snowking

I suspect that's down to Mr. Blob on the radar heading in from the West - just waiting patiently for that to get across to here too.

Having just received this from my folks, very much regretting not heading back to Essex for a 'surprise visit' last night

Yep back to mostly snow again here now, I think the Thames must be acting as the cut off point - looks as though the pivot is now in full force judging by the radar too so hopefully we are all good from here on in

Yep sadly back to sleet in Greenwich too I should have gone and stayed with my parents last night in Essex where it is still snow and a decent covering

Bigger and bigger flakes, starting to turn white outside Need to learn to touch-type, its difficult to look out the window and type at the same time...

It's finally turned to snow in Greenwich

Hopefully so. You can see that the home counties have hit the jackpot in terms of closest to the thermal boundary without spilling just over the 0c mark. Markedly higher dew points south of the M25 - hopefully we see these start to creep down again in the next couple of hours

Wet on the ground....but starting to turn here in Greenwich with plenty of flakes mixed in with the rain. and that's at pretty much sea level

Wow. They really word it as 'Yellow Snow' now do they Think I might give going outside in that a miss to be honest

Here's a link for the bookmarks for tomorrow: http://www.meteociel.fr/observations-meteo/point-de-rosee.php Shows the observed dew points in map format - should help with monitoring where the likely rain/snow boundary will lay

Good to speak to you again! Hope all is well with you I'm actually primarily based in Greenwich now - but hoping you guys get something nice and picturesque tomorrow. I'm not expecting all that much here sadly, I should have gone back and visited my folks this weekend!

Looks much more akin to the 12z EC det. Tom, lovely stuff

36 of the 51 EPS members have a very similar track to the ECMWF det., with the snowline for this region really bordering somewhere around the London area. About 12 have it even further south, and the remainder take a more northerly track That seems like fairly good confidence for now, but there might still be some tentative shifts either way

Sounds as though the Met Office are starting to smell the southward shift in modelling. Over to Nick for the 18z UKV then...

I am assuming this is the UKV: Looks a tad further north of the ECMWF and more in line with the EURO 4 - so the rain/snow boundary just to the North of London Just look out the window tomorrow folks....

Yes that's the det. run as shown over on Weather.us

Well then, what do we have here: ECMWF with a similar southward shift

Good to know UKV is on that trend too. I think most in here are hoping for the miraculous and for the models to have been too far north with this all along, but at this range it's a real long shot. Hopefully we can start getting a look at WV imagery later this evening and see how it looks latitudinally vs model output

What a nightmare to forecast!

Right so we have two very tricky situations to deal with then Sunday The overnight EPS have trended just a little further south with this - it is so unusual to be using ensemble suites to try and determine what might play out here but given the entropy shown in deterministic modelling at present, it's about our best guide. I suspect that when we see the updated warnings, the yellow area will have shifted southwards somewhat. Both the det and control runs of the ECMWF have pretty much the same boundary and this has shift about 15-20 miles South of the M4 now. Not exactly a huge difference but certainly a little further south than some of yesterday's runs might have suggested. Monday Basically, just look out of a window. Still a real 50/50 split in the ensembles as to whether we see wide scale snow across our region - I think we need to wait for this to start coming into range of the EURO4/UKV because the dynamics at play here are so finely balanced - evaporative cooling is likely to play a huge role and I do think there is the potential for some widespread disruption if we end up just teetering over the edge of the correct thermal profile to allow for snow to fall. In fact, to quote the Essex Weather Centre from yesterday: MONDAY: This has the potential of crippling transport networks across London + SE depending on exact track of the low. Latest data and guidance suggests a rain to snow event for Essex. Keep an eye on @MetOffice warnings over the weekend on this one #BePrepared Edit: In fact, in terms of odds, 40 out of the 51 EPS members have noticeable snowfall (2cms or greater) by 9pm on Monday south of the Thames - so a roughly 80% chance. For those in East Anglia, by the end of Sunday almost all of the runs have some snow on the ground.

It's the later (UKV) - although it's chief forecaster modified fields which are shown rather than the raw UKV output I believe

^^ The same scenario that 29 of the EPS members were keen on last night too You have to feel for forecasters right now. If Mondays low does take that track its even more of a headache trying to work out the rain/snow boundary given the incredibly marginal dew points wrapping back around the low

For the South-East contingent - the ECM Control has an almost identical secondary snowfall event via that channel low for Monday Morning (this stretches up into East Anglia too). In fact, by my counting 29 of the 51 members produce some significant snowfall across southern counties (primarily CS & SE England) from that secondary feature around Monday morning. The EPS overall still hugely varying on the snowfall line for Sunday, but the consensus remains M4 - M62 for the heaviest falls.

Yeah that's a fair point and I think in all the years this thread has been going we have mostly talked about coupling in the context of stratospheric influence on the troposphere (probably because that's what we've mostly been interested in) - so perhaps we need to start talking in terms of ascending and descending 'coupling'