Heatwave Definition?

[damianslaw]

I find that it's far too overused. In winter it's fair enough that we've been seeing the term 'big freeze' mentioned a lot because we have had very cool winters recently and it is much harder for areas like say London to get ice days than get 30C in Summer IMO.

But for places like London where on average there are 4 or 5 30C days a year then I think it is overused, a heatwave should be a rare event and not just a one of very warm spell. Average London maxima for July are about 23-24C now (using 81-10 averages) so 30C is too low for heatwave territory I think. Also, I remember last year we had a period of about 3-4 weeks of temperatures 24C or above and people were labelling that a heatwave, but it's fairly common to get sustained 24C+ temps here.

For northern UK I think the definitions are slightly better as it is much harder to reach 28C-30C, but again i think 15C night temperatures is a bit pathetic to class as a heatwave! that's not far too off average night time temperatures here in July and August!

Agree the classification of 15 degree nightime mins as a heatwave is odd. We can see temps higher under moist southwesterly flows in the summer even when temps struggle to get into the low 20's.. 15 degree nightime minima is very easy to achieve, indeed 13 and 14 degree mins can be achieved as late as October under a particularly warm moist sw flow... 18 degree mins probably a better marker..

[Derp Patrol]

Agree the classification of 15 degree nightime mins as a heatwave is odd. We can see temps higher under moist southwesterly flows in the summer even when temps struggle to get into the low 20's.. 15 degree nightime minima is very easy to achieve, indeed 13 and 14 degree mins can be achieved as late as October under a particularly warm moist sw flow... 18 degree mins probably a better marker..

Yes that's true and there were many awful days in summer 2007 with days of 20C and night mins of 16C under the atlantic dominated pattern. Even in winter it isn't unheard of to see mins of 8-10C

Edited June 26, 2011 by robthefool

[johnholmes]

It MIGHT help if some of you read the link fully and thought about what the figures actually mean!.

The request and values were those set by the Health Authority NOT the Met Office

I'm not always a fan of Wilki but this link explains that there is no absolute definition for a heat wave, many factors have to be taken into account the article says.

http://en.wikipedia.org/wiki/Heat_wave

Edited June 26, 2011 by johnholmes

[Thundery wintry showers]

Don't forget that the Met Office use 32C as the baseline for London rather than 30C.

[The PIT]

So would a day time max of 25c and overnight low of 20c count??

Or a daytime max of 34c and a low of 9c

It seems not.

Funny though every time we get a bit of sun now we get a health warning. Problem with warning this warning that people switch off and don't listen. Strangely without any warning I would have done exactly the same today regardless. Get the gardening done before it gets too hot then retreat indoors.

Tomorrow will be the same except I'm racing the breakdown in the weather.

[Eugene]

Heatwave to me is a spell of extreme heat more than 5 days, 2 days of temps just above 25C arent a heatwave to me, when it really starts to feel uncomfortable indoors and i start to sweat is a heatwave like in the summers of 1995/2003/2006, it feels pleasant today not too hot.

[johnholmes]

So would a day time max of 25c and overnight low of 20c count??

Or a daytime max of 34c and a low of 9c

It seems not.

Just to make a factual reply.

My understanding is that provided the daytime temperature REACHES or EXCEEDS the values quoted in the Met O link, AND at the same time, on the night between those two daytime values, the overnight low does NOT fall BELOW 15C then the criteria the Health folk have set will be met.

Hope that explains nice and clearly to anyone not too clear?

Edited June 26, 2011 by johnholmes

[The PIT]

I think the heat is getting to you John. LOL. Briefly a bit of the old style posting before editing.

To add more mud to the water it's surprising they don't take humidity into account either. 30C at 5% humidity would be more bearable than 25C at 95% humidity. Anyway my body has decided it's a heatwave and that's enough for me.

[jimbo36]

When I was a lad a heatwave was 15 days 30C and above. Looks like the meto have gone all namby pamby after 12 years of a Labour Govt...lol

[cyclonic happiness]

A "heatwave" is defined as and area of hot air that "waves" at us as it slips by on the other side of the English Channel

[damianslaw]

So would a day time max of 25c and overnight low of 20c count??

Or a daytime max of 34c and a low of 9c

It seems not.

Funny though every time we get a bit of sun now we get a health warning. Problem with warning this warning that people switch off and don't listen. Strangely without any warning I would have done exactly the same today regardless. Get the gardening done before it gets too hot then retreat indoors.

Tomorrow will be the same except I'm racing the breakdown in the weather.

The reason a health warning is put out under such conditions as we have now is because a fair proportion of the population no longer prepares itself for such conditions - just like in winter when we get snow and cold temps... Our buildings don't help neither with both poor insulation and poor air conditioning.

Unfortunately good old common sense seems to be dissapearing, if we had it we wouldn't need these 'health warnings'.. best words of advice are those past down by parents and grandparents..who were much more prepared with the absence of all the technology we have nowadays.

Hot weather - drink plenty of fluids, where light clothing, keep windows open, avoid the sun at its hottest, wear a hat and put plenty of suncream on - check on elderly neighbours and relatives.

Cold weather - stay warm, lots of layers, hot drinks, sturdy footwear, keep heating on - get that boiler checked in the autumn!

Good old common sense.

Edited June 26, 2011 by damianslaw