Could we see frigid weather from the east this January? A continuation



Context: the ECMWF 12z weather model on this date brought a cold easterly to the UK

What made this possible is the arctic high that's left over from the Greenland high migrating over to Scandinavia, contributing to the Greenland high. While this isn't guaranteed, this step isn't an unlikely scenario, especially due to the upcoming zonal flow being weak at most. It essentially acts as a block to the jet stream, so cold air from the eastern lobe of the TPV shifts into northern and eastern Europe





The next part is much more precarious, which is keeping Atlantic low-pressure systems just weak enough to allow the jet stream to move south, so the cold air over Scandinavia is lead our way. Subtle changes in the strength of lows pressure systems and their trajectory can have massive ramifications for the UK, which will be demonstrated below. Here's the GFS chart at 102h



As you can see, the slight ridge into west Europe is stronger, so therefore the jet stream is further north over the UK. As well as this, the low-pressure system over the mid-Atlantic is deeper and strengthening, while it weakens on the ECMWF. As a result, the cold pooling over northern and eastern Europe is forced out by the low-pressure system that may as well be an unstoppable force in this context before it crosses the UK





In contrast, the weakening low pressure systems on the ECMWF stops the cold air being blocked, and it stays over the same area, where it lays dormant before the zonal flow can be reduced. It's important to remember that this is only possible since the zonal flow in the Atlantic is weak, otherwise, the strengthening of low-pressure systems would be inevitable. Here's the last step, where you need an anomalous temperature contrast in North America that's not too far north to spawn a low-pressure system that rapidly spins anticlockwise, giving the Atlantic enough anticlockwise energy to drive ridging. I noted something like this back in mid-December, where the seemingly unfavorable position of the TPV over Canada actually was the essential factor that allowed what really wasn't far off a very cold easterly





And there you go, the ridging blocks the zonal flow, and the once dormant cold pooling over more continental Europe now hits us. It isn't a perfect setup, but worrying about micro details at the day 9 range is very unnecessary





Now here comes an optional last step, and a far more unlikely one that's more to do with demonstrating the importance of a temperature contrast, rather than making a forecast based off what's a realistic outcome. The TPV gathers over Canada, causing an exceptional temperature contrast between the warmer USA and the fridge Greenland, causing more ridging, in a perfect place, creating a second burst of a brutal easterly






Props to Mike Poole on netweather for reminding me of the ECMWF clusters. Here they are, and they show that such a scenario of a cold easterly (ignoring the last paragraph) isn't all that unlikely, and is actually at a population of 12/52, or 27%, on the top row




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