September 2021 C.E.T. and EWP forecast contests

[Roger J Smith]

GFS output looks fairly warm for another week to ten days, then cools to near average in zonal flow, hints at reloading warmth at end of run (which is currently 22nd). Would say likely to remain over 15 to then even if it does cool down a bit after mid-month. 

EWP currently only at trace amounts, shows 10 mm next ten days (on average in grid) and has potential for 20-35 mm days 11 to 16. Larry currently expected to zoom north after encounter with southeast Newfoundland and remnants nowhere near Britain, but swirling low pressure in Azores expected to move up and moisten the dry southeast flow around days 11-13 then Atlantic pushes back in with strong waves that for the GFS are often overdone at this time scale. Thus I would say the final estimate (by 22nd) is likely 30-40 mm. Without big doings at the end of the month, warm/dry forecast combinations favoured. Nothing carved in stone at that time range of course. 

[Summer Sun]

16.7c to the 6th

2.0c above the 61 to 90 average
1.5c above the 81 to 10 average

___________________________

Current high this month 16.7c on the 6th
Current low this month 14.4c on the 1st

[Scorcher]

6 minutes ago, Summer Sun said:

16.7c to the 6th

2.0c above the 61 to 90 average
1.5c above the 81 to 10 average

___________________________

Current high this month 16.7c on the 6th
Current low this month 14.4c on the 1st

Could be up there for warm first halves. Certainly the first 10 days are looking very warm indeed.

[Shillitocettwo]

5 hours ago, Summer Sun said:

16.7c to the 6th

2.0c above the 61 to 90 average
1.5c above the 81 to 10 average

___________________________

Current high this month 16.7c on the 6th
Current low this month 14.4c on the 1st

Wow....my 17.0.C is currently closest! May even jump over it after today!

  The challenge then is holding on to it.....

[The PIT]

Sunny Sheffield up to 16C -0.4C below normal. Rainfall 0mm 0% of the monthly average

[Roger J Smith]

So for warmest starts to September, I have this info ... first from the posting on 2nd about running CET values, 1898 held the highest values of running CET for 9th-10th, in the high 18s, then was tied on 11th by 1865 which then held the baton to the 22nd, passing to 2006 on the 23rd (tied 17.1 at that point). Mid-September 1865 was quite toasty and the highest running CET value the month produced in that stretch was 18.2 on 16th but it set the first half record at 18.1 on 15th. 

Besides that record, these are the top ten first half values of CET for September, and where they ended up for end of month CET values: 

(note Sep 17, have added the provisional value for 2021 and will edit that at end of month to show the actual value and the outcome Current estimates do not yet result in any changes to ranks for projected lower outcomes than 15.5 ... by the way 15.5 is a value that has never been recorded in the Sept CET.)

Rank __ Year ___ CET _____  final CET

_01 ____ 1865 ___ 18.1 ____ 16.3 (t3)*

_02 ____ 1898 ___ 17.6 ____ 15.2 (t14)

_03 ____ 2016 ___ 17.5 ____ 16.0 (t5)

_(04)___ 2021 ___ 17.4 ____ est 15.5 (est 10th)

t04 ____ 1795 ___ 17.3 ____ 16.0 (t5)

t04 ____ 2005 ___ 17.3 ____ 15.2 (t14)

_06 ____ 2006 ___ 17.2 ____ 16.8 (1)

t07 ____ 1780 ___ 17.1 ____ 15.6 (t8)

t07 ____ 1949 ___ 17.1 ____ 16.3 (t3)*

_09 ____ 1929 ___ 16.9 ____ 15.3 (t11)

_10 ____ 1999 ___ 16.7 ____ 15.6 (t8)

_11 ____ 1991 ___ 16.6 ____ 14.7

_12 ____ 1973 ___ 16.5 ____ 14.3

t13 ____ 1781 ___ 16.4 ____ 14.2

t13 ____ 1947 ___ 16.4 ____ 14.9

t13 ____ 1958 ___ 16.4 ____ 15.1 (t19)

