May 30th - Another dry month for the south of England...

Got sent this brilliant photo of a Cuckoo by my good friend and former colleague, Iain Richardson. Not just any cuckoo, he is called Colin and returns to the same area, Thursley Common Nature Reserve in Surrey, every year after migrating up from Africa.

Iain is a mega photographer and tends to specialise in Wildlife. When we are chatting about nature and a specific bird, he always seems to have a special photo tucked away, you can see his brilliant work here

On this occasion I was remarking that I'd heard my first Cuckoo whilst out walking near Pateley Bridge in Yorkshire, but hadn't heard any locally. I managed to call it closer by imitating (badly) another Cuckoo. That changed at the weekend when I heard my first local Cuckoo at Rutland Water. They are a really fascinating bird because of their unique lifestyle and migration as well.

My other half reminded me of the Cuckoo rhyme which I was completely oblivious of ;

The Cuckoo comes in April,

She sings her song in May,

In leafy June, she changes her tune,

And in July she flies away

Speaking of flying away (tenuous link alert), I had my first flight in a monoplane at the weekend down at Duxford when I enjoyed 25 minutes in a WWII Harvard trainer. (part of The Warbirds Flight)

I got a chance to fly it myself for a time and we barrel rolled and looped the loop. "Do you want to go upside down?" the pilot asked...."Why not" I replied. Well one reason is you pull a nice bit of G and the other is that your stomach gets quite a work out being upside down like. A brilliant experience though and to know that this was the plane that pilots trained in before moving onto The Spitfire and Hurricane was something else. I'd love to do it again, but maybe not after a previous night out in London at The Bikeshed Show with associated beer intake ! I did feel queezy for a time but apparently you get used to it !!!!

Onto the weather and as predicted we duly picked up that cooler north easterly breeze yesterday that had temperatures struggling into the mid-teens. Last week the models were again at odds with GFS and ECMWFF in disagreement as to how this week would pan out, so let's see.....

General Weather Situation

So on Monday we see a cool and pretty dull start to the week with low pressure swinging in a succession of showers and heavier spells of rain across the U.K & Ireland. Initially confined to the north and western coastlines, the showers will consolidate and move inland over the course of the morning / afternoon. Tricky to say exactly who will get them and who won't, so I would advise looking at the rain radar. Despite the presence of a south westerly wind, Monday will be on the cool side for the end of May, expect 14-16°C, maybe a little cooler in Scotland and Ireland.

Overnight into Tuesday and it'll be a cool night with single figure temperatures. That low pressure is almost sitting directly above the middle of the U.K, so again expect showers and then longer spells of rain from the off. Maybe more likely to affect the eastern coastline of England and Scotland initially but the showers will move quickly inland and consolidate. I would say the west, Wales and Ireland will see less of the rain on Tuesday with rain more likely on the eastern coast of Ireland. Again feeling cool as the wind shifts round to a westerly and north westerly aspect. Later in the day we may see more in the way of sunny spells.

Onto Wednesday and overnight that low pressure pushes off into The North Sea leaving behind some showers over North Wales and The North East. A much sunnier, drier day on Wednesday with less showers around though we may just see some lingering on eastern coasts and across East Anglia. Dry for Ireland, Scotland and Wales, maybe the odd shower across the west of Scotland but nothing compared to of late. The wind will still have a north westerly / north easterly edge to it but despite this temperatures will pick up into the late teens, so expect 16-18°C.

Above is the GFS schematic for Thursday and you can clearly see that we are in a cool air trough and surrounded by 3 low pressure systems with a weak high on the continent. So no surprise then that Thursday continues the cool and unsettled theme across the north and north west, though further south it'll be dry and with some spells of sunshine.

