peacockreports.bsky.social
Head Meteorologist at MetSwift, working to revolutionise delivery of weather information.
LinkedIn: https://t.co/pUCAQfAfRP
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Now for a daring statement: From what I'm seeing, this is setting up to be a summer where, if the right weather pattern sequence played out, 40°C would be reached in the UK.
Fortunately for those who'd rather that didn't happen, that's a very big 'if'. Just not as big as usual.
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Meanwhile here's the latest GFS deterministic run for 16 days time on course for something likely even hotter in the subsequent day or two.
Again, not something to be expected. The point I'm making is that there's sufficient heat to the south that such scenarios are plausible.
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Further to this point, here's the result of ECMWF's latest deterministic run bringing some of that very hot airmass into play (in 12 days time, I'm not saying this will happen).
34°C at noon suggests a 36-37°C max, which exceed the 35.6°C June record held by 1976 & 1957.
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Similar situation with Friday evening & following night. There's been a general trend to restrict the most intense thunderstorms to SE England (classic) but beyond that it's a bit of a guessing game for the details.
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@petagna.bsky.social kindly informed me a few weeks ago that UKV has a bias toward too much cloud cover, especially low-based. Good example of that today!
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However, a few have shifted the high further east, allowing very hot weather to spread northward from Iberia for at least a day or two.
A possibility to keep an eye on, nothing more at this stage.
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With such a vast area of such hot conditions in place, the positioning of ridges over NW Europe will have a big impact on temperatures there.
Lately, model runs for next week have tended to favour an overhead position with any hot weather 'homegrown'.
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Despite all the cloud, perhaps even partly because of it (reduced instability, fewer showers), rainfall to-date is only a little above the 1991-2020 average.
That might change tomorrow night, depending on how exactly the potentially thundery spell of rain shapes up.
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After an initially very askew run, GEM's deterministic model has been fairly consistent on a scenario akin to what ECMWF's has been trending toward.
If the true outcome is like the latest GEM & ECMWF runs, it will be an impressive showing by GEM if you ask me.
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Meanwhile, the GFS deterministic model has been flailing about, not really settling on any one outcome. It seems to be battling with a long-present bias toward depositing small cut-off lows near or over NW Europe (which hang about, producing showery, cool weather beneath).
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Past experience suggests the most likely outcome is somewhere between UKMET & GEM, on the basis that the GFS scenario requires the low to become 'cut off' from the jet stream, which requires the setup (jet stream position etc.) to fall within a narrow margin.
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If 35°C is reached in 2025, it will make a strong case for there having been a significant shift starting in 2015.
If not, the door will be open to 2015-2022 having been a shorter-term variation, albeit one without precedent in 140 prior years.
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What's more, it was very nearly 8 of 10 years. Yearly highest UK temps (°C) reveal that 2017 was only 0.5°C short, & 2024 a mere 0.2°C:
2015 36.7
2016 35.2
2017 34.5
2018 35.6
2019 38.7
2020 37.8
2021 32.2
2022 40.3
2023 33.2
2024 34.8
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The slower it lifts north, the higher the potential rainfall totals Friday night, though thunderstorm activity might not be quite as intense.
If it's slow enough, Saturday could see heavy showers widely, whereas a faster lift would restrict such weather to ~N half of the UK.
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A big part of the uncertainty around this event is with regard to how quickly the low that drives this swift change of airmass 'lifts' northward from the UK.
E.g. the GFS 00z det. run was a fair bit slower to do that than the subsequent 06z run.
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Such a rapid drop in temperatures aloft, even when occurring overnight, is a recipe for lively thunderstorms, usually of an elevated nature - the sort that produces a lot of lightning but nearly all of it cloud-cloud rather than cloud-ground.
5-6 days away so details are subject to change.
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...as we'll be seeing a hot airmass with 850 hPa temperatures perhaps as high as 20°C (which used to be rare but now happens at least one most summers) being displaced, perhaps swiftly, by one with temperatures at that height some 14-15°C cooler.
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Normally, this would introduce a fresher run of weather, but this time around, very warm to hot conditions are forecast to push back westward across E&W on Friday... only for a return push eastward to occur that evening!
The results could be dramatic by UK standards...
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On this basis, an outcome more like the GFS or GEM 00z deterministic runs seems a safer bet.
That being one where NW Europe experiences a dry, either warm or hot spell of weather for at least a few days next week.
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In S England this is turning out to be one of the most different to anticipated days in a while. Seemingly too little surface heating for thunderstorms & now this surprising mass of more persistent rain instead 🤨
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Usual caveats do apply, though, given this is looking 5-6 days ahead. We can't yet rule out the models having made presumptions that prove incorrect, causing the very hot airmass to visit at a different time &/or to a different extent.
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The result being that Wednesday is relatively sunny but with the airmass conducive to mid-high 20s °C, then Thursday has the potential to climb a bit higher in E/SE England, but this might be prevented by showers & thunderstorms, or the residual clag from such.
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I say 'encourage' because there's always some 'wiggle room' with these composites.
The phase 7 composite has little representation in ensemble forecasts for next weekend onward. It seems that if the MJO decays in that phase, the pattern is free to be steered by other forcing.
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Composites for similar MJO behaviour during past Junes suggest that it reaching phase 8 would encourage dry, warm or hot weather in W & E Europe with the UK joining in at times.
Phase 1 would encourage settled weather focused more upon NW Europe, with E Europe more unsettled.
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Away from western Scotland, temperatures will be trending upward during this time, especially in southern & eastern England where low 20s °C look to be reached in a few areas on Mon & widely on Tue.
For Wednesday onward, there's too much uncertainty to go into any details yet.
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That being a deterministic model run by the Japan Meteorological Agency.
Its version of events sees low pressure making slower progress against high pressure over NW Europe.
The Canadian GEM model's 00z almost took that route, but lacked sufficient high pressure over N. Sea.