September 2016 C.E.T. Forecasts

[Mapantz]

Currently at 17.2°C here - 3°C above the regional average.

[Summer Sun]

17.4 to the 7th

2.8c above the 61 to 90 average

2.3c above the 81 to 10 average

[BornFromTheVoid]

Min today is 14.6C, while maxima look like being around the low 20s, so remaining on 17.4C on tomorrows update.

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

17.4C to the 9th (17.7: +3.0)
17.4C to the 10th (17.2: +2.5)
17.1C to the 11th (14.2: -0.6)
17.2C to the 12th (18.3: +3.9)
17.4C to the 13th (19.3: +5.4) [Record High: 19.4C]
17.3C to the 14th (16.5: +2.8)
17.2C to the 15th (15.4: +1.8)
17.0C to the 16th (15.2: +1.5)
16.9C to the 17th (14.3: +0.5)

The warm spell gradually winding down after mid month on the GFS, but there has been a lot of variability from one run to the next. The 00z GFS earlier today would have seen 4-5 daily records broken and the latest date for a 22C+ daily average being recorded.

[Roger J Smith]

I will work up a table of top ten drops in CET from first to second half (which some of us are going to need). Also top ten first half CET values as this one might qualify. But as I can't start that until 6 p.m., if somebody else has the stats available, feel free to post. 

[BornFromTheVoid]

Top 10 first halves of September:

1st- 1865: 18.1C
2nd- 1898: 17.6C
3rd- 1795, 2005: 17.3C
5th- 2006: 17.2C
6th- 1949, 1780: 17.1C
8th- 1929: 16.9C
9th- 1999, 1991: 16.6C

Top 10 drops from first half to 2nd half (average drop is -1.6C):

1st- 1889: 5.9C   [15.8C - 9.8C]
2nd- 1872: 5.7C   [16.0C - 10.3C]
3rd- 1919: 5.3C   [15.4C - 10.0C]
4th- 1914: 5.0C   [15.8C - 10.8C]
5th- 1898: 4.8C   [17.6C - 12.8C]
6th- 1871: 4.7C   [15.1C - 10.4C}
7th- 1911, 1906, 1781: 4.6C   [16.2C - 11.6C, 16.2C - 11.6C, 16.4C - 11.9C]
10th- 1928: 4.5C   [15.1C - 10.5C]

(Some seeming discrepancies above are due to rounding.)

[Matthew.]

If September comes out the warmest month of the year we would have to go back to 1890. We might need this pattern to keep happening though:

[The PIT]

Sunny Sheffield 16.7C miles above average.

[Roger J Smith]

Glad to find I have no number crunching to do ... if September comes out warmer than August then it will also be warmest on record as 2006 managed 16.8 and August of this year 17.0 ... and the same GFS 06z output used by BFTV to 17th, from 18th to 24th, suggests to me that the 16.9 by 17th will shrink steadily to around 15.9 by 24th, but only if it verifies of course.

The 12z GFS looks a touch warmer than 06z for the long-range outlook, would say 16.1 by 24th from that guidance. The most it could drop from there to 30th even with unusual cold is about a degree. If this output is anywhere close to being right the best place to be at this point is probably 15.5-16.0. 

[BornFromTheVoid]

The 12z is a big upgrade in the warmth next week. The 3 days from the 12th to the 14th would average over 20C.

Only 7 previous 3 day periods in September have averaged at least 20C, the latest of which occurred from Sept 7th to 9th, 20.5C in 1898.

Of course, it might well switch back on the next run. It's interesting to see the possibilities though.

[Man With Beard]

5 hours ago, Matthew Wilson said:

If September comes out the warmest month of the year we would have to go back to 1890. We might need this pattern to keep happening though:

Hadn't thought of that but yes, should the warmest scenario for next week comes off, and then another round of the same pattern later in the month (well why not, we'll be onto the fifth round of southerlies next week!!), we may have half a chance here. 

[Summer Sun]

17.4 to the 8th

2.8c above the 61 to 90 average

2.3c above the 81 to 10 average

[BornFromTheVoid]

Minimum today is 14.2C, while maxima look like getting close to 21C, so remaining on 17.4C on tomorrows update.

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

17.3C to the 10th (16.2: +1.5)
17.0C to the 11th (14.1: -0.7)
17.1C to the 12th (18.3: +3.9)
17.3C to the 13th (20.0: +6.1) [Record High: 19.4C]
17.5C to the 14th (19.7: +6.0) [Record High: 19.3C]
17.5C to the 15th (18.1: +4.5) [Record High: 18.8C]
17.4C to the 16th (16.2: +2.5)
17.3C to the 17th (14.3: +0.5)
17.0C to the 18th (12.8: -1.1)

Remaining mostly quite warm next week with several daily records under threat. Also a chance of breaking into the top 3 warmest first halves of September on record. In the low res sections of the run things turn quite cool, with the CET down to about 16.0C by the 24th.

[Summer Sun]

17.4 to the 9th

2.9c above the 61 to 90 average

2.3c above the 81 to 10 average

[BornFromTheVoid]

The latest that a daily average CET of 21.5C or higher has been recorded is September 5th, with 22.4C in 1949.
The 12z GFS has both the 13th and 14th higher than 21.5C.

