chionomaniac

The common question. How long until the SSW impacts the troposphere? The Answer: It’s so different for every SSW that it isn’t even worth asking the question. one can only monitor the situation as it progresses for every different SSW, expecting a little bit more volatility in the trop modelling along the way.

For me, I am not too concerned about the change in model direction over the last 24 hours. I suspect it is SSW related. Also I think it is highly likely to be temporary. If you remember yesterday, I demonstrated that there was a minimal push of westerly winds propagating down prior to the negative u winds associated with the SSW. Well, I think the models may have underestimated this, as can be seen from the ECM u wind forecast. It appears that there is a greater push of westerlies into the trop. However, this appears temporary, before negative u winds are back in control. So, it won’t be long before the roller coaster changes direction again.

Hi interitus. What are the x and y on that chart. Otherwise it means nothing to me? Thanks

Lol. You will save yourself a lot of stress if you stick to looking no farther than day 10. When a sharp rise occurs in this timeframe then it is time to look up. After this timeframe ensembles will always trend to climatological mean. Quite often this is common but the trend stays post day 10. The significant thing about these ensembles is the below average mean up to this point- and this is far more worthy of a mention than what comes after.

So many chances coming up in the next few weeks. I would be very surprised if the majority of us have not seen a significant snowfall before the end of the month. Of course, some already have, and 850’s are getting colder.

Yep. Was just going to say the same thing. The limit I look at is 48 hours ahead ( for fun), the 24 hours ahead for closer detail. And then the radar. And just to be actually sure, I look out the window.

With cold lowers. Definitely

If only we could have a channel low thrown into the mix. hold on....

Ok and holding its position over the UK. Double wonderful

A slider, sliding into a cold airmass. No more. No less. Wonderful.

This to me is a boom chart due to the lack of mild intrusion Jj what could possibly go wrong...

I call this a three pronged attack!

I always look for a flow between NE and ENE for me. Also need strong temperature differences and lower heights to ensure they reach me

Yep. In short The SSW is effectively a done deal. The early tropospheric response is almost a done deal. How the troposphere responds is up for grabs and certainly not a done deal.

Yep this is critical. With the SSW showing signs of a quick response, the MJO will be struggling to override these signals as suggested by @Catacol earlier. And continuing on that note- What I don’t think Ian Pennell understood earlier is that you can’t put traditional tropical and QBO responses into times where we have not seen the La Nina expected atmospheric early winter responses ( more Nino-ish), and strat has been a dead duck. The train is on a completely different track, and you cannot carry on predicting as if it was on the original track as it will only lead to derailment. Big time.

Try looking at Jan 2009. Off the top of my head I think that is a likely candidate for January

Btw, I think the ECM is running with colder pooling to our east in the short term. Just sayin’

Lol. What? To 200%? ( I know what you meant - an increase in the longevity, but couldn’t resist!)

Yep. Certainly looks like it. The jet stream to our west has been slow all of December so no surprise to see it grind to a halt post SSW. I’m still awaiting that true frigid run that eventually verifies, but patience is the key here as I suspect we will have a fairly long window of opportunity..........

Lol. That’s nothing. Put it alongside the corresponding 12Z T+144 chart Trop ECM chart and you can understand why. Is this the increase in trop u wind that you are concerned about. Not me. I think most of us on here would take this if that is the most extreme in westerlies forecast.

Showers have pepped up over last hour for East Sussex and Kent

I have had a good look at the strat charts this morning and there appears to be a lot of guesswork as to how the SSW may affect the trop. All indications to me are that we have a good propagating event already in the early days after the SSW. One would expect normally a flushing down of westerly winds to the trop and therefore an increase in a flatter trop pattern for a while. But to me this is just not happening. This is the picture as of yesterday: We have the weakened residual positive u winds at the top to middle strat about to be crushed by the developing SSW. What is of particular interest here, is the fact that prior to the SSW, the middle to lower strat positive u winds are either very weak, or on the case of the troposphere, none existent. These (strong) lower strat winds would normally act as a barrier to propagation, or will be flushed down trop wards as the SSW takes hold. But as they are not present the SSW can propagate right down to the trop almost ‘unopposed’. So by day10 we have this: The whole polar field from strat top to trop bottom almost one complete negative anomaly. Not only is it likely that the quick propagation of the SSW will continue to deliver a more meridional NH trop pattern, but where cold is transported south to mid latitude areas the cold will likely be severe and long lasting. The effects of this SSW are likely to be felt for some time yet, probably til spring. What we can’t be sure of yet is how we are likely to be affected, though early indications suggest a continuation of the winter pattern we have seen so far. But with cold reinforcements added in for good measure. edit - just to explain that u winds are mean zonal mean winds at any given latitude and height.ie where when travelling around the earth at say 60°N and 10hPA height, the net winds are positive (westerly) or negative (easterly)

Love the cold air pool forming over mainland Europe in stagnant low height conditions. Beautiful.

Personally I think that this a great run. As steve says the UK will try and find the mildest solution, but all I can see is a fantastic opportunity for proper cold

Easterly cold pool. Northerly cold pool. Take your pick.