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  • Writer's pictureMark Hunt

July 1st, 2024

So we reach the first day of July and predictably as I look to pack up the campervan this week and head off to The Gower, the weather takes a turn for the worst as a cooler airstream and an unsettled, wetter weather picture comes into play :(

I knew it was on the way late last week as I fished the River Trent and above Mare's Tail Cirrus cloud formations signified ice crystal formation high up in the Troposphere. They pointed towards the south west to also signify the direction that change was coming from. Mares Tail's are one of the best cloud indicators of a weather change because they form at the leading front of a cool low pressure system as it slides over a soon-to-depart high pressure system.


After 8 months of pretty wet weather, June was a pretty dry month for most with very little rain, significant heat and E.T at the end of the month and a pretty chilly first half. A strange one for a 'summer month' and July looks to kick off in a similar fashion.

The GFS output above from tropicaltidbits.com for mid-week shows the lower-lying jet stream and the first of the Atlantic low pressures that will drop into the trough. You can already feel the change with a pronounced drop in the air temperature yesterday. Even though the actual temperature (17°C) wasn't bad, it felt much cooler because of the change from the previous days when we were +10°C higher. So how does it looks for this week.....?


General Weather Situation


So for Monday we already have a line of showers crossing Ireland and the west of the U.K, stretching from The South West all the way up to Scotland. As we progress through the day, these showers will move eastwards, so most people will see some rain today, although by the time it reaches the south east of England, it will have fizzled out in terms of intensity. A good deal cooler than last week with 16-18°C top temperatures and 10-12°C overnight. Westerly winds for Monday will be moderate in intensity.


Tuesday sees the wind shift round to the north west but the temperatures will stay in the 18-19°C region for most areas and it will be a reasonably dry picture for everyone until showers arrive later in the day across Scotland, the north west of Ireland and The North West.


Overnight more general rain will arrive into Ireland, Scotland and the north of England. With a north west airstream, this rain will vector south east into Wales and the southern half of the U.K during Wednesday morning. The wind will vector more westerly and strengthen through the day pushing those showers across all areas during the morning, clearing Ireland and the west as they go. Similar temperatures to earlier in the week.


Thursday looks reasonably dry as I type now except for the north west of Scotland where the showers from Wednesday will persist. That strong to moderate westerly wind will continue through the day but it'll be a day of pleasant sunshine with temperatures again around 18°C.


Closing out the week on Friday, it looks like we will see some heavy rain over The South West and South Wales (damn and blast) from first thing. This will clear the west during the morning as it pushes along the south coast into The Midlands, south and south east and east of England. A reciprocal front will push into the north west / west of Scotland and head eastwards. Ireland will start dry (ish), but showers will form through the morning across the west coast and move eastwards, urged on by a strong westerly wind. (groan)


The weekend looks reasonably dry on Saturday with more in the way of showers on Sunday before a heavy rain front pushes into Ireland on Sunday afternoon and quickly crosses The Irish Sea into Wales and most of England later on Sunday night into Monday morning. Some of this rain will be heavy across The North West in particular. Scotland should remain largely dry. Similar temperatures again in the 16-19°C range. with a moderate to blustery south westerly wind in place.



Weather Outlook


Hmmm, well last week I commented how unreliable the longer term (beyond 7 days) GFS output has looked lately and I echo those thoughts this morning with a changeable outlook with every time the GFS output refreshes. So here goes...


Next week looks to be a changeable week with a low pressure system pushing in slowly from The Atlantic. This will push showers across Ireland and the west and south of England, Wales through the first half of the week. Now this output has changed in terms of the position of the low pressure and I expect (hope) it will do again as it'll mean a crap break for me on a selfish note. So a sunshine and showers week as it stands now with similar temperatures to this week. As we approach the end of the week, it does look like high pressure will come into play with a suggestion of a heatwave for the middle of July. As I say, I don't have great faith in this forecast, more so because of the change in the position that low pressure system over the last few days. It could easily be the case that the high pressure to the south of us could assert itself and move the low pressure more northwards.


Agronomic Notes


I start this week with a look back at June from a GDD perspective using our default location. I said 3 week's ago that June 2024 wouldn't continue the run of record warmth and as we can see from the monthly GDD total of 264.1, that clearly is the case, ranking as the coolest June for 10 years and in the bottom 1/4 of June GDD totals since I started recording in 2005. In fact June 2024, was only slightly warmer than May 2024, when normally we see a significant uplift. Despite this low GDD score, as we will see later in the blog, June 2024 was a high stress month from an E.T vs. rainfall perspective, more on that later.



