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

[Scorcher]

150 hours of sunshine here up to yesterday and unbroken sunshine from the word go today- 200 hours plus is looking likely.

[damianslaw]

With nothing especially wet or warm on the horizon, headline title for April 2021 will be cool, very dry and sunny (some places very sunny but not everywhere). Quite an odd combination.

[Weather-history]

7 hours ago, damianslaw said:

With nothing especially wet or warm on the horizon, headline title for April 2021 will be cool, very dry and sunny (some places very sunny but not everywhere). Quite an odd combination.

I think the headline should include "exceptional frosty". We've had sunny and very dry Aprils in the past but rarely has an April has been this frosty.

Edited April 23, 2021 by Weather-history

[Frigid]

17 minutes ago, Weather-history said:

I think the headline should include "exceptional frosty". We've had sunny and very dry Aprils in the past but rarely has an April has been this frosty.

I've always associated cool April's with being wet and dull. But this April changes all of that. Haven't seen any rain since last week of March and it's been constantly cool and sunny. More like a winter month.

[The PIT]

Sunny Sheffield up to 6.1C -2.1C below normal, Rainfall 3.3mm 5.9% of the monthly average.

[Man With Beard]

19 hours ago, Summer Sun said:

6.3c to the 21st

1.1c below the 61 to 90 average
1.6c below the 81 to 10 average

___________________________

Current high this month 8.8c on the 1st
Current low this month 5.6c on the 12th, 13th, 15th & 16th

No chance of getting to 8C now. A genuinely below average month looks likely.

[damianslaw]

Question is whether we will finishing the 6s or 7s. Still looking like we will beat 2012, but only just perhaps. A far better month than that one which was dire being cold very wet and very dull.

[SqueakheartLW]

The warmth of today will push the CET up a bit but the last few days of April will be cooler based on this forecast for my location Scunthorpe

Assuming Scunthorpe currently has the CET value of 6.4C to yesterday so put 6.4 on all days from 1st to 22nd to simplify things

23rd          Today          Max 16          Min 0          Mean 8.0

24th          Tomorrow  Max 15          Min 7          Mean 11.0

25th          Sunday        Max 11          Min 5         Mean 8.0

26th          Monday       Max 14         Min 4          Mean 9.0

27th          Tuesday       Max 11         Min 8          Mean 9.5

28th          Wednesday Max 7           Min 4          Mean 5.5

29th          Thursday     Max 10         Min -1         Mean 4.5

30th          Friday           Max 11         Min 2          Mean 6.5

If these figures come off then to get the CET over 7c will be off completely

Assuming these temperature figures turn out correct then the predicted April mean for Scunthorpe will be around 6.76C give or take a margin of +/- 0.2C to allow for margin of error

6.76C if it comes off will be colder than March 2021 by almost 0.5C and will be significantly below the 1991 to 2020 average

[Summer Sun]

6.4c to the 22nd

1.1c below the 61 to 90 average
1.6c below the 81 to 10 average

___________________________

Current high this month 8.8c on the 1st
Current low this month 5.6c on the 12th, 13th, 15th & 16th

[BornFromTheVoid]

I won't bother with the graphs today, but a finish below 7C is now a 57% chance (with the GFS to the 28th, projections thereafter). Given the cold outlook for the final 2 days of the month and the likelihood of downward corrections, I'd estimate closer to 80% chance of a sub-7C finish.

[Thundery wintry showers]

To me, it's quite odd that in the archives there haven't been many dry and sunny but cool Aprils, considering that dry and sunny but cool Marches, Mays and Junes have been relatively common.  I can certainly think of Aprils that were dry and sunny with average temperatures, warm days and cool nights (1984 and 1990, and allowing for the recent warming of the climate you could add the Aprils of 2010 and 2015), but none that were substantially cooler than average. 

