Nick F

Storm Barbara has been officially named by the Met Office for the low arriving to north of Scotland on Friday, the north bearing the worst of the winds, their yellow and amber warnings suggesting 60-70mph gusts widely across northern areas, 80-90mph across northern and western Scotland. Strong gusts along the cold front but strongest gusts reserved for far NW closer to tight gradient beneath SW side Barbara passing to the north, though GFS wind gusts don't look quite so severe as the warning suggests away from the far NW. Then hot on Barbara's heels, I guess it looks likely Xmas day's low maybe named Conor, which anything, looks worse than Barbara atm on GFS, with the low centre passing further south between Orkney and Shetlands

00z EC ensemble mean and normalized standard deviation chart for day 10 suggests good confidence (greens) in a ridge building N over UK. So looks like the days of Atlantic influence are numbered, but still a long way from getting some sustained cold and wintry weather.

Morning all, pretty grim for the festive period, but for now at least it's blue skies rather than grey murk this morning for a change.

Sense of déjù vu from EC day 10, with the Euro high extending north, I suppose eventually we'd get a chilly but dry continental flow. At least the GFS and EC ops both agree on amplification upstream in the day 7-10 period, it's then whether the trough amping out west can stall as a standing wave or continues east that controls the destiny thereafter. With the strat PV forecast to get as strong as last winter at 10 hPa and a definite strat-trop connection, the outlook painted by the ops in the medium range could be worse, given weak tropical forcing signal from MJO/ENSO and the low AAM. GEFS has over the last few days been hinting at MJO coming out of COD into low amplitude 7/8/1 into early Jan, but EC and other models are yet to pick up on this. At least the Xmas day storm doesn't look so bad on EC det this morning, Friday night storm looks worse. GFS looking bad for both storms. So still some uncertainty re: track and depth of Xmas day storm, Friday night storm may affect the evolution and intensity of Xmas day storm following hot on its heels.

Such strong Greenland highs are a common trait of NWP trying to model mslp at 3000m high on the Greenland plateau! So surface pressure maps over Greenland don't truly reflect the pressure over the plateau, rather they reflect the frigid cold air on the plateau. If the temperature changes on the plateau the pressure maybe a lot lower the next day. The 960mb seemingly so nearby is actually more accurately depicted as the low is over open ocean/ sea level. In an ideal world, NWP should blank out the mslp lines around mountain ranges and plateaus such as Alps and Greenland respectively.

Well, well at last Low-res/FI GFS op update showing more interest for coldies as major amplification upstream takes place, leading to ridge north over UK and Norwegian Sea, then into a Scandi High - which is less reliant on a troughing undercut across SW Europe from the Atlantic but more reliant on cold pool dropping down across Russia into Europe. However, with no height rises over the pole not sure how this cold so easily gets pushed down from the arctic into Europe. I was thinking yesterday that it's been a long time since GFS or ECM gave coldies some eye-candy ... so long overdue. But being the depths of FI and no strong teleconnections signals other than GFS creeping into low amplitude 7/8 MJO phase, not sure this will appear again next few runs. Otherwise in the reliable, 06z GFS op another conveyor belt of deep lows in high res - bombarding the UK with little respite between. One on Friday, which could be the second-named storm of the season (Barbara), then perhaps Conor on Xmas day. More lining up next week to make a move across the N Atlantic, though hopefully as suggested on a more northerly track. Although Xmas Day low still looks worse for winds on GFS ops, Friday night's storm still needs to monitoring, as the models may not have the correct handle on depth and pressure gradients yet at this range, Friday's low could turn out deeper than Xmas day's low, certainly 00z EC was hinting at this. Strong 200mph+ jet and a lot unusually warm air being drawn into these lows emerging off eastern seaboard sourced from SE USA and Bahamas are a recipe for rapid intensification if phasing is favourable. Given the v. strong W/NW flow in wake of Xmas day's low, should be less modification at the surface of air sourced from a frigid southern Greenland and Labrador than a lighter flow, so we may see snow get to lower levels in the NW in the evening when the cold air kicks in. Certainly blizzard conditions for the Highlands I imagine.

00z EC suggests the deep low modelled passing north of Scotland Friday night looks like it could pack more of a punch across the north and west than the Christmas Day low, as the latter is further north in track. Long way off, but could be quite wintry across the north and northwest Xmas evening/night where we have the showers - as colder polar air filters in from the west. Frosty elsewhere. So looks like we could see a white Xmas in the north in terms of falling snow.

