September 26th

Hi All,

A lovely scene looking out over Rhossili and Worms Head on The Gower, South Wales last week but the absence of sunbathers, sandcastle makers and the like offers a clue that temperatures were a little chilly with a pronounced north wind. What a place though to get away from all the negativity currently doing the rounds.

Jumping into the heavens for a minute, tonight Nasa will attempt to crash a space craft on purpose into an orbiting asteroid to see if it can change its current trajectory (orbiting another asteroid). I did muse to myself that maybe tomorrow I'd turn on tomorrow's morning news to hear a good and bad news summary of the exciting project. The good news being that it is indeed possible to change the trajectory of an asteroid, the bad news is it is now heading towards earth 😂

You can watch a live (ish) stream here bearing in mind it is 7 million miles away !

This September we have seen quite a pronounced change from summer to autumn whereas in recent years we normally see summer extend into October with warm days and muggy nights. Not so this year with our first ground frost mid-month and a steep drop in both day and night air temperature.

Our old friend the jet stream is behind it as high pressure systems forming in The Atlantic have funnelled down a more northerly airstream this month and this coming week will be no exception. Early on in the week we have high pressure in the mid-Atlantic and a northerly low pressure pushing down these colder winds (image bottom left). By the end of the week (image bottom right) a new Atlantic low pressure arrives to push some very strong winds and rain our way over the course of Friday before settling down during the weekend.

General Weather Situation - w/c 26th September

So above we have the animated GIF's showing the two-part story of this week, cold northerlies for the start accompanied by some blustery showers followed by a pretty windy and wet end to the week on Friday. Putting some detail on it we will see showers crossing the U.K & Ireland during Monday and Tuesday pushed along by a strong north westerly wind that'll peg back temperatures to the low teens during the day and mid-single figures during the night time. Rain-wise, we have showers with us for the first half of the week but these will increasingly become confined to north eastern and eastern areas of the U.K and the north west of Ireland. Tuesday morning looks wet for west of Ireland and Wednesday afternoon / evening for north east Scotland. As we head towards Thursday, we look to dry up a little but by Friday we see that second Atlantic low push in and that'll bring heavy rain and strong winds into the equation. Currently this rain looks to make landfall early on Friday into the west of Ireland before pushing quickly across The Irish Sea into the west of the U.K and then moving across all areas during Friday. The weekend looks like a continuation of the unsettled, windy theme with showers on Saturday before a ridge of high pressure settles things down for Ireland and the southern half of the U.K during Sunday, but it'll remain wet and unsettled for the north and Scotland.

(All GFS images courtesy of tropicaltidbits.com)

Weather Outlook - w/c 3rd October

So next week looks like we will have high pressure in charge but with a nearby Atlantic low feeding in rain fronts across the U.K & Ireland, particularly for Monday and Tuesday. With high pressure sat south of us this means that the trajectory of these fronts will be mainly westerly to north easterly, however it'll only take a slight shift in the position of the high to allow these fronts to push further south. As we head towards mid-week, things settle down a little on the rainfall side of things and we dry up but we have another Atlantic low pressure due to make an appearance at the end of next week.

(Image courtesy of windy.com)

NOAA (National Oceanic & Atmospheric Administration) predicts a higher than normal Atlantic hurricane season.....

I was looking through NOAA's website recently as about this time of year they provide an indication as to the likelihood of Atlantic hurricanes which as we know tend to pitch up on our shores as autumn / winter storm systems. They are predicting higher than normal Atlantic hurricane activity which may then mean we pick up a wetter, unsettled theme for our weather leading through the coming months. To be honest whether you like the sound of that or not, quite simply we need the rain as however you dress it up, we are still very, very dry underfoot. You can read about NOAA's projections here.

Agronomic Notes

As mentioned earlier, the second half of September has indeed provided a reminder that autumn is very truly here. The chart above tracks the minimum air temperature vs. the soil temperature at 100mm depth in our default Thame location and you can clearly see the gentle decline in soil temperature from 17.5°C at the start of the month to just under 14°C currently. This location had a ground frost on the night of the 17th of September, one of the earliest I can remember but I'd say this is fairly typical of the type of soil temperature reduction we used to see.

That said, on the same date last year we were sitting at 16°C+ soil temperature so it is lower than we have come to expect in recent years with our balmy autumns. The next month will be interesting because in the past we would be down at 6-8°C by the first week of November but of late we have usually been still up in double figures into November.

It'll be down to the jet stream to determine which side of the autumn coin we end up on....

Looking at our monthly data so far in the reporting system I'm developing with Prodata for Davis weather stations, you can see September 2022 has some interesting stats which I have highlighted below ;

• Since the 15th of the month we flipped the coin temperature-wise and began to pick up some notably cooler nights with the majority in single figures.

• The rainfall and E.T figures up until but not including today in totality are just about at parity which in essence means we won't have reduced the soil water deficit situation that was created by this summer's drought. So whichever way you dress it up, we are still very dry.

• The rain that did fall on occasion did so in a torrential fashion with rain rates per hour > 150 mm per hour (6" per hour in old money) which would have caused it to wash off rather than soak into the soil profile. Not the kind of rainfall we need to rectify a record drought I am afraid.

• And reinforcing the stats above in terms of cooler air temperatures and lower soil temperature, we can see that the dominant wind direction for this location has been northerly. 19 out of the first 26 days of September showed the mean wind direction for the 24-hour period was northerly. I think that's odd.

• From an agronomic perspective we can see both Growth-degree-day (GDD) and Growth Potential (G.P) numbers have taken a reciprocal nose dive from the heady heights of optimum growth in the first half of September to on some days, less than 50% of optimum growth (G.P < 0.5).

• As a consequence, germination and establishment will take longer compared to an early September seeding date as an example. Whilst Festuca and Lolium species will still happily germinate at the soil temperatures we have now, Agrostis is a less compliant species and particularly Agrostis stolonifera. (Creeping bentgrass)

• Recovery from aeration will take roughly twice as long, so earlier this month Facebook was adorned with pages of newly-recovered surfaces 7 days after significant aeration, now the same process of recovery will take at least twice as long. This reinforces why mid-August to mid-September is such as good time to get aeration done and also why once we reach the end of this month, recovery begins to extend out and into a period when usually we have other issues (lack of drying days, higher disease levels with sand on the surface as an example) to contend with (other than temperature) which also impact on recovery significantly.

• Nutrition choice will definitely change from the usual summer suspects of urea, methylene urea, etc to more immediately-available nitrogen sources like ammonium sulphate and potassium nitrate or a combination of the above so all your eggs aren't in one temperate basket so to speak.

• Whilst September is 'usually' one of the lower Microdochium nivale pressure months, just typing 'usually' makes me grimace a bit nowadays. Looking at the Smith Kerns data from this location we can see we had 8 consecutive days when it hit > 40% and I'd associate this with high disease pressure. On the flipside of the disease pressure coin and instilling a positive mindset, the second half of September has seen that level drop back markedly so that explains the lack of "Oh no I have Microdochium" images on FB :)

• The cooler and drier conditions in the second half of the month have decreased to some extent earthworm activity and with some better drying days of late, cast dispersion has been less of an issue. We know this is a temporary lull in what is usually a perennial autumn issue and I expect to see (unfortunately) more activity next week (and over the weekend) after Fridays rain and next week's high pressure system kicks in. Sorry about that.

Ok that's me done for this week's blog, next week we will be into October and so I'll look back at September from multiple U.K & Irish locations.

All the best...

Mark Hunt