Model Output Discussion - Colder but how cold and for how long?

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[TillyS]

Thanks Paul.

The one thing I would mention is that these kinds of boundary snow events are always by definition nail-biting. Warmer air pushing into cold, forcing upwards, and bingo! It’s always a cusp event. Some places don’t see the front advance sufficiently into their area. Others see it advance too much and it turns back to rain. Whilst those in the middle are in the sweet spot and it can snow all day long, blanketing entire counties with beautiful soft snow.

The devil then comes in the detail: what’s the track, how far does it encroach, does it turn back to rain etc. etc.?

That’s not where my current concern is though. The tracking comes later as we’re far too far out for the models to pin it down. 

No, my concern is that the upper air temps this week ahead of the northerly are lifting and are not going to be particularly cold (+5C 850hPA temps over much of the Midlands) e.g.:

Conditions this week are not ideal. Which makes the northerly critical. How far will it penetrate south, and how deep will those upper air temps go? If it doesn’t make it far south, or if the upper air temps are gradually eroded before the warm front approaches, then this won’t produce the right kind of boundary snow set up for most people, at least in the south of Britain. This has shown as a possible trend on some of the recent model outputs, especially the progressive GFS. The ECM and UKMO, whilst still potentially very good, have just eased off the throttle slightly.

The northerly is everything. 

Edited January 10 by TillyS

[northwestsnow]

Excellent runs this morning..

Trend is good,really good...

[bluearmy]

Looking at the dogs breakfast that the nwp has become overnight, you begin to wonder if there will actually be a ‘northerly’ of any consequence away from Scotland ???

with the detached ridge heading se and the possibility that the shortwave could become a distinct feature, the Atlantic could then come in before we see any strong northerly flow in evidence for more than 12/24 hours at the end of this weekend into Monday. 
 

let’s hope that the fog clears somewhat through the day so that at least we get a new envelope in place (the old one needs chucking away) and that it’s got firmer edges! 

6 minutes ago, northwestsnow said:

Excellent runs this morning..

Trend is good,really good...

I couldn’t disagree more NWS - too much movement imo. What is the trend ? I’m really not sure at all. I did think I knew yesterday 

Edited January 10 by bluearmy

[MattStoke]

6 minutes ago, TillyS said:

Thanks Paul.

The one thing I would mention is that these kinds of boundary snow events are always by definition nail-biting. Warmer air pushing into cold, forcing upwards, and bingo! It’s always a cusp event. Some places don’t see the front advance sufficiently into their area. Others see it advance too much and it turns back to rain. Whilst those in the middle are in the sweet spot and it can snow all day long, blanketing entire counties with beautiful soft snow.

The devil then comes in the detail: what’s the track, how far does it encroach, does it turn back to rain etc. etc.?

That’s not where my current concern is though. The tracking comes later as we’re far too far out for the models to pin it down. 

No, my concern is that the upper air temps this week ahead of the northerly are lifting and are not going to be particularly cold (+5C 850hPA temps over much of the Midlands) e.g.:

Conditions this week are not ideal. Which makes the northerly critical. How far will it penetrate south, and how deep will those upper air temps go? If it doesn’t make it far south, or if the upper air temps are gradually eroded before the warm front approaches, then this won’t produce the right kind of boundary snow set up for most people, at least in the south of Britain. This has shown as a possible trend on some of the recent model outputs, especially the progressive GFS. The ECM and UKMO, whilst still potentially very good, have just eased off the throttle slightly.

The northerly is everything. 

Bearing in mind that fronts can produce snow with 850hpa temperatures as high as 0'C under the right surface conditions. More wiggle room than with convective snow.

[That ECM]

Ridge gate done, bulge gate nearly done. 
 

we now move on to northerly gate and low gate and then longevity gate.

[Cymro]

10 minutes ago, TillyS said:

Thanks Paul.

The one thing I would mention is that these kinds of boundary snow events are always by definition nail-biting. Warmer air pushing into cold, forcing upwards, and bingo! It’s always a cusp event. Some places don’t see the front advance sufficiently into their area. Others see it advance too much and it turns back to rain. Whilst those in the middle are in the sweet spot and it can snow all day long, blanketing entire counties with beautiful soft snow.

