The answer is, when it only lasts two days as it's recently done in the UK.

If this was 'Play your cards right' and this was Bruce Forsyth he would very likely being saying: 'You don't get anything for a pair - not in this game'!

Yes, the 1st of July was a hot day at Heathrow and broke the record for the hottest July day in the UK, but one hot day doesn't a heat wave make, you need that to happen for at least five consecutive with maximum temperature 5°C higher that the long-term average.

https://xmetman.wordpress.com/2015/0...t-a-heat-wave/

On Sunday, 5 July 2015 12:19:58 UTC+1, Bruce Messer wrote:
The answer is, when it only lasts two days as it's recently done in the UK.

If this was 'Play your cards right' and this was Bruce Forsyth he would very likely being saying: 'You don't get anything for a pair - not in this game'!

Yes, the 1st of July was a hot day at Heathrow and broke the record for the hottest July day in the UK, but one hot day doesn't a heat wave make, you need that to happen for at least five consecutive with maximum temperature 5°C higher that the long-term average.

https://xmetman.wordpress.com/2015/0...t-a-heat-wave/

I agree; not a heatwave - an interestingly hot day, or two (I got 29.5 on 30 June). Is "heatwave" a defined term, then? I thought it was simply a bit of journalese like "cloudburst".

Tudor Hughes, Warlingham, Surrey.

The wiki entry for heat wave makes interesting reading. No one country can agree on a common definition but the 5 days 5°C one is the WMO definition preferred by the UKMO.

On 05/07/2015 21:09, Bruce Messer wrote:
The wiki entry for heat wave makes interesting reading. No one country can agree on a common definition but the 5 days 5°C one is the WMO definition preferred by the UKMO.

-----------------------------------------------------------------------------
I'd have to disagree with you both there and say it was/is a heatwave,
at least for here. For a start I think as "heatwave" isn't a
scientifically measured parameter in this instance some credence should
be given to other factors, like sunshine hours and to some extent public
(not media) perception. It probably did pretty much meet your criteria
here anyway but here are some reasons why I think it was:-
1. Longevity - 12 days with average max of 26.6C and just one max below
24C, - 22.5C (For this period here best estimate of average max for same
period is 21.3C) (24th June -5th July)
2. One day breaks all time high temperature for the month - and it was
the 1st of that month.
3. High number of sunshine hours. (Don't have figures)
4. Most people thought it was a heatwave!
5. I'm getting on a bit and I didn't have to put a jumper on :-)

Dave

"Dave Cornwell" wrote in message
...
On 05/07/2015 21:09, Bruce Messer wrote:
The wiki entry for heat wave makes interesting reading. No one country
can agree on a common definition but the 5 days 5°C one is the WMO
definition preferred by the UKMO.

-----------------------------------------------------------------------------
I'd have to disagree with you both there and say it was/is a heatwave, at
least for here. For a start I think as "heatwave" isn't a scientifically
measured parameter in this instance some credence should be given to other
factors, like sunshine hours and to some extent public (not media)
perception. It probably did pretty much meet your criteria here anyway but
here are some reasons why I think it was:-
1. Longevity - 12 days with average max of 26.6C and just one max below
24C, - 22.5C (For this period here best estimate of average max for same
period is 21.3C) (24th June -5th July)
2. One day breaks all time high temperature for the month - and it was the
1st of that month.
3. High number of sunshine hours. (Don't have figures)
4. Most people thought it was a heatwave!
5. I'm getting on a bit and I didn't have to put a jumper on :-)


Well I hate heat and one day it reached 25C but most of the time it was
around 19C, but at no stage did I ever think it was a heatwave, it clearly
wasn't on Dartmoor, just pleasantly dry and sunny for once. If I was living
in Essex I would have suffered, as 12 days over 25C would be unbearable, and
then I would have called it a mega heatwave :-) It's all about perception.

Will
--
http://www.lyneside.demon.co.uk/Hayt...antage_Pro.htm
Will Hand (Haytor, Devon, 1017 feet asl)
---------------------------------------------

On 06/07/2015 08:51, Eskimo Will wrote:

"Dave Cornwell" wrote in message
...
On 05/07/2015 21:09, Bruce Messer wrote:
The wiki entry for heat wave makes interesting reading. No one
country can agree on a common definition but the 5 days 5°C one is
the WMO definition preferred by the UKMO.

-----------------------------------------------------------------------------

I'd have to disagree with you both there and say it was/is a heatwave,
at least for here. For a start I think as "heatwave" isn't a
scientifically measured parameter in this instance some credence
should be given to other factors, like sunshine hours and to some
extent public (not media) perception. It probably did pretty much meet
your criteria here anyway but here are some reasons why I think it was:-
1. Longevity - 12 days with average max of 26.6C and just one max
below 24C, - 22.5C (For this period here best estimate of average max
for same period is 21.3C) (24th June -5th July)
2. One day breaks all time high temperature for the month - and it was
the 1st of that month.
3. High number of sunshine hours. (Don't have figures)
4. Most people thought it was a heatwave!
5. I'm getting on a bit and I didn't have to put a jumper on :-)


Well I hate heat and one day it reached 25C but most of the time it was
around 19C, but at no stage did I ever think it was a heatwave, it
clearly wasn't on Dartmoor, just pleasantly dry and sunny for once. If I
was living in Essex I would have suffered, as 12 days over 25C would be
unbearable, and then I would have called it a mega heatwave :-) It's all
about perception.

Will
------------------------------------------------------
It's tricky in our household Will. My wife is badly affected by the heat
and anything over 20C is too hot for her if it's sunny but I'm Ok up to
27C as long as I am not working in it. So a compromise about 23C works
best for us but we've not had many holidays in the Med in August I have
to say!
Dave

On Monday, 6 July 2015 01:23:32 UTC+1, Dave Cornwell wrote:
On 05/07/2015 21:09, Bruce Messer wrote:
The wiki entry for heat wave makes interesting reading. No one country can agree on a common definition but the 5 days 5°C one is the WMO definition preferred by the UKMO.

-----------------------------------------------------------------------------
I'd have to disagree with you both there and say it was/is a heatwave,
at least for here. For a start I think as "heatwave" isn't a
scientifically measured parameter in this instance some credence should
be given to other factors, like sunshine hours and to some extent public
(not media) perception. It probably did pretty much meet your criteria
here anyway but here are some reasons why I think it was:-
1. Longevity - 12 days with average max of 26.6C and just one max below
24C, - 22.5C (For this period here best estimate of average max for same
period is 21.3C) (24th June -5th July)
2. One day breaks all time high temperature for the month - and it was
the 1st of that month.
3. High number of sunshine hours. (Don't have figures)
4. Most people thought it was a heatwave!
5. I'm getting on a bit and I didn't have to put a jumper on :-)

The only thing with the WMO definition is it doesn't consider minima. The summer of 1959 was notable by its maxima but temperatures fell away smartly at night and, from what I've read, humidity stayed low, allowing for comfortable sleep. An example of one hot spell in Greenwich is below. I still think the Heat Index measure picks out the really hot, unbearable hot spells better - when minima of 20C makes sleeping impossible.

04/07/1959 22.80 30.6 15.0
05/07/1959 23.35 32.8 13.9
06/07/1959 20.55 27.2 13.9
07/07/1959 20.30 28.9 11.7
08/07/1959 22.80 32.8 12.8

Last week's spell fell away miserably after 2 days so doesn't count
29/6 19.55 27.2 11.9
30/6 25.1 30.8 19.4
1/7 27.25 36.1 18.4
2/7 20.05 28.7 11.4

--

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