December 2020 C.E.T. and EWP forecast contests -- start of the new contest year for 2020-2021

[virtualsphere]

8 hours ago, Roger J Smith said:

Here are the CET values through 16th for past ten Decembers: 

2010 ___ 0.3 _ _ _ _ _ _ 2015 ___ 9.1

2011 ___ 5.0 _ _ _ _ _ _ 2016 ___ 7.0

2012 ___ 2.6 _ _ _ _ _ _ 2017 ___ 3.5

2013 ___ 6.7 _ _ _ _ _ _ 2018 ___ 6.6

2014 ___ 4.4 _ _ _ _ _ _ 2019 ___ 5.4

The one that surprises me there is 2012. I don't remember it being that cold: I recall there was an easterly modelled which never materialised then a wet and windy spell which must have been after 16th looking at your data.

[Summer Sun]

5.6c to the 17th

0.7c above the 61 to 90 average
0.7c above the 81 to 10 average

___________________________

Current high this month 5.6c on the 17th
Current low this month 3.9c on the 8th & 9th

[Relativistic]

3 hours ago, virtualsphere said:

The one that surprises me there is 2012. I don't remember it being that cold: I recall there was an easterly modelled which never materialised then a wet and windy spell which must have been after 16th looking at your data.

First half of December 2012 was a beautiful spell of weather in Essex. A surprise snowfall on the morning of the 5th brought three inches of snow, and we had the most spectacular hoar frost on the 12th. All very seasonal; shame it didn't last till Christmas!!

[The PIT]

Only sleet here in Dec 2012 and an average of 4.2C A very wet month at 155mm of rain though.

[Roger J Smith]

For continuity of the daily CET tracker ...

5.6c to the 16th

0.7c above the 61 to 90 average
0.7c above the 81 to 10 average

___________________________

Current high this month 5.6c on the 17th
Current low this month 3.9c on the 8th & 9th

 

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EWP update ... 79 mm to 16th, est 83 mm to 17th, est 85 mm to mid-day 18th

10d GFS then adds 30 to 35 mm (115-120 by 28th).

29th-31st, in widespread light snow or sleet apparently, 5-10 mm more, 120-130 the estimated landing spot.

=============================================================

My CET tracker suggests 4.9 the outcome after a peak of 6.0 around Monday 21st. 

(22-31 ... 6, 5, 3, 6, 5, 3, 0, -2, -1, 1) avg 2.6

21x6 = 126 + 26 = 152 (/31) = 4.9

==============================================================

Top ten ranking falls in CET from 21st to 31st 

 1 __ 1870 fell 2.4 from 3.0 to 0.6

 2 __ 1772 fell 2.2 from 7.0 to 4.8

 3t _ 1780 fell 2.1 from 6.8 to 4.7

 3t _ 1798 fell 2.1 from 3.6 to 1.5

 5t _ 1985 fell 2.0 from 8.3 to 6.3

 5t _ 2000 fell 2.0 from 7.8 to 5.8

 7t _ 1779 fell 1.9 from 5.0 to 3.1

 7t _ 1892 fell 1.9 from 3.7 to 1.8

 7t _ 1962 fell 1.9 from 3.7 to 1.8

10t _1836 fell 1.8 from 5.9 to 4.1

(1794 fell 1.4 from 5.1 to 3.7, followed by coldest January 1795)

This month would need to average about 0.5 for 22nd-31st to tie 10th.

[Summer Sun]

5.8c to the 18th

1.0c above the 61 to 90 average
0.9c above the 81 to 10 average

___________________________

Current high this month 5.8c on the 18th
Current low this month 3.9c on the 8th & 9th

[The PIT]

Sunny Sheffield at 5.3C -0.3C below normal. Rainfall 70.6mm 81.2% of the monthly average.

[BornFromTheVoid]

Here's the projected values, with the GFS 7 day forecast included. The values below in brackets are from 2 days ago, to show the change in projections.

Warmest: 6.9C (6.8C)
Coldest:  4.1C (3.3C)
Top 10:  6.5C (6.5C)
Bottom 10:  4.5C (4.0C)
81-10:  5.7C (5.5C)

There is now a 22.2% chance of finishing close to average (between 4.1C and 5.1C), 0.4% chance of below average (< 4.1C) and a 77.4% chance of above average (> 5.1C).
5.5-6.0C has the highest probability, 28.6% today. 6.0-6.5C is close now too, with 28%.
Overall, there's a 79% chance of finishing between 5.0C and 6.5C.

