Nick F

Really? Looking cold / below average on the daily GFS T2M anomalies from late next week if I'm not mistaken. OK, a northwesterly flow is certainly not ideal for sustained deep cold and snow away from northern areas, but it's look progressively colder on GFS and EC this morning. 00z ECM shows increasing snow potential by day 8 across Scotland, particularly over hills but perhaps lower down too, also hills of northern England and Wales. Days 9-10 it even shows a snow threat down the eastern side of Britain, with a 1 day strong northerly flow direct from he arctic, though by then good chance it won't verify. Certainly lots of wintry potential from tail end of next week from a NWly and perhaps briefly Nly direction showing, though obviously subject to downgrade this far off.

Would be some nasty conditions over northern hills with that deep low next Friday - blizzards anyone? Thankfully good chance it may not verify. Yet again the Scandi high in FI like the 12z, which maybe linked to the model taking MJO into phase 8 day 11 which amplifies the flow, but as I mentioned earlier, the GFS/GEFS maybe too progressive with the MJO. Snowy E/NEly for east coast?

I was never under the impression that the red/blue lines were denoting mslp, given they are 500mb anomalies. But enough humiliation from the ex MetO duffers, a nasty depression running SE across Scotland next Friday with some cold air tucked in behind. Quite a strong/active jet next week moving in across the Uk, so quite a stormy period we could be entering of the likes we haven't been used too.

Ok, I'm not going to argue as I'm probably being too verbatim re: the anomaly contours, so accept that the flow is probably NWly based on the 500mb contours alone. But back to my original comment, doesn't that the -ve anomaly over Europe and +ve height anomaly over N Atlantic and far south of Greenlalnd suggests something similar to 12z GFS op than 12 EC det?

The N/NEly flow comment was based on the anomaly contour John, OK perhaps a bit optimistic for a NE flow, but the anomalies in my eyes indicate a flow from the N rather NW over the UK. Of course they are a mean anomaly so are a rough guide.to potential mean flow in that period

Certainly some cautious cause for optimism for second half of January, yes we've seen the positive signals from ops and ens for early Jan in late December and got burnt on New Year's Eve, but this time there is growing support from various signals for changes in the status quo of the upper flow. Here's why: The stratosphere is looking interesting in the medium range, with a decrease in zonal flow evident at 10 hPa as has already been posted, and check out the 12z EC stratosphere z500 at 10 hPa: the GEFS and EPS are indicating an eastward propagation of an increasingly active MJO wave into phase 8, GEFS is perhaps being too hasty, hence the amplification over the N Atlantic from day 10/11, whereas the EPS is slower and perhaps why we aren't seeing such amplification yet. AO trending negative in the means on GEFS, also NAO trending neutral to slightly -ve. EPS trending AO slightly -ve, NAO neutral. So those nice looking charts from GFS post day 10 do have some backing from the oscillations, but maybe too quick IMO in bringing in the amplification. Patience required, despite patience wearing thin!

Cheers, thought as much, I suppose the EPS mean will hide possible shifts in the flow to N and NE like you mention, though does highlight the low chance of height rises to the north and northeast which are represented in the 12z GFS op and GEFS mean post day 10.

Not a particularly inspiring EPS mean in the 11-15 day range with the anomalies suggesting a continuation of the 500mb pattern in the 8-10 day of the deterministic with a NWly or Wly flow However, the NOAA CPC 8-14 day indicates support for the 12z GFS, with a flow more N/NE than NW with perhaps the Euro trough eventually cutting off from the upper westerlies. So, some divergence past day 8 GFS v ECM, so be interesting next few runs to see where we are headed. Now I'm ultra cautious since the New Year's Eve fail, I would go for the ECM as the form horse, but with the NOAA 8-14 day amomalies siding more with GFS, not so sure.

Had a spell of heavy rain move through around midday here in south London and still a bit grey after the rain cleared, depressing that despite being in a northerly flow in climatically the coldest time of year, we get 7C and rain.

