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Roger J Smith

December 2019 C.E.T. and EWP forecast contests -- start of the 2019-2020 competition year

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EWP estimated to be around 18 mm now (was 14 mm after 7th, then 8th and first part of today look to have added 4 mm over the grid) ... 10-day GFS showing healthy amounts that average at least 50 mm over the grid, perhaps 55 mm for a total of 73 mm. The six days after that don't look overly wet on the charts but it's a pattern that looks a bit dubious so anyway, we will likely be somewhere between 70 and 90 mm by Christmas. That probably doesn't entirely eliminate any of the wetter forecasts from consideration given how stormy the Atlantic has been so far this month, it could lash the UK at any point towards the end. 

As for CET, I don't see a lot of movement from current levels, some colder looking maps at times but the flow remains broadly speaking westerly and that makes me suspicious that the thicknesses either won't verify or won't perform as they might in a different sourced air mass. And a few days in the mix looking quite mild. So it will probably stay in the general vicinity of the mid-5 to 6.0 range although I could imagine it getting as low as 5.0 or as high as 6.5 given the set-up. 

Edited by Roger J Smith

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5.9c to the 9th

0.9C above the 61 to 90 average

0.5c above the 81 to 10 average

__________________________________

Current high this month 5.9c to the 9th

Current low this month 2.4c to the 1st & 2nd

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On 08/12/2019 at 00:33, sundog said:

It's been such a poor decade for December cold. It started with one hell of a bang. I know Decembers aren't noted for much in the way of anything too severe anyway  of course  but that said it has been a poor decade. Very little seasonal xmas weather.

 

I know 80s Decembers weren't great either from a cold pov but at least decent cold spells in other parts of a good number of 80s winters made up for them,unlike nowadays. 

December 2017 was actually quite a good one in this part of the country, despite not been all that cold (CET 4.8c) I saw more snow that December than I do most. In fact it was 2 years ago exactly today we had a really good dumping round here which stuck around for about 3 days I think. Also on Boxing Day there was snow the other side of Birmingham (just sleet here that time unfortunately) which I had the good fortune to see on the evening of the 28th when it was still lying. Although not as much as the event on the 10th it was still a full covering which looked really nice and festive with all the Christmas lights still up and such. Easily the second best December of the 2010's after 2010 itself obviously. Still time for December 2019 to challenge it yet though. 😉 

I almost forgot there was also a cold spell that began on Boxing Day 2014. It snowed here but was very wet and left only a thin slushy covering. There was a brief anticyclonic period immediately following accompanied with frost but this was brief. Apart from that can't think of much else at or near to the festive period, but as you say cold spells aren't overly common at that time of year in this country anyway so having 3 cold spells around then in a decade is probably around average. Not to mention I think 2010 raised our expectations a bit in terms of the perfect but rare type of sypnotics for a December cold spell.

I'd take how it was round here December 2017 every year though if it was on offer. Though even better would be the snow falling on Christmas Eve or Day rather than the 10th. Then it would be perfect.

Edited by Walsall Wood Snow

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There’ll be some downward corrections at the months end with the cold nights following milder incursions this week. Last night was cold even before 9pm yesterday and again it will be getting cold in time for tomorrow morning. The CET should lower slightly this week.

Edited by prolongedSnowLover

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Sunny Sheffield at 5.9C -0.3C below normal. Should be a normal or above by tomorrow. Rainfall unchanged.

Actually just done a quick check and it looks to be unchanged believe it or not.

Edited by The PIT

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7 hours ago, Summer Sun said:

5.9c to the 9th

0.9C above the 61 to 90 average

0.5c above the 81 to 10 average

__________________________________

Current high this month 5.9c to the 9th

Current low this month 2.4c to the 1st & 2nd

well, what a surprise, only 9th, but a so called winter month above avg in the modern eera

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5 minutes ago, I remember Atlantic 252 said:

well, what a surprise, only 9th, but a so called winter month above avg in the modern eera

Don't it make you sick!:bad:

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2 hours ago, I remember Atlantic 252 said:

well, what a surprise, only 9th, but a so called winter month above avg in the modern eera

Values significantly above (or below) the running average are more common earlier on in a month. A more extreme example akin to this statement (from 1st March 2018) is "It's only the 1st, but we're already 8.4*C below the running mean".

Edited by Relativistic

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10 hours ago, Relativistic said:

Values significantly above (or below) the running average are more common earlier on in a month. A more extreme example akin to this statement (from 1st March 2018) is "It's only the 1st, but we're already 8.4*C below the running mean".

This is true - the end of December should statistically be colder than the beginning, so it's not really surprising for it to be above at the start of the month..

