Model output discussion - The run up to Christmas

[Bobafet]

6 hours ago, Tim Bland said:

Morning gang. Loving the ECM this morning. Position is obvious subject to massive change but that low / PV ruminants drops 20cm of snow on its way down ️

Looks like Homer Simpson has made an appearance on that chart!

 

[weirpig]

Admiral Akbar   Ha Ha Ha.

 

Thanks for that  in these depressing times  that was quality 

[bluearmy]

slight shift west on the upper trough at day 6 on the 06z eps.  i only mention it as it isn't a shift to the east 

[Beanz]

36 minutes ago, Stu_London said:

In terms of upgrades/downgrades for 850temps, I've seen on a lot of occasions, slight upgrades in the just out semi-reliable time frame - this is what we are seeing over the last couple of runs for the period 27th-30th and there is still a little bit of scope for improvement. 

Often when we get what I would call the reliable timeframe (96hrs and under) there is a very small backtrack. Happened in Feb/March 18 which started as -15C ish - nearly made it to -20C at about five days and ended up being -18s and -19s in some places. That spell wasn't an issue as there was nothing marginal to worry about.

This one is a more of a problem, so some expectation management is not a bad thing. However, in here, expectation management for some is about as feasible as trying to get your cat to understand the concept of Norway.

 

 

I have a Norwegian cat, does that still apply??  

[Lukesluckybunch]

1 hour ago, Drifter said:

You are absolutely correct, no idea why he keeps  calling this a polar low. 
It’s just a low coming down from the north. 

Most likely because it's a low,coming down from the pole?

[MATTWOLVES 3]

Just looking at many of those 6z ens and we have so many showing troughs in bedded with cold air...i would imagine there could be surprise snowfalls popping up at short notice if these patterns hold firm. You know the drill,somebody up the road gets buried,while a stones throw away there is nothing. I feel many of us will get lucky though.

 

Edited December 21, 2020 by MATTWOLVES

[Battleground Snow]

6 minutes ago, bluearmy said:

slight shift west on the upper trough at day 6 on the 06z eps.  i only mention it as it isn't a shift to the east 

Hi @bluearmy, how far do the 06z and 18z ECM runs go out to and I don't suppose there is anywhere you can view them without a subscription?

[sheikhy]

13 minutes ago, bluearmy said:

slight shift west on the upper trough at day 6 on the 06z eps.  i only mention it as it isn't a shift to the east 

Is it a bit more amplified at 144 hours though!!?it seemed slightly flat compared to the ukmo 144 hours on the 00z!!

[mathematician]

6 hours ago, mountain shadow said:

The broad scale synoptic pattern does look good, but I remain concerned about the lack of proper cold air.

I guess we'll know in a week whether it's snow or cold rain.

I am totally with you on this. Of course I hope to be totally wrong but it seems to me that a lot of people her get carried away and overly excited at seeing all the blue colours over the UK.

 

In reality a -5 at 850 (which is the forecast temperature) is not going to be enough to see snow and for sure not lying snow where 90% of the population lives (big cities, flat land). In my opinion is going to be a repeat of what happened earlier this month: a lot of hype, huge expectations, nice models and cold rain with some occasional wintry mix.

 

Again I would be the happiest if I am totally wrong.

[Methuselah]

8 minutes ago, mathematician said:

I am totally with you on this. Of course I hope to be totally wrong but it seems to me that a lot of people her get carried away and overly excited at seeing all the blue colours over the UK.

 

In reality a -5 at 850 (which is the forecast temperature) is not going to be enough to see snow and for sure not lying snow where 90% of the population lives (big cities, flat land). In my opinion is going to be a repeat of what happened earlier this month: a lot of hype, huge expectations, nice models and cold rain with some occasional wintry mix.

 

Again I would be the happiest if I am totally wrong.

I think that that's a bit of an oversimplification... what if very cold air builds up beneath the 850hPa level? Widespread, persistent freezing fog?

[Kasim Awan]

I've seen snow with uppers of 0C in the occassion where heavy ppn erodes the top-down temperature lapse rates..

It's about the soundings rather than the uppers. Higher humidity reduces the 850 requirements due to lesser lapse rates. 

Edited December 21, 2020 by Kasim Awan

[Penicuikblizzard]

2 minutes ago, General Cluster said:

I think that that's a bit of an oversimplification... what if very cold air builds up beneath the 850hPa level? Widespread, persistent freezing fog?

We had heavy snow a couple of weeks back in Edinburgh under -3 850hpa level and it lay 2 inches on low ground and 4 inches in the higher parts of the city so it does happen 

[weirpig]

13 minutes ago, mathematician said:

I am totally with you on this. Of course I hope to be totally wrong but it seems to me that a lot of people her get carried away and overly excited at seeing all the blue colours over the UK.

