The ECM weeklies are below average for the entire run

Week 1

Week 2

Week 3

Week 4

Yes stunning means tonight a real upgrade from the ECM this evening. 

I don't believe that is correct. It is down to so many factors, dew points, evaporative cooling, boundary lair temps, the list is long!

Doesn't it seem that way because the situation for a particular time in the future will have been forecast umpteen times in different model runs before that time is reached? It wouldn't be surprising if the random "noise" was to occur in a few of those model runs in such a way as to result in a considerably more extreme outcome than the actuality will turn out to be. (Chaos theory suggests that randomness can take over to a large extent sometimes as little as a week or so out.) And of course that handful of extreme runs tend to be the ones that attract most attention.

I think it's more the case that what we regard as extreme events in terms of NWP modelling is skewed toward desired outcomes (extreme cold, heatwave, thunderstorm etc), and those extreme events get the attention when modelled correctly or not.

Quite often extreme flips in outcome go unnoticed as the previous scenario and end scenario do not fall within those "extreme/interesting" parameters. The tree falls over, but no-one is there to see it.

New week same old uncertainty with the weather models. Colder conditions arrive late this week with increasing wintry shower risk for much of UK by weekend. Slight shift on GloSea5 (seasonal model) today of average or slightly above temps for February and March.

— Essex Weather (@EssexWeather) January 14, 2019

From Matt H

For what it's worth, given current model volatility, but some very interesting clusters now with a bias towards a mean flow from the E and NE in the 12Z EC ENS next week. The final few frames of the 12Z EC does have some support. Some 'wild' solutions within the ENS longer term.

A cold 2nd half to winter IMO. The full influence of the SSW has yet to be 'felt', given the slow downwelling, the AAM remains interesting and with the MJO back into phases 4-5-6 then all the ingredients there for cold synoptics in coming weeks. To what extent is the unknown

Should be ok now. I'm rewriting a lot of the back-end services at the moment and adding in new features. 

I'd also add that whatever the NWP predicts has absolutely zero effect on how the weather actually turns out. Unlike financial modelling.

That's a very profound question and deserves its own thread.

My guess is that financial markets modelling is limited by the uncertainty in "sentiment" i.e human psychology which is way much more difficult to model than the physical world which obeys well understood laws of physics. The numerical modelling of the atmosphere is limited by the fact that the models are hugely approximating by using grids containing big parcels of air rather than individual molecules of air. The real atmosphere being a continuous medium "smooths" the atmospheric response a lot more than the models, so extremes appearing in the modelling output are less likely to occur in reality.

Taken from NW 

Absolute stonker of a set of ECM ensembles tonight. For the 24th January, 42 out of 51 members are certainly cold enough for snow in most places. Up from 27 out of 51 this morning!! 

What's noticeable is pretty good agreement on the pattern - deep trough just SE of the UK. In the sweet spot! But will it stay there? end

Got a feeling IF will comment soon

O/T apologies D 'MILD' Bett

"The cold air to come could last quite some time ",

I always follow the Beeb and Met , they see much more data than most of us ever will

Definitely the coldest set of ENS for De Bilt that I have seen this year.

The snow depth chart from Weather US for the UK (based on the ECM 12z) for midday on 24 Jan shows most places away from Central Southern and SE England having significant snow depths. Many parts of Wales, northern England and Scotland have a good 3+ inches of snow with over a foot on high ground and 28 inches showing on the peaks of the Lake District.

https://weather.us/model-charts/euro/england/snow-depth-in/20190124-1200z.html

That means freeze-up if that came from him

Yes the second part of my post may have been too simplistic, however I maintain that for most low lying parts of the UK, if the wind is strong and from an Atlantic source, with no continental influence present, you really need deep cold uppers (ideally below -8C, preferably close to -10C) to allow for snow below 100m ASL, especially close to western coasts. Yes evaporate cooling allows for snow, but only if winds fall very light. 

If T+216 ECM came to fruition I maintain that most of us in low lying areas would see rain (850s below) 

http://www.wetterzentrale.de/maps/ECMOPEU12_216_2.png

However we’re talking FI so totally hypothetical regardless. 

