Short range model discussion - into 2018

[wiltshire weather]

Long time lurker here and rarely post other than an occasional one in my regional thread so forgive this post if it's deemed off topic but didn't know where else to put it.

Really like the idea of a thread devoted to just the next few days but wonder if it should be up to 120 hours to promote a little more discussion as that's still in the realms of a more reliable timescale but without the ridiculousness of the FI charts that dominate the main model thread.

It just seems that with the shorter timescale all that can be talked about is the current weather forecast for the next 2 or 3 days which is usually pretty much agreed on between the main models. It always seems to me that it's around days 4 and 5 that things start to diverge so there would be more material for people to discuss with hopefully the more knowledgeable here more willing to add their input.

Just to add some chart info to make this post actually model related, up to T72 on the latest GFS it certainly looks as though the high pressure is still holding although upper air temps are beginning to be sourced from a much warmer area especially in the south.

 

 

 

[knocker]

Today sees the Atlantic ridge continue to expand north east between Iceland and Scotland whilst the upper trough deconstructs with the main area being forced south into France/Iberia.  Thus on the surface a cold north easterly wind sets in behind an old occlusion which is slowly moving south. Ergo clear behind the front with some showers in the east but cloudy with patchy rain further south in the vicinity of the front.

By Sunday at 06 the high cell is over the north of the UK, and consequently there is quite severe frost, with temps down to minus 10C and more in places. But as the day progresses the ridge/high cell is coming under increasing pressure from upstream energy pushing east and by 00 Monday the upper trough to the north west, with a strong low level jet delineating the boundary between the cold/warm air, has forced a realignment of the high cell which is now NW>SE over the eastern North Sea and thus cutting off the north easterly surface wind. Albeit it does create a strong easterly in the south which id squeezed between the low pressure.

This in fact heralds the start of the battle between the high pressure, which now starts to get organized to the east and Atlantic lows and  frontal systems driven by the aforementioned energy with the UK at the coal face. This is clearly illustrated through Monday

From this point, and after a quick glance at the T84 chart, one could be forgiven for thinking that the Atlantic breakthrough is inevitable but this is only partially correct and what happens is quite intriguing but outside of the remit of this thread.

This according to the gfs of course.

Edited January 6, 2018 by knocker

[knocker]

The surface charts for T48 and 72 from the ecm

[knocker]

Hirlam temps for Sunday morning

[chrisbell-nottheweatherman]

5 hours ago, knocker said:

The surface charts for T48 and 72 from the ecm

/

Is it just me, or does the jet chart from GFS show that the jet is still divioded between a northern and southern arm at T+72, while ECM for the same timeframe shows the northern arm dominant with the UK sitting in the apex?

[johnholmes]

I am sorry I still do not have enough time to do a full update, just dropping in now and then to see how things are but please use those links I gave as they will update with each run.

It is a shame for cold lovers in that the block has been shunted a bit too far east for its effect to be as great as earlier predicted. Mind you there was never any probability of bone chilling upper temperatures way beyond the original T+72, now T+00, surface cold yes. Nor did any upper air outputs really suggest much in the way of snow showers off the N Sea. It will be interesting to see how the next 72 hours and out to 120 actually turn out. I suspect that this scenario may last well into next week, it might even be longer. The 500 mb anomaly charts I use to get an idea of the upper air pattern in the 1 to 2 week period are a bit variable but do at times show blocking well to our NE and a strong Atlantic flow turning, what we call, diffluent near the UK. This suggests that fairly deep lows are likely at times, but generally beinmg held well out in the Atlantic by the block well to our NE.

Interesting for sure.

Hopefully either tomorrow or Monday I may be able to have an in depth look although I suspect it may well require going some way beyond the T+72h limit. I still think that the thread should go out to 120 hours, hoping we can keep the unpleasantness in the other model thread out of here.

Edited January 6, 2018 by johnholmes

[knocker]

37 minutes ago, chrisbell-nottheweatherman said:

Is it just me, or does the jet chart from GFS show that the jet is still divioded between a northern and southern arm at T+72, while ECM for the same timeframe shows the northern arm dominant with the UK sitting in the apex?

