Still on holiday (yes I know) so this week’s will be another mini-weather blog.
Last week I gave a synopsis for this week based on high pressure exerting it’s influence on our weather and returning us to a dry, settled and warm pattern. Sadly that’s not going to be the case for the whole week though it will be for the first part of the week but then it looks like low pressure will once again dictate our summer’s weather.
It kind of neatly illustrates the point that within a 7-10 day time frame our expertise at forecasting / predicting the behaviour of weather patterns is at the limit of current technology and algorithmns.
I took some pictures on the approach to Stansted airport as we came through the cloud base and you can see the energy in the clouds building from the top and then the resultant rain falling below somewhere over Essex I think…. Mega interesting I thought and it helped break up the monotony of yet another pleasurable Ryanair flight experience for me. That said, they were on time and if it weren’t for them, there’s alot of places we simply wouldn’t be able to get to for an affordable price…
When you look at the top image of rain clouds building and producing rain and then go on to imagine all the different factors impacting this process, one that is then described mathematically to produce a forecast scenario, it is hardly surprising that it isn’t 100% accurate. Summer rainfall is as I understand it from Meteoblue, one of the hardest weather events to predict accurately…So with that clever caveat underpinning the accuracy (or inaccuracy) of this week’s forecast, it is onto the weather 🙂
This week’s weather outlook
So last week I said that the bulk of any rain events would be north and west and that bit I got right because on Monday we have rain over Ireland in a line from Galway to Dublin extending into Wales pushing north and east through this morning. We also have some lighter rain still hanging on across the south east and this will move off into The Channel during the morning. The rain over Ireland is heavy and slow moving so expect some flooding where you get it. Eventually it will move off into the Irish Sea and across to hit the west of Scotland around tea time and then proceed to give significant rain for Scotland tonight as it moves eastwards slowly. South of this rain band (Ireland and U.K) it will be initially cloudy but the sun will break through eventually to give a pleasant warm day with temperatures in the high teens, low twenties. My only concern on this forecast is the rain over Wales which looks to be more on an easterly trajectory and so may affect The Midlands and north of England p.m. Winds will be light and from the south / south east.
Tuesday sees a similar picture with some rain over Ireland (Clare) developing through the morning along with the remnants of that overnight rain across Scotland clearing through the morning. Away from this we see another dry and settled day with a mix of cloud and sunshine through the day. During Tuesday afternoon though we see that rain over Clare begin to consolidate and this will spread to cover most of Ireland late afternoon. At the same time we will also see some rain develop across The Pennines and eastern coast of Scotland for a time before clearing later on Tuesday night. That Irish rain front looks to consolidate and become heavier as we go through Tuesday afternoon / evening so quite a bit of rain here I’m afraid. Away from this rain it’ll be a warm day with temperatures pushing up into the low twenties I think with light south / south easterly winds in situ.
Onto Wednesday and overnight we see that heavy rain over Ireland clear into Scotland to bring further rainfall here and potentially further south across The Pennines. Through the morning this rain will clear the north of England but I think it will be slow to leave Scotland. By late afternoon we see another rain band push into the west of Ireland and this will push east and north through the course of Wednesday evening / night. So another day of north / south / west divide because we have a dry and potentially warm day for the bulk of England and Wales on Wednesday with temperatures pushing up into the low twenties again, cooler if you have that cloud cover and rain further west and north. The wind will shift round on Wednesday from southerly to more westerly and that marks the notice of intent of a low pressure system coming in.
Thursday sees that low pressure begin to exert its influence and that means it’ll push rain further southwards to give a more unsettled end to the week with rain over Ireland pushing into Wales and then eventually across the south of the U.K later on Thursday. This low pressure will also spin rain into Scotland during Thursday in two bands, one affecting the far north and the other over The Borders. There’s also a risk of some rain just tipping along the south east coast of England during Thursday morning and pushing into Kent by late morning. You’ll notice the wind will now be south westerly and moderate to blustery so a marked change from the beginning of the week. It’ll feel a bit cooler as well with that change in wind direction and strength so high teens will be the order of the day.
