Wednesday 12th August 2020 – Thunderstorm Chances

Here we go again. One last day very hot day before temperatures slowly start to become less hot, though humidity may be even higher tomorrow than today.

We were the breeding ground for storms yesterday – some of you will have seen the towers going up, but then not being able to form properly, I assume due to the atmospheric cap, and fading away.

A few scattered thundery downpours did develop across the south – I had some rain and some rumbles of thunder in Harrow in the evening, and far from “clearing the air” (as per the well-intended myth) it was much more humid afterwards! And I suspect what we saw breeding across the south was what brought spectacular thunderstorms in some parts of the north of England and also Scotland last night.

So more hot sunshine today, temperatures should reach 33’C, perhaps 35’C. And it will be humid.

Thunderstorms will break out during the afternoon, perhaps as early as 1pm/2pm but that is uncertain. You’ll likely see them develop in straight lines at first, where winds converge from different directions and force convection upwards – and hence breaking the atmospheric cap.

Exactly where the afternoon storms will break out is uncertain, shock horror, though I think the sweet spot is somewhere between Bristol and Birmingham, with parts of Wales too. We’ll still have a 15% chance here.

In the evening there should be more widespread thunderstorms developing – though still many places missing them, so around a 25% chance in the evening.

And then there is the potential to import some French thunderstorms overnight – but this is also a small and uncertain chance.

Should you get a thunderstorm, large hail, damaging wind gusts, torrential rain with localised flooding and fairly frequent lightning are all possible.…

Tuesday 11th August 2020 – Thunderstorm Chances

There were two questions regarding thunderstorms today.

  1. Would they initiate?
  2. Where will they initiate?

I cannot answer number 2 – this will be a nowcasting thing – if you see clouds developing over you or just to your south/south-east, and they will develop fairly explosively I’d suggest, then you will likely catch a thunderstorm.

The first question, I do now think they will initiate. Impossible to be certain, but I think we’ve reached a good temperature profile considering current requirements, there seems to be some cumulus bubbling up, I’ve heard reports of unstable skies close to the south coast and there appears to be some cloud bubbling up to our south on the satellite – though I cannot ascertain whether this is potential future thunderstorm cloud!

So I think they’ll be triggered somewhere over the south/south-east this afternoon, perhaps into early evening. Will your area get one? I’m still around a 20% chance, maybe 30% chance at a push.

Catch one and largish hail and torrential downpours with localised flooding are the main risks, with fairly frequent lightning possible.…

Monday 10th August 2020

Very hot with an increasing chance of thunderstorms.

Thanks to Liz for the photograph. Wouldn’t mind seeing a rainbow or three this week…as long as I get a thunderstorm. Though I know not everyone shares my joy of storms.

There will be uncertainty in this forecast. Thunderstorms are very difficult to predict in advance – there are several opportunities this week, some small chances, some good chances. You may get several – you might get none. Several is more likely.

Also, to save repeating myself every day, the thunderstorms could be severe in nature – frequent lightning, largish hail, torrential rain, localised flooding, strong wind gusts – all very possible.

I’ll try my best to give you a realistic estimation of when they are more likely, but expect updates closer to the time.

This evening should be fine and dry. Overnight sees variable though generally increasing amounts of cloud, a small chance of a shower or a flash of lightning or two, very warm and humid – probably not below 20’C for most.

For Tuesday we still have high pressure to our east, sucking up hot air from the continent – with low pressure starting to develop over France/Spain.

Tuesday starts with one or two scattered showers, again only a small chance. The sun will really heat up – we should reach 33’C easily, perhaps as high as 36’C, yet there will be a bit of cloud around. For early/mid afternoon, a few scattered thunderstorms will break out – at the moment I’d suggest around a 25% chance of catching one. Another very warm and humid night overnight, minimum temperature of 22’C with some cloud around, probably dry but a small chance of a shower and/or a little lightning.

Wednesday probably starts sunny and again it will quickly become very hot. Temperatures likely to reach 32’C, but could reach 35’C. Good spells of sunshine but a much higher chance of thunderstorms – as always, not guaranteed, some places will miss out, but around a 60% chance. And very possibly in the severe category. Often cloudy overnight, very warm and humid once more – and further thunderstorms very possible.

By Thursday a fairly distinctive area of low pressure will have developed and will be roughly over the south of the UK.

Impossible to give details, but a good chance of further thunderstorms or general thundery and very heavy rain. Still should be some sunshine at times, still humid, still hot but probably less so – somewhere between 26’C and 30’C.

By Friday, things should be somewhat fresher, and we should be looking at it being very warm, around 25’C. Still quite humid, but a relief compared to previous days.

Unfortunately, other weather aspects are uncertain. Probably a mix of sunny spells and showers, thunder still possibly though less likely than recent days.

