Winter Approaching: Strictly Model Discussion (and highlights)

[nick sussex]

The week of the two or perhaps 3 shortwaves !

The first one the current drama with the shortwave low and we've been  chasing that one around for days.

The second one just highlighted by Mconnor.

The third one in relation to the shortwave heading sw from Iceland day 5 into 6 .

The third one is most important for either extending the cold or getting back quickly into the colder conditions after a milder blip . 

There's still a chance that the north particularly Scotland could remain cold throughout with any milder weather temporarily effecting other areas .

When you get phasing with a main low you're likely to see the combined system deepen and want to head ne .

So the question is how much that occurs and can the low possibly absorb that shortwave more readily . So definitely we want as weaker shortwave as possible in that instant .

The ECM is certainly a nice run but the shortwave low interaction at this timeframe won't be modelled correctly and so much hinges on that .

And we also need the right movement of PV and upstream troughing to box in those height rises to the nw .

Overall then a fun week coming up ! I'll be watching that day 5 into 6 shortwave like a hawk ! 

Original post: https://community.netweather.tv/topic/100917-winter-approaching-forecast-and-model-discussion-commentary/?do=findComment&comment=5161980

[Mike Poole]

ECM clusters this morning, T120-T168:

Variants on a theme here, with a return to westerly winds by day 7, but the amount of cold air in place is open to question.

T192-T240:

Cluster 1 builds back the Greenland high and becomes colder - this includes the ECM op and 16 members.  Cluster 2 looks even colder to me and has 15 members - so these two cluster represent quite a significant shift back to cold this morning.  

Cluster 3 looks +NAO throughout, and cluster 4 also, but this one is building heights into Scandi rather than to our south.  Cluster 5 sees us trapped between two highs and is cold, but only 5 members.

T264+:

This period is encouraging, because it looks blocked on all clusters.  They are quite different, cluster 1 holds heights in Greenland and has a ridge UK moving to the Atlantic, cluster 2 also has heights in Greenland.  Cluster 3 builds an Iceland, Scandi high - the extended op might it well here.

Overall, medium term is a big improvement. 

Original post: https://community.netweather.tv/topic/100917-winter-approaching-forecast-and-model-discussion-commentary/?do=findComment&comment=5162049

[Met4Cast]

 Nick123 

Other models show snow further south of the UKV area but I don't think the snow is likely to be disruptive, i.e any accumulations further south will likely be across the higher ground. 

Worth remembering that the Met Office warnings are impact based, i.e will snowfall cause disruption? If yes, a warning is issued where disruption is plausible, it's not a warning to show where snow may fall, with that in mind the warning area at least to me looks about right, most models have the highest accumulative snowfall within the Met Office warning area. 

FWIW here's my current thinking;

Original post: https://community.netweather.tv/topic/100917-winter-approaching-forecast-and-model-discussion-commentary/?do=findComment&comment=5162243

[Met4Cast]

MOGREPS extends the cold right until the end of the run, by the way.

Original post: https://community.netweather.tv/topic/100917-winter-approaching-forecast-and-model-discussion-commentary/?do=findComment&comment=5162271

[phil nw.]

Plenty of reading about this low approaching the country as hit engages the cold air and it's only mid-November!

Anyhow hopefully some of this interest is rewarded with some snowfall for some lucky people.Latest trends seem to be homing in towards the Lancs,Yorks area and south through the peaks and the north Midlands,maybe a little further south but not by much.

I hope that this is just the appetiser for more and looking at the latest operational charts for this coming Saturday holds some hope of the cold pattern not breaking completely.

The charts for the weekend sees a battle between the continuing Atlantic/Greenland ridging  and the sub-tropical heights squeezing the low pressure dropping down from Iceland towards the UK.

Looking at the day 10 mean 850s sees the difference in the suites on how this develops

GFS less cold as the milder up pushes further north but the other 2 staying colder.

Currently there is no sign of returning to a full blown +NAO/AO as there remains plenty of blocking  to our north which is keeping the bulk of jet further south so the cold air remains close by.

We have to pinch ourselves that we are still nearly 2 weeks away from the start  of Winter proper so this cold spell is an early bonus with hopefully more to come.

