December 6th, 2021

Hi All,

Just getting light outside on another winter’s day. Since we turned the clocks back it seems like to me it was both a time and meteorological switch as you can’t argue it has been more like a typical winter since, with some storms, snowfall and the odd frost thrown in to boot. Two weeks to the shortest day mind…

Storm Barra as portrayed on GFS output

The next storm is lining up to push down this week and looks to be a very intense low pressure with tightly packed isobars and a lot of rain associated with it. This one is called Storm Barra and as you can see from the projected output above, it’s a westerly / north westerly-orientated storm with potential for structural damage across Ireland and the U.K.

Met Éireann have issued an Orange warning for Co. Clare, Cork, Kerry, Limerick and Galway and the Met Office, a yellow warning for snow and high winds across Scotland and wind and rain across England and Wales. You have to feel sorry for those engineers putting right the damage caused by Storm Arwen, only for this to rock up just over a week or so later….

Incidentally sorry for you lot receiving 2 publications of the blog last week, not sure what happened there as its now on a different platform…ho hum….

GFS Output 06-12-21

General Weather Situation

So as predicted a week ago, we have a quietish start to the week with the right side of what will be Storm Barra already visible on the GFS output. So Monday looks to be a day of rain showers pushing across the U.K from the west to the east with Ireland clear for most of Monday after having a wet end to Sunday. Some of those showers across Scotland and the north of England will be wintry in nature at elevation but will clear the former first to leave a cold, dull end to the day there. Despite the presence of a south westerly / westerly wind, it’ll feel on the cool side with a nippy wind chill. Some sunshine across the west once the rain has moved through. Temperature-wise, expect 4-6°C.

Tuesday sees Storm Barra pitch up off the west coast of Ireland pushing heavy rain into the south west and west initially at dawn before tracking north and east across the whole of Ireland in time for the M50 rush hour. Strong winds and very heavy localised rain is predicted. On the run up to midday, the centre of the storm crosses The Irish Sea and pushes strong winds and heavy rain into The South West and West Wales initially before pushing eastwards across all western areas. As it does so, Ireland will experience a lull in proceedings. Some of that moisture may fall as snow across Scotland as the rain butts up against colder continental air. By dusk, the band of heavy rain will be across all but the furthest easterly areas of the U.K (East Anglia) clearing Wales and The South West as it does so. Ireland sees the next swirling arm of Storm Barra push showers into the west and north west whilst Scotland will sit firmly under the rain, sleet and wintry shower mix. In essence, Tuesday is a pretty messy weather day with some high rainfall totals predicted and very strong winds pushing in from the south / south east later in the day. Be wary. Remaining cold with 4-6°C likely and a negative wind chill I’d expect.

Wednesday sees the centre of the low pressure across the U.K, so a continuation of showers and heavier rain, mainly across the western coasts of the U.K & Ireland, but plenty inland as well. Still windy from the south on Wednesday but that wind will gradually decrease through the second part of the day. So remaining windy, dull and cold with plenty of rain around with similar temperatures to earlier in the week despite the southerly wind direction.

Thursday sees a much quieter day as Strom Barra departs. Still some rain around across eastern coasts initially but a much quieter day and a change in wind direction as it swings round to the north / north east. Some sunshine on Thursday to cheer up the day and much drier than of late. Around midday, a new rain front pushes into Kerry and this will make its way eastwards through the course of Thursday afternoon crossing the Irish Sea and reaching the western coastline of the U.K late on Thursday night. A bit brighter then but remaining on the cool side, particularly with the wind direction and still 4-6°C likely.

Closing out the week on Friday and overnight that band of rain is moving west to east across the U.K, so by Friday morning it’ll be across central areas of the U.K and stretch from the south coast to Scotland. Western areas including Ireland and Wales will have a chance to dry off on Friday I think after that rain passes through. That band of rain will fizzle out midway through Friday to leave a cool, dry day with some sunshine. Dry all day it looks like for Ireland. A northerly wind in situ so remaining stuck in that 4-6°C temperature range with a pronounced wind chill. It’s a legging job for my long run then 🙂

Looking ahead to the weekend and we have rain over Ireland and Scotland on Saturday that is projected to sink south and east through the day clearing Ireland and all but the east / north east of Scotland as it does so. So a wet start to the north and west but a wet end to the day for central areas of the U.K as that rain front moves down. More rain is projected for the southern half of the U.K on Sunday, so a pretty cack day I’d say for here. As usual with the weather though, there’s always a flipside and for Ireland, Scotland and the north of England, a dry day with less risk of showers and some winter sunshine. That rain should confine itself to south of The Pennines / Humber Estuary I think. A change in the wind direction for Sunday with a southerly wind pushing in and temperatures finally moving up a notch to 6-8°C, despite the rain across England and Wales.

GFS Projected Output 13-12-21

Weather Outlook

You can easily see why Sunday looks a wet one for the south of the U.K when you clock the orientation of the low pressure system above so it’s hardly surprising then that Monday next looks to continue the wet theme for Ireland and the southern half of the U.K, with Scotland missing the bulk of the rainfall. Tuesday sees a new low pressure system push across all of the U.K and Ireland with strong winds and heavy rain before breaking down into a more showery picture for Wednesday as high pressure begins to build south and west of the U.K. This has the effect of pushing rain up across the north of Ireland and into Scotland on Wednesday leaving the south drier.

