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  • Writer's pictureMark Hunt

March 21st - Weatherblog

Hi All,

Well, some beautiful weather at the moment during the day but some very chilly nights to boot. We dropped down to -2.7°C here overnight last night and it's panning out exactly as forecast. Pleasant day temperatures and cold nights with the odd ground frost thrown in.

I know it's getting warmer because the Wagtails that have frequented my garden (including this lovely Grey Wagtail above) are visiting less often. This is because we are seeing midge hatches and more insects on the wing and so they don't have to rely on my mealworms and suet sprinkles anymore. Fair weather friends, well the opposite really but I'm pleased to have helped them through another winter

This will a shortened weather blog this week as I'm off to Harrogate to talk at the Bigga Continue to Learn conference and need to get some shirts ironed !

So, from a general perspective we currently have a low jet stream speed and consequently a meandering of the jet stream known as a Rossby Wave. The jet stream is really the driving force behind our weather as it pushes weather systems from west to east (typically 10km above our heads !).

Imagine it like the current of a river, in the centre it flows strongly and straight, but at the margins where the water encounters resistance from bankside structures, it slows and forms into meanders. The jet stream behaves in exactly the same way - when it is flowing strongly it will typically move a weather system across The Atlantic in 18 hours and across the U.K & Ireland at the same speed. When it runs out of puff and flows weakly, it forms into meanders which mean weather systems stay in situ, sometimes for days and weeks.

It is these meanders that typically result in extremes of weather, not just here but also in the States as we both share the same Polar jet stream. There are actually 4 jet streams that circle the earth, one at each of the poles and two sub-tropical ones.

A meander last summer in the jet stream over the Pacific North West and Canada caused the record-breaking 'heat plume' event that I will be discussing as part of my talk at BTME. During that event, temperatures reached 49°C in British Columbia, in a region of cool season grasses.

How did turf managers cope, what was their experience and how can we learn from it ?

Back to the present, we have a meander over us at the moment, (what I call a peak pattern in the jet stream) and it has resulted in a blocking high pressure forming over the continent with the effect that low pressure systems are being kept out to the west of us over Newfoundland and Greenland, so we are calm, dry and settled.

Now I explained last week, whilst this is pleasant enough weather, it isn't great for grass growth because the cold nights suppress the soil temperature and hold back growth.

One of the plus sides though of a early spring blocking high though (and yes we are officially in spring now as yesterday marked the vernal equinox, a day of equal night and day duration and officially held as the 1st day of spring ) is we start to build a bit of daily E.T.

E.T stands for evapotranspiration which is the process whereby water is lost from the plant and soil surface by evaporation and so we start to dry out. Last week we hit 2mm per day on some of the weather stations I monitor and this week I expect that to increase further. (more on this later)

General Weather Situation - Synopsis

So as mentioned above we currently have high pressure in situ this week which will mean a very settled forecast for the U.K & Ireland so it's nice and convenient for me to produce a summary :)

As you'll know by now, the start of this week is a little chilly, especially on the eastern side of the U.K where we have some 'Haar' coming in off The North Sea. So a cool to start off the week in central and eastern areas and even some early showers across the east of Ireland today which will move across The Irish Sea into North Wales pm. The theme of the week is dry and settled with Tuesday through to Thursday forecast to have better night time temperatures and without the lag of a frosty start, this will allow day time temperatures to climb into the mid to high teens.

Last week, Scotland recorded 20°C in Kinlochewe, not their warmest March Day (that was back in 2012 @ 23.6°C). but nice all the same and this week we may come close to this in the south of England possibly. So Tuesday through to Thursday should be nice and pleasant spring weather with long spells of sunshine, maybe a bit more cloud cover on North Sea coasts but cracking nonetheless.

Unlike the weekend when I was fly fishing in a strong, easterly wind which made life blooming hard work for me, this week will see lighter southerly to south easterly winds.

The end of the week will see those winds freshen up a bit and that'll take the temperature down into the mid-teens from Friday through the weekend but again lots of sunshine and no sign of any rain on the forecast to blot the copybook :)

So the next question after 7-10 days of dry weather in the U.K & Ireland (remembering that we had 25 mm of rain here only last week on what was a miserable Wednesday) is how long will this dry spell last ?