April seems to have a history of following the warm-dry-sunny relationship that is mainly associated with high summer (July/August).  The high summer relationship probably has a lot to do with the dominance of the Azores High and the warm land, cold seas resulting in these slack anticyclonic/northerly types bringing a lot of cloud into eastern areas, although dry sunny cool Augusts were noted in many areas in 1993 and 2007.  But I can't think of any explanation why the warm-dry-sunny relationship has reliably held for April.  It might just be one of those statistical quirks that has been emphatically countered this year.

Edited April 23, 2021 by Thundery wintry showers

[Optimus Prime]

Quite possible this April will have the lowest average mean minima on record (since 1878). It's 1.4 °C up to the 23rd (2.7 °C below 81-2010 avg) 

top 5 lowest mean minima for April (°C)

1.4 (1917)

1.5 (1922)

1.6 (1887)

1.7 (1892)

2.1 (1879)

[Thundery wintry showers]

Looking at the latest model outputs, a couple of warmer nights should raise that figure a little, so even allowing for a downward correction at the end of the month I don't expect April 2021 to beat or equal 1917, but there's certainly a good chance of it making the top five coldest for minima.

It reflects my earlier points about dry sunny cool Aprils having been surprisingly rare.  Many cool Aprils in the past have been wet and/or cloudy (e.g. 1986, 1989) which has kept the minima relatively high.

Edited April 23, 2021 by Thundery wintry showers

[Weather-history]

Rostherne near Manchester Airport

 

 

[BornFromTheVoid]

It looks likely that April will achieve something no year in the 2000s decade achieved - getting more than 2C below it's recent climatological average.
The 1990s managed 5 such months, the 2010s had 3.

Conversely, for months more than 2C above their recent climatology, the 1990s managed 14, the 2000s managed 13 and the 2010s had 9.

[The PIT]

Could this month be the first where everyone has come in too high? Looking like we should end up around 6.5C. Could be higher if it turns cloudy and night time temps are kept well up.

Edited April 23, 2021 by The PIT

[Frigid]

57 minutes ago, The PIT said:

Could this month be the first where everyone has come in too high? Looking like we should end up around 6.5C. Could be higher if it turns cloudy and night time temps are kept well up.

I think no one guessed lower than 2.9c during March 2013. Other than that I can't rly think of any instance of the CET being lower than all predictions. A pretty rare occurrence if you ask me.

[Roger J Smith]

What we need are some archives, to keep track of these more extreme situations in the contest. I will work on that, perhaps a lot of the work can be reduced to checking old annual scoring threads but I think we can find most of the contest threads back to at least 2006. Will post some findings on cold months as I get to them, this post may get an edit or two in coming days. 

Here are some contenders, and reports on months you may have thought would contend but didn't ... all the way back to March 2006 (4.9) there were at least five below that one despite a smaller turnout than we got in later years (the contest had just begun on NW and it was a bit less formal without any scoring after the month ended), then later on, nine managed a guess below the 7.2 outcome in April 2012 and godber was right on there, then four were below the 13.0 outcome of September 2012. That improved to over a dozen for the 9.7 in October 2012. Nov 2019 a rather cold 6.2 but eleven went under that with their forecasts.

Turns out there were three more months at four forecasts colder than outcome ...

Four were also colder than Dec 2009's 3.1 C outcome with one more on the money for that one. With the cold start, Jan 2010 allowed ten forecasters to feel confident about going below 1.4 C. (Norrance ended up on that value), February 2010 stayed quite cold which surprised all but four (and a few others just above the eventual 2.8). August 2010 was a chilly month and four forecasts were below its outcome of 15.3 C. 

These following cases are a bit more what we were looking for ...

 

Three forecasts below outcome

JULY 2015 _ 15.9 _ only three forecasts were below that rather chilly outcome, weatherguru14 had 15.8, and won the month, IanR had 15.5 and was third to 22NOV2010Blast at 16.2. Coldest winter had 14.8 and was well back (with numerous forecasts between 16.2 and 17.0 having less error).