It is a finely-balanced weather picture as we commence the Queens Platinum Jubilee celebrations and probably nicer weather in the south and central regions as we hold onto that ridge of high pressure. Any rain looks to develop courtesy of that north westerly low, so Northern Ireland and the north west of Scotland could see rain develop later into the day and some of it may be heavy. The wind will usher round to the south east so for central and southern U.K will benefit from warmer temperatures pushing up into the late teens and possibly eclipsing twenty degrees across the south of England.

Closing out the week and we see central and southern areas holding onto that high pressure but the north westerly low pressure is sinking down and so they'll be rain around across Scotland, North Wales, the north of England / east of Ireland. This rain will tend to be confined to The North West and fizzle out through the course of the late afternoon / early evening. A wide variation in temperature with Scotland, North Wales and the east of Ireland only down in the low teens under that thicker cloud and rain but further south and east, we again see high teen temperatures and pushing towards twenty degrees for the finer south.

The outlook for the weekend is 'mixed' with low pressure to the south of the U.K looking to impact the weather picture. Now I've commented before about this type of rainfall and its predictability but at this stage it looks like the south of England may pick up rain moving in from the coast on Saturday. This may have a thundery element and tricky to say how far inland. Away from this southern incursion, Ireland, Wales, central and northern England and Scotland look like having a fair day with reasonable temperatures. Sunday looks pretty dire across the southern half of the U.K with rain extending across to The South West and Wales through the course of the day. In contrast, Ireland looks to have a much nicer day with warm temperatures and plenty of sunshine. Definitely a hitting The Strand day ! The north of England and Scotland look to remain dry with plenty of sunshine but that rain across the south moves slowly northwards through the course of the day and could be locally on the heavy side !

Now it is weather caveat time again as we have disagreement between the weather models with the ECMWF model painting a much finer picture for the weekend with none of that southern rain. Meteoblue appear to side with ECMWF so it'll be interesting to see who is right. It is the phenomenon that is continental rainfall that I know is so tricky to get right. Don't be surprised to see your weekend forecast go from good to bad and maybe back again through the course of this week !!!!

Weather Outlook

So above is the projected weather picture for the start of June (06-06-22). The legacy of that trough pattern in the jet stream is clear to see but we can also see high pressure building to the south, west and east. Now I have a particular affinity to the weather in June because as a lad, June the 16th marked the first day of the fishing season. In the past, all rivers, canals, ponds and lakes ceased fishing from March 14th to June 16th (except Trout fishing) and so the middle of June marked the end of a three month period of abstinence. Many a time I watched the calendar slowly tick off the days to the glorious 16th. Except many a time, the glorious 16th was anything but and June often plays out as a cool and wet month with a predominantly westerly air stream. It isn't usually a banker summer month in my books. (it was though in 2018)

So how are we looking for the start of this June ?

Well I think we will see a north-south divide next week as high pressure pushes finer, warmer weather into the south and central areas but a northerly Atlantic low will bring cooler and unsettled weather to the west and north. You can just see the leading edge of that low pressure in the top left of the GIF above.

So next week I think we will see unsettled conditions to start off, warmer in the south initially but still with rain around due to the continental low pressure, cooler and wetter in the west and north. As we go through the week that northerly low pressure will push in a south westerly air stream across all areas with major rain on Tuesday for most areas other than the south of England. Cool and unsettled mid-week for most areas but as we approach the end of next week we see high pressure begin to stabilise the weather and settle things down so warmer and drier with less rain around. So quite a chop and change week weather-wise. ECMWF and GFS models tend to agree on the appearance of the Atlantic low pressure so that appears more certain I'd say...

Agronomic Notes

It is always difficult to generalise in a blog like this both in terms of the weather and agronomically but I think May '22 has been an easier month in terms of turf management compared to April.

We had some rain for one but that rain was very hit and miss. For instance, our rainfall record will show 66.7 mm for the month but 30 mm of that fell in a heavy thunderstorm on the night of the 19th. A lot of places missed this storm and only received 3-5 mm that night and so their rainfall will be down at 30 - 40 mm which is on the dry side. That dry May will follow on from a dry April so we know we are up against it from a moisture deficit perspective on un-irrigated surfaces.