GFS Projected Output 17-12-21

As we approach the end of next week that high pressure keeps building and that’ll bring milder air into the picture for Ireland and the west. If you look at the GFS output above you can see the source of the air is southern Europe and Africa so that means potentially mild and humid potentially (more on that later) for Ireland and the western half of the U.K. Across the east it’ll be cooler, duller and windier with a pronounced northern airstream. That high pressure is projected to stay in place till the mid-part of the following week and that’s a concern I think. So in summary, a wet and unsettled start to next week with particularly Tuesday looking wet for all before the weather quietens down and we dry up. The tricky bit is trying to differentiate the likely consequences of high pressure on the run up to Christmas.

Agronomic Notes

So we start off looking back at November which was for most a pretty dry month and for some one of the driest on record.

No bad thing when you’re dealing with worm casts and the like…

November 2021 GDD – Location – Thame, Oxfordshire

November tipped its hat with a total of 60 GDD which puts it towards the lower end of what we have been recording since 2010 (37.5 – 122.5 is the range). The story of November 2021 wasn’t so much temperature as rainfall-related, with many locations picking up their driest November since records began. Coming after a wet October that is welcome.

That puts us cumulatively at 1803 total GDD to the end of November, which as I’ve pointed out previously means 2021 will not break the 2,000 total GDD mark for the year even if December turns out to be a mild month which I don’t think it will save for the high pressure incursion on the run up to Christmas. I expect 2021 to come in around 1840 for the year which is kind of average and shows how pronounced an effect that cold and dry April, followed by a cool, wet May had on the yearly temperature.

So yet again the model for the U.K and Ireland confounds the trend for increasingly high temperature (because after all that’s what we are measuring with GDD) and yet again I’ll reiterate that the presence of the jet stream across the U.K & Ireland will continue to have the biggest effect on our climate rather than a processional yearly increase in temperature. It is a double edged sword though because the jet stream as we know has the potential to deal us our extreme weather events and that’s what really what we have to manage from a turf industry perspective.

G.P & Rainfall – U.K Locations – November 2021

Now we have had some November months where I’ve had to redo the rainfall scale such is the magnitude of the rainfall but not November 2021. Most areas received around 20mm with the majority of that coming in the last 7 days of the month, so it was dry with a capital ‘D’….As mentioned before, that was great news because October was a wet one and it gave places a chance to dry out and manage issues such as worm casts. The lack of rainfall meant a lack of humidity and so November will go down across the U.K as a low disease pressure month on the whole with just a blip mid-month which showed on our disease forecasting model and the Smith Kerns model for Dollar Spot prediction.

I’ve mentioned this before as a feature of this year in that despite the geographical spread of the modest number of locations I have summarised, the Growth Potential is amazingly consistent. This indicates that the weather patterns were very stable across the entire U.K, with little evidence of a west-east or north-south divide. Scotland came in with similar G.P to Worcester for example. A really strange month when you consider it.

G.P & Rainfall – Ireland Locations – November 2021

A similar (ish) story across Ireland, except for Dooks and Valentia which showed significantly higher G.P than the other sites. Interestingly the south and easterly locations came in with very similar G.P and rainfall compared to the U.K locations and in most cases higher from a temperature perspective. That’s because the cold weather pushed in from the east during November and so westerly locations were warmer.

Disease pressure November 2021

In the past I used to think of November as the turning point to winter. Typically we got to early November, picked up some cold winds, night frosts and soil and air temperature dropped accordingly. This wasn’t the pattern for November 2021 with soil temperatures remaining much higher for longer and even increasing at the back of the month…

Soil temperature profile @ 60 mm depth – Autumn 2021 – Essex

So a warmer soil but November was a low disease pressure month for the U.K (less so for Ireland it has to be said) thus proving the lack of a link between Microdochium nivale activity and soil temperature. If we look at the Smith Kerns output for the same location we can see only one pronounced peak in November from the 11th November through to the 16th November when air temperature but most importantly humidity was high enough to promote disease.

Smith Kerns Disease Prediction Model – 2021 y.t.d – Essex

That was the story at least for the U.K in that we had a a dry month with consequently low humidity and that provided less of a challenge from disease and also worm casting. Ireland was different, here there was more rainfall, more humidity and if anything they were milder being further away from the cold air mass on the continent which affected the U.K from time to time during November. So more moisture = more humidity = more dew = more disease pressure.

Projected GFS Output 19-12-21

Looking forward I am concerned about the potential appearance of high pressure on the run up to Christmas with the GFS projection above showing a warm, humid high that draws its air out of southern Europe and Africa and pulls it up into Ireland and the U.K.

In recent years, a high pressure with this type of characteristic has resulted in very mild air temperatures, light winds, heavy dew and rampant Microdochium. Not really what we need and especially bearing in mind the run up to this features unsettled, wet and windy weather and the consequent lack of spray days. Now of course this is nearly two weeks off and things may easily change as we get closer to that date but for me it’s one to keep an eye on for sure.

I looked back and remembering December 2018 as a bad disease pressure month I pulled up this old Unisys Weather graphic from the Christmas period…

Quite similar high pressure systems I’d say…..

All the best.

Mark Hunt