 

Two forecasts below outcome (using three day late cutoff which was not in use then)

DEC 2010 _ --0.7 _ By current scoring rules, two forecasts were below this outcome, and a very late one (+4d) hit the number right on. Trickydicky said -1.1 and snowyowl predicted -0.9. (both before deadline) then cooling climate appeared on the 4th (after currently used deadline) with -0.7. Polar Continental posted -0.5 on the 5th, an even later forecast appeared for -0.1. Roger J Smith had gone for +0.8 (on time)  with mention of three very cold intervals (so why only 0.8? anyway ...)  and would be third using the three-day late cutoff rule. Those were the top forecasts followed by 1.5 (Gavin P) 1.7 (Aderyn Coch) and 1.8 (Terminal Moraine). It looks like most were having a bit of trouble believing that the very cold start would hold for very long into the month but the month was looking cold enough that Craig Evans went 6.0, a fact noted at the time. 

One forecast below outcome

NOV 2010 _ 5.2 _ Trickdicky was the lone colder forecast (4.9), finished second to Roger J Smith at 5.4. Gavin P, Terminal Moraine and Optimus Prime all had 5.9. There was a forecast of --2 from liltbrockie which was regarded as a send up although it could have been an anomaly perhaps, so technically this was also a two-colder-forecast scenario. 

No forecasts below outcome

AUG 2014 _ 14.9 _ Seabreeze86 had 15.6 for the win, Polar Maritime and Gael Force had 15.9. Diagonal Red Line and weather-history 16.0. 

We did not see the cold second half of Aug 2014 coming, apparently. Our consensus was around 17.1 C.

MAR 2013 _ 2.7 __ BARRY 4.7, Godber 4.8 and a number at 5.0 were the best of a bad lot there. Harve changed 4.4 to 5.8 at the last minute. 

... with the cold start, there was no shortage of below outcome forecasts for April 2013. 

____________________________________

will check the archives for any other contenders

Then there are the reverse cases, Dec 2015 of course the ultimate month coming in warmer than even Craig Evans at 9.0 (LG in his current version) -- I managed a distant second in that one, but I thought probably any other contenders would be cases of only Craig above the outcome, one that I remember was Nov 2015 (one forecast on that value from me which is why I remember) and then I looked up April 2011 (11.8), Ripley's believe it or not, a forecast higher than Craig's was entered (Backtrack 12.9), Craig said 12.0 and won the month, Atlantic Flamethrower had 11.6 and I was in for 11.5. 

Edited April 24, 2021 by Roger J Smith

[The PIT]

Sunny Sheffield up to 6.2C -2.1C below normal. Rainfall unchanged.

2nd driest month on record for us. Some rain on the forecast but unlikely to be a lot. The driest month here was April 1957 with 1.8mm of rain. The next driest will surprise people and this was 2007 when only 7.8mm fell. So Tuesday and Wednesday to decide whether this stays in second place or moves in to 3rd place or lower.

[Summer Sun]

6.5c to the 23rd

1.1c below the 61 to 90 average
1.6c below the 81 to 10 average

___________________________

Current high this month 8.8c on the 1st
Current low this month 5.6c on the 12th, 13th, 15th & 16th

[Roger J Smith]

The EWP remains stuck at 5 mm and the GFS suggests about 7 mm on average by end of the month, which looks like it could bust high rather than low since it all depends on a rather dry air mass picking up moisture from the North Sea and dropping 10-15 mm rainfalls in northeast England and parts of east Anglia, the rest of the country is expected to remain rather dry throughout. So that suggests that the record low value of 7.1 mm (1938) will be passed at some point around Tuesday or Wednesday and we will get a bit further into this list of driest 15 Aprils to date: 

 

1. _ 1938 (7.1) ___ 6. 1785 (10.1) ____t-11. 1842 (14.3)

2. _ 1817 (7.9) ___ 7. 2007 (10.4) ____t-11. 1974 (14.3)

3. _ 1912 (9.0) ___ 8. 1984 (10.8) ____ 13. 1783 (15.2)

4. _ 1957 (9.7) ___ 9. 2011 (11.6) ____ 14. 1954 (16.1)

5. _ 1893 (9.9) __ 10. 1854 (14.1) ____ 15.1844 (16.6)

There is quite a jump between 9th and 10th so perhaps we'll end up in that gap somewhere. 

