Altostratus

Cracking winter's day...a decent covering on the ground, some sunshine and frequent heavy snow showers. What's not to like?

Just visiting to say good luck folks. I was lucky enough to be living in SW London during the Feb 2009 event - really magical and stands out as one of my favourite snow memories. If I recall correctly that 'sea effect' event was not modelled too well and the warnings only really came out as it started! Hopefully this one has been underplayed somewhat by the models. Early radar returns starting to shape up nicely...

Decent fall here. Haven't measured but looks like there is around 6 inches or so on the garden table.

Looks like a good 3-4 inches fallen overnight. Good start to the day - fingers crossed for more snow showers today and tomorrow.

First heavy snow of the winter. Settling on all surfaces just now...long may that continue.

Heavy snow here for the last couple of hours. Almost whiteout conditions at times. Looks to be a good few inches additional cover so far. ..

Fingers crossed as the night goes on and the colder air digs in we'll see more and more parts of the city come into the game. Excluding western suburbs I would presume so. Good to see more snow being reported in the region!

Kingswells - still technically a city suburb but right on the city/shire border. Snow getting heavier now and building nicely.

Can confirm a good covering on all surfaces here. Hopefully it stays that way...

Good trend from the GFS within the 120-144hr time period...perilously close to unleashing the beast. If we can squeeze a wedge of high pressure between GL and Scandi the link-up would surely be in the offering. UKMO not so good but room for improvement. As long as that Siberian high lurks in the NE we will always be in with a shout. One to watch over the coming days.

Yes and I can't see the Met changing their outlook either as there are no strong signals for anything just yet. I know certain folk look for trends in the ens but that has proven useless time and time again. The movement of the Siberian high is notoriously difficult to predict, particularly on the northern fringes around the Kara strait locale. Historically, if we can get pressure to build into that territory it is a precursor to a cold shot into Europe. If there is more support for pressure building around Kara and into Svalbard in the next few runs things could get very interesting indeed. Let's not forget the Kettley high saga back in Feb 2001!

Hopefully the GFS is picking up on a trend for that ridge being thrown up to Scandi...interesting...and ties in with the Met outlook.

As has been noted, ECM op looks a bit of an outlier so don't think we should be reading too much into that run. Looking across all models, the picture isn't as bad as some are making out. Plenty of interest being shown on GEFS, GEM ens and a couple of the lesser models. Don't take any run in isolation, particularly given the highly turbulent background.

The ECM more or less follows the mean up to day 7 and the envelope is pretty tight. Thereafter, there is some divergence as expected, although that is well outside any semi reliable time frame. It's worth remembering how useless the ensembles have been so far this winter, so probably wise not to go looking for any trends beyond 120hrs as they are likely meaningless.

Knowing our luck there will be an instant downwelling of the w'lys that negates the e'lys! Seriously, given the lagged response and the fact that the PV will be weakening at the back end of winter anyhow, I'm led to believe its influence would be minimal. Let's hope we have some HLB in place prior to that though.

An improved 06z but still not liking that quasi stationary PV chunk sat over NE Canada. Even if we get the ridge up into GL there is potential it could be flattened quite quickly resulting in a transitory spell of colder air. If that chunk doesn't migrate south or west we could really do with some blocking assistance from the NE.

First snow of the winter here and about time! It's not much (probably an inch), but its a start.

How do we know it's flipped? Not sure that tweet the other day was from a reliable source...

Given the uncertainty, the MO are just covering all bases. They have always maintained that milder air may make inroads to parts of the south - usually indicative of waves of low pressure moving along the channel. This is a good thing if you want frontal snow...

The UKMO hasn't changed that much since its run yesterday pm and its difficult to see where that will lead as the key period is post 144hr. The ECM certainly isn't without support - look at the GEM op and many of it's ensemble members as well as the JMA. The ECM mean is also rock solid. You'd have to assume the higher resolution models have a better handle on this and you'd be a brave person to bet against the ECM suite.

Must be from GloSea as that is the only model that runs that far out. As you say, it is the duration of negativity that is an eye opener. Could be a modelling error but I wonder if previous SSWs had such a lasting impact. Back loaded winter looks odds on based on current data.

Dangerous cold over NE America. -30C 850hPa isotherm almost touching NYC!

I'm curious to see how well that matches with reality in 10 days time. If that forecast is to be believed it explains why there would be nothing of interest being shown in the models until well beyond 17th. Hopefully the models are underplaying the rate of downwelling. If someone has a link to view these charts as observed on a daily basis since the split that would be most interesting. Also curious to monitor if there will be moderation of the negative values as it propagates down into the troposphere.

The run has finished but seems stuck on Meteociel. The old fashioned way still works: http://www.wetterzentrale.de/en/topkarten.php?map=2&model=gfs&var=1&run=6&time=384&lid=OP&h=0&mv=0&tr=3#mapref The high eventually collapses into Europe but pressure build to the NE looks likely thereafter.

Yup completely agree with the environment being easier to model as less variables etc but I was specifically referring to forecasting SSW events - the initiator for these comes from the troposphere so surely usual limitations apply.