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Captain Shortwave
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Posts posted by Captain Shortwave
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Just a quick note on Monday, looking much better compared to previous days.
UKMO day 4
Yesterdays day 5
The cold air is much more potent, enough for more frequent showers on windward coasts.
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The ECM 06z is now out to T90, probably a touch better for than the 00z out to day 4.
I will confess that I find it annoying that we northerlies with this type of wind alignment far too often (AKA the perfect alignment to avoid onshore winds for the majority of the country).
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I am wondering whether in the end the secondary system moving down from Iceland might be the one to watch, rather than the Azores low in regards to a frontal snow event during the middle of next week. If the trough continues to correct south then there is probably very little chance of the Azores low reaches the UK as it will tend to run along the base of the trough.
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The one I will say is that the evolution during the middle of next weeks looks very delicate. A few tweaks here are there could be the difference between conditions quickly turning milder or being put into the freezer.
How strong will those weak height be, not only towards Greenland but other heights that could break off and squeeze those low heights over Scandinavia. Then we have a couple of areas of low pressure that could hit the UK but could also miss entirely (The Azores low and anything drifting down from Iceland).
It looks like the 06z has stopped the westward progression of those low heights over Scandinavia with an Atlantic ridge still in place. This could be a very cold run if heights can rebuild into the gap.
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The GFS still develops that secondary low around day 4
This feature is still uncertain in regards to the track, though these tend to end up shallower and move through quicker than usually modelled.
ECM for the same time
The low is shallower and already further south. One to watch as this will bring organised precipitation into the cold air over the UK.In theory a shallower system should end up curving slower and as such track further south and west over the UK and pull the trough southwards.
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4 minutes ago, JimBob said:
Looking like a very short lived or even non existent career cold snap for the south now.
The ECM has low single figure maxima at best from Monday through to at least Friday and the day8 chart shows the next system in the Atlantic will undercut the residue heights to our west, as such it will remain cold through to the end of the run.
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A better ECM, the core of the low heights is further south and less quick drifting west.
very little precipitation from the Azores low reaches the UK as the system moves through northern France.
At the moment the speed of the decline of the heights to our north west seems to have big impacts on what week 2 looks like. The slower the decline, the colder it will be.
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The ECM is a poor run, it drags the core low heights further and further west so at day 8 it is in line with the meridian and further west still at day 9, the pattern becomes cool and cyclonic rather than cold. Probably still good enough for some but the run isn’t too far from delivering very little.
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Given an easterly flow, we won’t need to be that much below 0c at 850hpa for the precipitation to be snow.
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A slightly stronger signal for heights to at least prove more resilient to the north west compared to the 06z suite.
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UKMO day 7
Low in question is going straight into France. We will need that area of heights to hold firm to continue forcing Atlantic systems further south and allow the low just east of the UK to dominate.
I should have added that there is a disturbance running down the western side of the UK, clearing the south coast at day 7, precipitation probably concentrated towards SW England and likely to contain some snow.
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4 minutes ago, AltonMatthew said:
Where are you seeing "Deep Snow" the current cold forecast looks very dry and the models are the same. Predicting precipitation is useless, cold does not mean snow.
Time to calm down abit lad id say.
However the models are keen on bringing an area of low pressure north east from the Azores carry plenty of moisture that hits the cold air coming down from the north. This would deliver a lot of snow on the boundary between the two air masses. This boundary will moving over the next several model suites but there is consistency on developing this battleground.
GEM is great out to day ten with winds generally from the north. The GFS is probably towards the poorer end in the longer term given low heights organise to our north, but I doubt many would care given there are two major snow events before westerlies return.
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The one thing the GFS has changed since yesterday is that whilst it still has the Scandi trough and the low heights over Canada interacting, we are not seeing the door shut in regards to the ridging, instead parcels of cold air are sheering off and the ridge is then allowed to try and push polewards again. As such that does give scope for a weaker cut off high on our side of the pole. But it is going to be a while before this is resolved.
Heh the 06z may actually restore the extended ridge later on here, despite looking iffy early on.
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The outlook looks like a real mess for week 2, uncertainty starting from next Monday where the northerly will likely be cut off as a weak area of high pressure builds in briefly.
Beyond, big high over the Pacific but uncertainty over the Atlantic.
Worth noting that the GFS always has some parcel of weak heights close to the UK to allow the cold air to be near or over the UK and later on you can see that the PV is still pretty mangled.
At the moment the worst case scenario is a quick return to westerlies helped by the low heights being held on our side of the Arctic by that Pacific block, however if any weak heights can survive then clearly there is scope for anything ranging from cold snaps with wintry precipitation to something more substantial if things fall our way.
I can’t help but feel that the initial Greenland high will probably ease away quite swiftly, but that doesn’t guarantee that things will turn wet and windy, if I recall the February 2021 cold spell still happened despite losing the core heights to the north west as surface height persisted and allow an ENE flow for several days.
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The models moving towards a cold but rather dry initial northerly as pressure rises quickly and the winds veer more westerly again. However this feature north of Scotland needs watching.
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Probably a good thing that the ICON 18z doesn’t go out beyond day 5 because the low heights over Greenland don’t want to clear on this run to link the Atlantic ridge with the heights that push from the Pacific.
previous run
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GEM
This won’t go the GFS route though the alignment of the cold air will probably spill into the Atlantic a little too quickly.
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Eventually if we can hold the ridge in place the the next pulse of ridging from the states will reenforce the Atlantic heights as the disrupting trough clears away. That clearly would be the evolutions we want going further forwards to keep the cold in place over the UK. As alluded to, it would be better if the trough was a little further south east than modelled on the ICON, purely to deliver a better northerly rather than having winds back north westerly as shown on this run.
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I must confess that after seeing the heights to our north west disappear as quickly as a professional magician, seeing the cold air hang on with the flimsiest surface high is kind of amusing.
Shame because there is heavy snow on the frontal boundary.
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The GFS over the pole is even worse than the 00z, that run had cold air spilling into the Atlantic, this time this cold air from the Scandinavian trough to pushing through Greenland and very early on compared to the other models.
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The elements to the south are better, however there is a secondary low forming near Iceland and the cold pooling is flirting with the upstream troughing. At least the cold air is over the UK at this point and the risk of persistent snow in the south.
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Quite a different handling of the Azores low on this run.
06z
00z
Most of that low is pushing towards the UK on this run instead of stalling near the Azores.
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Model Output Discussion - Colder but how cold and for how long?
in Forecast Model Discussion
Posted
Monday surely has to be approaching the point where that north to north west flow might deliver something.
It wasn’t long ago that Monday was looking like a northerly quickly backing westerly during the day. Now this flow persists until Tuesday morning. It is one to watch because you could rule out bands of showers pushing south from northern Scotland that are currently not being picked up at this range.