The Enforcer

How does the current UKMO 12z 850 chart at T+120 compare with yesterday's 12z 850 chart at T+144?

Carinthian was saying this was modelled for 20th Jan. Has this now shuffled back again?

Indeed, in my opinion, the viewer should always be looking at charts beyond 5 days with a high degree of scepticism, whether they are showing cold or mild.

Since when has GFS been able to display a high degree of accuracy at T+216 anyway?

I see the Easily Changed Mind model is projecting a cold easterly again at only 10 days out.

Thanks for the explanation. This is good and I look forward to seeing it at T+312 tomorrow.

I thought someone posted one yesterday?

.... the omnipresent SSW at T+384.

This is the key timeframe to focus on the ECM output. With such differences remaining at that point anything that happens afterwards is only conjecture.

I have observed this 'detached PV over UK synoptic' projected at range on several occasions over the years. Can anyone post a chart where it has actually happened?

Reverse the Synoptics over the UK and you'll probably have a good picture of what the weather will be like here on 15th January.

If I had £1 for every time GFS thought that was going to happen at T+384...

Could anyone post the 850 meteociel charts for the 00z and 06z GFS for 6am next Wednesday. I don't think the ECM is particularly reliable at T+168. It is conceivable that the block could move back gradually westwards at that timeframe over the next 14 runs.

Hmmm, conditions suitable for significant snow under the current best case scenario (GFS) still seem to be just over a week away. If my memory serves me well, this time last week, they were just over a week away under the then best case scenario (GEM). I suppose it's better than being two weeks away. This is the key timeframe to watch as each run comes out. In order to break the aforementioned 7 day hoodoo, we really need to see incremental changes in the form of the green over the UK getting replaced by blues and the darker blues continuing to edge further from Eastern into Central Europe. All of which is realistically possible.

Could anyone post a similar comparison for the last four ECM 12z for next Tuesday?

But the mildest solution on 7th.

I wonder if they were forecast to be classic easterlies 8 days in advance?

Well, T+0 would be better - only 12 more runs to go.

Now that IS ridiculous, how could it settle on the coast on both occasions, but not in Bramhall, much further inland?

I've been visiting Bramhall around this time of year for almost 20 years and I have only ever seen proper lying snow once (December 2009) and even then it was leftovers from a fall before I arrived. It's around 80 metres ASL and well inland, so I can't understand why some of the higher resolution model outputs have no snow at all here (and in some cases have none on the coast). My plan is to visit Lyme Park, but ridiculously the BBC 'Find a Forecast' has no snow for there either - it's at least 200 metres ASL for goodness sake.

The thing that interests me about that link is for all the obsession with SSWs, there are plenty of years without them where significant snowfall still occurs - two examples being one of the very snowiest winters 1995/1996 and the potent Feb 1991 easterly.

The key for me is whether the signals are current or whether they are projected. If the former, then, as set out in the NW winter forecast, there can be reasonable confidence in conditions supporting wintry weather emerging at some point. However, if it is a forecast for favourable background signals then it is just that - a forecast - and as such needs to be weighted accordingly. Hypothetically, a forecast today for a SSW on 1st Jan 2018 is not really any more reliable than GFS charts showing snow on xmas day at T+384. I have lost track of how many times the charts show MJO is expected to move into 'this' phase and a few days later they instead say that it is expected to move into 'that' phase.

If I have read that correctly, does that imply that the ECM mean is the go-to model for 500 charts? Is there an equivalent assessment for 850 charts?

I measured 2in / 5cm late morning, from memory similar to January 2013.

Starting Point: Objectives: Outcome: Analysis: I love it when a plan comes together!