thought it would be interesting to continue the comparison between Daily Light Interval levels from a location in Central England and Central Scotland.


Now many moons ago I worked as an arable seed contractor and one of my jobs was to inspect seed crops of Wheat and Spring Barley across the U.K. I spent a lot of time working across Scotland from Stranraer to The Black Isle, with my furthest farmer located 40 miles past Inverness. That was hard graft in my then 4-speed, Volvo 340 company car 😊(fortunately I wrote it off a few months later out of sympathy !)


Back then, I was amazed at how much longer the days were up north compared to when I got home back in Leicestershire and therefore how much more light the crops got. The yields were way better than back down south and Iin the middle of summer I could still crop walk at 10.30 pm at night in Scotland !


The sunrise and sunset times for locations used in our DLI comparison are already showing this difference with the Central Scotland location at 04:32 am-22:01 pm vs. 04:46 am -21:16 pm for the Central England location. So already, they have another hour of day light.


Now the turf significance relates to the now common practice of overseeding creeping bentgrass, which as I've explained before has a minimum Daily Light Interval requirement of 30 mols per m2 of PAR light per day.


So how days in May did we exceed this DLI level in Central England and Scotland ?

From the graph you can see that on some days we didn't get close to the minimum DLI requirement for Creeping Bentgrass. Crunching the numbers we had 19 days out of 31 in England and 16 out of 31 in Scotland.


Although the DLI readings from England were generally higher we can see that towards the end of May, the Central Scotland DLI readings were consistently higher and that trend continues into June. It means effectively that Poa would still be able to compete well with Creeping Bentgrass right through May which I suspect will only leave June, July, August and perhaps September as the best growing months for this grass species.


It's just a pity we don't have more DLI data available for some of the other grass species we utilise in overseeding, ho hum.


OK, that's it for this week's blog, all the best for the coming week..


Mark Hunt



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