Original post: https://community.netweather.tv/topic/100917-winter-approaching-forecast-and-model-discussion-commentary/?do=findComment&comment=5162367

[*Stormforce~beka*]

 Tim Bland 1cm is not my 7 inches ...

Original post: https://community.netweather.tv/topic/100917-winter-approaching-forecast-and-model-discussion-commentary/?do=findComment&comment=5162373

[nick sussex]

The ECM and UKMO handle that shortwave energy heading se quite differently .

From as early as T36 hrs you can see the elongated formation of the former with the energy splitting into several smaller shortwaves v the UKMO more oval with one main one .

Because of this the forecast is even more liable to change .

ECM

 

UKMO

Original post: https://community.netweather.tv/topic/100917-winter-approaching-forecast-and-model-discussion-commentary/?do=findComment&comment=5162460

[Mike Poole]

As the 12z ICON starts to roll, here’s my summary of where we are right now, and through December:

• The low forecast for Monday night/Tuesday morning is still uncertain.  The snow is likely just north of the track of this low, probably parts of northern England, the midlands, north Wales and East Anglia.
• The track was still uncertain by up to 200 miles in the north/south direction on the 0z models.
• Cold will flood south after this feature goes through, some may see snow on the back edge.
• The UK will remain under cold air until the weekend, during which time there is the potential for further snow should any features crop up.  
• There may be snow as milder air tries to push in from the southwest at the weekend.  
• At this point, the colder air may make a return, or the mild air may win out.  This is undecided.
• Medium range, the models still suggest potential for high latitude blocking, so further periods of cold weather still look possible into December, the following look relevant:
• The MJO is currently low amplitude (Circle of Death) in the Indian Ocean, where it is neither helpful nor unhelpful, it may become helpful again as it moves through phase 6 or 7 in a few weeks time.  
• The strat polar vortex is forecast to accelerate over the next few weeks, but remaining uncoupled with the trop vortex, which the models (ECM 46 dayer) suggest will remain disturbed.  This state will not last for ever, the clock will be ticking.
• I think these last two present something of a race, as to whether the MJO can reach favourable phases (plus a 10 day lag) before the strat and trop vortexes couple, if it does, then a further period of strong blocking is possible, if not, the MJO will struggle to override the impact of the strat vortex.  To that end, it would be beneficial if the MJO would stop nancying around in the Indian Ocean and get a move on through Phases 4 and 5.  
• A SSW is not currently considered likely before the new year.

Original post: https://community.netweather.tv/topic/100917-winter-approaching-forecast-and-model-discussion-commentary/?do=findComment&comment=5162543

[Easily sled]

Not sure you guys can keep this up for the entire winter, this is a 3 day cold spell and yet it’s being played out like Narnia is on our doorstep. You will be drained if you are going to over analyse every single run from here on in.  Not sure this new forum set up is working but good luck to you all! 

Original post: https://community.netweather.tv/topic/100917-winter-approaching-forecast-and-model-discussion-commentary/?do=findComment&comment=5162462

[Weather-history]

Something just struck me

18th November 2024

 

7th December 1981

 

 

Surely not.....

 

Original post: https://community.netweather.tv/topic/100917-winter-approaching-forecast-and-model-discussion-commentary/?do=findComment&comment=5162627

[blizzard81]

The milder relaxation is looking more and more like a blink and miss it affair. Especially the further north you are.

Original post: https://community.netweather.tv/topic/100917-winter-approaching-forecast-and-model-discussion-commentary/?do=findComment&comment=5162565

[Tim Bland]

Weds night on Arpege for the south of the m4 crew…

[Mcconnor8]

What is this Alaro model giving London snow? 

Original post: https://community.netweather.tv/topic/100917-winter-approaching-forecast-and-model-discussion-commentary/?do=findComment&comment=5162748

[Allseasons-Si]

UKMO HD animation from T30 - T45 hrs

 

Original post: https://community.netweather.tv/topic/100917-winter-approaching-forecast-and-model-discussion-commentary/?do=findComment&comment=5162757

[WYorksWeather]

Not strictly model related but hopefully this is useful - Meteociel has a section showing the current location and readings from buoys and ships, including pressure readings.

On the Atlantic view, the low is currently centred at 1013mb, looks directly west of Scotland at the moment, as of a few minutes ago. That roughly corresponds to T+6 for the 12z models. 

