Friday Jan 2nd onward, very cold with snow potential: Event buildup/discussion

This is of course assuming the 4th verifying model is correct. You could for balance mention what the the better verifying model ECM shows, which is the cold being prolonged.

Yes understand your point but it's a chart I regularly look at and Ivecseen the 528 line go into Northern Spain. I've also seen the 510 line hover in the Atlantic not far from our West Coast. Not common of course but does happen a bit when cold spells come along. But yes nice to see

The control also collapses the high by Sunday night. So the cold moves in Friday night and wanes by Sunday night. For the West Coast it's a 2 day toppler, IF the gfs is right

This cold period started 5 days ago approximately. It's going to get better. We are getting a arctic blast 1st week of January. Hasn't happened in years. GFS loves to bring in the Atlantic. ECM is the model to watch.

Well, i partially agree, if we use the broken clock analogy then we can't totally dismiss the GFS as not being right, but we can give more credence to the ECM as it's the better verifying model. The ECM run this evening if it moves to the GFS would be concerning, but having said that if it does i'd still take a two day potent blast. What would be reaĺly annoying is if the two day blast got watered down to a wintry mix.

Yes. It really has gone downhill with its verification in the past couple of years. Thats not to say it's wrong this time but if I was given the choice of which model to back it would be ECM every time (just not the snow depth charts).

For the Northern Hemisphere the best verifying model is the ECM AI but even that can have off runs. We're a small island and of course it is all subject to change but at the moment it is looking good.

Irelands climate really is quite benign so even our rain or snow events wont last longer than a day or 2 bar the rare 1947 1963 and 2010.

Hope we get some snow at the weekend. Would be nice. Let it be gone for back to school.

There's nothing to ramp about most models collapse the pattern either on Monday or Wednesday. See latest ECM AI below. A 3 day cold spell doesn't impress me. No Northern heights there!!

JS, you keep chasing some big mad Greenland high that beside a few rogue runs or ensemble runs, was never on the cards for a prolonged period. I have no idea why you keep referencing the high collapsing as some crazy new development when this was always on the cards and part of the story.

This entire period was resting on a mid-Atlantic ridge that ended up being allowed gain sufficient amplitude because of a pesky shortwave exiting Canada did so rapidly enough that it vacated space for WAA to push the ridge towards Greenland. This is not the same thing as a cut-off high. We are still very much on track for development of a strong ridge, centred just south of Greenland.

Ridges are topplers without either better background forcing or a disrupting low diving SE from the Atlantic that manages to cut off the high. I'm no teleconnection expert but there is very little in this spell that supports a robust strong long term Greenland high. I know you are chasing a big spell but you need to let it go at this stage and view the output for what it is, and not for it not showing what you want it to. The ingredients aren't there for a Nov 2010 style blocking episode, and frankly never were.

What exactly we can get out of the ridge is the next thing. Some runs are very snowy and others are much drier.

What we can look for in terms of something more long term, is the renewal of ridging after each 'waning' period. The ECM 0z is an example of this, right out to +360 has cold potential. Is 12-15 days long enough for some cold and snow chances? Once colder air is here, or much closer to nearby, you can get away with wedges and ridges. ECM this morning basically repeats the entire first phase of the spell with a new ridge towards Greenland setting up. All FI of course.

There is too much eagerness for people to get in their "won't happen", "average weather", "totally normal", "non-event" one-liners the last few years in so they can win imaginary internet trophies in two weeks time. I saw 10 minutes of sleet/wet snow in 2025 in Dublin. The years before that, only had a single snowfall in March (x2). Nothing normal about a snowfall in Dublin these days.

EDIT: We do need GFS to improve later today however. Better to have it on board, stopped clock…

Great post. You summed things up perfectly.

Yes the Ecm ai model is the best verifying (in general). However, it is definitely struggling at the minute, and often does when we have heights to our north. There is a huge spread in the ensembles even at only a couple days notice which none of the ‘regular’ models have.

The Met office have disregarded its output for the last week and for the coming spell of interest