Cold Spell Late Feb/ Early March Technical Discussion only MOD NOTE POST #1

JCX BXC wrote: »

78.6cm....you missed the 'point'.

786mm of rain would be a record, and probably put the area under water.

Ha ha, just realized that. Thanks!

pistolpetes11 wrote: »

So now that the dust has literally settled , which of the models performed best ?

I’d never given the ICON any credit before but thought it handled things very well

For me the UKMO really impressed me it kept it track regarding the original evolution of the cold , the ecm pick up emma as a kink in the iosbars quite early in the runs leading up to it becoming a storm, I believe it took at least 3 days before the other models seen it, ICON surprised me

Gaoth Laidir wrote: »

For some reason the Dublin figures above have been corrected. The synop reports now show still 15 cm of patchy cover at 11 pm tonight. There is a strange anomaly where it jumps from 10 cm to 15 again the following hour, but it may be because they had to sample a different area. Anyway, I was thinking the original figures seemed strange at the time.

So current depths/coverage/snow type at 11 pm are

Casement 16 cm/100%/uneven wet or compacted
Dublin Airport 15 cm/51-100%/wet or compacted
Cork Airport 9 cm/100%/even wet or compacted
Knock (still manned this late in the night) 2 cm/100%/wet or compacted
Shannon's cover all had melted by 6 pm.

The Shannon cover makes little sense, still a good albeit patchy covering left here in West Clare, where do they measure it?

sryanbruen wrote: »

Seems to me that we're going into a March 2013-esque scenario here, southerly tracking jet stream, northern blocking, warm stratosphere, low pressure invading from the south. I think nature is trying to tell us something!

That the Jetstream will eventually rebound to the other extreme and we'll have a fantastic Azores High Summer like 2013?

In scoring the February forecast contest, I found that the monthly sunshine for February was 150% of normal over the grid and probably close to 200% of normal values in the northwest. The month ended up somewhat drier than average as this snowfall event only got off to a sporadic start on the 28th and the week before that was essentially dry. The mean temperature for the month was about 2 deg below normal but was closer to 1 deg below normal as late as the 22nd. If February had been a 30 day month it would have been a bit less sunny, close to normal in precip, and about 3 deg below normal.

The CET record goes back a long way (daily records to 1772) and the records for 28 Feb and 1 Mar were set in 1785, very similar to readings this year. Monthly precipitation values are also available. So that got me to checking, what sort of year was 1785?

Here's the overview including the run up to those cold values (England and Wales precipitation is also available, no telling how much of the precip was snow from these records however) ...

JAN 1785 _ After quite a cold December (1784) (mean 0.3 C) and first week of January, the rest of January turned quite mild, the month averaged 3.4 but in those days not a particularly cold January, the mildest days were around 8 C from 17th to 21st. It was not a wet January but in the lower part of the average range, total of 50 mm.

FEB 1785 _ With the start of February, the weather turned very cold and stayed that way all month. It was dry like most cold months, with just 35 mm but that could have meant 35 cm of snow or a large fraction of that over the region. The average was only 0.4 C (same as December had been) so this was overall quite a cold winter. The coldest day was the 20th of February which set a daily record, a mean of -6.6 C. It stayed cold to mid-March and as I mentioned the reason for this report was that 28th (-3.8) and 1st of Mar (-3.5) set daily records also. The record for the 28th has been retained (2018 came in at -3.6) and provisionally the record for 1st of March was tied, that may change in the final figures at month's end.

MAR 1785 _ There was no real warming at all in March 1785. Following the record cold on the first, the month was second coldest March on record with an average of 1.2 C. All but one day averaged below zero from 7th to 13th. Very low values were recorded 21st to end of the month including more records of -0.3 (28th) and -0.7 (29th). This was an exceptionally dry March, and I am guessing the 19 mm precipitation meant 10-15 cm of snow and a bit of rain, but we can't be sure about that.

APR 1785 _ The severe cold persisted to 2 April then it turned a lot warmer and the month averaged 8.4 C which is slightly above the average in those decades. Most days had means near 10 C or higher, the average would have been well above 9 discarding the first three days. The very dry spell continued and worsened, in fact April had a mere 10 mm of rain and was about fourth driest in the 252 years of record. This would indicate that the blocking pattern that gave the cold Feb and Mar persisted but winds came from a warmed continent or perhaps the block dropped further south. Because of these three dry months, the year was well below average and ranked 9th driest out of 252 years, drier than any year in the past fifty even 1975 or 1976.

MAY 1785 _ May probably allowed farmers to catch up as it was quite a warm month that averaged 12.3 and there were days towards the end that were almost summer-like at 17 C. The drought persisted too although the rainfall did manage to produce 26 mm on average (in England and Wales).

JUN 1785 _ This was quite a warm month also, averaging 16.1. It was close to heat wave conditions at the end of June with daily means around 19 C. The weather continued relatively dry with 45 mm of rain. The first half of the year was considerably drier than the more normal second half.

JUL 1785 _ July was more average but pleasantly warm most days with a few towards the end reaching 19.5, the average for the month was 16.1. There was no severe heat during this summer, the warmest day (19.5) is about 1.5 deg below the average for that statistic long-term. However, the drought began to fade with a rainfall average of 62 mm.

AUG 1785 _ The summer had peaked early and August was a rather chilly 13.9 C on average. The 26th to 28th averaged only 11.0 C. There was no real warm spell the entire month. It was also a wet month that averaged 119 mm of rain. The harvest must have been quite stressed with the cold late start, the dry spring and early summer, and then this change to poor ripening conditions.

