UK Weather - Summer 2013

[NZstorm]

An interesting aspect of the British climate is the influences from Europe. Looks like a classic 'spanish plume' scenario coming onto the UK early week according to GFS. For those that don't know the term, its hot unstable air coming up from the south. Should be some high precipitation thunderstorms over the UK early to mid week.

[spwill]

An aspect of British Summer that we don't get here is the haze, the warm humid air from the south brings up a lot of haze onto UK, low visibility for thunderstorm watching. New Zealand has great visibilities and rich sunlight all year round.

The Dunedin Summer sunshine can burn you in 30mins, you can spend all day in the London sunshine and hardly notice it.

[Simon Culling]

Hot and sunny again yesterday, but with a NE drift over south eastern England the highest temperatures have shifted west and north with Ireland and Scotland joining us in the hot weather. Highest temperatures on Friday 19th July were recorded at:

31.4*C at Portmadog (Gwynedd in NW Wales - sheltered by the Welsh mountains to its east)
30.4*C at Bournemouth Airport + Hawarden (Flintshire, N Wales)
30.1*C at Castleserg (Co Tyrone - just 0.7*C shy of the all time N Ireland record)
29.7*C at Rostherne (nr Manchester) + Yeovilton
29.5*C at RAF Northolt, Rhyl (N Wales) + Prestwick (Ayshire, SW Scotland)

As highlighted by Steven, the synoptic pattern will change early in the new week to bring in more of a southerly feed and with it higher temperatures and humidity. We could see 32-33*C in the south by Tuesday and some rather powerful thunderstorms as a result. After mid-week we are looking at a return to a much more westerly flow and plenty of rain!

The high temperatures of the last few weeks have basically been 'home grown' because we have had high pressure over or to the north and it has been a question of high insulation and clear skies forcing the temperatures higher. We have not had direct advection of hot air from the south....that is due to change on Monday.

[NZstorm]

I see some big CAPE numbers there for Tuesday pm, 2400j/kg over the midlands 15hr. We don't get CAPE numbers like that in NZ.

[Simon Culling]

As I have never visited Dunedin (sadly), I cannot comment on its summer weather, although calling weather good or bad depends on your perspective. I am not keen on the hot weather, but I do enjoy the 'weather' it can bring with it. Here in the UK, and I am sure it is the same for NZ, its the wide variety of weather we receive that keeps our interest. To put some facts on the table regarding typical summer weather in the UK, below I have attached a table showing the average conditions for Kew Gardens, London for the period 1981-2010. Cannot get the table to format in the post.

As you can see, the weather is not that bad! What the averages do not show is that one day will be cloudy and dull at 18*C and the next one will be sunny and 28*C, followed by a storm in the evening etc.

[spwill]

To put some facts on the table regarding typical summer weather in the UK, below I have attached a table showing the average conditions for Kew Gardens, London for the period 1981-2010. .

Kew would be a warm location for the UK.

[Skywatcher]

The London urban heat island effect increases temperatures by 5-6°C and as much as 10°C (during heatwaves) compared with the surrounding rural areas.

It's the winter sunshine hours that I found more depressing when living in the UK - Edinburgh has less than half the winter sun of Chch.

[Simon Culling]

Thank you for all the comments on the UK summers, but I must correct a few misconceptions that you might have. I have added four more stations to the 'averages' tables with Heathrow representing built up areas of London (Kew is a big park which is cooler at night) and three stations 40-50 miles outside of London and to its north (Bedford), west (Oxford) and south (Edenbridge). From these tables you can see that the average maximums and minimums in London are only 1 or 2 degrees higher. The myth of a huge London heat island is just that and the facts show that on most days it is a degree or two above the surrounding counties. This can of course make a big difference in winter when it will rain in London but snow here in Milton Keynes only 50 miles to the north west.

However, the figures quoted of up to 10 degrees warmer can occur on clear calm nights (especially in spring and autumn) as the large built up area does not lose its heat as quickly at night as more rural areas.

[NZstorm]

Thanks for the chart Simon, those temperature numbers are more like the lower North Island than the lower South Island. The similarity between Dunedin and London's climate comes about when you aggregate the climate data for the year.

Urban heat islands tend to show up at night rather than day. The affect fluctuates depending on the synoptic pattern.

[spwill]

From these tables you can see that the average maximums and minimums in London are only 1 or 2 degrees higher. The myth of a huge London heat island is just that .

1 or 2C more in the averages for London is a lot of temperature difference and does very much show up the heat Island affect.
The heat Island affect will be more pronounced under certain weather patterns.

[NZstorm]

I notice there is a lot of info online about the London heat island. Auckland also has a marked heat Island.