I can't post the ecm but it's not dissimilar to the gfs

 

[chrisbell-nottheweatherman]

19 minutes ago, johnholmes said:

I am sorry I still do not have enough time to do a full update, just dropping in now and then to see how things are but please use those links I gave as they will update with each run.

It is a shame for cold lovers in that the block has been shunted a bit too far east for its effect to be as great as earlier predicted. Mind you there was never any probability of bone chilling upper temperatures way beyond the original T+72, now T+00, surface cold yes. Nor did any upper air outputs really suggest much in the way of snow showers off the N Sea. It will be interesting to see how the next 72 hours and out to 120 actually turn out. I suspect that this scenario may last well into next week, it might even be longer. The 500 mb anomaly charts I use to get an idea of the upper air pattern in the 1 to 2 week period are a bit variable but do at times show blocking well to our NE and a strong Atlantic flow turning, what we call, diffluent near the UK. This suggests that fairly deep lows are likely at times, but generally beinmg held well out in the Atlantic by the block well to our NE.

Interesting for sure.

Hopefully either tomorrow or Monday I may be able to have an in depth look although I suspect it may well require going some way beyond the T+72h limit. I still think that the thread should go out to 120 hours, hoping we can keep the unpleasantness in the other model thread out of here.

Confluent ridge then diffluent trough, John?  With a blocking high to our east/north-east, would that encourage lows exiting the jet to turn even more to the left than usual at that point if the only influence was the normal pressure gradient force overcoming Coriolis?  If so, that would put the lows on a SW-NE path, which would surely draw tropical maritime air into the circulation, or am I getting confused?

[chrisbell-nottheweatherman]

Just now, knocker said:

I can't post the ecm but it's not dissimilar to the gfs

 

I thought you posted it in your shorter second post this morning, Malcolm:

[knocker]

7 minutes ago, chrisbell-nottheweatherman said:

I thought you posted it in your shorter second post this morning, Malcolm:

That's the surface chart with 850mb winds, the 500mb chart shows the energy flows better IMO Chris

Edited January 6, 2018 by knocker

[johnholmes]

16 minutes ago, chrisbell-nottheweatherman said:

Confluent ridge then diffluent trough, John?  With a blocking high to our east/north-east, would that encourage lows exiting the jet to turn even more to the left than usual at that point if the only influence was the normal pressure gradient force overcoming Coriolis?  If so, that would put the lows on a SW-NE path, which would surely draw tropical maritime air into the circulation, or am I getting confused?

No I don't think you are getting confused Chris, correct ideas on the upper flow. It 'looks' at the moment as if the colder air will keep 'seeping' out of the upper ridge in sufficient amount to stop what you suggest. But it is very finely balanced. At the moment I tend to favour this and it seems some of the professionals also, UK Met and the link Carinthian has into their Met Office. For sure a situation that must be foremost in any operational forecast room for some few days to come at least.

[knocker]

Just a quick follow up to this morning's post and at T72 the front and rain just edged into western Ireland

[knocker]

A cold day tomorrow with a severe frost overnight with temps in some places in Scotland well below -10C,

[knocker]

After a severe frost in some places this morning today will remain cold for all (+6C in the south but struggling to get above freezing in parts of Scotland) as the UK remains under the influence of the high cell. But during the day the position and orientation of the latter alters quite significantly as the upper trough in the Atlantic edges north east.

Meanwhile a low has formed near the base of the trough away to the south west and is tracking NE and deepening rapidly and by 1800 Monday is 967mb SSW of Iceland with the associated front orientated N/S at 20W, Thus the battle lines are now in place with the high cell now centred over Poland and ridging west over the UK and resisting the pressure being exerted from the west. At this stage the UK is still in a quite cold fresh south easterly airstream.

But the pressure from the west slowly gains the ascendancy and on Tuesday the front gradually tracks east across the UK bringing sporadic outbreaks of rain to most places but also at the same time introducing milder air as the south east airstream is cut off

Before signing off here it's worth a look aloft to see the current state of play and orientation of the major players.