Some of the tabloid papers have headlines of ' A Christmas Day snow Superstorm' and 'odds of a White Christmas slashed' today. This blog tries to shed light over what may actually happen. View the full blog here

7 days is a long way off to alarm the public over a mesoscale feature that is subject to change in timing and track, but there is good support from GFS and EC ops for some damaging and disruptive winds beneath a deep low passing just north of Scotland on the 25th. There were enough pointers back in November to suggest we may have a cold start to winter, mainly the weakened state of the PV. However, there was always the risk, with a wQBO, that the strat PV would strength rapidly and that the circumpolar trop PV would drop a lobe into N America, like the last few winters, which ultimately ramps up the jet downstream across the N Atlantic. Only crumbs of comfort I can find from the NWP this morning is the jet amplifying upstream day 10, but if this does materialise, will the amplifying trough-ridge configuration move into a favourable position for the UK to allow more Pm air or will the trough end up west of the UK and pump southwesterlies like 00z GFS?

Yes, if the zonal spell does relax to invite high pressure back, I hope the Azores ridge doesn't link with the eastern European/W Russia high. As it will be back to square one with the same old tedium we have now and recent days. Really need to see more jet energy over the N Atlantic sent SE into SW Europe and maintained long-term, otherwise we see a cut-off low over Iberia and the Azores ridging NE over the UK. But before then ... we have some zonal to get through, but not without interest for snow fans in the north and west ...

What we are seeing on the 12z GFS op are lobes of circumpolar trop vortex pushing progressively further south over the N Atlantic toward day 10, which in turn is pushing the polar front jet on an increasingly southerly track. So despite the unsettled zonal outlook, there are bouts of cold zonality behind the surface depressions which could bring some whitestuff, mainly over the hills, over the Xmas period. I'm personally looking forward to some winter storms rattling the UK with some wintriness mixed in, as it makes it more interesting for a forecaster to talk about and follow than stagnant anticyclonic gloom. But I'm under no illusions that this spell of zonality will be long-lived. As others have mentioned earlier today, the ensembles have been hinting at retrogression of the trop PV to our NW in the 11-15 day range, so we may well see the high pressure system to the east spread it's influence further west, though it may also join with an extended Azores ridge if we don't get the southerly tracking jet energy to maintain to south of the UK.

I likened the 12z EC det to Joe Barstardi's recent bath-tub theory in action, with cold upper air / low heights in Siberia to start the cold season sloshing into N America then sloshing over to the far N Atlantic toward NW Europe, albeit with the usual maritime modification. 18z GFS op initially starts the cold slosh toward the NW Europe before sloshing back to Greenland and N Canada as ridging rebuilds over Northern Europe. Waxing and waning of the GFS/GEFS Northern European +height anomaly in the medium-longer range really doesn't excite me or give me hope for snow in coming weeks I'm afraid, give me the EC bath tub slosh any day. nice to see the hints of wintry precip even in the south next week on 18z though, but we have to look west for this cold and bear in mind that the models are often too cold from that direction at that range.

UKMO looks a marked improvement pro blocking close to the east compared to 12z run yesterday with more troughing/energy undercutting to the SW - similar to GFS and it looks better in this respect than EC at this timeframe Quite a few 00z GEFS members have high pressure centre over Scandi at day 8 We are left with an underwhelming 00z EC det. - but is it dealing with the blocking right? It has been the most progressive / keen to blow way the blocking influence over the UK over recent days, despite strong support from GEFS for blocking holding sway, though we have seen the EPS grow support for the blocking over recent runs.

I think they are well-regarded for tropical forecasting Thank goodness it's day 10! Though all models seem to be singing from the same hymn sheet this morning. Still think we may see changes to the wavelengths around Xmas due to tropical forcing / changes over the NE Pacific.

Desperate times when we start wheeling out the JMA, though I suppose that model has more cred than NOGAPS. The short to medium range we will just have to make the most out of the potential for increasingly colder/drier surface air arriving from near continent late week and next weekend as still advertised by 18z GFS, with return of frosty nights. But there are increasing signs we may see sufficient changes in the upper flow around Xmas to perhaps bring something more interesting ...