I see estofex have a severe thunderstorm risk for the UK today.

[Simon Culling]

With regard to my earlier comments about the London heat island, they were not intended to belittle the effect. The average figures reveal that the difference is of the order of 1-2*C, but on occasions it can be significantly larger, particularly at night....as I indicated above. However, it is not true to say that the temperature can be 10*C higher in a heatwave. Maximum temperatures during the current warm spell have remained in the 1-2*C range higher than the surrounding counties.

It should also be remembered that most of the sites outside of London would be considered more rural in location than the London sites. If these stations were located in the many large cities across the UK the temperatures they recorded would be noticeably higher than for those sites located in more rural areas. I am sure similar effects are noticeable around Auckland and Christchurch and some of the other larger towns and cities in NZ.

[Simon Culling]

Saturday and Sunday saw some cloud plague central and eastern England but it was still warm over southern and western areas and also in central and western Scotland. Highest temperatures recorded on Saturday were 29.6*C at Cromdale in the Scottish Highlands and 28.1*C at Bude (Cornwall) and on Sunday they were 29.8*C at Jersey Airport and 29.3*C at Chivenor (Devon).

It was a lot hotter in the south of England today (Monday 22nd) with 33*C reached in London, but 31-32*C was recorded over a wide area and it was much more humid. At 7pm this evening (it was still 30*C in Milton Keynes at that time) I took the photos below of some Ac castellatus (with a base at around 9-10,000ft) as thunderstorms began to break out over the far south. They will be here in a couple of hours time.

[Skywatcher]

The 10°C I saw was for a one-off reading for the centre of the city (about 13km from Kew) but it wasn't clear if that was day or night.

I looked up the study (in Sturman & Tapper) on the Christchurch heat island and on a winter's evening it can reach a 5°C difference between where I live on the rural boundary and the CBD which is about 14km away. However, you're right that it doesn't have as big an impact on average maximum temperatures.

Lots of rainy summer days in SE England with only 8 or 9 a month where it's "< or =1mm"

By the way, you can put a text table in a "Code" block which uses a fixed space font.

[Tornado Tim]

Nice lot storms over the UK Today (22nd July to them). Looked very active at times

[NZstorm]

That chart 6.53am. Its an odd time of day for lightning activity to be peaking but its all elevated mcs convection.

[Tornado Tim]

That chart 6.53am.

Hang on.... How can it be 6.53am when I stated it was UTC time not UK time.

[NZstorm]

Universal time is similar to GMT, can't remember what the difference is. I think essentially they are the same.

[Tornado Tim]

UTC time difference atm is:
-12 hours for NZDT, and +1 for UK time.
From what I understand there is no difference in UTC to GMT time.
The time stated on the file is correct.

[Simon Culling]

As reported earlier, temperatures on Tuesday 22nd July reached 30*C over much of England and Wales with a top of 33.5*C at both RAF Northolt and London Heathrow Airport. The surface air had been advected north from France and was very humid with typical dew points of 17-18*C and this had resulted in a pool or plume of very high 850mb values of wet bulb potential temperatures which maintained the high CAPE values into the evening. An approaching upper trough from the SW cooled the mid and upper levels in the evening and allowed a release of instability over the central parts of England in the early hours of Wednesday (23rd) morning. This gave a large arc of thunderstorms overnight and into the morning stretching from N Wales through the Midlands and into E Anglia and SE England with further storms following this main band eastwards during Wednesday morning,

[Skywatcher]

There was even a brief thunderstorm in Edinburgh on Tuesday morning. Rumour has it that lightning struck the new tramlines... but that might be wishful thinking by the locals

[NZstorm]

Britians spanish plume thunderstorm affect is replicated in NZ when we get the hot airmasses from Australia in summer but the storm activity just affects the west of the South Island. There was a lot of it last summer with the big lightning storms over the alps in January.

[spwill]

temperatures on Tuesday 22nd July reached 30*C over much of England and Wales with a top of 33.5*C at both RAF Northolt and London Heathrow Airport. The surface air had been advected north from France and was very humid with typical dew points of 17-18*C ,

Those dewpoint /temperature combinations would be very rare in NZ away from perhaps Waikato.

[NZstorm]

temperatures on Tuesday 22nd July reached 30*C over much of England and Wales with a top of 33.5*C at both RAF Northolt and London Heathrow Airport. The surface air had been advected north from France and was very humid with typical dew points of 17-18*C ,

Those dewpoint /temperature combinations would be very rare in NZ away from perhaps Waikato.

Waikato would get that more than the UK.

[spwill]

Central and eastern parts of NZ would see more 30C+ days than southern UK, less the humidity