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Except that the reporting of anomalies on a daily basis here is against running averages for this part of the month, so it's always equally likely to be above or below that statistic (not quite true in a warming climate it will be maybe 55% likely to be above and 45% below) ... what Rel was saying was, when you have only a few days, the average can be further up or down from normal than it's likely to be when you average 31 days at the end. The coldest running averages of December CET occur before the halfway point even though the second half is a bit colder on average. (check my post on 1st of Dec with normal and extreme values of CET, the lowest running CET was on the 8th of Dec 1879 at -3.65 C, the values then converge on the eventual coldest entire month, 1890 at -0.8). 

Also, the contribution of each day diminishes as you move forward. Today (the 11th) will be 1/11 of the average after today, tomorrow will be 1/12, the 31st will be 1/31, so if all three days are 3 deg below normal, today will have almost three times the impact on the running mean as the 31st would have. 

Edited by Roger J Smith

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EWP update -- 18 mm to 9th, looks like about 6 more on the 10th (much heavier in north Wales and Cumbria again, but grid average probably 6-8). Then the ten-day GFS is a little drier now than in recent days, as the focus of heavier rainfalls seems to be further west into Ireland. Would say 20-30 there, and maybe another 30-50 towards the end of the 00z run after the ten days are finished. Totals could be 75 to 105 mm from those estimates. Month also not quite over at that point, so 80-120 looking good. Despite having 119 forecasts on file, nobody is entirely out of the hunt yet. Although I predicted 77.8 mm, based on what I am now seeing my pick is 111.1 of Stationary Front to 120 (Relativistic, IIRC) or in that range of forecasts.  

CET still looks like mid 5 to low 6 is a good bet. 

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6.0c to the 10th

1.0C above the 61 to 90 average

0.7c above the 81 to 10 average

__________________________________

Current high this month 6.0c to the 10th

Current low this month 2.4c to the 1st & 2nd

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Sunny Sheffield still at 5.9C -0.3C below average. The mild day cancelled out by the low mind on the day. Rainfall at 19mm 21.9% of average so surprisingly on the below average side of things. If the trend for the GFS comes off looking like we end up with a mild month. Of course it's all lala land so anything can still happen.

Edited by The PIT

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11 hours ago, Roger J Smith said:

EWP update -- 18 mm to 9th, looks like about 6 more on the 10th (much heavier in north Wales and Cumbria again, but grid average probably 6-8). Then the ten-day GFS is a little drier now than in recent days, as the focus of heavier rainfalls seems to be further west into Ireland. Would say 20-30 there, and maybe another 30-50 towards the end of the 00z run after the ten days are finished. Totals could be 75 to 105 mm from those estimates. Month also not quite over at that point, so 80-120 looking good. Despite having 119 forecasts on file, nobody is entirely out of the hunt yet. Although I predicted 77.8 mm, based on what I am now seeing my pick is 111.1 of Stationary Front to 120 (Relativistic, IIRC) or in that range of forecasts.  

CET still looks like mid 5 to low 6 is a good bet. 

We had nearly 90 mm yesterday, everything was saturated already! Wetter than an potter's pocket!

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4 hours ago, JeffC said:

We had nearly 90 mm yesterday, everything was saturated already! Wetter than an potter's pocket!

Otter's pocket, blasted autocorrect!

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12 hours ago, The PIT said:

Sunny Sheffield still at 5.9C -0.3C below average. The mild day cancelled out by the low mind on the day. Rainfall at 19mm 21.9% of average so surprisingly on the below average side of things. If the trend for the GFS comes off looking like we end up with a mild month. Of course it's all lala land so anything can still happen.

How can Sheffield be below average when the CET is above normal for the same sort of temperature ? 🤔

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5.9c to the 11th

0.9C above the 61 to 90 average

0.7c above the 81 to 10 average

__________________________________

Current high this month 6.0c to the 10th

Current low this month 2.4c to the 1st & 2nd

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9 hours ago, prolongedSnowLover said:

How can Sheffield be below average when the CET is above normal for the same sort of temperature ? 🤔

It's just part of a general principle with temperature anomalies that they can vary from location to location by 1 to 2 deg. I've seen a lot of monthly reports of temperature anomalies and they often spread out over about that sort of range, so +1 here, -1 there, somewhat at random. It can be partly because Pit has already adjusted his data to the 24-hour calendar day while the CET preliminary data are being reported for intervals that will later be adjusted (which is why they often drop rather than rise since colder evenings get more involved in the overall picture). Also one would need to know what normal period the Pit uses as a base, if he's not using 1981-2010 but his station average over time, then we're not comparing anything since the CET might have a different anomaly value if compared to its own data for the same period of time. So maybe Pit can tell us when he reports a temperature anomaly, what's the period against which this month is being compared? I could then quickly work out what the CET anomaly for that same period would be. Also we need to know if his report is for a running mean 1st to yesterday's date or end of month -- I know his reports of precip anomalies are against end of month averages. 