 

In reality a -5 at 850 (which is the forecast temperature) is not going to be enough to see snow and for sure not lying snow where 90% of the population lives (big cities, flat land). In my opinion is going to be a repeat of what happened earlier this month: a lot of hype, huge expectations, nice models and cold rain with some occasional wintry mix.

 

Again I would be the happiest if I am totally wrong.

I Would have agreed with you a few days ago.  But since then we have seen a slight reduction in Uppers  forecast  which as you say as brought the mean to around -5  for the majority of the run.    This for me  seeing as the flow is from a northerly quarter       along with very lower dam levels   should enable snowfall to fall almost anywhere with modest elevation.     Ill take a punt  and  say that anywhere over 150metres   will see snow.  below that  certainly a possibility.   And if it dosent.  Then it certainly been an interesting model watching period.  

[Frosty_wsm]

12 minutes ago, mathematician said:

I am totally with you on this. Of course I hope to be totally wrong but it seems to me that a lot of people her get carried away and overly excited at seeing all the blue colours over the UK.

 

In reality a -5 at 850 (which is the forecast temperature) is not going to be enough to see snow and for sure not lying snow where 90% of the population lives (big cities, flat land). In my opinion is going to be a repeat of what happened earlier this month: a lot of hype, huge expectations, nice models and cold rain with some occasional wintry mix.

 

Again I would be the happiest if I am totally wrong.

Posted earlier in this thread about the Dec '81 snowfall, I'm at sea level just a few miles from the Bristol channel coast we had around a foot of level snow, snow drift up the back door of the house that we couldn't open it but looking at the archive charts the 850s were only -2/-3, there's more factors at play than just the 850 temps. 

[Jason M]

3 minutes ago, Smartie said:

Posted earlier in this thread about the Dec '81 snowfall, I'm at sea level just a few miles from the Bristol channel coast we had around a foot of level snow, snow drift up the back door of the house that we couldn't open it but looking at the archive charts the 850s were only -2/-3, there's more factors at play than just the 850 temps. 

Fair point but completely different circumstances. You had an embedded artic airmass through the different layers of the lower atmosphere, snow cover etc. This time we have none of these (I was a kid back then but I remember that winter really well).

[bluearmy]

33 minutes ago, Battleground Snow said:

Hi @bluearmy, how far do the 06z and 18z ECM runs go out to and I don't suppose there is anywhere you can view them without a subscription?

T144 and no there isn't afaik

27 minutes ago, sheikhy said:

Is it a bit more amplified at 144 hours though!!?it seemed slightly flat compared to the ukmo 144 hours on the 00z!!

v much the same as the 00z suite - i wouldn't expect  a mean at day 6 to be as amplified as an op once the models are on the same page 

[bluearmy]

1 minute ago, Jason M said:

Fair point but completely different circumstances. You had an embedded artic airmass through the different layers of the lower atmosphere, snow cover etc. This time we have none of these (I was a kid back then but I remember that winter really well).

there is much discussion re required uppers etc and memories of events where uppers seemed marginal. as you say, v few scenarios are comparable for many reasons 

[SteveB]

1 hour ago, Smartie said:

Yep, I've seen so much talk recently about the upper air temps not being great & then I think about the awesome snowfall event of Dec '81 with over a foot of level snow here & I'm at sea level just a few miles from the Bristol channel & looking back at the archive charts the upper air temps were only - 2/-3 at the time so you never know. Either way it's great seeing this thread buzzing & hopefully we all get lucky & see some snow. 

I remember that event, I was going to see some relatives a couple of miles away still in Weston, and it started to sleet while we were in the car. We were only 30-40ins at my relatives when the phone rang, and it was my Mum, she suggested we head home as the snow was already settling. I must have been not that cold, as it was sleeting to start with.

[LRD]

There were obviously other factors favouring snow in Dec 1981 but the 850s very rarely got below -5, -6 during the whole month if at all.

In Jan 1982 they did

Rain to snow event:

I'm sure parts of England experienced lows of around -20 in this scenario:

Edited December 21, 2020 by LRD

[terrier]

I’m sorry but I’m really struggling here to see the excitement I think a few people are getting confused with these blue areas over the U.K. at the moment.  Yes we are better placed than last winter admittedly.  But are we heading for a deep freeze with deep crunchy snow for many.  From what I’m seeing at the moment definitely not. Now before I get called a mild lover far from it. We have even had mr murr on here this morning saying the uppers are very marginal in this set up we are seeing. Do I think some will see some snowfall yes. But away from Scotland and the highest northern hills I think we are looking at cold rain and sleet. Unfortunately we just don’t have the cold available to the east at the moment. So let’s see what transpires over the next week. But just remember these areas of blue over the U.K. don’t necessarily mean deep cold and bucket loads of snow. And as Steve has already said this is a very marginal situation I’m afraid. So don’t expect much in the way of snowfall away from the far northern hills and Scotland would be my guess. 

