Cold Winter Night

That is crucial to understand about severe winters. It is never a pattern set in stone for weeks on end, it is waxing and waning constantly. The raging vortex usually limits (or ends) the number of cycles, but this year our hope is that Weak Vortex+Great pattern+SSW will let these cycles continue... We'll see!

GFS does not yet have a very strong connection between heights over Iceland and Scandi/Russia. It's close to ECM 0Z, but I think the ECM version is more likely, considering how Scandi heights develop. Anyone who witnessed Scandi Highs in the past knows that they can develop fast!

To all who are interested in the source of the air that is forecasted to be over our heads, following the isobars is one method, but that's very rough, since the directions change continually, and also the altitude of 'packets of air'. A very useful tool is NOAA's HYSPLIT model. It computes the trajectories of air at different heights, so you can see where your local air will come from, based on the latest model runs. Only for the US models, like GFS and NAM though. Lots of variables to fiddle with. https://www.ready.noaa.gov/HYSPLIT_traj.php Select 'Compute forecast trajectories'. See for example GFS 6Z for London on January 7th, where did the air at 10 meters and at 1500 m come from? And relative humidity along the way:

Usually with great cold spells, there is a role for North America. Low heights over the Hudson Bay, reinforcing a Greenland/Iceland High. It's odd to see nothing happening upstream on ECM, GFS, GFSP day 7-10. I can't recall charts that have shown such fairly strong hights all over the USA, Canada AND the Atlantic. It's as if the weather in that part of the NH has been switched off. Looks weird to me. Do we have historic examples of similar situations?

I like this EC at 240. Heights growing over Svalbard, heights beginning to drop over Kazakhstan.

The removal of heights in Russia and in the Atlantic would be quite a change, IF this would happen.

GEFS P8 shows what happens if a stronger Scandi high forces the cold to go around, instead of dropping down between Scandinavia and Greenland. With growing Scandi influence, this is one of the options. At first, we would be in the waiting room with many disappointed folks, but in the end we would look East, with a Trans Siberia express coming. At 192 and 240:

Again, in these runs the heights around Scandinavia are gaining influence. They are connected to the Russian high. At this rate there might not be a Northerly anymore by 12Z tomorrow, unless you're on a ship in the North Atlantic. And while I am typing this, the GFSP illustrates it at 192. The cold could take a little detour around Scandi if the Russian high deflates a bit, like it showed on ECM 192-240 this morning. Risky, but in line with some of the expected SSW effects.

The reason it drops that far West is the developing high over Scandinavia. To me, that stands out the most this morning. ECM, UKMO and GFS all make more of that than they did the last few days. A feature to watch in the 12Z's. With all these uncommon things happening in the atmosphere, from the ground up to high in the Strat, I wonder what kind of surprises we are going to see these upcoming runs. Exciting for sure! Like the good old days.

That makes following the model output so much more interesting when blocking is involved. The models always struggle with the exact placement, size and shape of the block, while the difference for us on the ground is huge. Dec 2010 was a Goldilocks situation, everything 'just right', in Feb 2012 it was just right for us in Holland (oh, what a cold spell was that!), but not for you in the UK and the situations where everything was 'just wrong' are countless

I noticed that trend too. The mean on both GEFS and EPS seems to be going up, but at the same time the spread is growing. There are some more extreme members, like the GFS 18Z Op and the one on the EPS that drops to -16C at 2m in De Bilt

True. But given the shape of the Atlantic/Greenland high, it seems to be going towards Scotland and Ireland. It would be better if it went straight South into Europe. Like P2 of GEFS 12 Z.

I think ECM day 10 is a bit too far West. Most of the cold will probably go to the Atlantic on day 11 and we will end up with Westerlies, like EPS this morning showed. However, I do like the renewed development of the Arctic high.

Small margins. West based -NAO or full Northerly hit, what will it be?

The Christmas card from GFS just came in: Merry Christmas and a Happy New Year! Very nice developments in the NE.

Hello, First post by a long time lurker from the Netherlands here. What stands out to me in the most recent output is not only what is happening upstream, but also the development of the high in Russia. The models are making more of it each run. Stronger and slightly further North. For now it is blocking the very cold Siberian air from moving West, but if it gets far enough to the North(West) it might link with the Greenland high. That would cut off the potential Northerly, but open a gate to the East. Yesterday's ECM 12Z for New Year's Day, and today's 12Z.