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  • Writer's pictureMark Hunt

July 18th - A bit of a hot one but well predicted by the forecasters....

Hi All,


Back from a lovely break in the campervan on the beautiful Gower Peninsular in South Wales. Bizarrely on a holiday where I spent 99.9% of my time outside, walking, fishing, a bit of running and body boarding, I came back with Covid and currently not enjoying the experience at all. On the flipside, Rhossili Beach and Worms Head must rate as one of the most beautiful sights to see on a lovely summers evening. I saw 2 Basking Sharks earlier in the day.


As is usual for me on holidays, the weather is never far from my mind and walking down to the end of the peninsular at Worms Head, I was greeted by the site of a Davis Vantage Pro weather station on top of a building. This building is part of the National Coast Watch Institution, an organisation that my erstwhile colleague, Peter Palmer from Prodata informed me we supply with weather stations. You seldom escape work eh ? 😊


Of course all the talk is of the anticipated record temperatures we are looking more than likely to hit over the next couple of days. In my previous incarnation of a blog, I did claim a few years ago that it was only a matter of time before we hit 40°C by virtue of a hot air plume pushing up under a peak in the jet stream and so it has come to pass. It is the first but it won't be the last.

To me there's a bigger story behind Monday and particularly Tuesday's record temperatures and it's our old friend E.T. For Tuesday, alongside record temperatures, they are forecasting strong southerly winds and relative humidity values down in the low teens. In other words the air will be very dry and so the potential to evaporate moisture into it, extremely high. This means the potential E.T tomorrow will also be record-breaking I think and from an agronomic perspective, it will remove a huge chunk of moisture from the land. If I get a chance I'll calculate the anticipated E.T, but I expect it to hit 8mm plus in some locations on Tuesday.


The other story of 2022 is that it is turning out to be an extremely dry year with many locations reporting only 50% of their normal y.t.d rainfall. Dove-tail that in with higher E.T as well and we really are facing a moisture-deficit situation in some locations. I'll look at that later. One ray of hope is that the end of this month is looking cooler and wetter with the possible resetting of the jet stream position further south. It's difficult to imagine when you look at the heat sink across southern Europe but we can hope.


Ireland as well could be on for a record day temperature today and if so, it'll break the existing one of 33.3°C recorded on June 26th, 1887 at the weather station located in Kilkenny Castle.

General Weather Situation


So we know Monday and for me, Tuesday will be incredibly hot with that hot air plume pushing up over the southern half of the U.K and Ireland. Surprisingly it isn't a completely dry picture though because that nearby low pressure will feed showers across The South West and east coast of Ireland from lunchtime on Tuesday and these will push northwards through the afternoon. We will also see rain across the north west and north of Scotland during Tuesday evening / night.


During Tuesday night / Wednesday we see that low pressure in The Bay of Biscay move across the southern half of the country. Now for me, introducing moisture into a very hot air scenario means thunderstorms but so far there isn't really much of a suggestion of these in the output for Tuesday night but I do think it's a possibility that we will see thunderstorms overnight into Wednesday across central areas. My hunch. Wednesday sees cooler and cloudier air push in across Ireland and the U.K and it's likely to bring rain across Wales during the morning. A good bit of uncertainty about this rainfall and its trajectory currently but then it is continental rainfall so that's normal from a forecasting perspective. This rain will extend north and eastwards through the afternoon. Some places will get a good bit, some none, it'll be on of them you know..."the rain just went round us" scenarios....Ireland looks to have a drier one with temperatures down to 20°C. UK-wise, expect 25-26°C across the southern half and 5-6°C lower for Scotland.


Thursday and Friday sees more of the same really with a weak high pressure system sitting over the U.K. A cooler high though so back down to the low twenties for the end of the week for all of the U.K & Ireland and most importantly, night temperatures dropping into the low teens, much more comfortable like. There's a chance of showers crossing Ireland overnight on Thursday but these are likely to be light and few and far between.


Now for those across the north and west wanting rain, well you may get your wish at the weekend with heavy rain likely to push into the south west of Ireland on Saturday night and cover most of the country before pushing north and east into Scotland. This rain looks to stay put for most of Sunday as well across Ireland and Scotland, clearing slowly from the west. There's a chance that this rain band will then move eastwards into Wales through Monday but let's see....Away from this rain we will see heat build again on Sunday with temperatures in the high twenties.