SEP 1785 _ Most of September turned quite warm and averaged 13.6 but more like 15 for the first three weeks and about 8 for the last five days. The month continued the August wet regime with 105 mm, a bit above average.

OCT 1785 _ The cooler turn at the end of September persisted for most of October which averaged only 8.7, about a degree below average even in cooler times than now. The first half was relatively mild (around 10 C) but the second half brought some wintry outbreaks, and the mean on the 26th was only 1.5 C. There was a rather normal precipitation of 99 mm but perhaps some was snow given the cold readings in late October.

NOV 1785 _ This was quite a typical November with fluctuating temperatures that averaged 5.6 C. Some days near the end of the month were close to zero. The precipitation was a bit below average at 67 mm.

DEC 1785 _ This was generally a rather cold month, the average being 2.8, and the first day sub-zero for CET mean (-0.1). A deeper cold spell set in before Christmas and lasted in the new year, 3 Jan 1786 had a non-record but very cold mean of -7.6 C. The rest of this winter was quite variable with further severe cold spells after some very mild weather in mid-January. There may have been some heavy snowfalls given that the average precipitation in December was 81 mm and many days close to or below freezing. Jan 1786 was also quite wet and some of that may have been heavy snow too.

So it's interesting that the year most similar to 2018 in the timing of this severe cold spell had a long episode of blocking, spring warmth and a reversal to a wet end of summer and back into the deep freeze without much hesitation the next winter.

OneEightSeven wrote: »

Would Emma be characterised as a blizzard or a snowstorm?

.... a let down?
Funny how I was envious of people in places like Lucan, Celbridge, Sallins etc the other day. I'm not envious now! They will have to look at this disgusting slushy mess for a lot longer than me.
It was more or less a three day event, a thaw set in as soon as the last flakes fell so if that isn't a let down then I don't know what is. Definitely more '87 than '82. And by the way, the "sun is too strong for snow to lie in March" argument is total nonsense. Its ALWAYS a rise in air temperature that prevents snow lying in Ireland for more than a few days. It just shows how exceptional 2010 was.
PS. I think in future we'll have to look to Greenland for a prolonged cold spell as Scand highs only last a couple of days.

Calibos wrote: »

That the Jetstream will eventually rebound to the other extreme and we'll have a fantastic Azores High Summer like 2013?

Yes please!!

I think the Canadian Warming impacts on the troposphere need a lot of monitoring as we could either go into a northerly or northeasterly (as the most favourable scenario in my opinion) or a mild, zonal pattern with the Polar Vortex getting itself together. The latter has a very low chance due to the state of the zonal winds.

Elmer Blooker wrote: »

.... a let down?
Funny how I was envious of people in places like Lucan, Celbridge, Sallins etc the other day. I'm not envious now! They will have to look at this disgusting slushy mess for a lot longer than me.
It was more or less a three day event, a thaw set in as soon as the last flakes fell so if that isn't a let down then I don't know what is. Definitely more '87 than '82. And by the way, the "sun is too strong for snow to lie in March" argument is total nonsense. Its ALWAYS a rise in air temperature that prevents snow lying in Ireland for more than a few days. It just shows how exceptional 2010 was.
PS. I think in future we'll have to look to Greenland for a prolonged cold spell as Scand highs only last a couple of days.

You're confusing Storm Emma with the cold spell here. The question was about Storm Emma.

MJohnston wrote: »

You're confusing Storm Emma with the cold spell here. The question was about Storm Emma.

Fair enough, point taken. But I think I can speak for the majority posters in the weather forum and most wanted a cold spell and not a cold snap. Sure, many are happy just to watch snow fall or play around with their kids who may not have seen snow before but those of us, the regulars who pore over charts must be disappointed after the SSW and synoptics that we haven't seen in years!
The golden rule in Ireland for snow to lie is for clear skies and not cloud cover. (as in 1982, first week of March 2001 and 2010)

wakka12 wrote: »

Surprised by that map
I thought an easterly travelling across the continent to us would have meant north germany/nort and west france and the benelux nations would have the same or more snow than us
Italy seems to have higher percentage of its country under snow in that picture than germany!

The air was so dry and stable that the only snow that fell across Poland and Germany was along the Baltic and North Sea coasts. For the rest it was just brutally dry cold.

Well the cold spell looks like it will continue from the models being posted, we're just getting a short thaw in before that happens. Frankly I'm glad of it - I really enjoyed Tuesday to Friday when there was constant lying snow in my location, but it was the type of snow depth that just made for a complete shutdown and I didn't really fancy it going on much longer. 2010 was easier to deal with being prolonged as there wasn't really very much snow and roads and streets could reopen fairly quickly. Here, without the thaw, I think the street would have been closed for another week.

I don't imagine many model watchers are too disappointed either - we witnessed an historic weather event, and were able to predict and track it from a week out.

MJohnston wrote: »

I don't imagine many model watchers are too disappointed either - we witnessed an historic weather event, and were able to predict and track it from a week out.

3 weeks ago I was f5-ing the GFS's FI charts looking for signs of impact from the SSW. An easterly was depicted, and eventually made its way here.

Obviously there was wild variations from run to run, but it was an incredible few weeks of model watching.
Such a strong background signal - a loose plot on which to hang this snowy story.

Quick question about ensembles and the various member runs in models.

Just taking the GFS for example, there are 20 different members in each run. Then a control and an operational.

Is the operational simply the mean or most likely result calculated from the 20 taken together?

e.g. GFS OP 6Z today for Monday week, which is cold eastery:



And the 2nd Member showing totally different, much deeper easterly (don't sell the snow shovels yet):