Nick F

If you look at the high res Arpege model, it pulls the precip along the occlusion/trough over Benelux over the SE tonight/Saturday morning

Look at the Dutch radar, band of precip looks healthy which is contrary to the MetO / Netweather radar http://www.noodweercentrale.nl/en/weather/radar.html

Can see the arc of precip pushing NW out of Benelux this evening on the radar link below: http://www.meteo-info.be/en/weather/radar.html The fax chart shows the occluded front bringing the arc of sleet and snow towards SE UK this evening Some light flurries of snow on and off all afternoon and evening here in Croydon, never getting heavy enough to settle.

A sneaky cold shot from the arctic for northern areas next Friday on 12z GFS, but high chance it would get shut off by the low crossing the Atlantic to the west before it reaches Scotland, 12z UKMO looks less inclined to develop a cold N or NWly over the UK. I guess all will depend on how quickly those winter storms over NE N America move out into the Atlantic, together with a strengthening jet streak. Before then, the Atlantic is pretty weak.

It's been a damp squib so far, as we do have a pool of dew points >1C across the SE of England this morning, while they are below 0C up north so why they are getting snow rather than slizzle But, there is a drier flow with DPs below 0C upstream over Holland heading our way So by mid afternoon dew points are below freezing again ECMWF showing some light snowfall for our area early Saturday morning as a trough arrives off the North Sea But after Saturday morning, looks like the higher dew points of 1-2C return, so any showers turning back to rain

2C, grey, raw breeze and some small flakes fluttering around here in West London

Yes I did read GP's post suggesting the RMM plots maybe too slow with the MJO propagation which may make sense why the block is on the move so much and why we are seeing a quick development of a Greenland ridge when the RMM plots would infer this happens too soon. Certainly the MJO is no guarantee of getting the block to stay in the right place for long enough, especially if it's progressing east quickly toward the Indian Ocean, much rather we saw the stratosphere having a helping hand with a PV split more likely to bring sustained HLB. Still, I remain open-minded for the 2nd half of February, the Atlantiic jet is looking rather weak and wavering from next week, so chance that the deep cold pool vortex dropping down toward Scandi could shift further south than models indicate. Just don't want that PV to the NE to dig too far SW and join with low heights/troughing to west of UK / western Europe.

Hmmm, abundant precipitation heading west on Saturday on 18z GFS T850s and partial (850-1000mb) thickness look good, need thickness of <129 gpdm But the dew points look rather marginal for some and mean the difference of rain, sleet or snow. But as ever with snow forecasting, we won't know whether surface conditions are ok for snow over one particular area or not until much nearer, literally now casting for some, with such marginality. Though suspect east coast would sleet/rain.

But if the Greenland high carries on retrogressing into Canada we could end up with troughing between it and us as troughing over Azores links with trough dropping down over NE Europe, see my post above, don't want the ridge to retrogress too far basically ...

Problem is that's a west-based -NAO look as has been advertised by recent ops and ensemble means in the 6-10 range, and we are the wrong side of the -NAO trough. The progression from there in the extended EPS mean is to merge the -NOA mean trough with the trough dropping down over Scandi - just hope that's the wrong signal, because that would indicate a return to zonality!

First post of evening focusing on models other than GFS for the next few days, scattered light sleet and snow showers towards eastern parts Thursday and Friday. But perhaps snow showers pepping up and moving inland across E England Friday night and spreading well inland toward the west on Saturday as upper low on near continent and troughing in surface isobars increases lift looking at 12z UKMET-G 500mb vorticity 12z EC similar Friday night shouldn't be a problem for snow to lower elevations but during Saturday dew points becoming marginal, so could be a messy mix of sleet and snow inland and probably rain on the east coast.