_16 ____ 1784 ___ 16.3 ____ 14.8

t17 ____ 1843 ___ 16.2 ____ 14.4

t17 ____ 1906 ___ 16.2 ____ 13.9

t17 ____ 1911 ___ 16.2 ____ 13.9

t17 ____ 1959 ___ 16.2 ____ 14.9

t21 ____ 1933 ___ 16.1 ____ 14.9

t21 ____ 1846 ___ 16.1 ____ 14.7

t21 ____ 2004 ___ 16.1 ____ 14.9

_____________________________________

* In the final rankings, 1729 (16.6) was 2nd but had no daily data so we don't know where it sat after 15 days. 

... also missing from top 20 ranks above were 7th place 1760 (no daily data), 10th place 1895 (below 16 at mid-point,

warmest weather was late in the month), t11th 1730, 1731 (no daily data), and t14 1750 (no daily data), 1779 and 1961

(both were only mid-15s on 15th). Finishes below 15.1 (t19) are not ranked in the table. 2011 and 2014 were also t19

but were not warm enough at mid-point to make this table. 

Edited September 16, 2021 by Roger J Smith

[Summer Sun]

17.4c to the 7th

2.7c above the 61 to 90 average
2.3c above the 81 to 10 average

___________________________

Current high this month 17.4c on the 7th
Current low this month 14.4c on the 1st

[The PIT]

Sunny Sheffield up to 16.8C +0.5C above normal. Rainfall 0mm 0% of the monthly average

[saintkip]

When was the last if ever a September was warmer than August? Apologies if this had already been mentioned.

[Roger J Smith]

2 hours ago, saintkip said:

When was the last if ever a September was warmer than August? Apologies if this had already been mentioned.

The last time was 2014, 15.1 vs 14.9 in August. That occasion was not warmer than July (17.0) and tied June (15.1). 

In reverse chronological order, other Septembers since 1950 that were warmer than August (and possibly other months as listed) were:

2006 __ 16.8 (Aug 16.1, July 19.7, June 15.9). 

1985 __ 14.6 (tied Aug 14.6, July 16.2, June 12.7).

1956 __ 14.3 (Aug 13.5, July 15.8, June 13.1).

(back to 1956, no September was warmer than the July of the same year but 1961 tied at 15.2, August being 0.2 warmer than both, and 1980 tied (14.7) with August warmer than both at 15.9). 

Before 1956, there was no year with a September warmer than either July or August until 1895 (15.4 was warmer than July 15.2, not warmer than August though at 15.8) and then 1890 when it was the warmest month of the year (14.6 vs July 14.5 and August 14.1, June 13.5). 

Before that I found warmer Septembers than Augusts (but not July) in 1865, 1784, 1750, 1737, 1729, (tied 1678), and warmer than July (but not August) in 1875, 1821, 1802, 1795, (tied 1713 and 1708), and there was never a case where September was warmer than both but not June. In fact if September was warmer than either July or August, it was almost invariably warmer than June, 1737 being an exception. 

__________________________

Another interesting factoid is that 19th of August 1898 to 17th of September would have been as warm a 30-day "month" as the actual Septembers of 2006 and 1729. That month really cooled off quite significantly after the 18th. September 1865 would have had little help from any part of late August though. And September 2011 would have been 0.4 warmer than its t-19th 15.1 finish if it had run from 6 Sept to 5 Oct. 

Aside from 1890, September has never been the warmest month of the year otherwise. In 1890 it was a case of the least of four evils, the warmest daily mean of that summer was only 18.2 on 5 Aug and the second highest mean was 17.5 on 27 September. The mean daily was below 10 on all three days 30 Aug to 1 Sep. 

[Shillitocettwo]

It would be interesting if data exists for top 2and half of September CET values.....

[Roger J Smith]

15 minutes ago, Shillitocettwo said:

It would be interesting if data exists for top 2and half of September CET values.....