For example with his rainfall report, at the last instance he says 19 mm, 21.9% of average, but that is for 11/31 of the month so in reality if we assume Dec precip falls at a constant rate, the 19 mm is (21.9 x 31/11) per cent of average which is 61.7% of expected amount to the 11th. If temp is similar, that creates a potential difference in itself since his end of month temperature average is probably 0.5 to 1.0 lower than his station 1st to 11th average. However, that would imply he should have a higher rather than a lower temperature anomaly (since CET compared to end of month is running closer to 1.6 above that normal). 

 

Edited by Roger J Smith

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11 hours ago, prolongedSnowLover said:

How can Sheffield be below average when the CET is above normal for the same sort of temperature ? 🤔

Further North and just outside the CET area is one reason and I'm using the 1981 to 2010 data. I then use a linear average over the month. The rainfall is as Rodger points out.

Anyway Sunny Sheffield down to 5.8C -0.3C below average. Rainfall 19.9mm 22.9% of the monthly average

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snowy Edmonton is at -8.8c which is bang on average for the time of year..currently been hovering around the -15c mark the last 3 days...as we straddle a boundary between very cold air just 50 miles to the east ..where it is close to -35c and warmer air to the west.

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5.8c to the 12th

0.8C above the 61 to 90 average

0.7c above the 81 to 10 average

__________________________________

Current high this month 6.0c to the 10th

Current low this month 2.4c to the 1st & 2nd

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Sunny Sheffield at 5.6C, -0.4C below normal, Rainfall 28.4mm 32.7% of the monthly average.

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On 08/12/2019 at 00:33, sundog said:

It's been such a poor decade for December cold. It started with one hell of a bang. I know Decembers aren't noted for much in the way of anything too severe anyway  of course  but that said it has been a poor decade. Very little seasonal xmas weather.

 

I know 80s Decembers weren't great either from a cold pov but at least decent cold spells in other parts of a good number of 80s winters made up for them,unlike nowadays. 

I do not think that 1970s Decembers were great from a cold perspective either, although most Decembers of the 1960s were on the cold side, with a good number of them having good cold spells at times.  That said, since the 1800s at least, Decembers have rarely been noted for anything severely cold.  Since about 1890, I think that only two Decembers stand out as having a prolonged freeze up (1981 and 2010), apart from that, not a lot, except a few other years that saw a good cold spell of a week or more.

During the 2010s, the first half of Dec 2012 was actually quite cold, but then turned much milder after mid-month.  The first half of Dec 2017 was another one that was quite chilly but then turned milder in time for the Christmas period.

Edited by North-Easterly Blast

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My latest review of the EWP shows a similar trend, about 40 mm probably at this point (29 mm to 11th and yesterday fairly wet in the grid), another 30 mm indicated by GFS ten-day maps, and perhaps 20 mm or more potential on maps 24th to 29th. That isn't going to add up to much more than 90 mm but I suspect the GFS might be underplaying the ten day totals a bit.

So I have the new contest year excel file ready to go, and I set it at 111.1 mm (the forecast of Stationary Front) since it is easy for my addled brain to make the error calculations with all those 1's, and the decimal eliminated all ties. 

If you go in and have a look, it's the old format with everything but the December forecasts and previous ranking tables removed. For newbies especially, I can point out that the provisional scoring is just for interest and has no bearing on contest results later. Your rank in almost every case is determined by the differential between your forecast and 111.1 mm. People who predicted less than 111.1 can hope I am overestimating, then they will rise up the table. The rather few who went significantly above 111.1 and are down the table can hope it keeps raining harder than envisaged in that outcome. 

This month, I have drawn up a scoring template that runs down beside the actual scoring. You'll see how the scoring works, if everyone had a different forecast and nobody was late, then there would be 119 different scores 10.0 to 0.0, which is 118 steps of about 0.08 points. But we don't deduct as many scoring points for later forecasts of some popular value (like 88 mm), only 0.05 per entry, so the template values are adjusted up for duplicate entries. Also there are four late entries who lose small numbers of points (0.2 to 0.6) from their template value, and in one case the entry drops down seven ranks, in three others it drops only one or stays as is because it was partially boosted by being a duplicate as well. (if you are 5th in at some value and one day late, those two factors almost balance out). 

Also in this scoring file are all the ranking tables from the first two years, all the total scores for the first two years, and after your forecaster name, your ranks in years one and two). 

I hope all the new forecasters stay with us in both CET and EWP contests (the amount of work to track 119 is considerable compared to the old average of 50). CET went up from about 65 on average to 144 or thereabouts, J10 has a massive task on his hands. 

So here's a link to the provisional scoring file, which of course will be adjusted around the end of the month when we know the actual outcome. 

 

EWP201920DEC.xlsx

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5.8c to the 13th

0.8C above the 61 to 90 average

0.7c above the 81 to 10 average
__________________________________

Current high this month 6.0c to the 10th

Current low this month 2.4c to the 1st & 2nd

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