19th May, 2025

Hi All,

Now then, a short blog this week because my go-to tropicaltidbits.com is currently offline (I am hoping it hasn't been hacked) so I can't show you what is happening / projected to happen.

The good news for all of you guys and girls short of rain is that my hunch from last week looks like being correct with a change on the way in terms of wind direction, night temperatures and most, most importantly, rainfall. The bad news is it makes our next Bank Holiday a little less tolerable weather-wise, but hey you can't have everything. Best take my waterproofs to Silverstone for MotoGP, my money is on Jack Miller, a renowned rain specialist.

I have to reveal I am writing this blog under duress...

Duress from Mr Robin, who is applying significant psychological pressure on me as I sit at the kitchen table and type. Whenever he and his cohorts (Blackbirds, Dunnocks and the like) are hungry, he hops onto the handle and trills at me until I put some food out. Boy he is persuasive.

Speaking of trilling, I was out walking in Fineshades Forest, Corby at the weekend and it was a dull, cool, Haar type of day. So dull, that an Owl was hooting and whilst I stopped to check at my watch, for it was nearly lunchtime, I heard another bird interloper, but one with such an unmistakable song it stopped me in my tracks, a Nightingale. So, so beautiful and a bird whose song holds some lovely memories for me. I remember sitting in a bar at Gleneagles in the wee hours, deep in discussion on the biology / fishing of The Great Lakes with Dr James Beard, ( himself a very keen and accomplished angler) sipping a Whiskey and hearing Nightingales singing outside through an open window. Cracking......

Onto our weather, because it is a changing....Above is an image lifted from meteoblue.com showing the current position and speed of the jet stream.

You'll notice from the scale on the left that the colours associated with it indicate a low speed (in mph) and it is split into two. As I explained last week this has given us our run of dry weather and easterly winds. Now you'll hopefully also notice that purple lump out to the west. Well that is a strong jet stream pulse on its way across The Atlantic. Must be all that hot air from old Trumpie 😂

Contrast the above with the projection for the coming weekend shown below ;

The 2nd image shows a strong Atlantic jet stream (purple), with high wind speeds and it is this that will push Atlantic weather fronts across the U.K, Ireland and Denmark over the coming days.

Note the snippet from Meteoblue.com for the coming week and in particular the wind direction. Monday to Thursday sees the now normal E and NE, but from Friday the wind swings round to the SW and that brings rain into the weather picture for the first time in nearly 2 months in some places.

The other feature of a westerly wind is that it'll bring more cloud cover at night and that tends to lead to an uplift in night time temperatures. A feature of this spring has been very low night time temperatures with a consequently negative effect on daily Growth Potential. So with a bit of luck and a fair wind (pardon the pun) we should pick up some moisture and better (more consistent) growth conditions.

Putting some detail on that rainfall, we should start to see some showers across Ireland through Tuesday afternoon. This rain across Ireland will intensify into longer spells of heavy rain, particularly for the south and south west of Ireland later into the evening. Through Wednesday it'll sink south into The South West and we could see showers breaking out across the south of England and possibly further north.

By Thursday, we will see a significant drop in temperatures across Denmark as a cool, low pressure ushers rain into Jutland, Funen and Zealand. This low pressure will circulate across Denmark and gather more moisture up to bring more rain on Friday and Saturday, before moving away. Hoping westwards across The North Sea to the U.K, Thursday will see a continuation of some 'hit and miss' showers, but don't despair if you miss them, as more significant rain is on the way. After Thursday's drop in temperatures across Ireland and the U.K (though not as much as the Dane's will experience!), Friday sees a recovery in temperature and the arrival of rain into the west of Ireland late in the day. This rain front will push eastwards on fresh, south westerly winds and make landfall across western coasts of England, Wales and Scotland on Saturday morning. This rain will push eastwards across all areas during Saturday bringing some nice and direly-needed rain to many areas. That rain continues overnight and into the early hours of Sunday before leaving a drier, showery outlook for the second part of the weekend. For Denmark, we will see this rain push into the west of Jutland on Sunday and cross all areas during the course of the day, clearing overnight into Monday morning. Just in time for the next rain front to push into the west of Ireland and I can see another lining up further out in The Atlantic. So a nicely unsettled period of weather looks to be coming up.