 

Edited January 7, 2018 by knocker

[knocker]

At 00 Tuesday the ecm has the deep Atlantic low 960mb SW of Iceland with the associated very active front orientated N/S at around 15W with the UK still in a south easterly. By 00 Wednesday the front is fragmenting over the Irish Sea bringing sporadic rain to the  UK and a warmer southerly drift whilst secondary features form in the general circulation of the trough and track east into France as a general area of low pressure moves into western Europe.

[johnholmes]

Not a lot to be said beyond the  recent, as usual good post in from knocker.

The interest really is post 72 hours indeed post 120 hours.

Compared to what was suggested/forecast for now if you look at one or two charts other folk posted in several days ago and they are quite close to what we have now. A Fax chart and an 850 mb chart both look quite similar to what we have.

The next 72 hours are probably not going to be much different from the current models. There was never any suggestion that by the middle of this coming week the upper air profiles would support any snow off the North Sea. Interest is centred on what happens post 120 hours.

[Frosty.]

12 minutes ago, johnholmes said:

Not a lot to be said beyond the  recent, as usual good post in from knocker.

The interest really is post 72 hours indeed post 120 hours.

Compared to what was suggested/forecast for now if you look at one or two charts other folk posted in several days ago and they are quite close to what we have now. A Fax chart and an 850 mb chart both look quite similar to what we have.

The next 72 hours are probably not going to be much different from the current models. There was never any suggestion that by the middle of this coming week the upper air profiles would support any snow off the North Sea. Interest is centred on what happens post 120 hours.

Hi john, don't know if you read my sticky note but it would have been nice if you had acknowledged it.

As for the short range models, some frost, dry weather and a little rain or even a few flakes of snow could be yours.

Edited January 7, 2018 by Frosty.

[knocker]

Interesting to note that the low that started life between Greenland and Iceland and was integral part of the recent pattern evolution is today causing a bit of havoc in central Norway with winds gusting at 110-140 km/h, locally at higher elevations

[knocker]

The Icon for 12 Weds

[knocker]

As John mentioned yesterday not much new to report in this time frame but perhaps worth a quick mention of something we have seen a fair bit of this winter and that is rapid cyclogenesis.

Yesterday evening a wave formed away to the south west and over the next 24 hours it is set track rapidly north east along a baroclinic zone to be SSW of Iceland 967mb by 1800 tonight with the associated front orientated N/S at 20W.

This ultimately redirects the energy and pushes the aforementioned front east to traverse the UK

 

[knocker]

So lets continue where the above post left off.

At 1800 tomorrow the front is just impacting the south west and this duly tracks east bringing some light rain but is dissipating at the same time whilst at the same time a couple of small lows are forming the south west.  Thus by 0600 om Wednesday there is rather a slack area of low pressure, with one of the aforementioned lows now 995mn SW of Ireland,. over the UK as the upper trough deconstructs and slips south east.

This process continues through Wednesday as the Azores ridges to the west forcing the low south east as it becomes quite an intense little feature off the coast of Cornwall en route to the west coast of France.

Edited January 8, 2018 by knocker

[knocker]

So take your pick on the handling of this feature

Edited January 8, 2018 by knocker

[johnholmes]

Yes, interesting, take a look at how Exeter move it in their Fax charts, or GFS 06z. The weather continues to fascinate even if the cold and snow so hoped for by many remains just as elusive. The 500 mb anomaly charts continue on their merry way with a marked trough from NE Canada down across the UK into Europe, with little sign of the hoped for easterly in the 6-15 day time frame. I'll have another look in the 72-120 hours later today and post charts in here. I might even make a prediction rather than jus setting the charts out!

[chrisbell-nottheweatherman]

3 hours ago, knocker said:

So take your pick on the handling of this feature

Heading south-east, perchance?

[knocker]

I was looking at the GEFS and EPS anomalies earlier and they are much as you say with a weakening of the ridge to the east further into the period

Edited January 8, 2018 by knocker