Captain Shortwave

Another element of the GFS run is that it sends significantly more energy between the Siberian lobe and the Canadian daughter vortex, this occurs just when the Atlantic ridge is starting to build northwards towards Greenland, as such the high tends to stall too close to the UK but unlike previous runs it doesn’t sink away. Whilst the GFS is consistent with rather underwhelming outcomes, how it gets there has not been consistent.

At day 7/8 the Azores low becomes temporarily cut off, what we want is for that time to be as short as possible as that low needs to phase with the trough exiting North America. When these phase you get the elongated trough and the subsequent push northwards of the Atlantic ridge. What you don’t want is the low to remain cut off because the jet stream will flatten out the ridge as all the energy rides over the top instead of splitting.

The more encouraging element is that is even if the Greenland high doesn’t come off, the failure looks like being a lack of amplitude and instead we end up with a persistent Atlantic ridge, which of course will deliver cold from the north regardless and offer other routes beyond. What we don’t want is the cut off high racing westwards and the Atlantic lows racing back towards the UK, that doesn’t look likely at this time.

The ECM evolution this morning is pretty much identical to the 12z so far. Not much else to say apart from the fact that the output will swing around and there isn’t much agreement over how the Arctic profile pans out. Worth noting that whilst we saw a lot of awesome day 10 charts, they often involved different solutions in the Arctic. No need to worry just yet.

Subtle differences between the 12z and this mornings run, no interaction between the Atlantic ridge and the weak heights on the Pacific side. For the rest of the run it is worth keeping an eye on the shallow system over Southern Greenland at day 7, this will track around the high and will be the system that will bring a cold front southwards at the end of the run.

Quite a signal for a ridge to our west and pressure lowering to our east for week 2. All thanks to heights near the UK retrograding towards Greenland. The reason why we are seeing consistent charts is because this type of evolution tends to be quite reliable to predict. Hopefully the models will hold firm on this evolution and the detail of any north to north east flow becomes clearer. Hopefully we won’t see the models trying to accelerate the retrograde either via the total drainage of low heights over Canada or the high merging with heights in the Pacific (both tends to quickly break down blocking in the Atlantic). Let’s see what the ECM delivers, at the moment next week is looking dry with the risk of wintry flurries or drizzle at times. So week 2 is going to be the main focus. For what it is worth the heights are day 3 on the ECM are a little further north than yesterdays day 4.

The models now agree on an easterly early next week, but we need heights to be a little lower and the cold air to be a touch colder to develop anything other than a few light wintry flurries and even then the winds look like backing towards the south east which will bring drier and sunnier conditions anyway. Next week does look quite raw for many, especially when the wind picks up early next week.

The ECM for what it is worth delivers low single figure maxima across the Uk, scattered showers but there is something more substantial moving through the English Channel impacting Kent. Not extreme but certainly would deliver something wintry. ECM ens now placing the centre of the high off the north west coast of Scotland now. We could do with edging this north but not a bad chart at day 7.

The only difference really is that the ECM gets the high a little further north in the 5-6 day range, hence the cold air reaching the UK properly and bringing the risk of some snow showers to parts (Eastern areas of course favoured). Not much in the models out to day 7, just that we could end up with a UK high or with the high centred just to the north of the UK. The outlook looks cold regardless as I suspect even the flatter solutions will end up calm with frost and fog becoming extensive. The trouble is we don’t really want to sit around for several days hoping the UK high will migrate in a favourable manner. Worth noting that whilst the UKMO isn’t as quick, it will get there eventually; Cold air advecting south west and high pressure should centre itself north of the UK, however the solution is slower than the ECM.

Well this is a surprise to wake up to. A solid dusting of snow on the ground.

The one concern I have at the moment is given the current modelling of multiple areas of low pressure pushing up against that developing ridge to our east is the potential for large amounts of rain. The GFS delivers 3-4 inches of rain quite widely across central/southern England in the next 7-10 days. We don't really want to be stuck halfway between the block winning and the Atlantic pushing through Europe because being on the battleground once the Atlantic air-mass has pushed through successfully is going to result in a lot of rain and historically we have struggled to pull the pattern back westwards again.

The ECM is pretty much a half way house between the GFS and UKMO with keeping the pattern further west but less aggressive with the link up of cold air to the north east and the lows coming into the Atlantic. Bare in mind the ECM has a slack northerly at day 6 whilst the UKMO had strengthening south/south westerlies. I am not sure where the run will go from day 7, looks like the cold pool breaks away from Scandinavia heights should build here but the upstream pattern looks too flat to develop the easterly later on.

