Nick F

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.

And there was a westerly QBO that winter as now too. 18z GFS op, only thing of note so far is that the high close enough to east later next week to allow a continental flow bringing slightly chillier conditions towards the east - maxes of 6-7C across eastern England next Thursday

Yep, we're reaching rock bottom with the 12 EC det. this evening, the EC/EPS MJO forecasts pretty incoherent today as well. EC46 may offer light at at the end of the tunnel later ... question is will GFS/GEFS give up the blocked signal or will EC move away from its more zonal outlook. At least there are these differences between the 2 models that hint at uncertainty from the medium range.

Hadn't noticed the new trend of the ens to move out of COD into phase 8, but thanks for highlighting this positive step in the right direction to perhaps shake up the wave patterns later this month to encourage more HLBs again. Still some uncertainties in the tropics, so not holding my breath until we see some solid changes in the NWP.

Slightly envious of my Greek colleague going home for Xmas by the time this happens for SE Europe with regards to the Scandi high, there's only one way that's going with most of the jet energy going over the top, though the upside is that we may see a chillier continental flow tail end of next week as the high to the NE sinks south. with the low heights expanding in the polar regions to our N and NW, it will always be a struggle to sustain a ridge over Nern Europe when there's a split flow, unless there is more energy undercutting the ridge over SW Europe and less in the northern arm.

I think there is a enough uncertainty and spread beyond day 7, not just from the GEFS members, but also the EPS members too, to calm the worries that mild SWlys are here for the long haul. Though not totally discount the worries either. The uncertainty seems to stem with how the models modulate deep cold trop vortices dropping down over Canada and Nern U.S. over the next 10 days and consequently how they handle amplification downstream of these vortices over the N Atlantic. One these vortices drops SE over E Canada next 24hrs - introducing cold continental arctic air south across much of northern, central and western U.S. But it's another, much deeper and colder vortex modelled to drop SE then E over Canada next week which could be causing GFS and EC op differences downstream to the upper flow. 00z ECM det. pulled this vortex E out into the NW Atlantic - flattening the flow, whereas 00z and 06z GFS swing the vortex NE toward Labrador Strait and Greenland, amplifying the flow more downstream over the N Atlantic. Just look at the 500mb vortices over N America heading toward NW Atlantic on 00z EC, and you might see what I mean Against the unfavourable background of weak MJO signal, low AAM, wQBO and deep cold over northern N America driving a strong and zonal jet stream, there does appear to be enough volatility to create some amplification downstream over N Atlantic/Europe ... just a case of whether these ridges will set up favourably to advect colder conditions back to us. There are, at least, favourable hints of cross polar ridging appearing on the models later on too - which could help lower the AO index.

The chart you posted on the left is up to 336hrs (week 2) and the right after 336hrs (week 3) though? Nevertheless week 3 does hint at a southerly tracking jet I guess ...

I don't think you can really infer any likely temperature range for the UK from the chart as it is 500mb height anomalies over a week, though it does suggest NW to SE axis to movement of troughing and weather systems, perhaps, rather than SW to NE as is case next few weeks.

That's the problem, too much zonality ploughing deep into NE Europe in next week to two weeks and then there maybe little deep cold to tap into when the synoptics could become favourable aka week 3 from the EPS. Anyway, there's still a weak flame left in the EPS long range to warm the optimism for the rest of the month.

Wrt to EC46 (weeklies), not completely out, but this is week 3 as a teaser ... H500 +anomalies to the NE this time

GFS getting a complete overhaul in a few years to morph into NGGPS http://www.noaa.gov/media-release/noaa-to-develop-new-global-weather-model

Really is going take something not well-modelled by the ops to change the pattern more favourably, like you say warming/+ve heights working down from the stratosphere. However, the MJO for a while is not looking favourable for sustained trop blocking in our locale, plus the upcoming deep and intense cold sweeping N America will only serve to stoke the fire of the PFJ downstream towards the U.K. Not really surprised the ops are churning out the mundane mobile Atlantic charts with unfavourable MJO, low AAM and slightly strengthening wQBO working against HLB ... for now. maybe the EC46 will give some relief from the op monotony later.

Looks like the wQBO has increased in strength from November's values with +14.16 on CPC, kind of to be expected I guess in early winter though but will surely help strengthen the PV. http://www.cpc.ncep.noaa.gov/data/indices/qbo.u30.index

With the jet going east under the Scandi high and N then E and SE over the top, you never really going to get deep cold to advect west under it, ideally warnt the jet to be moving SW under the Scandi ridge.

PV kind looks to elongate towards Wern Canada rather than wholesale move there, with the otherside still pushing a trough into NE Europe/Russia.

So, 12z GFS op offers us the tease of a Scandi High as the jet splits invof UK/NW Europe, but because of the strengthening jet upstream coming out of N America, the high gets pushed east too quickly to be of much use for us. However, the ops may not have the amplification ahead of deep storm coming out of NE Canada correct, nor speed or direction of the storm ... this could have consequences on how ridging downstream near/over UK evolves IMO.

00z GEFS H500 and anomalies go from this at T+240 to this at T+360 ... could be be worse

Sound advice from Matt to just sit back and see if any solid trends develop in the medium to long range which has been volatile of late, with the anomalies on the 11-15 day EPS and EC46 shifting with each run or generally just a weak/tenuous rather than a strong signal. In the short-to-medium range, fair few GEFS members supporting the 00z EC det idea of trough disruption over mid or east Atlantic, probably because of the deep cold vortex dropping SE over N America later next week causing some amplification downstream, throwing a ridge N towards Iceland/NE Atlantic, followed by a more southerly tracking jet across the Atlantic as the jet flattens out behind the wave. Maybe a trend to watch out for over coming runs ...

I know yesterday I cautioned about posting premium EC charts from subscriptions, there is some EPS available freely if you know where to look, this is the week 3 from the EC46 updated yesterday from an Icelandic Weather Service page and shows, as bluearmy and GP have indicated, +height anomalies to the W and NW. Though looking at the 00z operational GFS - a long way off getting anything like that kind of anomaly going on ... is a change from the last EC46 - which had +ve HGT anomalies more over the Norwegian Sea and Iceland around similar time scale.

High pressure likely to remain in control until the middle of next week, when milder, windier and more unsettled weather looks to return from the Atlantic. How long will the milder weather last? Read this blog View the full blog here