1353 replies to this topic

[happy days]

Hum vast majority of 12z GEFS ensemble suite look to be suggesting HP over or very close to the UK which is more obvious checking the precipitation spikes than say the 850's.The likelihood of drier and cooler weather under an inversion remians the form horse right now.(which i personally be very happy with after another vile wet grey day here)!!
UKMO at 144h is not going to bring about an Easterly any time soonafter IMO with the jet still in a thouroghly active mode still.

[Thundery wintry showers]

Tim Bland, on 01 January 2012 - 17:11 , said:

"Come on Gavin, we need more than that."

MORE! I'd settle for that! - 5 850s south of channel islands, low pressure, heavy snow showers pulsing across us as the cold air rushed across the mild Atlantic! Are we being greedy now!

In fairness I don't think lying snow would be particularly widespread from that chart as a glance at the 850hPa values and surface temperatures points to a pool of milder air in the north. We'd probably see scattered wintry showers from the Midlands northwards but with lying snow confined to northern hills.

A rather boisterous spell of weather coming up during the first week of January with frequent NW incursions bringing sunshine and showers, wintry on northern hills, and some longer outbreaks of rain, most especially on Tuesday when gales still look likely in the north. I can see strong hints of pressure rising over Scandinavia after the system at T+144-168, but as the evolution to the Scandinavian high falls outside of the reliable timeframe it is doubtful whether we will evolve into a Scandinavian high setup at the first attempt- let alone have the high far west enough to bring us continental air. However, a change to an anticyclonic and possibly colder outlook has fairly strong support for around the 10th January or so.

I don't think snow lovers should get too excited even if we get continental air at the first attempt as the cold pooling amounts to 850hPa values of around -5 to -7C- I think we'd struggle to get much convection over the North Sea off that airmass, though of course any reloads further down the line could be a different story.

[damianslaw]

Jason M, on 01 January 2012 - 17:12 , said:

It all looks a bit similar to this time last year. I'm still going for a near miss (possibly multiple near misses) with the high sat smack over the top of us.

The one constant on just about every chart we see is that dirty great high to our SW. The 'beast from the east' may come knocking but my money is on the displaced Azores high to once again prove its by far the biggest beast in our part of the jungle. We need low pressure to our South as there is no trigger to back the cold air west. High pressure to our South = no snow!!

Despite my own views though, its nice to see some interest again and i suspect that the next few days might throw out some really good runs before things settle down again.

Jason

Take a look at the charts from 9 dec 09 - you don't need low heights to the south for a quick evolution to something much colder and snowier. However, what you do need is a weak polar vortex to our NW and perhaps even more importantly building heights to our NE - these are two developments being shown by the ECM and GFS this evening.

[phil n.warks.]

Grimsby Snow Lover, on 01 January 2012 - 16:47 , said:

Quite a decent pressure build over the pole by the end too. First time I've seen green over parts of Greenland since October I believe
http://hw.nwstatic.c...384/npsh500.png

I think the real change is likely to come from the other side of the pole but not within the high resolution modelling.
I will try to explain but you will have to indulge me as i am going to use charts from the later part of the 12z output.

The pressure from the Greenland low hts. and the attendant n.Jet is still too strong to maintain ridging very far north around the UK. for a while yet.
Here from UKMO 12z T144


and running on through the GFS12z


However later on,although low resoultion,we see something stirring


showing the vortex in a weaker state,the sort of thing that`s showing up more now in the later output.
The High to our south being squeezed and the low heights becoming displaced south and east.

The best way to cold from this Zonal pattern would be Atlantic ridging getting established behind the piece of Greenland vortex diving SE in the later frames.
However we need more buckling of the flow from upstream which would drive the Canadian low heights south creating deeper troughing into the E.Seaboard,thus sucking up those heights from the Azores high.

GFS 06Z toyed with this -


I don`t think an Easterly in the nearer term is a goer because of the strong jet pattern running over the top,Untill the core of the Vortex shifts and starts to fragment from the Greenland area anything from the East will flatten under the pressure.


but once the vortex weakens further as modelled again in the low resolution then we should see a different outcome.


If the pattern doesn`t buckle into FI as i am looking for then we would still see a colder pattern with the jet further south as shown on 12zGFS.
I should add at this range the modelling of the PV will change many times but it will certainly add to the interest in chart watching through the next couple of weeks.

Attached Thumbnails

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Edited by phil n.warks., 01 January 2012 - 17:54 .

[Grimsby Snow Lover]

Thanks Phil, you have explained the possible developments very clearly. At least now I know what to look for in future runs.

[phil n.warks.]

Grimsby Snow Lover, on 01 January 2012 - 17:57 , said:

Thanks Phil, you have explained the possible developments very clearly. At least now I know what to look for in future runs.

Thanks GSL-i am glad you said possible-with the energy across the north at present it will take time as i have said.
The ECM will probably now show a raging Easterly in it`s later frames just to show me up.