It was the LP next week that showed ppn crossing the country , he wasn't bigging it up though 

If only those charts were even in a tiny way accurate! 

The weather models are mechanical - they calculate how conditions should evolve on the basis of laws of physics. Each set of inputs can only produce one outcome. The trouble is that the range of measurements you start with is never complete, so you're bound occasionally to miss one or two data points which might in reality have moderated an extreme outcome. 

The ensemble is supposed to be a way of testing whether this is the case. By tweaking your initial conditions 20 or 50 times, you're supposed to cover the effects of possible gaps in your initial data. But every one of those ensemble runs is another one-off event with only one possible outcome. None of the 20 or 50 runs is more likely to occur in reality than any other. So we have to treat every one, including the most extreme ones, as equally possible. Thus we have every right to examine extreme model runs as much as boring runs. And we do!

As I understand it, financial modelling, by contrast, is essentially statistical. You're looking for what is more likely or less likely to happen, and applying percentages to that, and comparing it with the possible financial gain to be made by taking different positions. To put it in horse racing term you're looking for which outcome should be the favourite, and determining whether the potential gain of backing that outcome outweighs the risk of one of the outsiders coming in instead. 

As you say, the favourite (as in horse racing) tends to be priced up just that little bit too short, as everyone piles in for the easy money, or the short-term gain. And when an outsider does come in, then everyone is shocked, even though a 1-in-a-thousand event had every right to occur at some point.

It takes me back to my grammar school, and doing my applied maths A level 42 years ago. There was a choice of two papers to take with the Oxford board back then: statistics or mechanics. Our maths teacher told us that statistics is a very straightforward subject, but essentially useless in scientific terms, so we covered the whole subject in four weeks, to a level which would have been enough to pass the exam. Then we spent the rest of the year studying mechanics, on the basis that it was much more difficult, but much more useful, so that would be the paper for which we would be entered.

It was a different world back then.

As regards uppers, I may have misinterpreted, but I seem to recall over the weekend Retron saying that snow could fall to low levels with not so cold uppers. You need colder upper temperatures in high pressure conditions. He seemed to think that uppers of - 6 could be cold enough for snow with air pressure of 985 mbs. 

Just checked them a day or so back and shows below average for Feb and March?

And with quite an extensive northern block:

Quite a difference in temps between the GFS Para 18z and the OP run firstly the OP @ 210:

Temps struggling to get much above freezing in the still north to north westerly wind! Maybe mid single figures at best! Perhaps lot's of sleet to snow showers or even soft hail! (not seen this sort of precipitation in a while).

Then the 18z Para - temps in double figures midday in the south and low pressure slower sinking southwards:

But eventually does it but later time than the Op run!

18Z Para @ 360 is showing more like a northern block developing over Pole and into Greenland:

Yes indeed. Down here at least I usually look for -10C at 850, but as I mentioned the lower the pressure the closer to the ground that 850 line becomes and thus the higher a temperature you can get away with.

Here's an example (note: NOT based on any particular model).

Say that it needs to be -7C at 4000 feet for snow to make it to the ground. The ground temperature is 2C. I'm using this calculator.

At an SLP of 1025hPa, the 850 line is at 4860 feet (therefore it'd need to be colder than -7 at 850 for snow to fall - probably closer to -10)

At 1005 hPa, it's at 4350 feet (so -8 or so would do)

At 985, it's 3840 feet (so you could get away with -6)

And at 965, it's 3300 feet (so -4 or -5 would do).

Obviously there's a lot more to it than just that (lapse rates, evaporative cooling, boundary layer modification via a warm sea etc), but it gives a rough idea of why the models have been so snowy with relatively modest 850s - this is the polar opposite of a typical "driven by a massive high" cold spell.

Incidentally the ECM showed this beautifully a couple of days ago. 850s under lowish pressure were -5C or so, then as a high built in situ, without pulling in a colder airmass, the 850s fell to -8C over the course of a day - just because the 850 line was getting progressively higher.

We could really do with seeing temperature charts at x height rather than x pressure.