Details sketchy for the weekend. Likely still very warm, perhaps quite hot, with some showers at some point.

Next week totally uncertain – depends on what our low pressure system does. Slight favourite is for it to nudge west and this may allow warmer and more humid air to spread from the south – with heavy, thundery showers again possible. Though only a slight favourite.

I do expect the latter part of August to be cooler and more changeable, more similar to the pattern that we had in July.

Apologies for the vagueness in the forecast due to thunderstorms and I’ll try to keep you updated when possible during the week…unless I lock myself out again like this morning. Doh.…

Sunday 9th August 2020

So Thursday’s forecast has gone well so far but we are getting to the tricky part.

Today will see more long spells of hot sunshine. Some high cloud at times, particularly this evening, also some fair-weather and mid-level bits of cloud bubbling up. 31’C should be reached – we might get to 34’C.

There is a very, very small chance of an afternoon shower, perhaps with a rumble of thunder, but we are talking 1% chance.

Overnight there is a very small chance of some showers moving up from the south-east, with some thunder also possible. Again, a 5% chance at best, as it stands. Otherwise it will be warm.

From tomorrow through to at least Thursday, the chance of thunderstorms increases, and they could be severe in nature. Frequent lightning, torrential downpours, localised flooding, largeish hail, gusty winds all easily possible. You there might even be reports of a tornado somewhere across England/Wales (they normally only effect very small areas, ie one street or one small patch of farmland).

For Monday, we are looking at more hot or very hot sunshine, at least 31’C, 35’C possible depending on how long it stays sunny for. Around a 25% chance of catching one of these thunderstorms tomorrow.

Such is the unpredictable nature of thunderstorms, you could miss them all and stay dry or at least lightning-free all week. However, it is more likely than you’ll get a few over the course of the coming week, and perhaps some general thundery rain either Wednesday or Thursday.

And they won’t “clear the air”. It is a bit of a myth that thunderstorms “clear the air”. Cold fronts clear the air, and sometimes cold fronts trigger thunderstorms – hence the belief that thunderstorms clear the air. However, if you catch a daytime storm this week, as soon as the sun comes out the temperature will shoot up once more. There is no cold front!

Probably less hot by either Thursday or Friday, though I don’t rule out the heatwave extended through to the weekend – it all depends on what happens with the thunderstorms this week as they likely develop into a low pressure system – and then what that does.

I cannot give you a forecast for Friday onwards yet and I doubt I’ll have the answer by tomorrow evening’s main forecast.…

Thursday 6th August 2020

It’s going to be hot. It’s going to be humid. It’s probably going to be thundery at some points.

It is also one of those forecasts where uncertainty sets in very quickly so please do excuse this, especially around thunderstorm potential. I expect that I will be needing to give daily updates!

Thanks to Nik for the photograph which I think is an attempt at Kelvin–Helmholtz clouds from last Friday. Very rare – though not fully formed.

This is going to be a really exceptional spell of weather – with a rather exception set-up. Record temperatures could be broken, whether that be all-time record set last year, the record overnight minimum temperature, the longest run of days over 35’C or some other record!

Tonight will be a warm night in clear skies, down to around 17’C.

Friday sees high pressure to our east and a hot southerly flow.

The morning will see long spells of sunshine and it will quickly become hot – though not quite as speedy as last Friday. Some mid/high level cloud will develop during the afternoon making the sun hazy and there is a very, very small chance of a shower later. Very hot, reaching around 35’C, give or take a couple. Some cloud overnight and very warm, minimum temperature of 20’C.

Saturday will be another very hot day. Some high cloud and perhaps a bit of fair weather cloud, though at worst hazy sunshine and generally we are looking at long spells of sunshine. 33’C for sure, perhaps 35’C. Some cloud overnight, a very small chance of a thundery shower, and still warm but less so, around 18’C.

Sunday again will be very hot. Good spells of sunshine but again some high cloud and some fair weather cloud at times. A small chance of a thundery shower, maybe 10% chance – this chance could be upgraded nearer the time. Temperatures between 32’C and 35’C. So, very hot again! And humid. Quite cloudy overnight, warm and a small chance of a thunderstorm developing later in the night – around 19’C.

Monday again looks hot, perhaps very hot. Uncertainty is creeping up – there could be some cloud around, perhaps some thunderstorms or general thundery rain developing. Temperatures somewhere between 30’C and 37’C. Very warm overnight, humid, a greater chance of thunderstorms or thundery rain – but at this stage impossible to be confident. Minimum around 21’C.

Tuesday looks hot or very hot once more. Some good spells of sunshine but also this greater chance of thunderstorms – far from certain but probably the highest chance so far this spell. Temperatures somewhere between 32’C and 37’C. Very warm overnight, further thunderstorms or thundery rain possible, around 20’C.