Weather Outlook

All GFS output courtesy of www.tropicaltidbits.com


At first sight, the GFS schematic for next Monday doesn't look very promising with a warm air peak settled over the U.K. That low pressure system though out to the west of Ireland is projected to move eastwards and that'll bring in both cooler and more unsettled weather along with it. Now the GFS projection for rainfall shows that in the early part of the week, most of the rain associated with this low pressure will be for Ireland, the north west and north, however as we move later into the week, the rain pushes into more central areas. Now the ECMWF model doesn't totally agree with this but it does have low pressure around for the first part of next week, so I think cooler and unsettled is the outlook extending towards the end of the month. Let's see who is right.


Agronomic Notes


Learning from across the water


First up, let's talk about the heatwave that we are experiencing. It is interesting to me because earlier this year I gave at talk at Harrogate on climate phenomenon and picked out the 3 main areas that provided a challenge turfgrass management. One of them unsurprisingly was heatwaves and the propensity of the jet stream to form these hot air peaks. Anyone that knows me knows this has been an area of interest for me since 2010. Now last year in the Pacific North West and Canada they had one of these hot air plumes (you can imagine the U.S media's viewpoint) and temperatures climbed to the mid-40's in what is predominantly a cool season grass area, bent, Poa annua and ryegrass. I talked to the USGA agronomists about their experiences of this heatwave and their feedback was interesting.


The big take home from them was that there was very little grass lost and horror stories from this event and the primary reason for this was that they knew it was coming.


When you look at our mini-heatwave, the same is true. Whatever you think about weather forecasters, they called this one accurately. The problem is not the weather forecasters, it's the media and their 'interpretation' of the weather. The first part of this heat signature (last weeks heat) showed up in the GFS forecasting on the 26th of June. This week's heat signature was the same. We had roughly two weeks notice.


The second reason they saw very little grass loss was because the heat built incrementally as it tends to do in a high pressure scenario. Again we share the same pattern here unsurprisingly of heat building over time.


As I write this I expect most of you had your preventative treatments down on fine turf areas last week. I'm not referring to pesticidal ones, I am talking of wetting agent, biostimulant, PGR and pigment maybe. All well in advance of this week's temperature peaks.


Organic matter is a hot topic !


The problem when it does come occurs on areas that are un-irrigated or perhaps irrigated but there's insufficient water to keep up with demand E.T. So we are talking fairways, semi-rough, rough and general outfield turf. Bunker banks are another.


Here we often have an excess of organic matter and this is the real enemy during heat. Organic matter heats up much faster than soil / rootzone and so typically we can expect much higher temperatures to actually occur in the region the grass plant is living as opposed to what we see on our weather stations which are typically situated 1.5-2.0m above ground.


In addition, at grass height we have less wind so the region of air just above the grass is at a much higher temperature than at 1.5-2.0m. Looking at some data from one of the weather stations I work with.....At 13:35pm, the weather station is showing 34.7°C @ 2m height, but the extra temperature / humidity sensor located at ground height is showing 39.8°C. So the air above the grass canopy is + 5.1°C higher air temperature-wise.


So areas of turf higher in organic matter are the ones most likely to check out, not just because of two days heat but because we are in a run of very little rainfall vs. higher than normal E.T.


2022 is not just a dry one...


Back in April, I started an E.T vs. rainfall dynamic graph at The Oxfordshire, Thame and today I updated the data to see how things are faring as we head past the middle of July.


Here's a summary of the monthly rainfall and E.T data year to date.....


So you can see for the first 3 months of the year we had more rainfall than E.T, but since then, it's gone very much the other way with April, May, June showing an average net moisture loss of around 60 mm. July is already exceeding this figure and we are only just over half way through. If you summarise rainfall vs. E.T since April 1st, here's how it looks....

So the graph is showing a net loss of -250 mm (10 inches in old money !) or thereabouts since April 1st, 2022 when you take into account rainfall vs. E.T.


I think that is the real story of 2022, a year so far of limited rainfall and much higher E.T than usual. That's why reservoir capacities are low, the groundwater table likewise and water companies are sending you those "Please be careful with your water usage"-type text messages.


We are in a drought year.


As I finish typing this blog, it is 14:05 pm, my highest weather station air temperature is 35.3 °C and the E.T has shaded 4.0 mm for the day so far. I reckon we will peak at 37-38°C today with the magical 40°C exceeded tomorrow.


All the best, enjoy the heat sensibly and don't forget to look after your local wildlife. My resident Hedgepigs drank loads last night !!!


Mark Hunt

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