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Roger J Smith

September 2016 C.E.T. Forecasts

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CET maximum for yesterday was only 24.3C, so still a daily record but not actually managing to top the 20C mark (19.9C).

The minimum today is 16.4C, so maxima need to be 22.3C or higher for a daily record, and 23.5C or higher to average at least 20C.

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So provisionally we have 19.9C and 20.7C as the daily values for 13th and 14th respectively, requiring a value of 19.4C or higher today to achieve what would be provisionally the latest ever 3-day spell with a mean of over 20C.

The provisional mean of 20.7C yesterday was the joint 13th warmest September day on record (the other being 4/9/1880). There are only two days on record that recorded higher daily means at a later date in the month: these were 19/9/1926 (20.9C) and 21/9/2006 (21.4C).

Edited by Relativistic
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Minimum today of 14C, while maxima look like climbing into the 25s, so an increase to 17.6C is likely on tomorrows update.

After that, the 06z GFS has the CET at:

17.5C to the 16th (16.2: +2.5)
17.3C to the 17th (14.7: +0.9)
17.1C to the 18th (14.3: +0.4)
17.0C to the 19th (15.3: +1.7)
16.9C to the 20th (14.3: +0.3)
16.8C to the 21st (13.7: +0.0)
16.7C to the 22nd (15.3: +1.5)
16.7C to the 23rd (15.8: +2.3)
16.4C to the 24th (11.2: -1.6)

A max of 23.7C or more is required for a daily record today (though current temps are way down on that and most forecasts). After that, a return to slightly above average conditions looks likely, with a CET around 16C by months end

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4 hours ago, BornFromTheVoid said:

 

A max of 23.7C or more is required for a daily record today (though current temps are way down on that and most forecasts). After that, a return to slightly above average conditions looks likely, with a CET around 16C by months end

I think we could be close to that 23.7C max as it warmed up a lot in NW England in the afternoon- not sure what Stonyhurst has managed (one of the CET sites) but it's 24C in Manchester right now.

Edit: 22.7C at Stonyhurst at 5pm which should be enough I'd have thought. Most places have reached forecast values after a slow start.

Edited by Scorcher

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Certainly looking odds for a very mild CET return, how mild is the question, can we beat 2006? I doubt it, but could well end up at lest 2 degrees above the norm.

September is fast becoming a better month than June CET wise, and the best month for consistent spells of dry calm weather. Meteorological summer should be defined as June- September. 

I guess there is a greater chance for sustained warmth in September compared to June, continent is far warmer now than in June, SST values are far warmer as well, any northerly airstream is much warmer now than in June.. westerlies far warmer as well. Its such a 'benign' month, all so temperate and very unexciting, I always rejoice when October arrives.

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On 15/09/2016 at 11:12, Relativistic said:

So provisionally we have 19.9C and 20.7C as the daily values for 13th and 14th respectively, requiring a value of 19.4C or higher today to achieve what would be provisionally the latest ever 3-day spell with a mean of over 20C.

The provisional value for yesterday was 18.8C, which gives the mean for the 13th-15th as 19.8C, so just missing out. But corrections may see to that. Even if this was to be the final figure, nothing as warm has occurred as late in the year, so as short, sharp September hot spells go, it's been pretty remarkable.

The most comparable transient hot spells were 17th-19th September 1926 (19.7C, perhaps a figure to aim to beat after corrections), and the 28th-30th September 2011 (19.5C, which, frankly, blows my mind).

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14 hours ago, damianslaw said:

Certainly looking odds for a very mild CET return, how mild is the question, can we beat 2006? I doubt it, but could well end up at lest 2 degrees above the norm.

September is fast becoming a better month than June CET wise, and the best month for consistent spells of dry calm weather. Meteorological summer should be defined as June- September. 

I guess there is a greater chance for sustained warmth in September compared to June, continent is far warmer now than in June, SST values are far warmer as well, any northerly airstream is much warmer now than in June.. westerlies far warmer as well. Its such a 'benign' month, all so temperate and very unexciting, I always rejoice when October arrives.

June and September do seem to be growing closer temperature wise. The latest difference in the 30 year average is just 0.3C

uEa3Hkw.png

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47 minutes ago, Summer Sun said:

17.5 to the 15th

3.4c above the 61 to 90 average

2.8c above the 81 to 10 average

First half is provisionally the third warmest on record (behind 1865 and 1898), even September 2006 was lower by this stage (17.2C).

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Sunny Sheffield at 16.8C if I remember correctly. A very dry month so far with less than half the normal rainfall.