Weather Outlook

So you can see above on the projected GIF from that next Monday potentially (And I say potentially as always there's a weather caveat) marks a change signal in the weather, with the formation of a huge low pressure system over The Black Sea looking to pull down northerly, cold winds on its trailing arm.

This is our weather nowadays, one week, a warm air peak in the jet stream, the next, a cold, low pressure trough. So I think the start of next week will be cooler, with more cloud cover and characterised by a much windier scenario. As we go through Tuesday we will see the dry spell break down and showers push into the north and west and possibly down the east side of the U.K, dragged down on a cold, northerly wind. Towards the end of the week we see an intense Atlantic low pressure system push in to mark the first day of April with very strong winds and rain for the U.K & Ireland. If this does come to pass, it'll be Storm Gladys no less and it'll mark the first weekend of April with very strong south westerly winds and rain for all of us.

Now that's a lot of weather events, a lot of 'ifs and 'buts' that have to fall into line for this to happen. It could quite easily be that the high pressure maintains rather than breaks down. A quick look over the fence at the ECMWF long-range forecast (as opposed to the GFS long-range forecast that I prefer) has them showing the high pressure persisting through next week albeit with cooler temperatures. So a clear demarcation line between the two, GFS calls it as a breakdown in the weather pattern and ECMWF, suggests settled conditions will persist. Next week's blog will be able to ascertain which one was right !

Agronomic Notes

One swallow doesn't make a summer.....

Not that I've seen a Swallow yet or more realistically, a Sand Martin, as they are usually the first species to arrive on our shores, but it's a good saying isn't it and a very apt one for our profession.

I'm referring to the fact that a few dry days doesn't offset what has gone before...

So I was talking to a golfing buddy of mine that had been down to play course 'X'...."What did you think" I said...."Bloody disgrace, sopping wet, shouldn't have been open".....

Now everyone is entitled to their opinion and he is probably right to some degree, but it is quite typical of our industry that we get a few days of dry weather and then golfers expect the course to be bone dry but of course 'receptive'. 'Receptive', now there's a contentious word from a golfing perspective, one man (or woman's) receptive greens are another's, too-soft...The problem is that people make subjective comments and these are often not only wide of the mark, they are counter-intuitive.

So, I thought I'd drag up some weather data from the south of England and chart out the daily rainfall vs. the daily E.T and see how it shapes up. Now it's a bit superficial because not all rainfall is absorbed into the rootzone, some major rain events obviously shed off the surface, but it's a good marker to indicate how much rain we have had vs. how quickly we are drying out.(By measuring E.T of course)

So here's the daily rainfall and E.T from a course down in Kent. A nice dry(ish) part of the country I'd usually say.

So above you can see that January had a wet start and then they had a run of dry weather through to the middle of February but of course at that time of year, E.T levels are low so we didn't see much dry down of the rootzone.

Come the middle of February, we ran into a succession (3 if I remember rightly) of Atlantic storms with their biggest rain event of 14mm occurring on the 13th of February.

Now I know a lot of other places received far more rain, Scotland, Ireland, Wales in particular so this is the most favourable position I'm presenting in terms of how much drying has occurred vs. rainfall.

The next thing I charted out was the cumulative rainfall vs. E.T, so for example if we had a day of 3.5 mm of rain and 1.3 mm of E.T, the net difference is + 2.2 mm of moisture. I then added these up from January 1st to the present day at the same location.

This is how the resulting chart looked ;

So you can see we were positive for moisture vs. E.T at the start of the year but not by much really and I'd say this would represent the best case scenario not only location-wise but also stats-wise.

It all started to go wrong in the middle of February as you can see from the graph with an ever-increasing moisture surplus vs. E.T. Now of course there's a point where the rootzone on your particular course / facility is saturated and this is obviously different dependent on soil type and / or construction type. The fact is though from mid-February onwards we have received a surplus of rainfall vs. E.T and even though the last few days have seen a reversal of that trend, it'll take a lot more good E.T days to make an impact on the ground conditions. So that's why you'll still find very wet areas out there despite the pleasantly warm weather I've documented as likely this week and then we have to take a sniff of those 'reality salts' and understand we are only just tip-toeing out of winter.

OK, short and sweet this week. I hope I manage to catch up with some of my colleagues this week at BTME and above all that I manage to deliver a useful talk on Wednesday afternoon as it will have been awhile since I stood up in front of an audience. So if you are attending, please bear with me :)

All the best for the coming week...

Mark Hunt

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