Rocheydub

As I said in the MOD thread, the big bonus is that the vortex is most disorganised! That's always positive. We will get some snow midweek, it'll feel properly wintery too, and while it warms up slightly, it will still remain on the cold side of normal... then the ECM throws in a quasi Scandinavia high with an undercutting low cell. Mad to tease us!!!

At 216, that low should slide under, dragging cold air from the continent.... Academic at this range of course, and typical of the ECM!

At least the polar vortex is anything but organised. *crumbs of comfort*

When the GEFS come out in expecting to see a massive spread from about 72 hours onward. Ms Entropy is singing aloud. Great at end to the UKMO, so the ECM tonight will as usual, be crucial!

Agree fully BFTV, just as I said there would be downgrades, I wasn't expecting such a big shift though! I await tonight's 12z runs and make a call then.

Ah F F S! I didn't see that coming.

Another fantastic ECM tonight. Coldish night tonight, getting colder all the time as we get to midweek next week, with a mix between heavy snow and scattered wintery showers for all! It would take THE biggest backtrack by all models for this to not occur I feel now.

I've seen enough here to know that we're OK. The rest of the run is LaLa land anyway! Its coming folks!

Copy and paste this for every future: "Oh, this looks worryingly different at 72 hrs" post from here on. Bravo sir!

How does it look wrong? I'm sorry, but the broad picture remains the same. It's still absolutely game on, and we're well into FI now on this run. I'm more than happy with it I have to say, a much earlier incursion of the cold than the 12z run. Nothing wrong with it IMO.

Some astonishing rain here for the last 2 hours. I'm up to 10.5mm in that time, absolutely chucking it down. I'd imagine there will be some localised flooding out of this. Just a respite from all this model talk to the here and now!

Hate to be a party pooper... But there will likely be downgrades of this. I mean, it can hardly upgrade... And we know it won't stay the same!!! I do of course hope I'm wrong!

I'm now 90% sure this will last 4 days or more now, if the G HP cell does set up, as per the post 180 hr models say, this will become entrenched for 2 weeks! Tomorrow will confirm if I fully believe. I told my kids just there at bed time... Probably a bad idea, but his face lit up like the tree we just took down! looking forward to this now!

Can't find any data on 1982/3 winter for some reason, but we did have a polar low in 2001 which dumped 5 inches of snow overnight.

Not in Ireland....

Would it be a real polar low though? Does it not have to originate in the polar regions and travel down in the flow? I think we may have had one in 1983, but again, I would have to look at the historic charts.

It was indeed, you are correct. It was 1025 for some of it. Apologies. That was a fantastic night. I was in work in the city centre, and remember the fright I got when the first clap of lightning-thunder came, I was expecting it, but not so close to where I was!!!

Generally speaking any pressure above say 1020 makes it more difficult to get precipitation going. It can happen of course. Again, all very academic at this range. A wee shortwave can pop up and give you an absolute dumping of snow!

I thought it was 1015hpa... I'll have to look it up, but the big difference then was that upper 850's were -9 and -10 weren't they?

Correct. These disturbances in the flow usually mean an uptick in precipitation, Will have to keep an eye on the MB pressure though, a few runs have shown the western side of the country on the upper end of pressures for precip... This is all subject to lots of change though at this range. The most important thing is to get the cold embedded, and I'd say at this stage, I'd say we're gone on from my "4 days" prediction up to a 6 day cold spell. I'm 85% positive, and if we get through the 12z's still intact, I'll be telling family and friends to dig out the woolies and snow crampons!

Absolutely correct, but all subject to change at this range. I'm concerned that some of the runs show in my locale that we'll be too high in pressure at times for precip. If the runs are still like this after the 12z's I'll be telling the family.

Who'd be a moderator... Anyway, the 18z GFS is rolling now, and ot be honest, the important features have been maintained. There is an Artic HP cell, a rise in pressure from the Atlantic northward, and a weakened P-Vortex. There will be run to run changes. Look at the ES and ensembles for the bigger picture. My hunch and experience says this will be a 3 or 4 day event. Maybe more as we go later into Jan. Remember, it's only a computer programme, not a design of the future!

I'd imagine, looking through the ensembles and what i can see of the EPS, this may well be a 3/4 day event. I could be wrong, I hope not. I haven't had any snow here since 2010 and I'm starved of it. If it lasts 4 days, I'll be glad to see most of the north or NW or NE winds, as the uppers could be potent. Alas, we won't know that until closer to the time. Fingers crossed. My hunch on Mr. Murr is that he had a punt on a Scandi HP cell, and it didn't materialise. He craves the old Scandi HP, and that he was bitterly disappointed. Now Stewart has come up with his theory, that makes a lot of sense to me anyway, and he tried to pluck holes in it. As always, time will tell.

Well, it's absolutely chucking down large droplets of rain here now!

Agreed, it's unlikely, the difference here is that it's quite a plausible process. It's also in line with the MJO and other drivers. Have a read of Glacier Point's posts in the MOD. He's confident of -NAO and -AO. It's certainly in line with his thoughts. I am not getting my hopes up yet, but if they're still showing these charts mid week, it will grab me by the balls!