bluearmy

February 16

Just noticed that some of the AI models now go to day 15

be interesting to see how their verification stats check out

February 16

phil nw. I think the lack of strong reversal below 65N has meant we’ve not seen an appetite to drive blocking at a latitude that delivers deep cold uppers to where we would need it to

we’ve had a lot of neg AO this winter (likely a consequence of the warmings early dec and first half Jan) but this hasn’t forced the cold far enough south. If we’d seen those reverse flows properly getting down to 60N then maybe we’d have seen the February many expected

February 16

49 minutes ago, CoventryWeather said:

There's a risk of something cooler later next week, looks like a core of the polar vortex moves near to Scotland.

Most wish that were so

sadly it’s just a deep low spawned from the remnants of the Newfoundland segment

the Atlantic is way too warm for anything to survive the long sea track from n America. Certainly opportunities for snow over the north of the U.K. with elevation

we’ve seen a couple of gfs ops headed more blocky - is that a consequence of the reversal high up now being in the starting data ? if it continues then you’d have to wonder …

February 16

There is a chance

a few runs sniffing at a trough extension from the west which undercuts the ridge behind the northerly. The cyclonic northerly on offer looks v unlikely to be cold enough away from elevation in the north. But with uppers -3/-4 in place behind the low, a trough extending across and undercutting the ridge would bring a neg tilted front into the U.K.

timing around 26 feb /28 feb

February 14

Blessed Weather

yes - the tech reversal at 10 hpa 60N is looking brief and doesn’t get much below 10 hpa at that latitude

however, it you look at the wider picture, it’s a large reversal

and the gfs00z op still has a sig area of reversed flow by day 13

the direction of travel on the movement of the spv fits with an active Atlantic feeding systems into a broad sceuro trough. Possibilities for some wintriness but no sign of any deeply cold 850’s. Elevation could do quite well.

It does look like a split/displacement hybrid with the split v short lived indeed at 10 hpa whilst in the mid strat it is very evident and lasts a couple days. The fairly rapid rejoining of the split looks to be responsible for the Atlantic jet strength and the upcoming nw euro trough.

the reversal up top due to arrive later today - not sure when it will be incorporated into the starting data but always worth looking out for any subtle changes once that has happened. The nwp should have this by now though and over the past few days the drift towards the nw euro trough would seem to be the ‘’surprise’ that this reversal has delivered

February 13

Penrith Snow because the Atlantic has generally won out fairly swiftly, the gfs will usually win the model battle as it reverts to type ! on a very broadscale level, gfs has looked good but closer analysis of the heights would reveal that it’s probably no better than any of the others.

February 13

Dennis yep dennis - even on a gfs op at such a range that’s unusual. It doesn’t hang around on its way towards Iceland but it does leave a broad w euro trough behind lower down.

I’ve been pretty impressed with the gfs op in the upper strat this winter. Of course you can’t look at one run in isolation and need to check them all so you get a handle on likely continuity.

February 13

daz_4 of course it’s more complex than that but in general I agree with your point. We can’t micro analyse charts at such a range - there’s no point.

February 12

feb1991blizzard phil nw. although you wouldn’t bet against that pattern verifying further north than currently modelled aswell

February 12

Next weeks attack from the Atlantic long wave trough is now at latitude Scotland on the gefs

a few days ago it was into the southern half of the U.K. as higher heights to our west and nw deflected it south. More evidence that everything is verifying 10 degrees further north than we need.???

February 12

The gfs ops are not interested in quick downwelling of the reversal wave beyond 100hpa (and that’s towards the pole)

so whilst we see the strat pattern trying to imprint into the trop in the form of the scandi trough, we wouldn’t expect to see any drastic impression into the trop of reverse flow away from the ongoing neg AO which is predicted to trend towards neutral post warming. You’d deduce that last weeks output was generally seeing that reversal wave headed down to lower latitudes and perhaps below 100hpa. It still seems likely that we get a split in the mid strat - unless we see that becoming wider and more sustained, we’d probably be better off with a straight displacement over scandi which would probably have allowed a proper Atlantic height rise to manifest. Could be argued that the strat reversal pattern has screwed up a promising trop pattern again and pushed things back 10 days or so. (At least)

February 12

Rain All Nightcertainly looks that way

all the ens suites have a ridge trough profile for the back end of the month. We don’t seem able to get there sooner. That could be strat related too but I’ve lost the will to analyse it. In general it looks like I posted the other day where the mid levels split properly and the upper levels don’t. The split is readily put back together again which means the Atlantic doesn’t quieten.

the promising week 2 arctic profile on many op runs over the past week has failed to materialise.

going back to the back end of the month - it’s the end of feb. As far as the prospects of a decent non transitional snowfall is concerned, it would be a struggle - maybe 20% chance that cold enough 850’s involved and then you need to throw a double six!

February 10

Froze were the Days Gowon

We should wait until closer to the reversal to see if the models begin to show better grouping around a different way forwards and certainly until afterwards for signs that they didn’t work it out

Re timing - whilst there will be a degree of variance on dates for reversal at 60N 10hpa between the 16th and 20th, the action up top starts 15/16th and thats the date to use to check continuity.