IMO seems to be a theme in the GFS in particular today, as played out by the 12z GEFS z500 and now 18z GFS, to go from an east based -NAO on to develop a west-based -NAO with time? We start off with Iceland/Greeny height rises in next 7 days as east coast trough amplifies flow downstream, with increasingly -ve NAO, but strengthening southern stream over N America may pull back west the troughing over SW Europe too. Not ideal, just have to hope the trop PV can drop down into Scandi quickly like EC high res day 10, certainly supported further by 10-15 day 12z EPS z500

Tomasz Schafernaker not particularly excited by the upcoming cold 'snap' other than some flurries, so lets see if we can be more enthusiastic than Tom re: snowfall? T+72 fax chart shows a developing 'warm' front moving west from N Germany and Denmark toward the UK, IMO this marks a plume of moisture, rather than warmth in the literal sense, being drawn NW out of central Europe and, with lift from the 500mb trough and surface low moving east over the N Sea will probably enhance snow showers Friday PM and Friday night into Saturday morning t+72 fax and PWAT (Precipitable Water) A look at forecast skew t for Essex Friday PM shows increase in moisture in lower layer (more snowfall) between T+72 and T+82 i.e. where dew point line (left) is merged with temp line (right) the air is saturated ... notice thicker layer of moisture at T+84 between 950 and 800 hPa. This fairly representative for eastern coastal counties of England T850s down to -11C across England Friday night and not often we see partial thicknesses (850-1000hPa) 127 gpdm 500mb trough providing plenty of lift Friday night So looks like there is the dynmaincs there to pep the snow showers Friday night and probably through Saturday too as that trough and increased moisture moves in.

00z GFS/GEFS still keen to keen to retrogress the Scandi block over to our NW in day 10-15 period, while keeping low heights over SW Europe and dropping low heights down across Scandi - which may lead to to a northerly down the line. Yesterday's EPS z500 mean hinted at this idea too, though less strong signal, certainly this morning's 00z EC high res not keen on this idea, so maybe another outlier from its members. Although we see the transfer of +ve height anomalies west to the NW with time on ENS guidance, there is fairly good agreement on the surface high over Scandi sinking south in the medium range, which will cut-off the deep cold advection from Russia, but we are still left with a chilly SEly flow until at least Thursday next week on 00z GFS op, when it turns 2m temps into double figures across the far south. I think the main reason why we are not seeing the easterly sustain is because there is no jet, of any strength, returning SW across northern Europe beneath the Scandi blocking high to maintain low heights over central Europe and prevent the block sinking. Looking at the strat forecasts, both ECM and GFS seem keen for a displacement toward Scandi/NW Russia by day 10, rather than a split as was advertised by GFS a few times recently, if there is a connect between the strat PV and trop, then that maybe why we are seeing the blocking retogress towards Greenland in the means and trop PV dropping toward Scandi longer term. We also have the MJO phase 7/81 amplification working through around 15-18th - which will probably aid in the next trop displacement after its brief rebound toward the pole/Greenland and the MJO will help maintain high latitude blocking from mid-month, perhaps most likely to our NW? Shorter term, I think Thursday-Friday we will see some snow flurries in the E/SEly flow, perhaps light snow showers towards east coast, Saturday looks like best chance of moderate to perhaps locally heavy snow showers along east coast, as a trough develops in the isobars to the east over N Sea and upper cold pool moves west and enhances lift.

Doesn't look overly exciting from a snowfall perspective late week and the weekend once the sub 0C dew points set in, probably grey for many with some flakes blowing around in the raw breeze. Though 00z EC does show a trough in the isobars / perhaps a front too bringing a more organised band of light/moderate snow to S England and S Wales early Sunday morning - BUT likely to change this far off Could get some ice days out of the initial cold surge, Thursday and Friday most likely looking at 00z GFS 2m temps, perhaps slightly less cold air drawn in from SE after that for the weekend.

