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December 2018 CET forecasts and EWP contest -- start of 2018-19 competitions


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On behalf of J10 and myself, welcome to another new competition year with the winter season of 2018-19 fast approaching. The contests will include the CET forecast and the (still optional) EWP forecas

Another mild washout whimper to end another naff year and my worst year ever.  Rest in pieces 2018!  12C    Last sub 0C, last sub 1C, last sub 2C, last sub 3C and last sub 4C December all in 2010.

Hadley is confirmed as 6.9C. Joint 15th warmest. The annual CET was 10.69C, 4th warmest.

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Sunny Sheffield at 7.5C +1.4C above normal. Rainfall unchanged. GFS all over the place at the moment with temperatures down on yesterdays 12oz but not low enough to take us anyway near average at the present time. Looking like we could be in the top five warmest Decembers recorded for us in Sheffield and this says no cold winter Ladies and Gentleman. Plenty of time for it to change yet. 

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Here's a look at how other Decembers ended up when running 7.4 or higher by 12th (which will be tomorrow's report, I would expect 7.9 perhaps for this month which would rank 16th warmest) ...

1820 ___ 8.5 to finish 4.7

1827 ___ 7.4 to finish 6.9

1831 ___ 8.9 to finish 5.8

1841 ___ 7.5 to finish 4.4

1848 ___ 7.7 to finish 5.6

1852 ___ 7.8 to finish 7.7

1857 ___ 7.6 to finish 7.3

1863 ___ 7.5 to finish 6.3

1868 ___ 8.2 to finish 7.2

1876 ___ 7.4 to finish 6.0

1898 ___ 9.8 to finish 7.3

1900 ___ 8.2 to finish 7.2

1918 ___ 8.9 to finish 6.9

1934 ___ 9.4 to finish 8.1

1948 ___ 8.4 to finish 5.7

1953 ___ 8.3 to finish 6.9

1956 ___ 8.7 to finish 5.7

1974 ___ 8.3 to finish 8.1

1979 ___ 9.3 to finish 5.8

1985 ___ 7.5 to finish 6.3

1986 ___ 7.4 to finish 6.2

1994 ___ 8.6 to finish 6.4

2000 ___ 9.9 to finish 5.8

2006 ___ 8.0 to finish 6.5

2015 ___ 9.3 to finish 9.7

Just outside this range, 1794 was at 7.3 on 12th, fell to 3.7 by end of month, and Jan 1795 averaged --3.1 the coldest month on record.

In Dec 1841, the change to cold occurred fastest of these years (if any cold arrived at all) ... it was --2.7 for the 18th. In 1820 the coldest day was --2.5 on the 31st, the entire period of 25 Dec 1820 to 4 Jan 1821 was subzero. So this gives us some idea of what has taken place in similar years, many (as Pit was saying) don't cool down much at all although only 2015 managed to warm up from this range. 

 

 

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Rodger out of interest how many of those produced a cold winter overall? I'll rephrase that one or two of the months were below average.

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1 hour ago, The PIT said:

Rodger out of interest how many of those produced a cold winter overall? I'll rephrase that one or two of the months were below average.

Looking at the stats, it seems,

Dec 1841 was followed by a cold Jan at 0.6c.

Dec 1852 was followed by a cold Feb also at 0.6c.

Dec 1857 was followed by a cold Feb at 1.8c.

Dec 1863 was followed by both a fairly cold Jan and Feb at 2.4c and 2.3c respectively.

Dec 1900 was followed by a fairly cold Feb at 2.3c.

Dec 1918 was followed by a fairly cold Jan and an even colder Feb at 2.9c and 1.9c respectively.

Dec 1953 was followed by both a fairly cold Jan and Feb at 2.9c and 2.6c respectively.

Dec 1979 was followed by a fairly cold Jan at 2.3c.

Dec 1985 was followed by a very cold Feb at -1.1c.

Dec 1986 was followed by a cold Jan at 0.8c.

Dec 2000 was only followed by a coldish Jan at 3.2c, but did have a pretty potent cold spell in late Dec.

So it seems in conclusion a fair few of these December's were followed by some cold months, some very much so, so it seems we can't really draw any conclusions for the rest of Winter based on the first 12 days of December alone.