With the potential for the trop PV retreating west over Canada because of the +EPO / break down of Aleutian high I mentioned in my last post, certainly feasible for a high to the west as per 18z GFS FI, though equally the high may ridge north over or east of the UK, depending how the wavelengths adjust.

The NOAA prognostic 8-14 day 500mb HGHTS/anomalies bears some resemblance to the 11-15 day 00z EPS 500mb mean below. They both actually advertise a pattern change from day 10 with the removal of the ridge over the Aleutains and replacing it with lower heights and a trough over the Gulf of Alaska and Western Canada (+EPO) - so we actually see the deep cold over northern U.S. and eastern Canada retreat west and a SE ridge develop. This *may* relax the jet downstream over the Atlantic heading NE to allow the Euro high to ridge further north. But we still need more energy/troughing to undercut over SW / S Europe - aka -NAO, something that seems to be increasingly hard to attain in winters these days. But the fact that there is this pattern change upstream indicated, not just by EPS, but GEFS too, plus tropical forcing is pretty active over the maritime continent (SE Asia) despite the incoherent and conflicting MJO forecasts from many models, there is a glimmer of hope that we may see changes later in the month to shake up the stagnant pattern.

View the full blog here

Don't envy you and Tony trying to fathom out how the winter may pan out, as there seems to be a lot of conflicting signals. A weaker than average PV to start winter but is increasing in strength, but even so, there is the question of whether there is a disconnect between the strat and trop atm. The lobe of the PV shifting into Canada and cranking up the jet may not have been easily foreseen back in late November either. The persistence of deep cold over N America over the coming days really has the writing on the wall for our fortunes, so not surprised you have the hunch that the EC/EPS maybe calling correct on a mobile run up to Xmas. And if so, this does really question the credibility of those EC monthly runs with the +ve anomalies to the NE it has shown recently. I'm torn between whether I like the idea of the zonal train taking over, as from a cold and snow potential it favours the north. But the Atlantic storms with their wind, rain and cold and potentially wintry Pm flows would provide more interest for us forecasters to write about compared to the quiet and unexciting anticyclonic conditions close to the east proffered by 00z GFS/GEFS. Though, with the high close to the east or over the UK, there is potential, if the flow buckles and splits with more energy going to southern Europe, that the high may build N and NE across Scandi in a more sustained fashion. But the current upper pattern doesn't favour this outcome in the coming 10 days at least. Would need some increased tropical forcing, i.e. MJO through 7-8-1. to change the upper pattern, but any favourable movement would not impact the upper pattern for us until later in the month anyway. For now the deep cold over N America and the strong jet it drives NE over the Atlantic is dictating our destiny for now.

06z GFS says NO to blocking ... picking up the EC trend our just a rogue progressive run out of the other members?

Despite the progressive pattern painted by the majority EPS members as tweeted by Matt, 00z GEFS still going for a blocked signal, I count 15 out 20 members with anticyclonic synoptics over UK at day 10 Christmas Day now on GFS, and still half of the GEFS members look blocked to me on the 25th F Jury's still out for me on where we are headed toward Xmas given the ECMWF progressive vs GFS more blocked ... though can't see any deep cold coming anywhere near the UK unless some big pattern changes occur ... more likely a chance of a chilly continental feed with high pressure close to the east or NE.

... but unless there is a strong upper flow undercutting that ridge over Scandi ... that high is only ever going to sink south I'm afraid. Too much energy heading NE over the Atlantic due to the steep temp gradient over far north Atlantic beneath the deep cold over NE Canada and Greenland. Really need to weaken or retrograde the deep cold pool upstream over Canada to have a fighting chance of keeping a ridge to our NE.

Hmm, H500 pattern ain't ever gonna look like that by mid month! Pinch of salt needed for the weeklies?

Perhaps veering slightly off topic, and not one for pattern matching, but December 2005 bears some similarities as per GFS in that it was quite an anticyclonic and dry month, November that year was colder than average like this year, both now and then weak Nina to neutral ENSO. But December 2005 had a snowy spell in the east to end the month via a Scandi high - despite the run up to Xmas that year having low pressure to the NW and the Euro slug high in place ...

Could be one of the driest Decembers on record if recent GFS runs came off. EC46 weeklies out and it goes for +ve anomaly to the NE and E and -ve anomaly to the west for week 3, more expansive +ve anomaly to the NE week 4 over Scandi. Must admit, not knowing how well they verify at such long lead times, not sure I have a great deal of faith in them yet.