[Model output discussion - heading into 2018]

Interesting that the 12z EC operational run was at the warmest end of the spread between the 6th and 8th, when that not very cold easterly is shown, the mean a few degrees lower and some much colder members in there by the looks of it, indicating a colder source is possible around then.

Be interesting to see if the operationals in the morning carry through this hint from the ensembles to show some colder solutions.

[Model output discussion - heading into 2018]

27 minutes ago, Catacol said:

I dont have time to post more tonight - but as I watched a video of snow falling in Buxton earlier and read yet more FB posts from a friend in the Highlands who has had snow day after snow day so far it occurs to me that we are seeing a spell of weather at the moment that illustrates how effective a proper polar NW airstream can be in delivering snow. This hasnt been the case in many winters in the last 20... but quite clearly we have a sufficiently cold airmass to our NW to deliver good winter synoptics for many areas of the north and midlands. Even some areas of the south have seen snow (though not Somerset of course.... ) and perhaps I need to modify my benchmarks for success a bit. I still see high lat blocking as the pathway to a really good sustained spell of deep cold winter, but 2017/18 has so far shown that polar westerlies can deliver well for many parts of the UK even at low levels, though the cold will tend to be transient as systems pass through. Time perhaps to show a bit more respect for a NW airflow.

I recall easterlies in winters since the 90s that have disappointed more than the recent wintry NW'erlies have for cold and snow, they certainly aren't a wind direction that guarantees deep cold and snow unfortunately, some easterlies past have brought just leaden skies and drizzle in winter. The classic convective snow showers easterly off the North Sea is probably quite a rare beast these days. We have benefited from the polar northwesterly flows tapping into some very cold air over NE Canada and Greenland, though because they are inherently involved with low pressure systems moving east or southeast they tend to be transient. Certainly shades of Jan 1984 recently, though the cold and snow then was probably more entrenched rather than transient across the north.

But onto the current models and the 18z run from GFS, a more fruitful run for coldies in that a Scandi trough and high pressure to the W and NW of UK brings a NELY that taps into deeper cold than the easterly. It looks like the models are firming up on the amplification over the N Atlantic late next week, then the ridge building NE into the GIN corridor, it's whether we see the high build further east into Scandi or not looks to be less certain, but expected to be uncertain at that range.

[Model output discussion - heading into 2018]

The 12z EPS control builds a surface high centred 1030mb between Iceland and Scotland as early as Saturday 6th Jan before the high relocates east to be centred over Scandinavia by early 2nd week of Jan. However, the control has the similar issue as the deterministic in dragging in mild air from southern Europe into the easterly around the low centred to the south of the UK. Ideally would want the low pressure to elongate further east across central Europe to prevent this.

However, we need to get down the route of pressure building close to northern UK then across Scandi first, the steps for this would likely be:

1. The eastern N America trough amplifying/digging south middle of next week in response to amplifying +PNA ridge upstream, this in turn amplifies a ridge over NW Atlantic

2. Further downstream response from the amplification of the flow over NW Atlantic is trough disruption close to the UK, as the jet dives SE toward Morocco.

3. A 'trigger' surface low then drops SE across UK which allows pressure to rise to the NW then N of UK

4. High to the north of the UK stays or drifts east over Scandinavia, a northesterly or easterly develops.

5. If we get as far as the above, then the question of how cold the NEly or Ely, depending on shape of high to the N and NE and shape of low over mainland Europe to the S and SE.

The 12z EC 300mb wind/jet stream loop below puts into context how the upper flow behaves to get the above evolution to happen, note the initial amplification upstream over N America, then subsequent amplification, trough disruption and jet diving south over E Atlantic / W Europe.

 

However, a lot could go wrong in the early stages mentioned above stages 2 and 3 mostly likely to go pear-shaped, the amplification over US more of a cert 

It would be ironic if an easterly does develop, it will be less cold than the NWlies we've experienced recently, given all the hype of the potential for them to develop, sometimes easterlies can be marginal or wrong side of marginal and just bring stratus and drizzle in winter unfortunately.

[Model output discussion - heading into 2018]

Yes Steve, UKMO looks more amplified in 500mb flow at t+144 than GFS on 12z. Quite marked difference on wetterzentrale.

GFS

UKMO

 

[Convective/Storm Discussion Thread - 1st August onwards]

4 minutes ago, Mapantz said:

Just had another bout of activity, convective gusts close to 50mph.