Does anyone have any sense of which models this looks closest to? Might be best to focus in on ones that are correctly representing the situation as of now, and then forecasting further ahead.

Original post: https://community.netweather.tv/topic/100917-winter-approaching-forecast-and-model-discussion-commentary/?do=findComment&comment=5163019

[Jordan S]

The Arome highlights well the differences in projected track of the low between a couple other models especially with the centre.. centre of the low through far south Wales through M4 corridor and through London, sleet and snow to the north of the centre, which would be much of Wales, much of the Midlands and parts of east Anglia.

The snow accumulation chart which are not to be taken literally due to certain factors is still quite realistic if we are talking for ground around 100-150m wherever the final track is, upto 2-5cm quite widely at these elevations but there would be much more than 5cm above these heights in some areas, perhaps as much as 15-20cm on ground above 200-300m, limited settling below 100m for most of the area, but not to be ruled out, especially on the very northern area of the precipitation.

Later tomorrow night It interestingly shows a reintensification of the precipitation as another disturbance moves east just behind the main low, this would bring a period of snow further south.

The below shows my thoughts over the last few days on track from a few days ago to most recent thought..

As you can see not huge swings really and it helps when not being influenced by odd operational runs.

I believe this may be the final track and subsequent snow risk area, snow may fall slightly south of this as the low pulls away.

Original post: https://community.netweather.tv/topic/100917-winter-approaching-forecast-and-model-discussion-commentary/?do=findComment&comment=5162836

[WYorksWeather]

EC clusters below.

Days 3-4

Cold air flooding back in after the low passes through the UK.

Days 5-7

Cluster 1 (41%) has a fairly weak build of pressure to the south, and hence any milder weather is likely limited to the south.

Cluster 2 (39%) raises heights more strongly to the south, and hence likely significantly milder. Cluster 3 (20%) is similar.

The OP was in Cluster 2.

Days 8-10

Cluster 1 (37%) has high pressure building from the south and also through the UK. Potentially cold by night with a south-easterly, but mild-ish by day.

Cluster 2 (25%) starts wet and mild at day 8, but builds high pressure from Europe through the UK. Again, likely reasonably mild by day, but cold by night under the high. Winds from the south-east.

Cluster 3 (20%) is fairly unsettled at days 8-9, and possibly cold-ish with winds from the NW. By day 10, a ridge builds just to the west of the UK, possibly allowing a cold snap.

Cluster 4 (18%) has a ridge from Europe through to an area of high pressure centred to the west of the UK. Quite a complex pattern, with a colder north-westerly or northerly influence into the north of the UK, and a milder southerly for areas further south.

The OP was in Cluster 1.

Days 11-15

All very uncertain by this stage, but here goes.

Cluster 1 (35%) starts with a mild southerly at day 11, but the high eventually becomes centred more to the north of the UK. This could allow a cold northerly or north-easterly.

Cluster 2 (33%) starts fairly wet and mild at day 11, then has an unusual pattern with a high ridging from Iberia up to Greenland through the UK at day 13, then reverts back to a flat westerly by day 15.

Cluster 3 (31%) starts with a mild southerly at day 11, but eventually ridges the high further north, with an extension over Scandinavia. This brings in a cold easterly.

Summary

Overall, a clear picture for cold to continue through most of next week. Towards the weekend, signs of heights rising to the south. The ensemble favours by 60-40 a scenario of a more substantial build of heights bringing significantly milder conditions. The other 40% has a weaker build of pressure, and stays colder, especially further north.

Beyond that, the day 8-10 range is dominated by a quiet and fairly non-descript scenario, with a UK high ridging back to Europe, but centred to our west. This would be cold by night, but probably mild-ish by day. A minority (20%) sets up a cold snap, with a ridge appearing almost out of nowhere to the west of the UK, blocking off the Atlantic and bringing back the northerly winds.

In the extended range, perhaps hints of some more blocking scenarios. Overall, the ensemble favours a renewed colder scenario by about 65-35, but clearly very hard to know where any blocking will set up at this stage.

In the days ahead I would suggest continuing to look at the extent of any build of pressure to our south, which will probably change somewhat from run to run. We want to avoid The Curse of the Iberian High if we are to hang onto colder conditions.

