General summer chat

[Addicks Fan 1981]

 raz.org.rain at this stage I think the chances of a hot summer are very possible, but we need the la niña development delay for it to come off and also we need a QBO transition as well from easterly to westerly.   Im sure i will have the backing from @summer blizzardon this as although the QBO effect isn't as significant in the summer months it can still play a pivotal part in how the summer behaves.    

[raz.org.rain]

 Addicks Fan 1981 if La Niña does arrive during the summer then I think a 2019 repeat is a safe bet, wet but often very warm. Given the state of the global climate I'm not convinced we'd see anything like a 2007 repeat in terms of temperature.

[Addicks Fan 1981]

 raz.org.rain also sunspot activity is much higher than in 2007 as well, we went into a deep minimum between SC 23 to SC 24.   We this year are gonna be in solar maximum and as things stand solar activity is raging literally, seriously it is really high currently.    

[Jonnoramo87]

I hope we are going to see 30C for a week in October for compensation for this bitterly wintry April, surely that's fair right?

[WYorksWeather]

 Jonnoramo87 The biggest problem with this April has been the lack of sun to be honest. Temperature wise this late April spell has been a bit below average and the earlier spell was well above average. But of course at this time of year the strength of the sun is far more important to the overall feel. The same average temperatures but with clearer skies bringing warmer, sunnier days and colder nights for most of it would have felt much warmer despite being the same statistically.

[Metwatch]

 Jonnoramo87

Certainly wouldn't mind experiencing an October 1921 repeat!

[Topclassweatherforecaster]

When do you think we will see first Summer heatwave?

[WYorksWeather]

 Topclassweatherforecaster Depends on what we mean by heatwave. If we mean the 'official' heatwave definition, then we need three consecutive days to surpass the following daily maximum temperature threshold depending on where you live:

There have been occasions that have met this criteria as early as late April or early May in the past, but usually heat in the UK is 'backloaded' towards the middle or end of summer. In short, there is more likelihood of a heatwave in September than in May, and in August than June.

Any prediction beyond the 10 day timeframe is fraught with difficulty so anything anyone says here including me will be nothing more than a guess, but given various background factors pointing to a warmer than average summer I think this one might go against the general rule. Therefore, I'll take a wild stab in the dark and say that we'll see an early heatwave in either late May or early June.

If you mean the more general sense of a heatwave as in a spell of warmer than average weather - well then next week may well produce it - moderately warm, temperatures quite widely into the low 20s being the most likely scenario.

[Addicks Fan 1981]

 WYorksWeather I've noticed that the niña development maybe delayed or may not even happen at all according to the new CFS members that are in blue and this could do our summer a big favour.  It all depends really if this WWB can come off as that to me could be a game changer coming into the summer months.    

[Addicks Fan 1981]

 summer blizzard what are the current analogues for this summer if say like the niña doesn't come off?   

[Jack Wales]

 Addicks Fan 1981 Hi, the transition to Nina looks pretty much nailed on when you look at the weekly CPC outputs...

 

[WYorksWeather]

 Addicks Fan 1981 The other thing in our favour is the stronger than average polar vortex, which I mentioned on the model thread a few weeks ago. Generally if the May polar vortex is stronger than average it correlates moderately with a warmer and drier summer via a positive NAO.

[Addicks Fan 1981]

 Jack Wales according to Gavs Weather Vids he says you should always look at the blue members and not the dotted line.   

[summer blizzard]

 Addicks Fan 1981

Posted earlier in this thread but essentially the La Nina's that are not declared by JJA on ONI tend to be relatively blocked with the Azores High close to the UK. 2016 was in that group.

La Nina's which go guns blazing tend to have a cyclonic July and August and end up stronger on average. 

Currently we are marginally on course to be in the slower group (dropping around 0.3 per month). 

[summer blizzard]

 WYorksWeather I'd be pretty dubious of that and suggest it's likely noise rather than signal. 

That is to say that years with a late final warming and stronger than average vortex may be followed by a +AO but the forner is not likely the cause. 

I don't really see much reason why slightly weaker net easterlies in the stratosphere would result in westerlies further down the troposphere. They are still trying to impinge net easterlies on the troposphere.

[Summerlover2006]

One of my biggest wishes for this summer would be to have some extreme heat in June like a 35+ day beating the 1976 because I think is such a boring month for extreme heat with the highest temperature of the basically the the last half century being only 34.5 and yes June has been pretty good recently it’s not had that much exciting weather so if I was going to design a summer I think I would have a heatwave starting on like the 28th June and lasting to mid point of July.

[WYorksWeather]

 summer blizzard It may be correlation rather than causation (I wrote my post carefully to avoid any implication of direct causation).

Here is a paper with some more details if you're interested (which I posted on the model thread a couple of weeks ago). But to summarise, if the polar vortex is stronger than usual in May, this tends to correlate to a later final warming in the lower stratosphere, and this then propagates down to possibly increase the chance of +NAO in at least early summer.

Skilful predictions of the Summer North Atlantic Oscillation

WWW.NATURE.COM

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The Summer North Atlantic Oscillation responds sensitively to an anomalous strength of the stratospheric polar vortex in spring, which can be exploited for seasonal predictions, according to large-ensemble...

Again though, causation with this stuff is difficult, so I will continue to refer to it as a correlation.

[damianslaw]

 WYorksWeather Surprised only 25 degrees for Manchester needs to be breached 3 days, same as Highland Scotland, I think Manchester and W Yorkshire should be 26 degrees. 

Edited Tuesday at 22:04 by damianslaw

[Don]

Latest Metoffice contingency forecast covering the final month of spring and first two months of summer.

https://www.metoffice.gov.uk/binaries/content/assets/metofficegovuk/pdf/business/public-sector/civil-contingency/3-month-outlook-may-june-july.pdf

[WYorksWeather]

 damianslaw It's based on the 90th of maximum temperatures at the hottest part of the year (July), for 1991-2020, with a minimum set at 25C for the qualifying threshold. The definitions are redone every 10 years - I expect the 2001-2030 definition will see a number of areas increase. Probably a first 29C for parts of London and the SE, and many other areas being raised accordingly. I expect West Yorkshire must have been pretty close to reaching the 26C definition last time it updated, so I think we will do next time.