 

Looks like some nice mammatus in the 2nd pic too!

[Model output discussion - heading into 2018]

Don't want to steal Man With Beard's thunder, but a look at the 00z EPS clusters shows fairly good confidence actually in the mid-Atlantic amplification, that then leads onto pressure/height rise over northern Scandi:

However, it maybe a short-lived affair the effect of the height rises to the N and NE, before the next surge of the trop PV moves in from the NW/W.

Given the strength of the trop PV influence upstream and the strat-trop coupling profile, it would be difficult to get a block to develop to the NE and keep the Atlantic at bay from the UK, unless more energy from the trop PV goes SE under the UK.

[Model output discussion - heading into 2018]

06z GFS delaying amplification over the Atlantic (vs 00z) until the low res part of the run it seems, but boy does look like putting on a show for coldies in FI!

[Heavy Snow & -12C In The North VS Heavy Rain, Gales, Hail & Thunder In The South]

There is no escape from the inclement weather across the UK today. Heavy snow or heavy rain, thunder & gales ... take your pick.

View the full blog here

[Model output discussion - heading into 2018]

Yep, the GFS op not without credibly large enough support from ens members for the ridge to build NE near the north and west of the UK and eventually leading to a Scandi high

Is the ECM high res too progressive in breaking down the Atlantic ridge? Could be, but we'll need to see where the det. sits with the ensemble spread.

[Convective/Storm Discussion Thread - 1st August onwards]

Yep, pretty active cluster of storms off Devon atm and also SW Wales. Interesting radar signature over Cardigan Bay

http://en.blitzortung.org/live_lightning_maps.php?map=12

[Convective/Storm Discussion Thread - 1st August onwards]

Risk of some squally thunderstorms Friday morning across southern Ireland and towards SW UK, could be some isolated damaging gusts and even a tornado associated with this vigorous convection, which can already be seen to the west of Ireland.

Link to my storm forecast for Netweather in the tweet below:

 

[UK Storm and Severe Convective Forecast]

UK Severe Convective & Storm Forecast - Issued 2017-12-28 23:12:49

Valid: Friday 29th Dec 6am to Saturday 30th Dec 6am
DAY 1 CONVECTIVE / STORM FORECAST

Click here for the full forecast

Check the full storm forecast here

[Model output discussion - heading into 2018]

The 00z EPS control shows big amplification NE to the west and north of the UK days 9-10 - which then leads to a Scandi high by day 12, but unless if forms a solid block through the layers it may be difficult to hold back the Atlantic, which subsequently moves back in by day 15 on the control. Interesting to see this evolution played by one of the EPS members nonetheless and may be a growing cluster around this potential for pressure rises to the NE.

[Model output discussion - heading into 2018]

Despite the Polar Vortex strengthening to almost record levels looking at GEFS 10 hPa U-wind charts, the GFS op on 18z run continues to suggest some amplification still possible over the N Atlantic enough to split the trop PV into lobes over Canada/Greenland and NE Europe, before the Euro trough fills and sinks to allow height rise to the NE. The amplification likely a result of the return of the  poleward -EPO ridge amplifying the flow downstream.

Alternating cold and mild zonality seems certain and also worth noting the strong undulating zonal jet will bring a conveyor of lows and plenty of rain and occasional snow which could start to pose flooding issues over the next week or so, given a lot of rain has fallen since the weekend.

The potential for height rises to the NE still needs plenty more runs to indicate whether this is viable though, so sitting on the fence on this idea, despite the eye candy popping up. Nice to see the GFS show something else other than endless zonality though.

[SE and East Anglia generalweather discussion 08/11/2017 onwards]

Nice to see the  snow falling outside behind the Christmas tree in the living room making it feel more festive, albeit a few days late. Much to the disappointment of my 6-year-old son, doesn't look there will be enough snow falling and drop in ground temp for it to settle to make a snowman.

[Model output discussion - heading into 2018]

Morning all, hope you all had a good Christmas.  Snowing here in south London as I type, only a few days late, but my son getting excited.

Someone's broken the ECM this morning but hopefully it'll appear later, but looking at GFS, seems little has changed in the broadscale pattern ahead since I last posted before Christmas. 