[kold weather]

Better model runs today, the trend for the height rises to our north looks solid, but nothing too impressive being forecasted yet, still a little far out yet.

Anyway ensembles are interesting, looks like a real mixed bag, some members do give us some cold weather, quite a few more produce a mid latitude block and hold it fairly close to the UK. That wouldn't be a bad solution IF we can get another wave of warming to totally finish the vortex.

MUCH better prospect then this time last week...

[Frosty039]

The Gfs 12z op run shows a very anticyclonic outlook for southern britain once we get past friday but the north of the uk probably remaining changeable or unsettled, although it's still unclear whether the high will push into northern areas but that currently seems unlikely and the high could end up being centred to the southwest of the uk with cloudier skies pushing down it's eastern flank. There are some very wintry synoptics towards the end of the run with a southerly tracking jet and lots of frigid arctic air not far to the west, north and east of the BI so the models are starting to look like they should with the downwelling effects of the moderate strat warming. The polar vortex is going to come under immense pressure to split during the next few weeks and there are potential northerly blasts not to be ruled out but a calmer and colder spell is now looking more likely for the south at least after the next 5 days but it probably won't stay settled for long.

[mountain shadow]

ECM backs off from the 0z. Less amplified and looks like we will have the HP over us.

http://www.wetterzen...cs/Recm1441.gif

[Springmadsam]

Frosty039, on 01 January 2012 - 18:16 , said:

The Gfs 12z op run shows a very anticyclonic outlook for southern britain once we get past friday but the north of the uk probably remaining changeable or unsettled, although it's still unclear whether the high will push into northern areas but that currently seems unlikely and the high could end up being centred to the southwest of the uk with cloudier skies pushing down it's eastern flank. There are some very wintry synoptics towards the end of the run with a southerly tracking jet and lots of frigid arctic air not far to the west, north and east of the BI so the models are starting to look like they should with the downwelling effects of the moderate strat warming. The polar vortex is going to come under immense pressure to split during the next few weeks and there are potential northerly blasts not to be ruled out but a calmer and colder spell is now looking more likely for the south at least after the next 5 days but it probably won't stay settled for long.

Thank you frosty you have presented this in a nice basic way . Totally agree with your own words.

[Snow? norfolk n chance]

If we cant have snow, lets have high pressure over us, good agreement on all models for things finally drying up, could even be very cold due to inversion, although for a time with HP to the SW can be miserably wet for my area

[mountain shadow]

Yup, a dire run for coldies. What a difference 12 hours makes.

http://www.wetterzen...cs/Recm1921.gif

12 hours ago the ridge was way up past Iceland. Not good from the ECM for the second time this winter.

[Nick F]

There shouldn't be any surprise that 12z ECM wasn't going to follow the 00z run though. Beyond t+144 will often change anyway. Given the stubborn deep vortex over Greenland and the continuing strong jet across the Atlantic, any ridging building to the east is under alot of pressure. It doesn't even offer GFS's fairly cold northerly toppler next weekend either, rather a half-hearted NW'erly, though more amplification upstream coming through than suggested by ECM tonight could change this.

[Cheese Rice]

Interesting weather

Monday

Throughout Sunday night into Monday we see a brief PM incursion. 850's projected by the NAE to be around -5/-6



The colder 850s will promote rapid convection across the Irish sea. These showers will affect the areas highlighted on the PPN map above, so most western areas of the UK. Showers will fall as snow inland with a wintry mixture towards the coast, temporary accumulations expected across Northern England with several cm's over North West/West Scotland. Winds will be westerly with a south westerly tilt as the day continues, meaning areas that usually see snow in PM incursions may miss out due to the South Westerly element (usually winds from the North West).

Tuesday

During the early hours of Tuesday morning a deepening area of low pressure will track north of England, with the center of the low over Scotland.



Previous runs projected a slightly deeper area of low pressure, current projections suggest between 970MB-960MB (as seen on the ensembles above). The main cause for concern in the strengthening winds and large rainfall totals.



Winds gusting up to 60 knots (70 MPH) across the areas highlighted in red. Heavy rainfall will lead to localized flooding across Wales and North West England. Previous GFS runs projected exceptional totals of 50 mm for a 12 hour period. This has been downgraded to 28 mm for wales, 23 mm for North West England and 26 mm over the Lakes. There still remains a high risk to disruption to travel. A wet ground creates instability in the soil thus increasing the fragility of trees. When subject to high winds trees can easily topple. Expect disruption to road, rail, and electricity, with some trees falling.



Amazingly the NAE projects snowfall across large parts of Scotland and Northern England when the front arrives. I can't see any snow except transient snow across the highest ground over Scotland, 850s as seen above are not supportive in the slightest.

Wednesday

During late Tuesday the associated mild sector will quickly leave followed by colder 850s. Setup is very similar to Monday, with colder 850s promoting convection. Any showers falling as snow with a wintry mixture across the coasts.