A lot going against this winter delivering anything other than transient cold snaps delivering anything more than snow over northern hills and perhaps occasionally to lower levels in north. Most importantly, I think, we have a westerly QBO which tends to enhance the strength of the PV, despite being weak back in Nov, it has strengthened considerably and likely IMO to stay like that most of the winter. Also there are some anomalously warm SSTs off the eastern seaboard - which is perhaps enhancing the thermal gradient = stronger jet entrance over eastern NAM. Also, we have a few years until the solar minimum and also the MJO has been rather weak, despite the neutral to La Nina ENSO. I, like others, were easily taken in by the models and the ensembles, when they were showing bitter northerlies and easterlies just before New Year before the plug was cruelly pulled. I put my hands up and should have known to be more cautious, given the background signals that were against such winter nirvana for the UK. Not throwing in the towel for a long while, but really need to see drivers such as MJO, GWO and AAM work in our favour to work against the strong PV to perhaps deliver more in the way of blocking in the right place, but it will be an uphill struggle this month IMO. Perhaps next winter or more likely winter after, when we see the solar minimum arrive and perhaps an easterly QBO phase, we will see better chances for HLB and weaker PV. Though these in between years between the solar mins do seem an uphill struggle to get deep cold over the UK, especially in a wQBO. Perhaps the warming oceans maybe playing their part? As continental interiors still get very cold in winter despite this.

If it's not the Euro slug preventing any sustained deep cold and wintry weather setting in across the UK, the strong Azores ridge is sitting there ready to keep the deep cold at bay too on GFS, a product of the deep 500mb vortex over Greenland/Iceland and strong N Atlantic jet. At least 00z ECM + EPS does retrograde the sub-tropical Atlantic high to the other side of the N Atlantic which keeps the cold NW to SE flow, though with little amplification out to day 10, any sustained wintry weather away from the north seems a pipe dream for now.

06z GFS op ridges NE as the deep Euro trough to our E and NE cuts off from the upper westerlies toward Greenland/Iceland, so we end up with surface high pressure from the Azores linking with surface high pressure over NW Russia. However, IMO Azores ridging NE to link with high pressure over Scandi is never great for sustained and progressively cold E/NE flow - particularly with a strong 500mb vortex close to the NW over Iceland and Greenland, so fairly swiftly the unsettled westerlies return. The Euro trough is a step in the right direction and will direct the upper flow NW to SE keeping us flirting with cold NWlies with the ocassional brief Nly shot, whether the Euro trough will cut-off from the upper westerlies to allow pressure to build NE over the UK is uncertain though ...

No update to the RMM MJO plots today, but be interesting to see tomorrow, if they update, if the ECM gives more amplitude to the MJO wave which is phase 7 by mid-month. This maybe hold the key to why the potential for something a little more amplified and sustained for cold and wintry weather around and from mid-month may hold more sway this time and not just another false-dawn.

Just for fun, Euro weeklies has the southern half of UK with below average temps in week 3 So, retrograding troughs and ridges, GFS keeps throwing out cold scenarios in FI, EPS monthlies/weeklies saying look to the east in a few weeks, just need to move that goalpost to mid-month now

Interesting running the GEFS and EPS z500 mean that they both retrograde the N Pacific ridge into eastern Siberia while replacing it with low heights over Alaska and much of western N America, while downstream we see +ve height anomalies over the Atlantic shift a little west while -ve height anomalies 'grow' west across Europe including UK. We can see this in the 18z GFS operational retrograde the Atlantic high and digging a trough over Europe much further west to bring us a northerly, northeasterly then back to northerly at the end of the run. So, certainly some cautious optimism mid-month onwards that with the troughs and ridges shifting west enough (and with enough amplification) to allow perhaps colder N or NE flows with pressure low enough for wintry precipitation. No guarantees but all is not lost after the New Year model hangover!

Just for fun, this caught my eye on the day 10 EC at 10 hPa, wave number 2 attack and PV split?