[Roger J Smith]

A general weakening of the cold signal for 27th-31st makes 5.5 the model over-under at this point. 

[damianslaw]

A mild middle third followed by a colder last third, a three way sandwich, cold first third, mild middle third, cold last third, a bit like 2008..

A finish in the high 4s could be a good bet at this stage.

[The PIT]

Sunny Sheffield at 5.5C bang on the average value. Rainfall 72.8mm 83.8% of the monthly average.

Looking like a slightly above Dec for here is the likely outlook. We may get another 100mm plus month which will make a really odd year. Record dry spring yet still have five months hitting 100mm mark. Yet 5 months well below normal as well which is in the bag. The only month not going to for the very wet or very dry is July.

Edited December 20, 2020 by The PIT

[Summer Sun]

6.0c to the 19th

1.2c above the 61 to 90 average
1.1c above the 81 to 10 average

___________________________

Current high this month 6.0c on the 19th
Current low this month 3.9c on the 8th & 9th

[BornFromTheVoid]

Here's the projected values, with the GFS 7 day forecast included. The values below in brackets are from yesterday, to show the change in projections.

Warmest: 6.6C (6.9C)
Coldest:  4.3C (4.1C)
Top 10:  6.3C (6.5C)
Bottom 10:  4.6C (4.5C)
81-10:  5.6C (5.7C)

There is now a 21.8% chance of finishing close to average (between 4.1C and 5.1C), 0% chance of below average (< 4.1C) and a 78.2% chance of above average (> 5.1C).
5.5-6.0C has the highest probability, 37.9% today.
Overall, there's a 84.7% chance of finishing between 5.0C and 6.5C.

[Roger J Smith]

EWP is currently very close to 100 mm, the tracker showed it at 92 mm after 18 days, and yesterday's grid average was 6-7 mm. The ten-day projection is around 25 mm and it looks relatively dry in the small amount of time left from 12z 30th to 00z 1st Jan 2021. 

Not quite "in the bag" for SteveB at 125 mm given that coldest winter is lurking at 123.6 mm, but looking like the outcome will be 1-2 for them in whichever order, so the provisional scoring would be just about a done deal for everyone else (LG awaits the final outcome also). 

Looking at the temperature projections, we've reached 6.0, probably won't go much higher now to Monday 22nd, then it's a matter of how far down will we drop? (if the models are anywhere near right, that looks to be at least 0.5 and perhaps as much as 1.0 down). My estimate from 12z GFS would be 5.0 after adjustments. The mean for 23rd to 31st appears to be around 3 C. 22x6.1 = 134, 9x3 = 27, 161/31 = 5.2, bit of an adjustment to 5.0, is how I see that going. 

Some guidance is a bit milder and would end up closer to 5.5. Would say 4.8 is about as low as the current model output could possibly take it, staying near 6.0 is near the upper limit of indicated possible outcomes. 

[Roger J Smith]

As there's less uncertainty about scoring order for EWP, here's how the race for best combined forecast in December looks ...

at 5.0, Summer Shower takes it with 1st CET, 4th EWP. 

4.9 or 5.1 work for Summer Shower who only drops to 4th either way in CET (and stays 4th in EWP of course). 

4.8 changes the lead to Born from the Void at 1st CET, 10th EWP (Summer Shower then 15th CET and 4th EWP).

5.2 drops Summer Shower to 9th CET but it's still good enough as Feb1991Blizzard's 5.3 ranks 6th CET and 13th EWP.

5.3 would change best combined to Feb1991Blizzard at 1st CET and 13th EWP, compared to Summer Shower's 12th CET and 4th EWP.

5.4 also works for Feb1991Blizzard who drops to 2nd CET (and 13th EWP), while snowray at 1st CET would be 17th EWP.

5.5 allows snowray to edge closer to best combined, at 2nd CET 17th EWP, compared to Feb1991Blizzard's 3rd and 13th. However at that point SteveB passes both of them with 9th CET and 1st or 2nd EWP.

SteveB has the lead for any CET outcome below 6.4, then coldest winter (6.8 CET) would be in front at 6.5 to any higher outcome.

Although snowray has no path to best combined at 120-125 mm EWP, a lower outcome might work at 5.4 to 5.6 C if that dropped Steve B to 4th EWP or lower. 