Edited by Cheese Rice, 01 January 2012 - 19:07 .

[happy days]

mountain shadow, on 01 January 2012 - 18:54 , said:

Yup, a dire run for coldies. What a difference 12 hours makes.

http://www.wetterzen...cs/Recm1921.gif

12 hours ago the ridge was way up past Iceland. Not good from the ECM for the second time this winter.

i wouldn't say dire,although the northern arm of the jet is still far to active to allow stable northern blocking at the moment.
Too much energy going North aided by the mind numbingly stubborn PV.
If we consider Dec Jan and Feb as winter months that damn PV will have ruined half the winter soon enough with the majority still waiting for their first snow letalone lying snow.
I guess pateince really is going to be a virtue this time round..

[kold weather]

I wouldn't describe the 12z ECM as dire, its not as good as the 00z though thats for sure.

What i will say about the 12z ECM is the vortex remains quite stubborn this run, doesn't really weaken all that much, but it does start to shift further east, so hopefully we can get the building blocks for change in by the 10-15th...

[Stormyking]

Hmm a much different look to the ECM 12z. I would say it would be very dry with some frosty nights and fairly chilly at day time, which in my opinion wouldnt be all that bad, an improvement anyways to recent

Edited by Stormyking, 01 January 2012 - 19:09 .

[Geordiesnow]

I'm still struggling too see where we are going to get much in the way of significant cold air from in all honesty from the ECM output, I mean what happens if everything does goes to plan and we get an easterly with the -10hpa barely reaching us because Scandinavia is way above average at the moment, even the NW'ly toppler at 96 hours is moderated because of the persistant less cold air around the svalbard isles. As I been menturning previously, the Svalbard isles must be having one of its mildest first half of the winter on record and conditions on our side of the poles has been quite mild due to the frequent nature of Southerly winds from the Russian high and low pressure further west pumping warmer air on our side of the Arctic.

Frustrating output for cold lovers and for once I have to admit its hard too see where a significant cold spell will come from. I'm not ruling out any cold set ups because the models are hinting at what would usually be cold set ups(like the NW'ly toppler at 96 hours) but due to the weather patterns so far, every cold set up so far has been moderated by the lack of cold air!

[TonyH]

My take in this weeks weather specific to west Wales and the central Midlands:

Weather guide Monday 2nd January to Sunday 8th January 2012 (west Wales and central Midlands)

Headline: More rain and showers; drier end to the week. Quite mild on the whole.

West Wales could do with a break from the rain! December's total at Llanwnnen was 212mm (8 1/2 inches), and it rained on every single day of the month at some point. On the other hand, a bit of a respite from the exceptional dryness for the Midlands last month, with Coventry at least reaching average with 60mm in December.

2011 was the second warmest year on record, even though the Summer was rather cool. No real cold to come this week either.

Some rather cold air is over us for a change during Monday. Showers moving into west Wales later tonight may be of sleet and hail perhaps leading to icy conditions first thing on Monday morning. Further showers at times through the day, some heavy with hail, a smidgen of snow on the hills perhaps too. Only a few showers extending east into the Midlands, so a mostly dry and bright day here.

Monday night into Tuesday, an intense low crosses northern Britain, so it looks like gale force SW to west winds could cause damage in places. A very wet night too, and with possibly over an inch falling on west Wales, localised flooding could cause problems on the roads on Tuesday morning, so something to be wary of along with the wind. The rain should have cleared most by midday, but with more showers following in the afternoon, these again heavy with hail at times, with some even getting into the Midlands as the the wind turns more north-west through the day.

Further Atlantic troughs cross the country on Wednesday bringing some more rain and wind but milder.

Thursday onwards is difficult to pin details on but pressure should try to build in from the south-west, so that it will turn somewhat drier at last. Winds will be coming around the high from the west or north-west, and temperatures will be just above normal to mild, maxima from Thursday to Saturday between 7 and 10c, and no more than the outside chance of a touch of frost or two. GFS brings in colder air next weekend on its latest run, but I would be inclined to largely discount this just now, although a trend to cold may be emerging in the models for following week.

So, although probably mostly dry to end the week, and for next weekend, the odd shower or spell of light rain cannot be ruled out at this stage, but certainly not the deluges we have seen here in west Wales over recent weeks, and will see again early this Tuesday.
.
For supportive charts see the Welsh thread:

http://forum.netweat...48#entry2201048

Edited by TonyH, 01 January 2012 - 19:12 .

[nick sussex]

The ECM 12hrs is a continuation of its morning theme but with the pattern a little further south and with the GFS giving support in the higher resolution output theres a decent chance of this verifying.

Looking at the broader picture of the NH it is however a step backwards with the PV showing no sign of moving away from Greenland and still very strong.

Even if the models manage to edge the pattern further north giving a stronger continental feed the jet will eventually sink any high, at this point a surface inversion is as good as it gets with the PV where it is.