5-8c isn’t bbq weather, even in Newcastle Note the type of ridge building, this could get pretty close to delivering something from the east a couple of days down the line. The ridge is very sharp with troughing either side, that is a recipe to squeeze that high northwards and bring the cold in from the east.

Some large differences again at five days out. The UKMO again more keen to move that Atlantic low towards the south of the UK with heights lowering quickly through the Northern Atlantic. A possible snow to rain event but conditions likely to turn less cold and wetter as the jet stream bends under that Greenland high. The GFS is very messy again Mostly dry with some severe frosts and freezing fog probably becoming a bigger player. Not sure what the prevailing movement is going to be, the UKMO result is one we have seen many times with the Greenland high almost intimating the route out of cold weather via a west based NAO, the GFS on the other hand is more reflective of the sluggish pattern we are currently seeing and as such the UKMO modelling might be too quick.

A little bit of caution in regard to “less cold”, yes we may lose the cold air above but at the surface conditions could still remain cold. The ECM suite is more bullish on high pressure taking more control compared to the GEFs.

The ECM very close to developing a butter easterly underneath that developing Scandi high (It would probably just fall short this time). However it is a set up worth watching as we will likely have low heights over southern Europe with the Azores high trying to build over the top. So the easterly is certainly a possibility.

The ECM seems consistent on trying to build the Azores high north eastwards, though with varying degrees of amplitude. This run looks like a good attempt to build heights to the north/north east of the UK. Still lots of uncertainty from Friday onwards, the first element being how long and sustained any north easterly will be before the winds back towards the north west and cut off any showers.

It looks like the cold pool that reaches Iceland may curve back towards the UK on this run. A snow event possibility and it also should extend the cold period as the phasing of low heights pushing into the Atlantic will be slower.

Looks like the main emphasis will be on showers pushing south west from the North Sea on Thursday night into Friday. Obviously this gives scope for streamers to form in favoured spots, so anywhere downwind from the Wash looks a good bet for example.

The ECM tracks the low so far south that any fronts barely impact the UK, on the other hand there is a disturbance in the North Sea that could enhance convection north of the Humber; Day 5 is cold with showers in eastern areas; These should fall as snow away from the direct coastlines. I would add the low across south west England looks to be the same one shown the day before in the North Sea, that could very well bring precipitation well inland, a potential snow event from central and northern England perhaps?

It seems quite common in these Greenland high evolutions that the models underestimate how far west the cold pooling can extend out of Scandinavia and as such the models can flip from blocked to effectively a flat pattern with wind and rain returning. This may not happen this time but obviously if it does, then you will need be looking to where that Atlantic system could track, a southerly track could deliver frontal snow and of course keep the UK cold for longer. The usual wish would be that this occurred later in the season where we would probably have conditions that were more conductive for low level snowfall rather than middle single figures where everything is on a bit of the knife edge.

Whilst the 850s may lift a little, the day 5 chart is still as cold at the surface with a chilly feed between the south and east. The only question would be whether conditions were conductive for low level snow before this point because that rise in 850s should make much difference given we will be seeing fronts move through. Day 6 sees the same flow between the north and east return. The ECM is certainly progressive in terms of reducing the heights to the north at the end of week 1, especially comparing the the 00z run.

Better output this morning in regards to next week thanks to a generally more southerly track for that Azores low. These are pretty decent (though we will need some luck to generate proper snowfall). A lot of uncertainty but most models do get us on the cold side of the divide but with low pressure pretty close and quite shallow at the surface, we will need the flow to align or see disturbance to generate anything of note. Still this is much better than seeing the Azores low dragging up air from the south across sizeable parts of the UK.

All models have an east/north easterly developing early next week; After this looks complicated due to some shallow lows running along the subtropical jet stream as well as cold pooling sinking south from a rapidly sharpening Atlantic trough. Good luck modelling these interactions accurately at this range. I will say that I would put high confidence that any resulting low will probably be weaker and more elongated than the current solutions on offer. This doesn’t mean that the location of said low will be conductive to cold/snow for the uk, though a shallower system would obvious give a higher chance of a positive outcome. Original post: https://community.netweather.tv/topic/99428-model-output-discussion-mid-autumn/?do=findComment&comment=4956968

In the nearer term we have early next week and in particular we have two systems interacting, shown here; One west of Norway and the other being the low tracking through the southern half of the UK. How these interact and the strength of any ridging behind will decide the strength of any easterly we get behind that low, there is certainly scope to upgrade the depth of cold early next week and as such could allow snow showers for some of things go the right way.