Finishing off the week on Friday we see that low pressure continue to extert its influence though it should be a drier day save for some showers over the north of England and Midlands accompanied by a thick cloud base. These showers may sink south later in the morning. Otherwise it’ll be a drier and sunny day for Ireland, Scotland and Wales but staying on the cool side even though the winds will lighten and change round to the north during the day. That northerly wind change will knock another degree or two off the temperatures so probably mid-teens is likely, maybe a little higher down south.
So how do we look for The Bank Holiday weekend and just as importantly MotoGP at Silverstone ?
Well Saturday looks unsettled with plenty of sunshine and showers around, initially in the north and west but sinking south for the 2nd half of the day to bring rain to most areas. The wind is also likely to strengthen from the west again so that means similar temperatures to the end of the week, mid to high teens. Sunday looks the better day of the weekend with any rain confined to the north and west of Scotland. Onto Bank Holiday Monday and it looks potentially wet and windy in the north and west with a strong westerly wind in situ. Drier further south but with low pressure in charge we can expect sunshine and showers I think and mid to high teens temperatures.
So we know next week looks to start off unsettled but will it remain this way ?
Well currently the synposis is for high pressure to try and push in from mid-week, next week but it will butt up against the low pressure that we had over The Bank Holiday impeding its progress. We know what happens when a high and a low butt up against each other and principally this means the wind shifts to a more northerly orientation pulling cool air down from mid-week onwards next week. So we will have a west / east split for the latter part of next week with finer, warmer weather to the west and cooler, dull and potentially more unsettled weather across the east.
Beginning to sound a bit like a scratched record this summer I’m afraid but it’s a fact that with high moisture levels, a wet plant leaf and high humidity, summer disease pressure has been pretty much the highest I’ve known it since the weather pattern shifted and introduced a change from hot, dry conditions back in July (remember them ?)
I’ve got a new weather station that I’m looking at as a cost-effective option to the more expensive units available on the market to supply temperature, humidity and rainfall data (more on this in the future when I’ve seen more of how it works accuracy and durability-wise)
So I decided to download some data over a 24 hour period for August 20th to see where and when during the day we are experiencing the highest disease pressure…
So what we have in the graph above is a trace of relative humidity shown as blue columns, the maximum air temperature as a red line and The dew point as a blue line. The dew point is the temperature at which point the atmosphere becomes saturated with water (in other words reaches 100% humidity) and if cooled further the water condenses out of the air to form droplets on the plant leaf. So as the red line and blue line become close then we are reaching saturation point in the atmosphere and this in my mind is when we face the highest disease pressure…i.e conditions are ideal for mycelium development…
Diary of a Day in August…
Starting on the left hand side, the graph above begins at midnight with humidity in the low 80’s and the air temperature and dew point seperated by about 2.5°C and this is pretty much how it stays through the morning. So I’d classify this as a lower disease pressure night.
You can see the point when the sun came out quite obviously as the air temperature increased markedly at around 8 a.m. and the humidity dropped off down into the 70’s as moisture was being evaporated from the atmosphere. Around 4 p.m, the air temperature begins to drop and consequently the humidity begins to increase as the moisture content of the air begins to build.
Around 9.30 p.m we had a light rain shower and the humidity point reaches 90% very quickly thereafter and the dew point / air temperature graphs almost touch so the atmosphere is becoming saturated with moisture and again conditions become conducive to disease development.
The humidity then stayed > 90% all through the night and I can tell you that as I type this it is still > 90% at 10.47 a.m.
So if we look at the potential for disease development on this particular day it started at 9.30 p.m. and has continued right through to the time I’m typing this, that’s a 13-hour period.
Now if you were in removing dew from your surfaces at say 6 a.m. this morning then the plant leaf would have been sitting wet for 8 1/2 hours prior to that.
And that is the rub as to why diseases like Microdochium nivale, Dollar Spot, Leaf Spot and Red Thread really like this type of weather. Long periods of high humidity and a warm enough air temperature for their populations to reproduce quickly from spore germination, mycelium development and then onto spore formation / production.
With the Bank Holiday Monday next week, I’ll be back to normal (whatever that is ?) on Tuesday..In the meantime, all the best.