The devil then comes in the detail: what’s the track, how far does it encroach, does it turn back to rain etc. etc.?

That’s not where my current concern is though. The tracking comes later as we’re far too far out for the models to pin it down. 

No, my concern is that the upper air temps this week ahead of the northerly are lifting and are not going to be particularly cold (+5C 850hPA temps over much of the Midlands) e.g.:

Conditions this week are not ideal. Which makes the northerly critical. How far will it penetrate south, and how deep will those upper air temps go? If it doesn’t make it far south, or if the upper air temps are gradually eroded before the warm front approaches, then this won’t produce the right kind of boundary snow set up for most people, at least in the south of Britain. This has shown as a possible trend on some of the recent model outputs, especially the progressive GFS.

The northerly is everything.

What's interesting however with all the chase on next week for meaningful snow we're currently much colder than average. Temperatures here have failed to breach 1 degrees since Monday.

Yesterday was an ice day and the ground, ponds and ditches are frozen solid under warming upper air temps. Definitely inversion cold pool developing at the surface and despite the increase in upper air temperatures 2m temperatures are still 3/4 degrees below normal so that chart doesn't necessarily paint a complete picture. 

For me the cold spell started on Saturday and will continue into next week. 2 weeks at least of below average temperatures in mid winter. Wonderful! 

Edited January 10 by Cymro

[Mark wheeler]

Mogreps seem to have most runs under the -5 line . A few that don't, would be nice to see everyone in the action. Haven't looked at the stamps as at work but hopefully some snow about on them.

[Malarky]

3 minutes ago, That ECM said:

Ridge gate done, bulge gate nearly done. 
 

we now move on to northerly gate and low gate and then longevity gate.

Do we want the low in the Atlantic to phase slightly with the low heights in Europe? Will that help keep the Iberian high suppressed? (Still much to learn on my part)

Edited January 10 by Malarky

[northwestsnow]

3 minutes ago, bluearmy said:

Looking at the dogs breakfast that the nwp has become overnight, you begin to wonder if there will actually be a ‘northerly’ of any consequence away from Scotland ???

with the detached ridge heading se and the possibility that the shortwave could become a distinct feature, the Atlantic could then come in before we see any strong northerly flow in evidence for more than 12/24 hours at the end of this weekend into Monday. 
 

let’s hope that the fog clears somewhat through the day so that at least we get a new envelope in place (the old one needs chucking away) and that it’s got firmer edges! 

I couldn’t disagree more NWS - too much movement imo. 

That's suprised me nick I 

I thought EC / UKMO looked fairly solid this morning ...

The Northerly looks nailed on , the rend post Northerly is a brief relaxation followed by another push south of the pattern...

[TSNWK]

1 minute ago, Mark wheeler said:

Mogreps seem to have most runs under the -5 line . A few that don't, would be nice to see everyone in the action. Haven't looked at the stamps as at work but hopefully some snow about on them.

Mogreps 2M temps are about 3 by day in the south Day 8/9 - if I was in the north I would be super pleased with an average of about 1C top around day 7 / 8 - mix in some mositure............. and little height.

[northwestsnow]

As an example MOGREPS Leeds looks solidly cold 

 

[northwestsnow]

Maybe I'm being too optimistic !!

That would be a first !!

[Wivenswold]

Monday's snow was widespread in the South despite marginal conditions and it being only being suggested as a South-east streamer in the models the night before.
And we're getting in a panic about 7 days time.  This likely won't be resolved until we're in a Nowcast situation so the pessimists need to stop worrying and the optimists need to tone it down a bit.

[sebastiaan1973]

A part of the sea between Sweden and Finland, the northern part of the Gulf of Bothnia. is frozen. This is quite remarkable. Please look at the extent. 

This can be important if the wind will turn to the northeast later on. In the weatehrmodels we see a persistence of cold (er than average) weather in Scandinavia.   