 

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I guess it only lowers our chances by the amount by which 12 of 90 days have gone into the books with a large positive anomaly, so if the definition is just below average for the whole season, and that first 12 days go in at +3 then the other 78 have to average about --0.5 (anomaly) to balance them out. But as WWS shows above, there are plenty of cold months in the mix. In other words, it does alter the odds of an overall mild winter but it leaves more or less unchanged the odds that Jan or Feb will be colder than normal. 

If this level of warmth is sustained to end of December, then it just makes the colder winter that much more improbable in statistical terms because if the month goes +3 then the other two months have to average colder than --1.5 to balance it out. But as 1986-87 showed, the raw numbers may show one thing but one exceptional outbreak can perhaps last longer in the memory. I don't imagine the winter mean for 2017-18 will be recalled as easily as the weather at end of Feb and beginning of March. 

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If I remember right Dec 1986 was very mild first 2 weeks but then a colder second half took hold.  Not exceptional cold but  the warm SW’ly regime went away....and looking at archive charts the hemispheric pattern was priming itself for the cold surge. I wonder what the running CET was on 13th Dec 1986?  I Don’t buy the GFS Op this morning, but I do buy blocking being in the wings

 

BFTP

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24 minutes ago, BLAST FROM THE PAST said:

If I remember right Dec 1986 was very mild first 2 weeks but then a colder second half took hold.  Not exceptional cold but  the warm SW’ly regime went away....and looking at archive charts the hemispheric pattern was priming itself for the cold surge. I wonder what the running CET was on 13th Dec 1986?  I Don’t buy the GFS Op this morning, but I do buy blocking being in the wings

 

BFTP

The C.E.T. for December, 1986 up to the 13th was 7.2. There were a few exceptionally mild 10+ days around December 4th but it never got as mild as that there on. As you mentioned the second-half was cooler but then dragged up by some very mild days from December 28th onward.

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Sunny Sheffield at 7.4C +1.4C above normal. Rainfall unchanged. Another drop for the next three days expected before the mild air digs in. Although the cold keeps getting extended. 

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December 79 here was just above average at 5.2C again the cet area would be different.

I found our best attempt for a cold winter was 71 to 72 when Dec 71 was 6.7C.  Jan was 0.6c below average and Feb came in at 0.4C although the winter as whole would be on the mild side. All this is from 1955 which is an interesting quirk. 

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Well, to finish off that study of mild starts to December, not counting 1794, two of them led to a colder than average winter and about half a dozen finished within 0.5 of the average, the rest were all on the mild side including some of the mildest on record. So this kind of start requires a fast change to colder that is sustained in January, otherwise little or no chance of the winter finishing much colder than average. It should be noted however that 1794-95 ended 5th coldest from a current position just half a degree below 2018. The three or four best outcomes were 1820-21, 1841-42, 1900-01, and 1985-86 (the coldest winter average in this set, 2.9 C (tied 87th coldest). Winter 1841-42 finished at 3.1 C. Maybe we can beat 2.9 C this winter, not expecting to reach top twenty coldest but 21-40 sort of ranking is possible with a sustained cold period.

 

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Sunny Sheffield at 6.9C +0.9C above normal. Making some big dints in average temperature now. As long as we avoid a silly mild spells we may even get below 6C by the end of the month.  

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2 hours ago, The PIT said:

Sunny Sheffield at 6.9C +0.9C above normal. Making some big dints in average temperature now. As long as we avoid a silly mild spells we may even get below 6C by the end of the month.  

Sub 6c is very much on, how close we get to 5 is the interesting part.....

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On 14/12/2018 at 20:58, DAVID SNOW said:

Sub 6c is very much on, how close we get to 5 is the interesting part.....

Is it? Sounds like the prediction you made about below average last month. The outlook looks pretty mild to me now.

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Sunny Sheffield at 6.2C +0.4C above normal. A smaller drop than expected mainly due to the overnight max. Rainfall 56.8mm 65.4% of normal. Coming week for us shows no sign of any more major drops as generally the temps are averaging out at 6C No sign of any cold weather so a very mild December on the cards for now. CET zone likely to finish in the 6C to +7C. Sunny Sheffield 6C to 6.5C region. 

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