 

[damianslaw]

Even chance I would say of a below or above average finish against 61-90 average. 

[Summer Sun]

6.0c to the 20th

1.2c above the 61 to 90 average
1.2c above the 81 to 10 average

___________________________

Current high this month 6.0c on the 19th & 20th
Current low this month 3.9c on the 8th & 9th

[The PIT]

Sunny Sheffield at 5.5C Bang on average. Rainfall now at 73mm 84% of the monthly average.

[BornFromTheVoid]

Here's the projected values, with the GFS 7 day forecast included. The values below in brackets are from yesterday, to show the change in projections. Estimate of the next 7 days from the GFS is 5.2C (8.0C from 21st to 23rd and 3.1C from 24th to 28th)

Warmest: 6.3C (6.6C)
Coldest:  4.5C (4.3C)
Top 10:  6.1C (6.3C)
Bottom 10:  4.7C (4.6C)
81-10:  5.6C (5.6C)

There is now a 19% chance of finishing close to average (between 4.1C and 5.1C), 0% chance of below average (< 4.1C) and a 81% chance of above average (> 5.1C).
5.5-6.0C has the highest probability, shooting up to 44.8% today.
Overall, there's a 74.2% chance of finishing between 5.0C and 6.0C.

[cheeky_monkey]

sheet forgot to post in here this month...anyway Cloudy Edmonton is at -6.5c to 20th which is +2.3c above normal..without doubt from looking at the models this will be the first above average month since Jan 2019!

Edited December 21, 2020 by cheeky_monkey

[Roger J Smith]

EWP now very close to 100 mm (97 mm to 19th), about 3 mm fell yesterday (more like 10-15 in the southwest, close to zero in many other parts). The GFS ten-day projection is close to 30 mm and that takes us to mid-day 31st, no adjustment required from maps for late 31st. That 30 mm is a blend of widespread 20-25 mm amounts in south and north, and 40-60 mm amounts across Wales and central England. The main reason for that is how two events are modelled to unfold, one fairly short-range, one closer to the 28th. 

Anyway, it's beginning to look more certain now that the outcome will edge past SteveB's 125 mm but there's still some uncertainty about whether top forecast will be that one or coldest winter's 123.6 mm. The provisional scoring is maintained for now (based on 130 mm). I will attach the supporting excel file so you can have a look at such things as your most recent "all-time" scoring update and the layout of the new contest file with the new scoring system (which tweaks the old basic system as explained earlier). 

As for CET, both leading models seem to have converged on a solution at least as far as temperatures go, my estimates for those remain the same so I would still say that we're heading for a range of 4.8 to 5.5 and most likely outcome is around 5.0 or 5.1. (that includes an entirely hunch-based 0.2 downward adjustment to provisional values which I think will end up near 5.2). 

EWP2020_21.xlsx

Edited December 21, 2020 by Roger J Smith

[The PIT]

Sunny Sheffield at 5.6C +0.2 above normal. Rainfall 82.3mm 94.7% of the monthly average

Looking like an above average December but not by a lot though.  Rainfall up in the air whether it passes the 100mm mark. I guess Wednesday and Boxing day will decide that.

[Roger J Smith]

For continuity ...

6.1c to the 21st

1.2c above the 61 to 90 average
1.3c above the 81 to 10 average

___________________________

Current high this month 6.1c on the 21st
Current low this month 3.9c on the 8th & 9th

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EWP 102 mm after 20 days, est 110 mm after 21 days

GFS 10d (taking 9.5d) adds a much higher 50 mm for total of 160 mm, which would move LG from 77th (130 mm) to 3rd place, first goes his way at an outcome of 162.6 mm or higher. All other scores except those below 77th in the provisional scoring would drop one rank and about .14 (not as much protection for error ranges with the higher outcome). We'll see if this higher total remains in the forecast, looks to be mostly based on two events, next 24-36h in south, and around 28th in central England. 

CET looks under downward pressure from tomorrow on, would say mean of 2.5 for rest of month (incl today) gives an outcome near 5.0 C. 

[The PIT]

Sunny Sheffield at 5.5C +0.2C above normal. Rainfall 86.4mm 99.5% of the monthly average.

[Summer Sun]

6.1c to the 21st

1.2c above the 61 to 90 average
1.3c above the 81 to 10 average

___________________________

Current high this month 6.1c on the 21st
Current low this month 3.9c on the 8th & 9th