 

Original post: https://community.netweather.tv/topic/100917-winter-approaching-forecast-and-model-discussion-commentary/?do=findComment&comment=5163114

[manutdmatt1986]

I can guarantee the track of the low and subsequent snow risk will be certain by Wednesday.

Original post: https://community.netweather.tv/topic/100917-winter-approaching-forecast-and-model-discussion-commentary/?do=findComment&comment=5163255

[Allseasons-Si]

This shortwave has developped a little friend to the NE,run the animation by using the arrows,you have to keep refreshing the site for nearly live data.

Meteociel - Pression atmosphérique observée en temps réel en Atlantique

WWW.METEOCIEL.FR

---

Pression atmosphÃrique en temps réel des stations de France et des pays limitrophes.

 

Original post: https://community.netweather.tv/topic/100917-winter-approaching-forecast-and-model-discussion-commentary/?do=findComment&comment=5163226

[Kasim Awan]

..

Original post: https://community.netweather.tv/topic/100917-winter-approaching-forecast-and-model-discussion-commentary/?do=findComment&comment=5163326

[WYorksWeather]

With all the talk about the snow, no one has really dissected the GFS 18z later on in the run.

The cold spell has a decent amount of longevity. At day 5, all of the UK is still under the cold air.

We then are looking at the weekend low. This is a very deep low, passing just to the NW of Scotland on this run. Could well be a named storm if this came off.

However, unlike some other runs, the low exits more to the north / NE of the UK rather than directly east.

This then allows the Azores high to inflate massively in FI. Right chart, wrong time of year. That would have been a nice warm spell even a couple of months ago, but right now it would just be mild. 

By day 14 though, the high escapes northwards up towards Iceland, producing a northerly.

The high then escapes to the NE from there and brings in a cold north-easterly.

Certainly would be a very varied and interesting next couple of weeks if this came off! We'd have the current cold spell, a significant storm, a very mild and dry period, and then another cold spell.

 

 

Original post: https://community.netweather.tv/topic/100917-winter-approaching-forecast-and-model-discussion-commentary/?do=findComment&comment=5163436

[booferking]

UKMO North by 10.8 miles

Original post: https://community.netweather.tv/topic/100917-winter-approaching-forecast-and-model-discussion-commentary/?do=findComment&comment=5163387

[Met4Cast]

It's worth noting that while it seems models are massively different, we're only talking about a difference of 100-150 miles at most, in terms of the size of the planet that really is quite small. 

We're only tracking these minute changes/details because we want snow!

Original post: https://community.netweather.tv/topic/100917-winter-approaching-forecast-and-model-discussion-commentary/?do=findComment&comment=5163353

[Met4Cast]

After reviewing the models this evening (the day job really is starting to get in the way of this model watching lark!) here's my latest thinking;

Absolutely no idea.

Original post: https://community.netweather.tv/topic/100917-winter-approaching-forecast-and-model-discussion-commentary/?do=findComment&comment=5163445

[Blessed Weather]

Interesting discussion about whether there are two different low pressure systems at play over the next 24 hours. Checking this morning's 0z runs the first thing to notice is the remarkable difference in the SLP charts from GFS and ECM - and this at just 12-15 hours away. GFS low centred over Wales, ECM main low centred over the Thames Estuary and with a secondary feature over Ireland:

10pm Mon GFS  ECM

The fax chart from the Met Office at midnight tonight shows one low pressure and one elongated front, as per GFS:

And whilst Arpege supports the GFS view of where the main centre of the low will be (Wales), in contrast to GFS it has the secondary low clearly showing, as per the ECM.

Arpege Mon 10pm

So the difference in models with whether there's one or two low pressure centres and the timing - particularly ECM timing - seems extraordinary at such short time scales!

Edit: Adding the sources:
https://www.meteociel.fr/modeles/gfs/royaume-uni/pression/3h.htm
https://weather.us/model-charts/euro/europe/sea-level-pressure/20241119-0600z.html
https://www.netweather.tv/charts-and-data/fax

Original post: https://community.netweather.tv/topic/100917-winter-approaching-forecast-and-model-discussion-commentary/?do=findComment&comment=5163619