Now, I can't bring you any outlook detail because of the tropicaltidbits.com outage but looking at other GFS sites, I can see this westerly, stronger airstream projecting into the 1st week of June as it stands now. Let's hope that is right as we need a breather.

Agronomic Notes

So as I have indicated already, we should be in line for some nice moisture which will be a welcome tonic after the weather of late. Charting out some daily E.T's from our default Thame location, you can see why May has been a testing month ;

The above E.T readings add up to a combined moisture loss of 64mm month to date but when you look at the soil moisture surplus and deficit and run the stats for rainfall vs. E.T from the beginning of April, you can see why the water companies are getting nervous.

So we are sitting at a cumulative soil moisture deficit of 126mm , that's 5" of rain in old money.

Looking back to 2020, our last dry spring when we had from memory another Diffluent Blocking Event, from the same location, for the same date range, the soil moisture deficit was -120mm, pretty similar.

I joined an RMets (Royal Meteorological Society) lecture recently which looked at global weather patterns, weather drivers like El Niño and La Niña (known as teleconnections) and their effect on rainfall patterns in the east of England. I was surprised to learn that droughts in the U.K tend to occur in La Niña years. Guess what year we are in now ? Yep a La Niña year.....You can catch up with the lecture here

I ran some stats from other locations to see how they compare and they are listed below ;

Location Soil moisture surplus / deficit

Fife -122mm

Ayr -111mm

Bath -111mm

Tiverton -36mm

Beccles, Suffolk -146mm

Bury St Edmunds -124mm

Guildford, Surrey -105mm

Sevenoaks, Kent -110mm

Milton Keynes, Bucks -112mm

Thame, Oxfordshire -126mm

Leicester -119mm

Scarborough -117mm

Limerick -67mm

Dublin -50mm

Silkeborg -57mm

Copenhagen -93mm

Now it should be pointed out that the numbers above only reflect the soil moisture surplus / deficit from April 1st. Many locations were showing a soil moisture deficit for March as well. It is clear the East of England has fared the worst I think and that is logical because a) It is a drier area of the country and b) The winds have primarily been easterly in nature and so the area affected by the strongest winds would be the eastern coastline of the U.K. The same is true for Denmark when comparing Zealand from Jutland. The west has fared better, but not always massively so.

What does this mean agronomically ?

Well, as discussed last week and evident on the Daily E.T graph, the grass plant has been under significant stress of late. It is under these conditions that PGR's, biostimulants and sensible cultural management come into play. It isn't the time to stick a Graden or deep verticut through your sward for example. (Not that you would currently I know). On the flipside, humidity levels have been on the low side and this has meant that periods of plant leaf wetness have been relatively short.

For this reason, the Smith Kerns Dollar Spot Probability levels have been running along on the low side compared to last year as an example. With the arrival of moisture, that plant leaf wetness dynamic will change as atmospheric moisture levels increase. Now it will also be cooler so I don't expect to see a massive increase, but we have to be on our guard. On the plus side, growth will also be better because of the higher night time temperatures and natural moisture (better coverage for one !!!) levels in the form of rainfall, so hopefully it'll grow out as fast as it comes in.

Now we have also seen some high temperatures of late and thoughts no doubt will turn towards another disease, Anthracnose. This disease requires high air temperatures (>=23°C) to germinate the spore first up and then critically it also needs a period of plant leaf wetness for the developing fungal mycelium to grow on the surface of the grass plant leaf. Now time will tell here, but my data obtained from Davis plant leaf wetness sensors has shown limited periods of dew formation because humidity levels have been low and wind / E.T levels higher than normal, drying out the plant leaf.

That's not to say we haven't had dew formation but the intervals have been shorter and of course they have occurred exclusively at night. At the same time, we have been cold at night, temperature-wise. Way away from the sort of temperature range that Colletotrichum cereale (Anthracnose) likes to grow. So my conclusion is that in general (not for everyone) the warm / hot conditions of April / May have not represented Anthracnose trigger event. Time will tell if I am right.

OK, that's it for me now, all the best and hopefully the forecast proves correct and you get some rain 😀

Mark Hunt