Cumulatively-speaking, the end of June 2024 hit a total GDD of 811.2 and this means it comes in as the 2nd warmest, first six months of the year, courtesy of the warm winter and spring months.


Looking at the Prodata Reports output for June 2024 from the same location we can see how the 2nd half of June 2024 featured some high plant stress days with E.T readings close to or exceeding 4mm moisture loss in a day. The other giveaway is the balance between rainfall of he month (21.8mm, with the last significant rainfall on the 15th) vs. 113.51mm of moisture loss by E.T. This gives a soil moisture deficit of -91.7mm for the month, which is significant.


The relationship between temperature and E.T is an interesting one, not least because it is tenuous. I took data from 3 days last week, two of the warmest ones on the 25th and 26th June, followed by the first cooler day on the 27th June.



Date Max air temp Time Max wind gust Total E.T Max E.T loss per hour Time

25-06-24 27.3°C 17:00 12mph 5.56mm 0.64mm 12:00

26-06-24 27.8°C 19:00 10mph 5.49mm 0.64mm 13:00

25-06-24 21.1°C 14:00 23mph 4.83mm 0.66mm 14:00


Evapotranspiration (E.T) to give it its full name is a complex calculation that relies upon temperature, humidity, wind speed and solar radiation but for our purposes the key drivers are temperature, humidity and wind speed. If the air is very humid, it contains a high level of moisture as water vapour. This means that regardless of the wind and temperature, the E.T will be low because it is very difficult for moisture to evaporate into an atmosphere that is already close to saturation. That is why in humid climates when you sweat it doesn't evaporate from your body / clothing. The converse is true, lower humidity = drier air and the potential for higher moisture loss.


Looking at the chart above shows some interesting data when we had those very warm days.


Firstly, the temperature built slowly through the day and didn't peak till very late in the day, 19:00 on the 26th of June. E.T-wise, this peaked a lot earlier in the day, 13:00 on that same day, so maximum drying / evaporation was occurring 7 hours before maximum air temperature. We saw the same pattern on the 25th, max temp @ 17:00 vs. max E.T @ 12:00. Although E.T peaked much earlier, moisture loss continued right through to beyond 10:00pm.


What are the practical consequences of this data ?


Well on one golf club I correspond with, we know that for every 1mm of moisture loss by E.T, we lose 1% of moisture from the rootzone. Now this will differ from facility to facility dependent on rootzone type, green design (contours) and green aspect (high - low E.T).


On the example I have mentioned, it means an 18% volumetric moisture content reading early in the morning will be sitting down at 12% at the end of the day. Peak moisture loss is likely to be between midday and 14:00pm, but this will vary depending on humidity and particularly wind strength. If we look at the data from the 27th June, the air temperature dropped by over 6°C vs. the previous day, but the maximum moisture loss per hour was actually higher on this day than the two previous (0.66mm vs. 0.64mm), despite the fact that they were warmer.


Why was this ? The answer is in the wind strength which peaked at 23mph on the 27th vs. 10-12mph on the previous days. Bottom line your hottest day will not necessarily be your highest E.T day and that's why knowing your E.T is vital to correct mains irrigation and hand-watering practices.


In turn the areas that dry out quicker are susceptible to more localised plant stress and can then develop into Anthracnose later on in the summer, or perhaps not so later on....


I mentioned last week about that fact that last week's temperature followed by rainfall this week will definitely constitute an Anthracnose trigger. This will be the 2nd trigger event of the year, with the 1st occurring on the 9-11th May as detailed in an earlier blog. Over the weekend I had some images sent to me (thanks Ben) showing clear disease development with the now familiar blackened base of the grass plant. If you looked at these areas under a microscope, you'd see the familiar fruiting structures called Acervuli with hair-like setae (image above) usually present as well. It means this disease has gone through its whole cycle from infection to sporulation (spore production) by the time the symptoms are visible to you or I from a grass plant leaf perspective.


That is why preventative control is the only effective strategy for this disease.


So the occurrence we are seeing now would be due to spore germination back in May, fungal growth into the plant thereafter and then plant symptoms developing when the plant experienced a high stress period (late June). I wouldn't be surprised if Take All has already made an appearance as well given the high E.T days at the end of June and wet spring.


OK, that's me for another week, I might get a chance to do a blog next week if its raining and the campsite WiFi is behaving, if not, it'll be in a couple of weeks.


All the best.


Mark Hunt




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Glenn Kirby
Glenn Kirby
01 lip

Enjoy Gower Mark, Beautiful area of the world (if its dry!).


Great Blog

Polub
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