Despite the differences in the microscale re: the position of the Atlantic high towards the end of the week/next weekend when the flow re-amplifies,which is causing much angst, in the broadscale its interesting to see how persistent the N Pacific and N Atlantic ridges are in the means from now right through to day 15. This persistence of the ridges and the anticyclonic wave breaking could impact the upper strat too, the 12z EC day 10 strat forecast for 10 hPa suggests a sPV split by wave 2. Already the N Pac and Atlantic ridges are apparent in strat forecast lower down at 150 hPa. With regards to the N Pacific/ E Asia area of interest where the changes appear to have originated, there is a weak La Nina / low AAM base state. Indeed, the most recent NOAA Climate Prediction Centre ENSO analysis (26th Dec) indicated La Nina conditions are present, with negative sea surface temperature (SST) anomalies present across most of the central and eastern equatorial Pacific. Despite the weak La Nina / low AAM base state, atmospheric wave breaking off the eastern Asian continent combined with wave propagation from anomalous tropical convection over the Pacific, as depicted by an MJO wave progressing eastwards on vertical velocity (CHI-200hPa) charts (albeit depicted at low frequency on RMM charts) – is likely behind developing a strong ridge northwards in the dateline area over Alaska and far west of Canada. This in turn amplifies the flow downstream over N America (deep trough) and the north Atlantic (ridge) and Europe (deep trough). Such a wavy configuration of course creates cold arctic air to surge south into the troughs (N America and Europe). The position of these troughs and ridges to me that looks showing little signs of shifting to at least mid-month and perhaps well beyond looking at the extend EPS and GEFS. So don't get too worked up because the second northerly fails on the 12z, because eventually things may work in our favour and we strike lucky at the surface over the next 15 days which show little signs of budging in the upper levels.

Recent NWP model high resolution runs and ensembles indicating increasingly 'blocked' pattern with temperatures falling below average towards mid-January. View the full blog here

Not quite so amplified as the 06z op the flow behind the 2nd northerly developing later next week, but at least we do get the 2nd northerly and it looks decently cold. Now what will the vortex over Labrador/NE Canada do to the upper flow? Looks deeper this run, drum roll ....

Liking the 2nd northerly on 06z GFS, with a deep low down the North Sea helping less modification of a stronger arctic flow, pity it will unlikely verify like that at the surface at that range but overall the upper pattern from the ops and ens continues to support the 2nd northerly

IMO has been and still looking a slim chance of snow falling away from hills of Wales, northern England and Scotland from that precip band along the cold front as it moves south, just don't think there's enough inertia in the surface flow to undercut sufficiently cold and dry air for snow to fall low down. If it moved through overnight, might be better chance at lower levels. Potential for snow to lower levels across N/E Scotland and perhaps NE England from the wintry showers following in the northerly Sunday night into Monday though.

I'm always uber wary of Atlantic troughing undercut of an Atlantic high, as it's been so rare in winters since 2010 and models, particularly ECM, are keen on the idea out at day 10 and beyond before backing off subsequently. However, with the PFJ undercutting the N Pacific block and tracking way south and strong over the U.S.A with deep cold sinking way south there, thus stronger likelihood that the PFJ energy will transfer under the block over the Atlantic than over. But not guaranteed. Hopefully the 12z suite will firm up on this idea or garden and path spring to mind.

Looking at the GEFS z500 mean/anomalies days 7-11 and 11-15, there seems little impetus to push the mean N Atlantic block SE into Europe as per some of the operational runs yesterday, thanks to cold air / low heights draining down from NE Europe into central Europe Stunning 00z EPS mean days 11-15, can't show them, but picture the troughing beginning to undercut near the Azores at day 10 on chart below spreading further east into SW Europe, with a blue band of -ve anomalies from SE of New Foundland all the way east into southern and central Europe beneath +ve HGHT anomaly over Iceland.

If anyone wanted a taste of how good the 12z EPS control was, Joe B has kindly posted a chart on twitter ... now imagine that trough undercutting the Griceland block and you get the picture

Again the GFS operational (18z) is progressive at pushing the N Atlantic block E/SE into western Europe much faster or contrary to GEFS and EPS guidance - which keep the block to the W and NW. Be interesting where tomorrow's operational rollercoaster takes us ...