I’m tired just thinking about all this! Wednesday will be similar, perhaps a bit less hot, say 28’C to 34’C and again with sunny spells, and a good chance of thunderstorms.

Thursday/Friday probably less hot, down to around 23’C to 26’C, the thundery low might not be too far away so further showers possible. Not especially confident though.

Next weekend is way too far away!

I remind you of the uncertainty both on temperatures but especially on thunderstorms – so difficult to predict even a few hours away, and the best chances are currently a few days away. Anything before Monday night is only a small chance – from Monday night onwards is a good chance, but they will still be hit and miss. Potentially could be frequent lightning, sizeable hail, gusty winds and localised flooding – but that’s to consider nearer the time.

Good luck with the heat! I very highly recommend an air conditioning unit.…

Monday 3rd August 2020

Heatwave upcoming. But for how long and how hot will it get? 35.7’C was the maximum we reached on Friday, could it be beaten?

Thanks to Paul for the perfect photograph – a nice size so the quality looks good, and arguably even more important – cricket.

Globally we’ve had a bit of a shuffling of the weather cards, which shook us out of the dominant pattern of those north-westerlies interspersed with the Azores High ridging in, which we had for most of June and July – and offered the opportunity for much hotter weather at times from the very end of July.

You may recall in my seasonal forecast that I expected July to be mixed and August to potentially be the best summer month for sunshine and warmth – this will probably happen now (and July was mixed, broadly as forecasted), but if you had asked me 10 days ago before the shuffling of the global weather pattern then I was losing confidence.

Anyway. Now.

Tonight will see clear spells, down to around 12’C.

Tuesday sees low pressure close to the north-west of Scotland and the Azores High ridging in across the south of England – very similar to much of July.

The band of rain stays well to our north, but we’ll have the associated cloud making sunshine hazy at times. Mid-late morning sees the thickest cloud, but still quite bright, otherwise pleasant with warm, hazy sunshine. Around 22’C and breezy. Some clear spells at first overnight, cloud tending to thicken as the night goes on, around 15’C and notably breezy.

Wednesday starts rather cloudy, the odd spot of rain possible, likewise a bit of brightness. As the afternoon goes on, the sun will increasingly shine, and it will be very warm, around 25’C – still breezy. Rather cloudy overnight, the odd spot of rain possible from a decaying weather front but mostly dry. On the warm side, 16’C as the breeze turns southerly.

Thursday sees high pressure to our east and a southerly flow from the continent – which means it will be hot.

There will be some cloud around in the morning – this will break up and as the day goes on sunshine amounts increase, to very little cloud by mid/late afternoon. A bit of uncertainty as to how hot it gets, depending on exact wind direction and how long it takes for morning cloud to disperse – almost certainly at least 28’C, though anything up to 32’C is possible. Mostly clear and fairly warm overnight, down to around 17’C.

Friday looks set to be the second very hot Friday in a row. As it stands, I think more likely a shade below last Friday, say 33’C – but this could easily upgrade…it did last week. Long spells of sunshine, but a bit of high cloud around. Warm overnight, around 19’C.

Saturday remains hot with good sunny spells – likely a bit of cloud around but not much. Temperatures most likely somewhere between 30’C and 34’C – though there is a small chance that less hot air may spread in, so something closer to 26’C is instead possible.

Sunday again has uncertainty over temperatures – fresher air will likely be trying to filter down from the north, but the heat may hang on for us in the south. Either way, it looks very pleasant with good spells of sunshine. Temperatures anywhere from 23’C to 32’C.

I cannot totally rule out a thundery shower at some point over the weekend – but there is nothing more specific at this stage, so only around a 5-10% chance as it stands.

Next week will likely follow one of two patterns.

One option seeing high pressure building over the UK, pushing the heat south but keeping us very warm with sunny spells. The other option keeping it hot/very hot with thunderstorms possible. The latter option arguably slightly more likely at this stage.

Suggestions of something more changeable later in the month, though still with the potential for brief hot spells.…

Monday 3rd August 2020 – Mini Update

Just a small update as I left you with open questions the last time I wrote.

Today will see sunny spells with fair weather cloud bubbling up. A scattering of showers, around a 40% chance of catching one or two. Around 21’C.

Tuesday will see hazy sunshine – a band of rain to our north will stay there, and it will be very warm, around 24’C.

Wednesday also sees hazy sunshine, a very small chance of a heavy shower afternoon/evening. Very warm, perhaps quite hot, around 25’C.

And from Thursday? Hot and mostly sunny. At least 28’C, possibly 30’C on Thursday, 32’C or more on Friday. Likely still hot during the weekend but a small chance of some thundery showers…small chance.

More details tonight.…