Edited January 10 by sebastiaan1973

[Mike Poole]

A look at why the clusters were struggling, here’s day 9 from the EPS:

A large uncertainty!  Some cross polar rippers in there, some with a clearly defined ridge int Greenland in place, some with a declining ridge, and on some it has completely healed up.  

Let’s go back 3 days, day 6:

This is actually looking quite clear, most have the ridge holding providing a decent northerly to this point.  The ones that have a GFS style mess in mid-Greenland are few.  So I think we are further forward this morning.  The trend could still be that the block is underestimated, more runs needed.

[danm]

1 minute ago, northwestsnow said:

Maybe I'm being too optimistic !!

That would be a first !!

My take on it is that an Arctic northerly is almost nailed on, but the period of time we get that direct feed looks to be fairly short before a more complicated pattern emerges. There is the potential for huge amounts of snow for some areas - however, we simply don't have a scooby doo at this point on where that will be. Could be a very exciting week, but with the nature of these things, some will be elated, others will be deflated. 

[feb1991blizzard]

Thought we started off quite well, was hoping GEM would have support though, ECM spoils things though, eps still decent in that things have stabilised to about a 4-5 day cold spell when it was reducing all the time 36 hours ago.

[Met4Cast]

I can’t say I’m liking the overnight runs either. 

We seem to be losing the more robust Greenland high signal & relying more and more on the low dropping into Scandinavia. There is no consistency between models. It’s not ECM/UKM vs other models it’s every model vs every model. 

Pretty much impossible to see where we’re actually heading this morning. 

[northwestsnow]

Just now, Mike Poole said:

A look at why the clusters were struggling, here’s day 9 from the EPS:

A large uncertainty!  Some cross polar rippers in there, some with a clearly defined ridge int Greenland in place, some with a declining ridge, and on some it has completely healed up.  

Let’s go back 3 days, day 6:

This is actually looking quite clear, most have the ridge holding providing a decent northerly to this point.  The ones that have a GFS style mess in mid-Greenland are few.  So I think we are further forward this morning.  The trend could still be that the block is underestimated, more runs needed.

Yes I thought the same Mike but Nick has induced a bit of doubt now , mainly because he one of my " go to" posters...

[bluearmy]

4 minutes ago, northwestsnow said:

That's suprised me nick I 

I thought EC / UKMO looked fairly solid this morning ...

The Northerly looks nailed on , the rend post Northerly is a brief relaxation followed by another push south of the pattern...

As I said, what exactly is the northerly now ?   it was supposed to be a sustained northerly flow (possibly becoming cold cyclonic under a trough) with attacks from the Atlantic to our sw

 is that still the case?  It all looks to be lifting too far north overnight - this is a follow on from a general slow trend to lift the Azores low further north over the past few days. Without the initial plunge of cold being entrenched (and the detatched ridge and shortwave prevent this occurring) the cold in place is unlikely to be effective in deflecting the lw Atlantic trough when it makes its way in.

Let’s see how things adjust through the day.  Hopefully the gem has this on a broader scale 

[bluearmy]

5 minutes ago, northwestsnow said:

Yes I thought the same Mike but Nick has induced a bit of doubt now , mainly because he one of my " go to" posters...

I thought mike’s post was indicating that uncertainty has increased over the past three days. maybe I read it wrong 

[winterof79]

This is as far as i care to analyse

After that its up in the air...

[bluearmy]

Icon 06z run is a small step away from more amplification with a smaller Arctic ridge and some phasing to our nw looking more likely as the greeny ridge closes up compared to the 00z run 

just one run though 

perhaps I should go back to bed ! 

on a brighter note, the chances of a surprise rise in heights as week 2 progresses like the pub run last night have increased imo 

Edited January 10 by bluearmy

[Anthony Burden]

Morning all,charts will chop and change even up to 24hrs before nailing the exact track of low pressure,this morning the charts ECM UKMO going for the colder prolonged theme in my opinion with some disruption due to snow and freezing conditions.Met office extended forecast will be interesting today see if any milder interlude for next week is forecast.