Nick F

Storm Doris, the fourth-named storm since beginning of last Autumn will cross northern UK on Thursday, bringing damaging 60-80mph wind gusts to central parts and snow to Scotland and higher ground of northern England View the full blog here

IMO we are beginning to see the models finally latch on to the upper flow amplification effects of MJO passing through P8-1 ... having passed through P8 at an unusually high amplitude. Also the troposphere will eventually start to reflect what's happening in the stratosphere too end of month and early March, i.e. a warming at the pole and displacement of the sPV across Scandinavia and NW Russia So it's inconceivable that there won't be extra-tropical impacts from both the lagged colder 8-1 phases of MJO and the stratospheric downwelling. The typical MJO lag is about 10 days, so P8-1 impacts in a window from 28th Feb/1st March through into the first week of March + the tropospheric upper flow pattern beginning to reflect the stratosphere too. What looks most likely, looking at medium range and extended EPS and GEFS is height rises near or just east of Greenland while the Candian trop PV sinks south and the jet + trop troughing sinks south over the Atlantic. So we are likely to see increased chance of colder air leaking south then perhaps eventually SW across the UK from high latitudes as we enter early March. Obviously, this could go wrong for the south, with the low pressure systems perhaps not tracking far enough south - which means the cold air stays over northern UK while the south stays mild. But a lot of water to go under the bridge until we can firm up on this IMO likely pattern change away from low heights dominating to our north like now. But, don't think today's temps reaching 17-18C in the southeast marks the end for deep cold and snow potential this season ... yet. Remember, the models guidance for the trop can often play catch up with what the MJO and stratosphere precursors are indicating ...

Spring on Monday, with mid-teens over Midlands and E England ... to winter next Friday, as a N/NWly flow brings temps struggling to get higher than low single figures Midlands north. 00z EPS z500 mean indicating support for the brief N-NWly end of next week, as upper flow amplification moves out of NE N America downstream over N Atlantic. Unfortunately, good agreement, the flow switches back to SWly thereafter, as a trough digs SE from N Canada out into the NW Atlantic

There is typically a lag time of around 10 days for an MJO-induced Rossby Wave to reach high latitudes (Hoskins, B. J., and D. J. Karoly, 1981: The steady-state linear response of a spherical atmosphere to thermal and orographic forcing. J. Atmos. Sci., 38, 1175–1196) - phases 8 more favourable than 7 for UK so like you say around the 25th, but not because of the subsequent return to phase 7 shown on the GEFS, but from the current phase movement through 8 and 1. The GFS forecast for it move back into phase 7 around the 24th may not have an impact until into early March. For example, MJO went into phase 7 on the 9th Feb, 10 days on from then we can compare the phase 7 composite for amplitude >1 with the forecast GEFS z500 mean for the 19th Feb, not too dissimilar upstream other then the lower heights downstream over Scandi Feb MJO composite for phase 8 with amplitude >1 (below), 10 days from current phase movement into 8, takes us to around the 25th, IMO movement from 8 into 1 more favourable than 7 into 8, but obviously MJO propagation in 8/1 and the resultant increased amplification of Rossby waves into higher latitudes does not automatically = blocked/cold/snow for us unfortunately, as more mesoscale changes in the atmosphere can ruin prospects. However, we do also have the wave number 1 warming helping to displace the sPV over toward NW Russia / northern Scandi after its current return to northern Greenland / N Pole area. This appears to have the immediate response of increasing the 500mb zonal flow over far N Atlantic into Scandi, but with time height rises / amplification transferring east over N America under a stratospheric high developing and moving east towards Greenland may allow height rises over N Atlantic and perhaps into Greenland to end the month. Of course, I could be completely wrong, the atmospheric patterns don't always follow the historic composites of oscillations and/or there is disconnect between the trop and the strat. But I think there is some positive indications from both the MJO movements and next sPV displacement to give tentative signs of winter returning at the end of this month and into early March. Not ideal, as snow tends not hang around as long as Dec-Jan, but don't be fooled by the warm up and early Spring feel over the next 10 days or so.

Another winter storm about to hit New England, from summer heat back to winter chill in the southern U.S. High Plains and the Australian heatwave. View the full blog here

Both GFS and ECM displace the sPV back to NW Russia/northern Scandi by around T+120, currently its centred over N Greenland/ N Pole. If you remember last time this happened in late January we saw the zonal flow in the troposphere strengthen over the Atlantic, with the NWP churning out zonal charts out to day 15, something similar at the moment it looks too. But IMO we could eventually see mid-Atlantic ridging building north as the core of the trop PV moves over Svalbard and Norway while more amplification works downstream, certainly at day 10 the flow is looking more amplified over N America on 12z EC.

Moderate fall of big fat fluffy flakes in SE25, but struggling to settle, pffft

Quite an impressive area of precip moving into E Anglia and earmarked for Thames Estuary, hopefully it doesn't turn too marginal when it arrives in London area - dew points holding out for now.

Chucking it down with a fine snow here near Croydon, settling on cars and fences and now trying to on grass but not roads/pavement. Not sure we will even reach a Kentimetre though.

Yes, coldies better not look at the 18z GFS for next weekend, really is a horror show with a SWly flow sourced all the way the other side of the Azores with +10C T850s above the UK.next Sunday. Though it does redeem itself in FI. Is rather at odds with the 12z ECM for noon on Sunday 19th, which has an prominent upper low still over Iberia. 12z EC for 12z Sun 19/02 18z GFS for 12z Sun 19/02 On the 12z EC and GFS operational runs we saw differences between the two models on how quickly they exit the upper low over NE N America and also trough disruption SE towards Iberia in the 8-10 day range So certainly the models are not unanimous with the upper flow pattern in a weeks time over the Atlantic or even with to the north - with regards to how far down the low heights extend from the trop PV over the arctic.

Getting a measly dusting now on cars and grass here in sarf London, keeps up might even be enough to make a snowball in the morning.

Hope it's still snow by then

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.