Not sure what you're asking there but if it's the top first half CET values, I posted that list yesterday about four posts back in the thread. 

[Summer Sun]

18.0c to the 8th

3.3c above the 61 to 90 average
2.9c above the 81 to 10 average

___________________________

Current high this month 18.0c on the 8th
Current low this month 14.4c on the 1st

[The PIT]

Sunny Sheffield up to 17.4C +1.2C above normal. Rainfall 0mm 0% of the monthly total.

[Roger J Smith]

The EWP has opened up its account with 1 mm on 7th, estimate 5 mm now, 25 mm predicted to 18th, and 20 mm additional indicated days 11-16, for a total of about 50 mm by 24th. CET looks like it could stay well above 15 C right through to then as some zonal intervals continue to draw in rather warm air at times, so would look for just a slow decline from current levels for the next two weeks. 

[The PIT]

Sunny Sheffield up to 17.7C +1.6C above average. Rainfall 2mm 3% of the monthly total.

[Summer Sun]

18.1c to the 9th

3.6c above the 61 to 90 average
3.0c above the 81 to 10 average

___________________________

Current high this month 18.1c on the 9th
Current low this month 14.4c on the 1st

[Scorcher]

There must be a good chance of this month ending up 16C+. Obviously hard to predict what may come in the last third of the month but there appears to be nothing cool in the offing. Minima look like remaining high which will mean any decline after today will be a slow one.

[The PIT]

Sunny Sheffield at 17.7C +1.7C above average. Rainfall an unimpressive 2.6mm 4% of the monthly total.

[Summer Sun]

18.2c to the 10th

3.7c above the 61 to 90 average
3.2c above the 81 to 10 average

___________________________

Current high this month 18.1c on the 10th
Current low this month 14.4c on the 1st

[Roger J Smith]

I suppose that 18.2 will drop slightly in the final figures but it does tie the highest running mean for 1st to 10th (1898 18.2) and the record for the 11th is 18.1, then back to 18.2 on the 12th as 1865 takes over for about ten days (setting record high running means), 2006 gets the baton on the 23rd. 

[damianslaw]

Very warm start to September, didn't see it coming.. outlook looks a little above average. Can't see anything but an above average month on the cards, possibly notably so. Unclear how the latter part of the month may pan out. 

Also a very dry start to September, and no much precipitation on the cards. We are in a notably dry spell at present in some western parts. River Lune exceptionally low. 3 weeks since we've had any appreciable rain, we missed anything notable on Thursday and Friday.

[The PIT]

Sunny Sheffield at 17.9C +2.0C above average. Rainfall unchanged.

[Don]

5 hours ago, damianslaw said:

Very warm start to September, didn't see it coming.. outlook looks a little above average. Can't see anything but an above average month on the cards, possibly notably so. Unclear how the latter part of the month may pan out. 

Also a very dry start to September, and no much precipitation on the cards. We are in a notably dry spell at present in some western parts. River Lune exceptionally low. 3 weeks since we've had any appreciable rain, we missed anything notable on Thursday and Friday.

As many of you know, I've never been a fan of notably warm September's as they tend to be bad news for the following winter if you want it cold!  Gavin Partridge has done some analysis on this in his latest winter update and although there is only a small data set for 16C+ September's going back to 1659, they were all followed by mild to very mild winters!  

Edited September 12, 2021 by Don

[Earthshine]

6 minutes ago, Don said:

As many of you know, I've never been a fan of notably warm September's as they tend to be bad news for the following winter if you want it cold!  Gavin Partridge has done some analysis on this in his latest winter update and although there is only a small data set for 16C+ September's going back to 1659, they were all followed by mild to very mild winters!  

Correlation doesn't equal causation.  I wouldn't give much notice to potential "trends", particularly when we have so few 16°C+ Septembers.  With such a small dataset it's bad science to draw any conclusions about what the following winter will do.