GFS again has the best evolution compared to ECMWF that's keen to sink the high by day 10. Surprised ECM is flip-flopping so much with the positioning of the block, given normally it's the most stable model and verifies better most the time in the medium range. Given both GFS and ECM both take the MJO on a similar amplitude and timing through 7 and 8 - odd why the ECM is so keen to sink the high so hastily with energy going over the top rather than under as would be expected with these particular phases, though could be the lag time after reaching the phases. Can only think that it is because the sPV is forecast to rebound back to the pole after its displacement. The GFS is still going for a sPV split from day 10ish, so perhaps that's why we are seeing more HLBing rather MLBing from its recent extended outputs. Therefore, really difficult IMO to make any assumptions over where the block will go past day 7, though my gut feeling is GFS is more likely then EC, not because it'S what I want to see, but the state of the strat and MJO supports it.

Atlantic in charge to start the week, but high pressure expanding over Scandinavia will introduce much colder conditions from the east by Thursday. View the full blog here

Have to factor in that the weather is always evolving, so inevitably sometimes new data fed into each new model run may improve/expand the depth of cold advecting west that may make last run obsolete for same sector, good to see the deeper cold expanded further south on the 06z GFS. Small steps at such an early stage suggests that detail is FI at and early timeframe!

The sinking of the Scandi high in the means on the extended EPS increases the doubt that we can achieve a reload with a clean and deep cold easterly in the days 10-15 period, best on offer is several days of cold and dry surface flow off the near continent, though how cold will depend on how cold it gets on near continent, maybe squeeze a few ice days with cloud cover and also chance of some snow flurries. Deep cold and convective easterly flow looks like a pipe dream for now. Of course the EPS z500 mean maybe hiding some colder more easterly clusters that we can't see that may still come to fruition, but consider it a low probability for now unless new data swings the high res & ensembles in a better direction.

Depends what model and time frames you look at, winds seem to swing between easterly and southeasterly, don't be fooled by the pressure contours, as winds tend not to always blow parrallel to them either. Either way, both cold directions - SEly has advantage of shorter sea track if near continent is cold, though greater risk of less cold air mixing in from S Europe. But it's also looking dry from either direction bar some flurries, without deep cold pool moving west or Atlantic fronts pushing up against the cold and dry air.

At least the 12 EC high res stays tight to the mean to day 10, as the run brings in a colder easterly flow at day 10 whilst the GFS op (blue) perhaps warming it up too much with the greater Atlantic influence. The moral of the story is the GFS can often be too progressive at sinking blocks to the NE shutting down the cold flow and introducing the Atlantic cyclonic SWly flow. 18z backtrack to more blocked now. Plenty of mileage out of the block and cold air advection west over coming days I think ...

Although the surface pressure pattern on 18z GFS is not ideal for best cold air advection, upper block still there over Scandi up to day 12 and generally blocked way out to the end of the run. MJO getting stuck in cold phases 8/1 could mean we stay blocked and cold for much of Feb IMO, with plenty of time for a colder easterly to evolve mid-month onwards.

Can get T850s in 12hr increments up to T+120 here: http://www.3bmeteo.com/carte-meteo/ukmo_europa_3b_12.php Not a bad UKMO, with better orientation of the high, better than GFS anyhow. EDIT, still yesterday's

I wouldn't be too hung up over how cold the uppers are, GFS predicts the surface easterly will be cold and dry with dew points generally at or below 0C, which will support light snow flurries even across southern UK later next week. Where the cold is deeper towards the NE the pressure/heights are higher anyway, so any ppn looks light and confined to coasts. The NWP depiction of the upcoming cold spell, so far, has never looked like showing a big snow event. Bit dubious the Atlantic will coming rolling back in as quick as the GFS consistently shows next weekend, often the model is too progressive in this respect, particularly with such an established and strong block as shown mid-week, surely it can't be broken down so quickly?

Interesting on the 18z how the deep cold pool becomes trapped beneath a flabby high inversion with little impetus to move it! If and when the Atlantic comes in, it does eventually on 18z but probably too progressive, it would take some budging.