Seems a shame to go this deep into the month and lose the top spot, however, one thing to keep an eye on will be the adjustment of tracker to actual value on the 5th, since this 5 mm is made up of a few days that got 1 mm out of very hefty traces. We could actually be at some lower value than 5 mm now. 

All of this inspires confidence in the provisional EWP scoring, a list of those results was given back on 18th April, will put up a longer list this week with a link to the file, and assume that only very minor changes in that will be forthcoming since the EWP is going to get nowhere near even the lowest forecast in our group this month. 

Best combined forecast may turn out to be a tie between Polar Gael and myself, PG has best EWP and 5th best CET (7.1) if the result is 6.8 or lower; I'm at third in both, so 1+5 = 3+3 ... the outcomes that change that result are warmer CET than our lowest forecasts (6.8 by two) -- 6.9 CET where I move to first CET while PG remains fifth is the only outcome where I move ahead, if it goes to 7.0 then PG is the best combined with an earlier entry into the contest than me, so that he's second CET and I'm third (even the other way round, it would still be 2+3 for me and 3+1 for PG, so that order only makes it more decisive). By 7.1 CET outcome, Polar Gael has it sewn up all the way up to about 7.4 C with few entries below 7.8 to knock the CET rank down much compared to anyone with half a chance through a low EWP (syed2878 had 7.5 C, 55 mm, so at 7.5 would be 1+9 compared to PG at 8+1 ranks, so syed2878 needs a 7.6 CET to take over the lead, with Reef at 7.8 51 mm a few spots better in EWP rank).

I don't think with the cooler turn next week that the CET will make it much past 7 C and then there's the end of month adjustment to consider, so all things considered it looks good for PG to have best combined, any outcome but 6.9 will be good. 

[The PIT]

Sunny Sheffield up to 6.4C -2.0C. Rainfall unchanged.

First double digit jump and surprising so late in the month. Looking like we will finished between 6.6C and 6.7C which would be 2.1C to 2.2C below normal. This would be the coldest April since 2012 if we finish on 6.7C and 1989 if we finish on 6.6C.

[Summer Sun]

6.7c to the 24th

0.9c below the 61 to 90 average
1.4c below the 81 to 10 average

___________________________

Current high this month 8.8c on the 1st
Current low this month 5.6c on the 12th, 13th, 15th & 16th

[damianslaw]

Outlook looks distinctly cool for late April, would not be surprised to see the CET flatline in the days ahead, and not breaching the 7 degree mark, with further cold minima, and maxima below average as well. Indeed we could see a fall as the week wears on.. possibility now even we may end up colder than April 1989, but a good bet is in a finish in the high 6s...we've had quite a few milder or nearly as mild Decembers in recent years!

[Frigid]

9 minutes ago, damianslaw said:

Outlook looks distinctly cool for late April, would not be surprised to see the CET flatline in the days ahead, and not breaching the 7 degree mark, with further cold minima, and maxima below average as well. Indeed we could see a fall as the week wears on.. possibility now even we may end up colder than April 1989, but a good bet is in a finish in the high 6s...we've had quite a few milder or nearly as mild Decembers in recent years!

Yup, December 2015 and 18 were 9.7 and 6.9 respectively, very mild and could come in milder than this April. Only took 32 years for a sub 7c April when there were 3 in the 80s. 

Edited April 25, 2021 by Frigid