To get an idea of how this looks, I charted out the daily E.T (evapotranspiration) and rainfall for April and May (well up until the 29th that is). As a reminder, E.T (evapotranspiration) is a measurement of moisture lost from the soil surface and turf canopy and it is calculated by a complicated equation known as the Penman-Monteith equation. You can read about it on Wikipedia here

From a turfgrass perspective, we know that this equation over-estimates the moisture loss from a close-mown turfgrass canopy and typically superintendents would work on replacing 50-60% of the stated E.T loss in order to keep the plant healthy. Obviously nowadays with the advent of the Pogo, Delta T and TDR moisture meters, these help to establish and reinforce the effectiveness of the irrigation strategy and the impact of high daily E.T.

So here's how the daily E.T / rainfall and soil moisture deficit / surplus looks at our default location of The Oxfordshire, Thame ;

You can clearly see the dry period in the middle of April when daily E.T levels reached 4mm per day on occasion and the arrival of some rainfall in early May. Not great amounts at this location but enough to keep the plant just this side of healthy. That said, the windy period at the end of May really pushed up the E.T and on the 27th of May, hit 5mm per day, which is high and would typically put the grass plant under stress.

So not quite a stress-free month and away from irrigated areas, the soil moisture scenario is definitely on the dry side as the graph below shows ;

This graph plots the hypothetical soil moisture deficit / surplus and assumes we start April with neither a deficit or a surplus. So it takes the amount of moisture from rainfall and subtracts the amount lost by E.T. More rain and less E.T gives a surplus and vice-versa. By the end of April we were at -60mm, so just over 2" of soil moisture deficit in old money and by the end of May, we are at - 120mm soil moisture deficit.

So despite more in the way of rainfall in May at this location, the soil moisture deficit grew again by the same amount as April, - 60mm. This (and the associated rainfall humidity) probably explains why I noted a good amount of Yellow Rust on grassland yesterday whilst out walking. A clear drought indicator that one.

The respective figures for this site were ;

Month Rainfall E.T Monthly Soil Moisture Deficit / Surplus

April 19.6 mm 77.9mm -58.3mm

May 30.0mm 91.7mm -61.7mm

May was also a humid month and that meant disease pressure was significant with Microdochium activity in the early part of May and then some of the more humidity-related pathogens like Red Thread and Fairy Ring putting in an appearance.

Using the Smith Kerns Dollar Spot Probability Model we can see the underlying disease pressure during the month. To give some sense of perspective, if this was the U.S, they would spray a preventative fungicide (for Dollar Spot), once the probability hit >=20%.

Over here I think that serves as a baseline for disease activity be that Microdochium or Red Thread or Dollar Spot.

At this time of year we are normally enjoying good growth so we are typically growing out disease as fast as it is occurring and with May '22 looking like it was a good growth month (I think in next week's look back at May, the average daily Growth Potential figure will be around 0.6 or 60% of optimum), this should be the case unless the plant has had a high PGR application. You can see from the disease probability model that we had two small peaks, one at the beginning of May and one in the mid-part of the month. The latter coincided with some locally heavy rainfall and that one in particular would have kicked off Fairy Ring activity.

Personally I don't think we actually see high disease pressure in the summer (from Dollar Spot or other foliar pathogens) until the Smith Kerns gets up to >50% so we are still someway to go yet thankfully. I also know I don't start to see diseases like Downy Mildew (on garden plants and the like) until we hit this sort of figure.

With rainfall in May it wouldn't surprise me to see Take All doing the rounds next month, especially on collars and approaches as bentgrass levels increase with overseeding. A wet and cool June normally leads to summer / autumn Take All but let's see how June pans out first and hope better weather prevails although I quite like the sunshine and showers weather that has typified May.

All the best.

Mark Hunt