With no sign of deep low heights to the  N and NW shifting we will continue to see a strong and zonal jet stream over the UK, bringing a conveyor of depressions off the Atlantic. However, although the jet will be over or near the UK, it will drift north and south and back north at times, with parts or all of the UK alternating between cold zonality when on the poleward side of the jet, bringing some marginal threat of snow at times, perhaps like today. But we will inevitably end of up the milder equator side of the jet, for a few days, with lows tracking close to Scotland rather than across the south. 

So it could be worse IMO, as I guess it's better to have east to west alignment of the jet rather than SW-NE, as albeit zonal, as when the jet does drift south it brings air cold enough at time to bring snow, even in the south. 

Fortunately there are no signs of protracted height rises building east across mainland Europe, in fact the GEFS suggests a EURO trough in the means days 10-15

A look at the 5 day average, although turning milder in the 5-10 period across the south

GEFS suggests slight below average for all in the 10-15 day period as the Euro trough carves out and the flow is from the NW in the means, the means perhaps concealing the odd brief northerly:

So although the pattern ahead is not ideal for protracted and deep cold and worries over marginality when there's a snow signal, at least we do have cold enough air at times for some snow events, my glass half full today.

[Mild & Green Christmas For Most, But Turning Colder from Boxing Day, With Snow Risk]

No white Christmas Day for most, apart from over Scottish hills. But Boxing Day onwards colder with snow for some parts.

View the full blog here

[Model output discussion - heading into 2018]

FWIW, 12z UKMET-G further north in track with 26/27th low compared to the 00z this morning:

12z T+60

00z T+72

Will the 12z EC edge further north?

 

[Model output discussion - heading into 2018]

Not huge difference between the models with Boxing Day night's low track in the grand scheme of things given we are still a good 60hrs away, but the differences of 50+miles makes a difference to the northern/southern limits of potential snowfall on the northern flank and back edge as it clears east.

00z ECMWF, UKMO and 06z ICON furthest south at 00z Weds, taking low centre through the E Channel:

EC-Hi res UKMET-GICON

00z/06z GFS and 06z ARPEGE further north at 00z Weds, 06z a little further north than 00z GFS

06z GFS 06z ARPEGE

EPS mean and standard deviation shows the lower confidence around the track of the low too:

Be interesting to see where the models track the low on the 12z output, plenty of room for change in track with the low yet this far out. Like other have said, we may not no until later tomorrow or early Boxing Day on most likely track!

 

[Model output discussion - heading into 2018]

27 minutes ago, snowblizzard said:

High 1036 over Greenland

High 1029 over Northern Europe linking into Scandinavia?

Low pressure heading into Spain

Azores high slipping SW

Encouraging signs or just a temporary position?

 

There's generally always a surface high over Greenland because of the dense cold over the ice sheet covering much of the landmass creating higher pressure (which is adjusted to mslp given the high elevation of the ice sheet) - meanwhile to the south we have a succession of lows barrelling in from the Atlantic across western Europe.

True, the jet is on a southerly track next week, bringing some transient cold and snow risk to northern areas, especially over the hills. But the models are consistently signalling an upper trough amplifying over the NW then mid-Atlantic next weekend onwards, which would amplify the jet north again over the UK downstream. There is the possibility that if the upper trough moving in from the west amplifies further it may undercut resulting ridge  building N toward Scandi downstream - but this potential is too far off in FI land to have any credibility for now. So realistically we are at the mercy of Atlantic lows rolling through next week before any concrete changes away from this pattern may become apparent.

[Model output discussion - heading into 2018]

00z EC and 06z GFS below showing a heavy snow signal for northern England and Northern Ireland Boxing Day evening/night on northern flank of low pressure system clearing east over central areas. Too far off to know whether the low track will be further north or south though and whether it will be cold enough for snow to fall and settle at lower levels. But some upland areas of the north could see spell of quite heavy and disruptive snow.

Reminds me of an evening in January 1995 when I was in Leeds at the time studying, when a similar system crossing central areas in a zonal flow had some snow on the northern edge and brought the city to a standstill.