We are seeing inconsistencies run to run on gfs ops ref the reversal and what strat pattern follows

what seems fairly solid for now is that a split spv is more likely lower down than high up. That throws in a degree of uncertainty.

Original post: https://community.netweather.tv/topic/99814-model-output-discussion-22nd-jan-2024-onwards/?do=findComment&comment=5035593

February 10

Re the gefs 06z suite

the mean Atlantic low anoms head in around T300. Looking through the stamps there are plenty of runs which don’t do this. But the ones that do are not at a good latitude to bring a snow event.

the scandi trough pushes sw a couple days later - that looks a better set up

February 10

Froze were the Days Gowon

We should wait until closer to the reversal to see if the models begin to show better grouping around a different way forwards and certainly until afterwards for signs that they didn’t work it out

Re timing - whilst there will be a degree of variance on dates for reversal at 60N 10hpa between the 16th and 20th, the action up top starts 15/16th and thats the date to use to check continuity.

We are seeing inconsistencies run to run on gfs ops ref the reversal and what strat pattern follows

what seems fairly solid for now is that a split spv is more likely lower down than high up. That throws in a degree of uncertainty.

February 10

Incidentally, upcoming ssw says we shouldn’t be taking too much from week 2 ens nwp until mid month output once it gets a handle on the switch

I didn’t think the eps did a bad job in jan with the reversal at a high latitude. It’s surely the same issues for the nwp to handle. But we’ll see within a week if there is a solid change in direction.

February 10

Nick F we are in the midst of a solid period of neg AO and neg NAO. Indeed since Xmas, only the period 19th Jan to 4th feb was positive and it looks like the remainder of feb will remain negative. That would be only 25% of the 65 day period positive.

The NAO is pretty much the same stats

there has been plenty of northern blocking on offer. Are we just unlucky? we could easily have had a countrywide snowy period mid jan with a tweak here and there. Similarly, it wouldn’t have taken much of an adjustment for us to in that situation now. Perhaps Aaron had it right when he lamented the failure of the early jan tech reversal, with the negatives staying mainly above 70N. The general patterns aren’t bad for winter (see Scandinavia’s numbers) but they are that bit too far north.

a lot of talk of Iberian heights - sometimes these are relevant as an issue but more often, they’re referenced incorrectly as being the problem when merely a consequence of downstream ridging of persistent upstream Atlantic troughing at lowish latitude (that neg NAO ). Without blocking in the right places to deflect the jet into europe we can’t advect cold across nw europe

Many won’t accept we can just be unlucky and need to find reasons. CC seems an easy one to pick on. Could be. We don’t know.

February 9

This op develops quite a strat split so I’d assume we’ll see a decent trop pattern in far off fi

February 9

Bricriuwas back up to 74% after the 06z run

if it’ keeps swinging back and forth in the 60-75% area then would begin to wonder a little

it should gain traction with around a week to go

February 9

I’ve been watching gfs ops playing later week 2 with the strat pattern and we begin to see some consistency now

if we take current modelling on gefs, eps and the ec and gfs op at face value, there will be an ssw just beyond mid month

this will be caused by an Asian ridge moving across the Alaska and then pushing into the pole and stretching the spv over our side of the pole

this at 10hpa. As we go down through the strat, the vortex is more stretched and infact has begun to split

a couple days later we have a n russian master and Icelandic daughter split

At 50hpa this split is more evident with the daughter almost making it to Newfoundland.

so by day 10 we have a scenario where the split in the atmosphere is more defined lower down with clarity in the trop ref a split

so you could argue that the stretching of the spv is fairly instantaneous through all levels of the strat but it seems lower down the split is clearer

the concern I have had over the past couple days is illustrated later in this run

A day later and at 10hpa, the split is no longer evident with the Icelandic daughter absorbed back into the Asian master as a trough extension across the Atlantic sector

meanwhile, lower down in the mid strat, things look pretty good at the same timescale as far as split sustainability is concerned

But this is where it gets ‘ugly’ (and has often done so for the past few runs ). Initially the mid strat split tries to widen further but quickly begins to return east to join back up with the master segment which is itself drifting west into n Scandinavia and extending further west. So we end up with 10hpa , 30hpa and 50 hpa like this at day 16

this is mirrored as we head down through the strat

so to begin with, we have the whole strat moving very much in tandem as it splits but high up, that split is brief and like an elastic band, it begins to pull the vortex segments further down back together over the next few days.

this is an explanation as to why we are likely to see the Atlantic jet firing up as we go through the latter part of week 2. It may not be so different to what we saw in January where a decent looking trop profile was blasted away quite quickly.

we would need a wedge or weak ridge to deflect the jet onto a southern trajectory such that we stay on the cold side when it arrives nw europe.

it’s not a done deal by any means but I think this is where the modelling is getting the strengthening atlanttic profile from. it may not be a bad thing if we get our ducks in a row when it happens. The gfs 06z op looks like it re amplifies behind the system heading east.

just thought it interesting to see how the waves seem to head down/up/ down through the atmosphere

Original post: https://community.netweather.tv/topic/99814-model-output-discussion-22nd-jan-2024-onwards/?do=findComment&comment=5034946

February 9

BarnetBlizzard it’s possible

But so were many things over the past few months that didn’t happen !

February 9