beng

What stood out for me from those stats is that where the cold pool was over the country for >1 day, snowfall totals were extremely high.

This is probably a complete ramp & it remains to see whether it's a valid one or not, but looking back at the Feb 1991 event and comparing to what's currently modeled for next week, the coming event looks considerably more severe in terms of snowfalls. I remember in Reigate that the snow didn't set in until 5-6 pm on Wednesday 7th. My local school was open the next morning (so depths can't have been massive by 9am Thursday), but it closed Lunchtime and that was it until after half term! I seem to recall that it then snowed most of the day Thursday and into the early hours Friday (became light on the Friday and gradually petered out). The area had about 9 inches of snow once it stopped; we probably had ~48 hours of falling snow, with 24 hours at peak intensity. A rough guess would be that this time around we're possibly looking at 72 (maybe a bit more) hours of snow (Tues-Fri) - with 48 hours peak intensity - so if we're 'lucky' then my area may be looking at 12 inches of snow - depending upon the exact wind direction etc. That said, the lake effect snow streamers may behave slightly differently to Jan 87, Feb 91 and Dec 2010 (all delivered 9 inches plus here - more on the downs above the town); the reason I say that, is because during Dec-Feb, surface conditions inland are obviously a bit colder than we'll get next week, due to the longer nights. The slightly warmer land temps this time will increase the temperature differential in land between the surface and streamer systems in the atmosphere relative to 87/91. I would 'guess' the impact of that will be that the streamers may maintain a higher intensity further inland - so snowfall amounts/hour may be higher that we saw back in 87/91/2010 etc. What I'm not sure on is what the North Sea temps were in 87 and 91 - possibly slightly higher so that might negate things to some extent. Would be great if some of the more knowledgeable convection experts could say whether I'm barking up the wrong tree with regards the streamers and the impact slightly warmer inland surface conditions may have.

That's probably a reasonable approximation of where the deepest snow will end up by the end of the week, just think we might in reality need to multiply the amounts by 3 based on the convection that will ultimately occur with the forecast temps.

Even if Fridays low stays further South, the wind direction should in that scenario remain more North of East which ought to continue the streamers for a bit longer instead. :-)

Bring back the magnetic weather charts and snow symbols that used to go over the top of the sunshine ones

It really depends on your location and the wind direction. Down here Nov/Dec 2010 delivered close on a foot with an ENE wind (similar in 91 and 87 - more on the downs). You probably need the wind more NE I would imagine. Right now, it's still too early to say what the exact wind direction will be and who will get the most snow, although we can say places like Kent are obviously favoured since they have more margin for error with the wind direction.

Speaking for my own area - Reigate Surrey, we need an ENE wind - from experience typically we could then expect 4-6 inches per day (maybe more on the downs). SE wind won't deliver convective snow here (hopefully GFS is wrong as it edges the wind SE fairly quickly) - If the wind veers more NE, then it becomes a bit hit and miss here - less convective showers, but troughs can swing in and drop a few inches. Of course in 2009, the ENE wind flow delivered a super streamer with some places North and West of here getting > 1 foot in a single night - so it'll be very much a now-cast in the end.

Ignoring the detail since that'll change, I think the idea a system droping down from the North after the Easterly is quite plausible.

If that sinks South, could draw in some deeper cold again from the East. Great ECM, hopefully UKMO is further South due to its slight bias in under doing low pressure systems, meaning less trouging beneath the high to support a higher latitude. GFS looks a bit messy and out of sorts with its own ensembles.

I agree (and I'm based in the SE) - if the UKMO went any further South and was accurate, no one would be seeing any snow. A bit further north would give more margin for error so that's what we should hope for - but of course sadly, we can't control it. We possibly need more short waves to form in the flow on the Southern flank (plus a bit of luck) as that might help prop the high further North.

I'm no fan of the BBC - it's output has become so dumbed down over the years, however on this occasion I think we have to remember that there's a significant cluster in the ECM ensembles that raise pressure over the UK and keep the lowest thicknesses South of the UK. Whilst this cluster currently has no real backing from any of the other models that we see, the Beeb are probably right to wait another day before going too big on the Snow word. Maybe if that cluster is hugely reduced tonight, we might see them become a lot more bullish; on the other hand if the number of members in that cluster suddenly increases, then they're going to be relieved they didn't go all in snow. If they weren't so dumbed down though, they would be giving out percentage risks - e.g. 60% chance of disruptive snowfall next week as things stand etc.

I'm not sure the 'really' cold air ever makes it in cluster 2 (high presumably moves West at a lower latitude across the UK, with lowest thickness kept South of the UK) - has 39% of ensemble members too. Let's hope it's reduced/gone in the 12Z run.