[Model output discussion - heading into 2018]

42 minutes ago, bluearmy said:

The slp probability charts provide for that nick and show less than 10% support (as per standard). Of course there could be some upper ridges with surface pressure below 1030mb but they would have pressure higher to the south and therefore not be the type of feature we would be searching for re Scandi highs 

I certainly wouldn’t discount the potential for this to evolve beyond two weeks 

there remains a disconnect with the gefs on this 

Ah well, it's a straw to clutch, but an outsider obviously at the moment, given that the trop and strat PV look to cool and strengthen in an unfavourable position for any sustained cold in the UK/Ireland and certainly HLB is off the cards for a while.

At least we have the Christmas period coming up to divert our minds onto other things and perhaps forget about our impending slide into domination by the trop PV and zonal express, with the possibility of some better signals showing up in the New Year. 

[Model output discussion - heading into 2018]

1 minute ago, bluearmy said:

sadly it isn't really - the extended eps are not showing the little drop of low anomoly post day 12 this morning, nor is there a small upper trough sinking to our se. Micro changes globally  but changes where they are important to us.  any troughing to our south is purely transient at the moment 

Having browsed the extended EPS, they appear to be retrograding the tropospheric PV back over northern Canada in the means? Still we are left with a SWly 500mb mean flow though, but means could smooth out the potential for some members building heights to the northeast in the extended. Will need to see the  clusters later I guess of any credible hints of what 00z GFS op shows in FI.

[Model output discussion - heading into 2018]

39 minutes ago, Steve Murr said:

however in the past 5-7 days the GFS peak forecasts for the zonal wind have continually increased - & now see the crest just 2 or 3 M/S slower than the all time strat record- in this case then its total wipeout for Northern blocking- you can liken the speed to the most positive AO phases of the 90s or the December not to remember a couple of years a ago.

So the expectation has changed now & the  GFS 16 day ensembles all have a high peak of zonal winds for the start of Jan - however a sharp gradient of decline in Jan back to below ave levels.. so based on that week 2/3 may yield a high prospect of HLBs

until then - continual battering of westerly winds will be in offering often storm force straight through the nose of the UK.

Can't argue with that, certainly the +PNA / -EPO ridging helped amplify the flow enough downstream to bring so many northerlies in 2nd half of November and into early December I lose count! That was when the troposphere wave patterns were ruling the show, but like you say, it looks increasingly like the uptick in zonal winds in the stratosphere are downwelling to influence the tropospheric flow as we end the year. The cross-polar ridging over into Greenland from the anomalous -EPO ridge perhaps the 'last gasp' from the tropospheric wave  influence over the AO domain, before the SPV looks to return from displacement back to its more usual home over the pole as we head into the New Year.

However, given the eQBO and fall toward solar min, I'm of the optimism that the seasonal cooling and strengthening of the strat PV and its coupling with the trop may not be long-lived and that we may see the SPV weaken and perhaps displace again, even could see signs toward a SSW late Jan, but this a great unknown for now. Kyle Henry earlier today mentioned the potential of tropical cyclone activity recurving and throwing a lot of energy toward the pole on the N Pacific side which may cause further warming over the AO domain.

So, I agree, first half of Jan maybe hard to swallow, given we will likely see a zonal outlook for a few weeks at least. But, we surely can't have such a long run of winters without HLB coming along, and the eQBO this year compared to wQBO in recent few winters would favour this more through a weaker SPV.

[Model output discussion - winter proper underway]

20 minutes ago, blizzard81 said:

I'm not saying the Arctic high is bad. However going on past experience,  more often than not, it just doesn't seem inclined to make that last leap towards us unfortunately. Who knows, maybe this time it can but I am not hopeful. 

I think the problem is that without some meaningful amplification in the polar front jet across the N Atlantic to join the cross polar ridging moving south into Greenland, the strong zonal 200mph jet stream will carry on regardless, albeit in a more supressed southerly track into Europe. That's until the Greenland height rises fade, which brings me on the other issue that the ensembles eventually dampen and shrink back the anomalous -EPO ridging building into the arctic. This could be because the ridge has built so far north that it has allowed troughing to undercut over the EPO region and the N PAC jet to extend into Wern U.S./W Canada cutting off the WAA north across Alaska which maintains the -EPO ridge. But it may return to full strength after temporary relaxation.

Still, the southerly tracking jet will at least mean we will be increasingly on the cold polar side of the jet through next week, with snow likely for the usual suspects of cold zonality up north, but maybe a few snow surprises thrown in elsewhere. But we can't get any sustained wintry weather out of such a pattern in our maritime climate without blocking lending a hand.