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17.4 to the 16th

3.3c above the 61 to 90 average

2.7c above the 81 to 10 average

I suspect 17.5 was the high point for the month remarkable just how long it stayed so high

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23 hours ago, BornFromTheVoid said:

June and September do seem to be growing closer temperature wise. The latest difference in the 30 year average is just 0.3C

uEa3Hkw.png

Whats really interesting is how little June has "warmed up" over the years. Not sure why there would be any reason for that.

Another factor to consider with September is that the the day length is much shorter. I remember being struck a few years back when after asking on here and finding out that the CET mean for June 1st-21st is almost exactly the same as as September 1st- 21st. I often think the best way to think of a summer is to look at the period known as astronomical summer (June 21-September 21) as that first 3 weeks of June often feels like it is a separate season to that what follows where as the first three weeks of September often feel an extension of summer.

Edited by GRHinPorts
typo
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On 19 August 2016 at 21:08, Roger J Smith said:

September CET averages and extremes

16.8 ... warmest (2006)

16.6 ... second warmest (1729)
16.3 ... third warmest (tied 1865 and 1949)

16.0 ... fifth warmest (1795)
 

A very warm September looking at the rest of the month. We might scrape joint 5th warmest:) Incredible!

Edited by Matthew Wilson

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Sunny Sheffield down to 16.4C dropping quickly at the moment.

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3 hours ago, The PIT said:

Sunny Sheffield down to 16.4C dropping quickly at the moment.

Yes similar here with 16.3c, 2.8c above 1981-2010 mean. A steady drop likely now untill the end of the month, guessing the month may end 1-1.5c above average.

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Euro and GEM for the next 10 days would probably make it likely that we'd finish the month under 16C. 

GFS6z probably guarantees that top 5 finish.

*This assumes a near average final few days.

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Crosby at  17.7°C for the month, the warm nights  accounting mainly for this. 

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(edit Oct 1st)

With three new record highs (one a tied occurrence) from 13th to 15th September, then there were 16 CET maximum daily mean records (includes two ties) in the period running from 6 Nov 2015 to 15 Sep 2016 (315 days). 

The previous record for that short an interval appears to be 13 records (also one tied) from 31 May 1947 to 9 March 1948 (284 days). This expanded to 17 (one tied) when the four records 27-30 July 1948 were added, a period of 427 days. Also, from 4 August 1975 to 8 July 1976, there were 15 records until 1 July fell to 2015, so now in the records, 14 (three ties) in 340 days.

There were ten records (includes one tie) from 11 Jan to 14 Oct 1990 (277 days) and ten (one tie) in the period 19 Nov 1994 to 9 Oct 1995 (325 days). These are the only periods when ten of the current records were set within a year (nine were set from July 2006 to April 2007 but 13 September 2006 was lost to 2016 so that now stands at eight) If we go back to Oct 2014, we have set 19 records within two years (earlier I said 20 but then realized that one of the (Dec) 2014 records was overtaken in 2015. Over 245 years that would average three (perhaps closer to four given that we are counting ties as records set). 

Edited by Roger J Smith
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On 17/09/2016 at 12:33, GRHinPorts said:

Whats really interesting is how little June has "warmed up" over the years. Not sure why there would be any reason for that.

Another factor to consider with September is that the the day length is much shorter. I remember being struck a few years back when after asking on here and finding out that the CET mean for June 1st-21st is almost exactly the same as as September 1st- 21st. I often think the best way to think of a summer is to look at the period known as astronomical summer (June 21-September 21) as that first 3 weeks of June often feels like it is a separate season to that what follows where as the first three weeks of September often feel an extension of summer.

Yes there is a lag effect in September, the warmer continental air mass and ground temps combined with warmer SST values seem to cancel out the lower levels of daylight and weaker solar strength when compared to the first 21 days of June.

A similiar effect occurs with the first 21 days of Dec and first 21 days of March,  I suspect the Cet values for those periods are fairly similiar as well - anyone have the stats? However a sunny calm day in mid Dec always feels colder than a sunny calm day in mid March.

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12 hours ago, damianslaw said:

Yes there is a lag effect in September, the warmer continental air mass and ground temps combined with warmer SST values seem to cancel out the lower levels of daylight and weaker solar strength when compared to the first 21 days of June.

A similiar effect occurs with the first 21 days of Dec and first 21 days of March,  I suspect the Cet values for those periods are fairly similiar as well - anyone have the stats? However a sunny calm day in mid Dec always feels colder than a sunny calm day in mid March.

For the period 1981-2010, the CET for the first 21 days of December is 4.8 and the CET for the same period in March is 6.2, so significantly closer in value than their respective monthly averages of 4.6 and 6.6. These values get even closer if you go back through earlier years, as historically March tended towards cold starts.

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