The Atlantic SSTA were absolutely terrible for cold at the beginning of the winter - I posted something in the winter thread during (in Nov or Dec) about them being the polar opposite of Nov 1962 so it's been interesting to watch things play out. Even though we've had no negative NAO, it's been a reasonable winter I in Scotland and the midlands have done okay too - so could have been worse. Crap here though. I think the 'atmosphere' has been better suited for cold this winter than the previous couple, but the Atlantic SSTs have fought that signal all the way. We should be in a much better position (my opinion only) from an Atlantic SST position when we start next winter as the solar minimum begins to take hold and the AMO cools a bit more, although the QBO will then be against us. I think we'll actually get one decent cold shot during Feb - based on the MJO cycle (which I admit is based on a model forecast that could be wrong) and the sheer amount of surface cold over Russia now: - starting 8th-10th Feb is my prediction (similar start point to the 1991 - won't be on the same scale as that one though (probably).

The SST anomalies have become slightly more favourable for cold in W Europe since the beginning on the month IMHO. Waters to our SW have cooled, but remain elevated further West. If anything I'd expect that to increase the changes that the azores ridge may be centred further westwards on average through Feb; that should allow any troughing that occurs to our East a better chance of backing west. Plenty of fuel off the US/Canadian coast for developing deep lows though (as you allude to) so SST by no means perfect.

He did predict it.

Should go through the UK initially and then build to the East or NE (early Feb - hopefully) - if the MJO move goes for us.

This would be consistent with MJO Phase 6 - can we get it beyond that though?

Looks like a few ensemble member from this morning GFS get into Phase 7 - judging by a few developing a block of sorts to the East towards early Feb. By no means big agreement on that from the GEFS though yet. It won't guarantee a Feb 91 repeat obviously - but probably the last chance for most of us in the far south (sorry my back yard!) before the spring (March snows don't deliver in Surrey). If we do get a phase 7->8 transition in early to mid Feb, it might deliver a decent surface pattern though.

I reckon this 240 hours chart from ECM will be along the right lines in terms of the broad pattern. Assuming the MJO forecasts are to be believed we'd be somewhere around phase 6 towards the end of the month - which would favour high pressure developing around the UK - so expect the high to our South to edge northwards after this 240 hour chart. If we then progress into Phase 7/8 - which is quite possible/likely (we did do during previous cycles this winter/last autumn - http://www.bom.gov.au/climate/mjo/) - then there's every chance that this will develop into some kind of Scandi block which then retrogresses - I'm thinking along a similar time frame to Feb 1991 - whether it packs any punch remains to be seen, but this winter may have a final kick to it. http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/foroper.shtml Basically we can forget about January (although it's been decent for some), but February really does like quite promising for now.

oh great With a few tweaks you could develop an Easterly from that, bring on the next weather model wild goose chase...

Who'd be a forecaster. I hope we get some model agreement by tomorrow on this storm (or non storm), don't want another 1987 mess. The trend now seems to be for nothing too bad based on the models moving it South, so let's hope that's correct.

Just reminds me of this storm so much - timing is different with this one peaking overnight, but could be quite something.

I'm going to be a bit negative with regards to us getting lucky here - I'm quite happy though for someone to tell me I'm wrong and why! :-) None of us know for sure how the warming (assuming it happens) will play out for the UK, but I think it's worth having a stab at it based on hopefully logical reasoning. Although there's every chance that we're going to see the vortex take a battering at the end of the month (looks like a great call from Chio!) with the stratosphere playing ball, it's how that diminshed vortex then interacts with the other teleconnections, SSTs, land temps etc that will then produce the surface level synoptics that we see. One thing that has been hurting us all winter (IMHO) are the Atlantic SSTs - with a lot of warmth to our SW and colder than normal waters just South of Greenland. That combination makes it hard to sustain blocking to our NW due to the temperature gradients there. Let's just take the latest GFS output at face value (of course it won't verify exactly like this) - You can see the Arctic playing ball, with the vortex in a bad way, but the Atlantic pattern not really joining in as much as we'd like to give us a sustained block. I suspect that idea is about right, and if we do finally get a decent block, then it will have taken several attempts to lock in - so that may well eat up the first half of Feb. Whatever happens it's fascinating and I'm extremely interested to see how the strat warming plays out and then assuming we get the vortex reduction - am I right about the Atlantic SST hindering its impact in terms of how we'd want for cold?

What about this morning's UKMO output though - decent cold pool in place by t144?

Can someone find me an archive chart similar to this morning's UKMO - with low pressure over Greece and the high over Finland? I just don't remember that really happening - to me it either ends up several hundred miles further east, or more likely (given the trends) the whole pattern should be shifted several hundred miles West, with the low pressure over Italy and the centre of the high Sweden/Norway. UMKO is leading the way probably, but still too progressive at 144h. EDIT, the closest I can find is Jan 31st 2009 Jan 31st 2009