Captain Shortwave

A low of -5c Saturday morning, managed to reach +5c under clear skies. Another clear start here with the fog dispersing before first light, a low of -6c. The last few days will likely mean that there is a good chance of recording another sunny January in respect to the average.

A few differences in the placement of the parent low. UKMO north east of the U.K. with a stiff north westerly breeze. GFS More complex with a generally slack pattern, at this time of year we don’t want to have a slack pattern really as it could easily lead to clear skies over many inland parts.

Not going to get overly excited about the ECM, purely because the model manages to send the low ESE and also have it deepen substantially. More likely the system would track further south and remain a shallower wave feature. The ECM does look more amplified compared to the 00z though and it looks cold from a period within the reliable timeframe now.

Not really seeing an overly strong Atlantic ridge in the next 10 days, but we do see a deep Euro trough develop by day 5/6 as it pushes against a strong area of high pressure over Russia/Siberia. The Atlantic ridge is sufficient to orientate the winds towards the north at times with the risk of snow in the form of showers or potentially more prolonged spells of wintry precipitation from any systems that run into the base of the Euro trough. The Scandi high scenario is a plausible way forward as the Atlantic ridge pushes over the top of the Euro low and merges with the Russia ridge, the ECM is heading that way for day 10. The JMA is also trying this route too;

Some very heavy rain on the way to work today. A clear line of convection embedded in this frontal system.

The JMA probably offers the most potent flow from the north (even if it will be brief). Possible gales down North Sea coasts for a time as the low clears. Showers will be of snow at this point.

The ECM day 6 against squashes away the higher heights. So essentially unless the GFS is somehow correct then we are relying on the models in the shorter range picking up a wedge or two that could steer things in a better way (if the lowering of heights is being overblown). At least the ECM offers a little olive branch that perhaps our prospects won’t simply get steamrollered.

Day 5 It will probably still get squashed away but it is a better offer than the UKMO. Cold air arrives into Scotland during Christmas Day so possibly some places will see a white Christmas (Possible locations including Glasgow).

I must say that ICON does give that ominous feeling, that is more extreme in terms of westerlies than any output we have seen. Hopefully it was a rogue run as the UKMO/GFS/GEM roll out now.

I must admit the GFS is quite dubious, where we have a high to our north west, yet the cold air on the eastern flank of the high actually moves northwards. That said it gets close to developing that Scandi high in week 2 (it sinks due to it connecting to the Euro heights). An easterly with that level of cold moving around could produce something of note. The GEFs do tone down the signal for a high to our north west around or just after Christmas.

There has to be questions as to why we are seeing this divergence occurring. The ECM again seemingly starting to organised the lower layers of the polar vortex into something more typical for the time of year and in a location that is similar to the higher layers. Meanwhile the GFS remains adamant that an area of heights will develop between Iceland and Greenland as a result of the winter storm developing in the US. There has to be an explanation and given the post by @MattH it has to be something other than a coupling between the lower and upper strat if the evidence suggests that this isn’t happen&long. Just curious really because one or more computer models are getting this very wrong at quite an early timeframe. That said the westerly or more block regime may not work out for the UK regardless.

Quite a crazy difference at day 6 The ECM not interested at all at building a cut off high to our north west. Funnily enough Boxing Day would be pretty cold on the ECM with wintry showers in western parts falling to low levels.

A lot of model runs to get through, but this is encouraging for early week 2. Winds likely to come from the north for a time with settled conditions developing after a more unsettled period that could include Christmas itself. The high is most likely to drift east and sink into Europe as seen later on. So a window for wintry showers because another spell of chilly and frosty conditions. It does look like we will see an Atlantic trough approach so potential blocking is going to come from high pressure building to the east. If we are lucky then an evolution towards new year of a Scandi high is plausible, but considered unlikely at this point. The ECM is generally flatter and as such offers a briefer chillier period before we get a more north/south split that is milder than the GEFs. So at the moment for wanting cold we want the GFS to be on the right track as this offers better short term and medium term potential.

After an hour of precipitation not reaching the ground, we now have rain. The CET is close to 0c so it is fair to say that this spell has been a decent effort. But I have to wonder whether we will look back at December as one of those “What could have been” months. We got one snow event that could have not materialised at all given the luck needed when low pressure is overhead at this time of year. The initial northerly got quickly cut off and every attempt to develop a strong flow between the north and east seemed to get snuffed out. As such we saw a lot of slack and very cold conditions as opposed to the wintry nirvana we crave. overall this spell gets a 5/10 for me, decent length but only a dusting of snow and the ice days were thanks to freezing fog sticking around rather than developing deep cold. I hope this winter has some more chapters to go through.

Looking at the output, it would be nice to get a trend to suppress those Euro heights a little more for the big day. The GFS control run is a little too late for the south, but brings snow to northern England before cold air flushes south for Boxing Day. It does look likely that high pressure will build towards New Year. GFS ens ECM So after a wet week, we should see more settled conditions develop for a time. It is the window preceding this that is of interest, note the proximity of the Scandi trough on the ECM suite even at day 10. A potent toppling northerly is the best we could hope for, but given the airmass to the north it might be enough to deliver snow to many of the flow aligns favourably.

A low of -4c and one last hard frost. We might need to be wary of the rain falling onto frozen surface initially but ultimately temperatures will rise strongly this evening and this will thaw most of the snow across the region.

The UKMO initially looks good, but I have to admit I can see the process that will try to push the Iberian high northwards again. The low that will separate from the trough near the U.K. Again the winter storm upstream is going to crank this up to be amplifying the ridge near Newfoundland. That said Christmas Day may end up mostly fine and chilly away from exposed coasts where there could be wintry showers.

The next potentially frustrating hurdle is going to be seeing how the winter storm over the Eastern Seaboard pans out downstream. The models are now starting to develop a significant Atlantic ridge in the week 2 range. Shame about that slow moving area of low pressure west of Iberia because again the set up looks primed to send cold air southwards towards Western Europe.

Day 5 UKMO/GFS The UKMO is again squashing that low more than the GFS and as such has a good chance of running through the base of the Scandi trough. The GFS is still an improvement with the cold boundary further south on the 23rd. The UKMO is probably good enough for most of the U.K. the Euro ridge is being suppressed too. Rain clearing east with cold air pushing southwards as a north westerly flow develops.

Down to -5c again last night and another thick hoar frost. Another sunny day coming up with just some patchy high cloud.

It looks more likely that high pressure will build over the top of low heights west of Iberia. However another solution would be that the Jetstream begins to push strongly west to east and we see a more typical westerly patter establish (Sort of like the GEM). At this point I don’t think there will enough gusto to go this route, so a mid latitude high close to the U.K. post Christmas is probably favoured in my opinion.

Conclusion for Christmas… Santa needs to spend less time delivering presents and have a good sit down… on the Euro ridge….. The models are relatively consistent with the notion that the trough will get squeezed out in week 2. Before then a north/south split looks likely with a lot of rain for some thanks to stalling frontal systems, yet there is also the chance of significant snow for some lucky parts of the UK, if the boundary sets up in a favourable way.

I’ve heard of model runs that should be out in the bin, but the ECM 12z is the bin….. Let’s hope for better next suite.

UKMO It is a little better compared to the morning run. A more significant upstream ridge, cold air is getting into the north and the Atlantic low is starting to struggle and could allow cold air to push further south.

The warm front on Sunday is being modelled to only bring mostly light precipitation and its arrival time may very well be well our location is under positive 850s. So there is the risk of snow if the precipitation is heavier and more extensive, but otherwise Sunday will be a pretty raw day where the temperatures will rise more significantly during the evening.