[Radiating Dendrite]

2 minutes ago, terrier said:

I’m sorry but I’m really struggling here to see the excitement I think a few people are getting confused with these blue areas over the U.K. at the moment.  Yes we are better placed than last winter admittedly.  But are we heading for a deep freeze with deep crunchy snow for many.  From what I’m seeing at the moment definitely not. Now before I get called a mild lover far from it. We have even had mr murr on here this morning saying the uppers are very marginal in this set up we are seeing. Do I think some will see some snowfall yes. But away from Scotland and the highest northern hills I think we are looking at cold rain and sleet. Unfortunately we just don’t have the cold available to the east at the moment. So let’s see what transpires over the next week. But just remember these areas of blue over the U.K. don’t necessarily mean deep cold and bucket loads of snow. And as Steve has already said this is a very marginal situation I’m afraid. So don’t expect much in the way of snowfall away from the far northern hills and Scotland would be my guess. 

We are well aware of your thoughts @terrier

I am not sure you need to keep repeating yourself. I do not think people are expecting some kind of 87" repeat, we are just happy to see some seasonal charts showing and the chance of possible lowland snowfall in the UK at times, something we cannot call until much closer to the time.

I would rather have a ticket for the raffle and I feel we have that.

[Tim Bland]

8 minutes ago, terrier said:

I’m sorry but I’m really struggling here to see the excitement I think a few people are getting confused with these blue areas over the U.K. at the moment.  Yes we are better placed than last winter admittedly.  But are we heading for a deep freeze with deep crunchy snow for many.  From what I’m seeing at the moment definitely not. Now before I get called a mild lover far from it. We have even had mr murr on here this morning saying the uppers are very marginal in this set up we are seeing. Do I think some will see some snowfall yes. But away from Scotland and the highest northern hills I think we are looking at cold rain and sleet. Unfortunately we just don’t have the cold available to the east at the moment. So let’s see what transpires over the next week. But just remember these areas of blue over the U.K. don’t necessarily mean deep cold and bucket loads of snow. And as Steve has already said this is a very marginal situation I’m afraid. So don’t expect much in the way of snowfall away from the far northern hills and Scotland would be my guess. 

Oh well if Steve Murr says that then does anyone want to buy my sledge Here’s the uppers for Bournemouth. Red line is the average. We are at or below -5 on almost all runs. This is all coinciding with the shortest day of the year so little solar input and cold ground. It may be marginal at times but I would be shocked if most areas don’t at least see falling snow in the week after Chris9FDC9948-E1CA-41C2-8EED-A4700668E91C.webptmas 

Edited December 21, 2020 by Tim Bland

[Jason M]

1 minute ago, bluearmy said:

there is much discussion re required uppers etc and memories of events where uppers seemed marginal. as you say, v few scenarios are comparable for many reasons 

Cheers.

I think one of the problems on this thread sometimes is that (some) people don't take the trouble to understand the basic qualities of the various airmasses the UK is subject to and how they interact. For example -2C at 850 with a cold undercut from a PC (Polar Continental) airmass is literally about as different as can be from a PM airmass. People see a northerly and assume certain things, but as we know a northerly can have PM qualities or it can be a true Arctic airmass. Without understanding about these factors its not possible to really know what the charts are telling you. In Dec I tend to add 9c to the 850s of a PM to get a rough (and it is rough) approx of 2m temps. So -5 could easily equate to +4c (and I'm being generous here). With a PC airmass in Dec you can add as little as +6c so -5C at 850 is giving +1c 2m temp. Factor in lower due points with a PC flow and its suddenly 'white' not 'wet'. By Feb with added solar input these numbers can change a fair bit.

 

[terrier]

4 minutes ago, Radiating Dendrite said:

We are well aware of your thoughts @terrier

I am not sure you need to keep repeating yourself. I do not think people are expecting some kind of 87" repeat, we are just happy to see some seasonal charts showing and the chance of possible lowland snowfall in the UK at times, something we cannot call until much closer to the time.

I would rather have a ticket for the raffle and I feel we have that.

Can’t see much in the way of lowland snowfall in this set up but I will happily be proved wrong. All I’m trying to say is away from Scotland and northern hills I can’t see much but rain and sleet for many.

[Radiating Dendrite]

1 minute ago, terrier said:

Can’t see much in the way of lowland snowfall in this set up but I will happily be proved wrong. All I’m trying to say is away from Scotland and northern hills I can’t see much but rain and sleet for many.

We shall see.

I am expecting to see snowfall in many places away from the coast, even if it is transitory in nature.