Model discussion highlights

[sheikhy]

 HarvSlugger this little bump here!starts of as nothing a lot of the times but then interacts with the colder air and explodes and wrecks everything for us snow lovers....

Original post: https://community.netweather.tv/topic/100704-model-output-discussion-autumn-2024/?do=findComment&comment=5155925

[Geordiesnow]

 chris888 Because a polar maritime low pressure system tends to be clean and don't have fronts wrapped around it so you can have a situation where it's low pressure but for the vast majority it's dry and sunny. We have seen it last year and it surprised people.

Original post: https://community.netweather.tv/topic/100704-model-output-discussion-autumn-2024/?do=findComment&comment=5156004

[Cambrian]

It’s always good to look at the trend, but particularly when the trend is your friend.

The first wave of cold air is now set to land in the UK and Ireland by day 5 or 6. 

This is what was modelled for day 6 (18th), three days ago, when it was at day 9 and people were contemplating insufficient retrogression of the heights and topplers. 

 

These are from today’s 6z GEFS at day 6. 

 

The upper flow into the UK and Ireland is coming from Greenland in today’s chart, the Scandinavian trough is a lot deeper and extending a good deal further south, compared with an Atlantic flow and the shallower trough envisaged a few days ago, and this has an enormous impact on the local T850s. And look at that warm air advection into Northern Canada. 

Following the contours further back from Greenland, around the top of the ridge, they can be traced back to around Seattle / Vancouver on the North American Pacific coast, providing plenty of time for the Arctic to cool the air.

But believe it or not, as currently modelled, things are about to get even better!

By day 9 on today’s 6z GEFS, all that WAA heading up into Northern Canada is continuing to feed that build of heights centred on Baffin Island, but a build of heights now also extends west through the whole of Canada and into Alaska, which has bent the heights contours signifying the upper flow…

 

..so that they not only provide the UK and Ireland with an upper feed from Northern Greenland, but when traced back, the feed originates over Arctic Canada, Alaska, and can even be followed all the way back to Siberia. 

I cannot recall ever seeing an upper flow setup like this.

The T850s are responding with a signal for being 7 degrees below normal. This is on a mean at day 9.

The last three days of the models have provided a striking trend towards a compelling and rare hemispheric profile. Loads to enjoy! 

Original post: https://community.netweather.tv/topic/100704-model-output-discussion-autumn-2024/?do=findComment&comment=5156347

[Uncertainty]

The thing I like about recent runs, and indeed the longer term prospects on the 46, is the emergence of a potential Ural high. As much as this coming cold spell is an exciting novelty it will almost certainly get turned over in short shrift by the Atlantic late week 2 / early week 3. Perhaps earlier. The mjo passing into the warm phases, ec output etc all support this. However, we haven’t even started with winter yet, and thus my eyes are drawn not to Greenland but to the Urals. It is here that a semi- permanent high could perturb the strat to unlock arctic cold into the heart of winter. We are now starting to see this in the extended GEFS and eps.

Here we have the Ural high forming, pumped up by our euro low

A few days later, on the GEFS, the Atlantic pattern is no longer favourable for cold and snow lovers in Blighty - as expected- but the Ural high persists.

Importantly, it looks like sticking around on the ec 46

W2

W3

W4

 

If we get a 3-4 week spell of Ural heights, you would expect to see a response in the strat around the turn of the year. This might seem like ‘jam tomorrow’, but if we don’t manifest the high in that region, the SPV will power itself up and ensure that this coming spell is the only one we get for a rather long time. 
 

Obviously, for us coldies, we’d like to have our cake and eat it - e.g have a proper cold spell now and ensure an ssw down the line for the heart of winter. Is that plausible? Well, tonight’s ecm just about manages it. And I have to say this cold spell is looking rather potent, we have had many November cold snaps recently and few have gone on to deliver the goods in the heart of winter. Will this be our year? Perhaps. Perhaps not. The seasonals seem to think the latter. But they blew it last year and I’m not convinced they’ve got the central based Nina quite right. Also, if you squint a bit, there’s a hint of an Atlantic tripole

Furthermore, the IOD is more negative than positive. Always a good thing if you want to avoid an Atlantic onslaught. 
 

Im curiously optimistic about this whole season ahead, but we have been burned so so so so so so so so so so many times that it can only be a faint hope. But it is there, somewhere over the Urals, waiting to blossom into the winter we’ve all been waiting for. 

Looking forward to getting back to it.

Josh

 

 

 

Original post: https://community.netweather.tv/topic/100704-model-output-discussion-autumn-2024/?do=findComment&comment=5156769

[Kasim Awan]

Yes we've seen model convergence towards less jet stream energy which was responsible for strengthening the sw flow. This means less interrupted northerly. This now the more favoured result. Getting into reliable time frame now. -5 at 850hpa is ample for snow to lower levels given the lower isotherms associated with 525dam air. On this consensus the flow isn't particularly strong but the low pressure allows for strong convection. This means big rain showers on the coast moving inland and falling as accumulating snow 10-15 miles inland onwards.

Original post: https://community.netweather.tv/topic/100704-model-output-discussion-autumn-2024/?do=findComment&comment=5156865