[Summer Sun]

17.2 to the 10th

2.7c above the 61 to 90 average

2.2c above the 81 to 10 average

Edited September 11, 2016 by Summer Sun

[BornFromTheVoid]

Minimum today is 8.8C, while maxima look like getting close to 19C, so a drop to 16.9C is likely on tomorrows update.

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

16.9C to the 12th (17.2: +2.7)
17.2C to the 13th (21.3: +7.3) [Record High 19.4C]
17.5C to the 14th (21.5: +7.8) [Record High: 19.3C]
17.5C to the 15th (17.1: +3.5)
17.3C to the 16th (14.5: +0.8)
17.0C to the 17th (12.1: -1.7)
16.8C to the 18th (13.0: -0.9)
16.7C to the 19th (15.7: +2.1)
16.6C to the 20th (13.9: -0.1)

An exceptional few days coming up before dropping back closer to average. 3rd warmest first half of the month on record still looks a good bet too.

[Relativistic]

Will be very interesting to watch the CET over the next few days, as we could achieve a three day spell with a mean of 20.0C+. If so, it would be the latest ever in a calendar year. The current latest is 7th-9th in 1898 (20.5C), so we may beat this by five or six days!

This feat last occurred in 1906 (1st-3rd was 21.4C, the warmest such period on record). If 2016 pulls it off it will only be the sixth year ever to do so. (The others were 1780, 1824, 1880, 1898, and 1906.)

Edited September 11, 2016 by Relativistic

[DAVID SNOW]

At this point, I estimate a CET finish close to 15 degrees  (after corrections)

[Summer Sun]

16.9 to the 11th

2.5c above the 61 to 90 average

1.9c above the 81 to 10 average

[Man With Beard]

Wonder what the CET forecast is now the GFS has come on board with the longer heatwave - three days with a CET above 20C looking a very good bet, and how close would we be to the warmest first half of September ever?

Should we hit halfway at 17.5C, say, it would require 12.5C for the rest of the month to get down to 15C. Can't really see that happening unless a NW flow sets in. So I'd guess somewhere in the 15s or 16s is the most likely outcome, and would anyone write off another blast from the south later in the month - some ECMs suggest it is a possibility?

[Roger J Smith]

Looks fairly cold at times after this coming weekend, current 12z GFS would suggest 15.2 by 28th, although the range would be something like 14.8 to 15.6. A lot of forecasts are still in play depending on how strong this cooling trend becomes. Agreed that we will be at or near 17.5 by end of Thursday. A second half of 12.5 isn't all that cold really given that the normal for that period is around 13.2 in recent data and close to 12.5 longer-term. 

[The PIT]

Sunny Sheffield down to 16.1C but expect some big rises in the next few days.

[summer blizzard]

I think the highest probabilities are for a finish between 15C and 16C but it at least looks near normal after this final attempt to melt me. 

[BornFromTheVoid]

Minimum today is 15.4C, while the maxima look like reaching about 27C, so an increase to 17.3C is likely on tomorrows update.

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

17.6C to the 14th (22.1: +8.4) [Record High: 19.3C]
17.8C to the 15th (20.5: +6.9) [Record High: 18.8C]
17.7C to the 16th (16.2: +2.5)
17.5C to the 17th (14.7: +0.9)
17.5C to the 18th (16.6: +2.7)
17.5C to the 19th (17.5: +3.9)
17.3C to the 20th (14.6: +0.6)
17.1C to the 21st (13.0: -0.7)
17.0C to the 22nd (13.1: -0.7)

Some very warm days coming up. The max today only needs to be 23.5C or higher to set a new daily record. The record for the latest 3 day period averaging over 20C is likely to be broken, and possibly the warmest 3 day period on record for September, 21.4C (even more remarkable it we beat it mid month!)

[Relativistic]

It's interesting to look at the mean CET for astronomical Summer (AS), which, for simplicity's sake, I have defined as being 21st June to 20th September for every year (obviously this isn't totally accurate). By taking the mean CET of every day within this range, provisionally the AS of 2016 has a mean of 16.7C. However, it looks as if by the 21st we may be up to 16.8C, which overall would rank 2016 as joint 14th warmest on record (going back to 1772). The other years that equalled this were 1779, 1868, 1899, 1959, and 1975.

Interestingly, no AS has ever recorded a mean CET of 16.7C, despite the fact that there have been five years at 16.8C and six years at 16.6C. It's possible that 2016 will be the first year to do this.

By calculating the meteorological Summer (MS) mean in the same way (simply take a mean of all days), we find that MS 2016 has a mean of 16.4C; quite a bit lower than a possible value of 16.8C for AS 2016. For a particular year this is not unusual however, and it's actually become more common in recent decades (starting circa 1920) for this to be the case. The graph below shows the value for a year's MS minus its AS (y axis, years are on the x axis).

 

This is to be expected, since September has warmed since 1772 (especially so in recent decades), while June has not.

Something that I thought was noteworthy when looking at Summers in this way was that 1995 was easily the warmest of the lot (17.7C), beating 2006 in second place (17.4C). Summer 1976 "only" ranks fifth (17.2C).

Edited September 14, 2016 by Relativistic
Graph inserted directly.