What do you consider “Early Spring temperatures”...and "Late Spring temperatures"? (records, seasons)

[dunno what to put here]

If we had the same definitions as Finland/Sweden/Norway, winter would never begin here and summer would probably start in April and last until October.

[P London]

Originally Posted by dunno what to put here

If we had the same definitions as Finland/Sweden/Norway, winter would never begin here and summer would probably start in April and last until October.

Yep our climate is truely Subtropical...

[Ariete]

Originally Posted by dunno what to put here

If we had the same definitions as Finland/Sweden/Norway, winter would never begin here and summer would probably start in April and last until October.

Why should you use it? You have a oceanic climate.

And would it? Tutiempo claims that the 24h mean went permanently (7 days in a row) above 10C (also 12.83C and 15C) in Leeds-Bradford on May 22 2012. Fell below 10C on Oct 3. Your winter started on Jan 13 2013, and well... ended on Jan 26.

Heatrow's summer was from May 17 to Oct 26.

I don't know how reliable those figures are. Are there better sources for Leeds?

[dunno what to put here]

I'm not saying we should use it, just that if we applied the same definition, our winter would be nonexistent in any average year. A mean below freezing is not a certainty. April was exceptionally cold last year in the UK, too. 1997 is a good example of what I am talking about - a 7-day stretch of temperatures above 10C which started in late April, but only three days with a mean below freezing (including December the previous year). Autumn also didn't begin until early November, so I guess if (for entirely hypothetical reasons) we had that definition, summer would have started in late April and ended in early November.

One question: if, for example, there were seven consecutive days with a mean below freezing in December, but the rest of the month is above freezing, and virtually every day in January and February had means above freezing (say one or two in each), and then there is a seven day stretch below freezing in March, did spring arrive in December, or did winter arrive in March? Or would it be irrelevant?

[Ariete]

Originally Posted by dunno what to put here

I'm not saying we should use it, just that if we applied the same definition, our winter would be nonexistent in any average year. A mean below freezing is not a certainty. April was exceptionally cold last year in the UK, too. 1997 is a good example of what I am talking about - a 7-day stretch of temperatures above 10C which started in late April, but only three days with a mean below freezing (including December the previous year). Autumn also didn't begin until early November, so I guess if (for entirely hypothetical reasons) we had that definition, summer would have started in late April and ended in early November.

Yes, that's the problem when you don't have permanently sub-freezing conditions, you can't apply the same criteria as we do, because it gives stupid results. E-mail the Met Office and tell them to make up their own which can be applied to the UK. I don't know, should the UK use like 3-4C or something? Then I should think that you could define winter on a somewhat realistic time frame.

I'm looking at April 1997 from Leeds-Bradford right now. There is four days with a 24h mean above 10C, two of them were in a row. I'm still talking mean temps, not high temps. The first consecutive 7 day period was beginning from May 26 1997. The summer started on that day.

The London Weather Centre station is a bit trickier. It had a 7 day period with means above 10C on March 12-18, but the next one was starting on April 23. But as on March 12 there weren't grounds to believe that the mean temps would stay permanently above 10C, the first period could be classified as unusual summerlike conditions in spring. The summer started on April 23.

This is not completely unheard of here, either. The summer of 2000 started in Helsinki on April 19, so the criteria sometimes gives stupid results here as well.

Originally Posted by dunno what to put here

One question: if, for example, there were 7 consecutive days with a mean below freezing in December, but the rest of the month is above freezing, and virtually every day in January and February had means above freezing (say one or two in each), and then there is a seven day stretch below freezing in March, did spring arrive in December, or did winter arrive in March?

This is exactly the question the Finnish Met Institute had to face in 2008. In Helsinki Kaisaniemi and the Åland Islands there wasn't a meteorological winter at all. The only cold strech was ironically in late March. The decision was: Winter started on Mar 19 and ended on Mar 28, before it it was autumn. Spring started on Mar 28.

Spring has nothing to do with December, it's autumn when the >0C conditions just drag on.

[dunno what to put here]

I was looking at Leeds Weather Centre, which is in central Leeds. On 26 April, the mean temperature reached 11.8C, and the mean temperature was above 10C for 8 days continuously. So summer would have started nearly a month in Leeds city centre before Leeds Bradford Airport.

To be honest, I think the setup we have right now is probably for the best.

Originally Posted by Ariete

This is exactly the question the Finnish Met Institute had to face in 2008. In Helsinki Kaisaniemi and the Åland Islands there wasn't a meteorological winter at all. The only cold strech was ironically in late March. The decision was: Winter started on Mar 19 and ended on Mar 28, before it it was autumn. Spring started on Mar 28.

Spring has nothing to do with December, it's autumn when the >0C conditions just drag on.

Gotcha.

[Ariete]

Originally Posted by dunno what to put here

I was looking at Leeds Weather Centre, which is in central Leeds. On 26 April, the mean temperature reached 11.8C, and the mean temperature was above 10C for 8 days continuously. So summer would have started nearly a month in Leeds city centre before Leeds Bradford Airport.



Gotcha.

Oh, right. Exactly, the summer started then on April 26th in central Leeds, a month earlier than on the airport. We don't have to face similar problems, as usually the summers starts within a few days for several hundred miles, and none of the stations are affected by urban heat islands.

The SMHI had to make a deadline for autumn after the winter of 2008. The last day possible for autumn is now February 14. In many places, the autumn of 2007 actually never ended, the transition between autumn and spring was classified as "a season that cannot be classified".

Hmm, autumn until February 14. These definitions make less sense to me all the time.

[Weatherfan2]

Early spring, temps in the teens, late spring, temps in the mid twenties.

[Ariete]

Originally Posted by dunno what to put here

One question: if, for example, there were seven consecutive days with a mean below freezing in December, but the rest of the month is above freezing, and virtually every day in January and February had means above freezing (say one or two in each), and then there is a seven day stretch below freezing in March, did spring arrive in December, or did winter arrive in March? Or would it be irrelevant?

I found another tricky example, which I didn't remember. The winter of 2006. It 'should' have started on Nov 1 (cannot start before that), but as after the first week the temps recovered rapidly and went back permanently above freezing until mid-January, winter was not 'declared'. The mean for November was 1.5C and 3.0C in December.
2006 was a freak year anyway, so the meteorologists were probably used to weird weather at that point.

[nei]

Originally Posted by Ariete

I'm replying to a year old posts, but as both posters are still active, why not.



We use the same criteria, I made a thread about it, and was a bit surprised that very few countries do this. Our meteorological seasons are:
spring = begins when the 24h mean temp is above 0C/32F for seven consecutive days
summer = begins when the 24h mean temp is above 10C/50F for 7 days
autumn = begins after 7 days of a 24h mean temp less than 10C/50F
winter = again, 7 days below freezing
growing season = when the 24h mean temp has been above 5C/41F for 10 days.

The three-month-seasons are referred as 'calendar seasons'.

The seasons can't be reversed, so if the temps fall below freezing in spring for example, it's still spring and not temporarily winter again.

This method is no way very satisfactory, as it makes summers unrealistically long, and springs very short. On average that time is from mid May to late days of September. Raising the temperature threshold to 12.83C or 15C pushes the summer forward, which is not good as well. June is very much summer, and September autumn, at least mentally. Chilly Junes, like last year, can mean that the whole month is a 'spring' month, if using 15C.

I rather like this system, but it seems excessively prone to being thrown off early spring heat waves (or midwinter warmth). For very variable climates, this system might have issues. For my climate, I'd replace 10°C with 18°C (maybe a degree less?) but keep 0°C.