Winter Approaching: Strictly Model Discussion (and highlights)

[nick sussex]

The T24 hrs fax chart looks interesting . Pretty sure they've modified this from the raw output .

The low seems to be exiting further south and there's that wave on the front near Bristol. 

Original post: https://community.netweather.tv/topic/100917-winter-approaching-forecast-and-model-discussion-commentary/?do=findComment&comment=5163793

[Met4Cast]

We’re into full nowcast territory where analysis charts, say images & radar should take president over model data. 

Low is on track to move in just north of Pembrokeshire and exit around the Thames Estuary. 

This places the main snow risk between Birmingham & Manchester. 

Original post: https://community.netweather.tv/topic/100917-winter-approaching-forecast-and-model-discussion-commentary/?do=findComment&comment=5163780

[Allseasons-Si]

Just a quick one from me about the latest ob's

a secondary feature formed to the NE at 10:50 pm last night and is now to the NW of the shortwave,this is that secondary feature that is showing on some of the models and it will be interesting to see where this tracks as it continues to pivot anticlockwise around the low.

Original post: https://community.netweather.tv/topic/100917-winter-approaching-forecast-and-model-discussion-commentary/?do=findComment&comment=5163850

[Mike Poole]

ECM clusters this morning, looking at the medium term.  T192-T240:

Cluster 1 is straightforward westerlies, cluster 2 trends towards a UK high, cluster 3 trends towards a Scandi high and cluster 4 is a UK high.

T264+:

The signal is increasing for some kind of blocking over Scandi to take hold - this is something that @Cheshire Freeze, @Dennis and I have been suggesting as an eventual outcome, and the red borders show this regime, and the increased signal for this also shown on the regimes plot from the 46 dayer:

The thing is, though, this red Scandi blocking regime, well it seems to be quite a broad church (we see this in the summer too) and while it is a welcome step away from +NAO zonal, there is some work to do to get a high pressure over Scandi correctly aligned to bring in cold from the east.  Work in progress…

Original post: https://community.netweather.tv/topic/100917-winter-approaching-forecast-and-model-discussion-commentary/?do=findComment&comment=5163813

[sheikhy]

@bluearmy any update on the 06z ecm?!!

[Paul_1978]

 Met4Cast Yes exactly. The professionals don’t often know all year round exactly where a low is going to track and normally no one bats an eyelid!

[Eagle Eye]

Snowfall risk - TODAY 

A significant early season snowfall risk as a low pressure system pushes through bringing rain for areas along the southern portion of the system, but with significant heavy snowfall for the midlands and northern parts of the country. Some heavy snowfall for northern parts of Ireland and parts of northern Ireland too spotted in with the same low pressure as it may get cold enough there for rain to turn into snow but further south it's less likely. 

Back building may occur a lot over north Wales meaning that there may be a rather significant amount of snowfall laying. Initially there may be rain falling but as the warm front getsa further away and the evening comes in, it should get cold enough for snow to fall across the Midlands and the rain initially streaming in to not mean much towards snowfall totals as the dewpoint gets well below freezing.  Scotland continues to see snowfall showers streaming in through Monday and Tuesday some of which may be heavy showers as well laying on top of what was previously layed and expending the size of the slight snowfall height area.

This is the main snow risk day by the looks of it. But there's the risk of falling snow from showers for large parts of the country for the rest of the week before the breakdown of the cold occurs. 

Original post: https://community.netweather.tv/topic/100917-winter-approaching-forecast-and-model-discussion-commentary/?do=findComment&comment=5163935

[bluearmy]

 sheikhy playing golf !

 it’s a little north due to a change in the structure of the low 

but the distribution of the snow further south from the second push is different  

so more uncertainty 

[Paul]

 Met4Cast It's pretty much at the furthest reaches north and east that the MOGREPS UK expected it to be this morning - this is the rain risk at 1500. (Please note rain risk, these maps are pre-production and don't include precip falling purely as snow at this point)

The UKV 12z has caught up a bit from this morning's runs but still a step to far southwest. 

Original post: https://community.netweather.tv/topic/100917-winter-approaching-forecast-and-model-discussion-commentary/?do=findComment&comment=5164132

[bluearmy]

Interesting gfs op which brings a n pacific and n Atlantic sector height rise 

This wave 2 splits the spv up to at least 30 mb and it’s something we should be looking for in respect of what damage a developing trop pattern could do do the strengthening spv. This run still shows the trop leading the dance (which makes forecasting what the spv is likely to do more difficult).

Original post: https://community.netweather.tv/topic/100917-winter-approaching-forecast-and-model-discussion-commentary/?do=findComment&comment=5164476

[Cold Winter Night]

EC 12z is an excellent example of a feature that to an untrained eye may look like a great Scandi High when viewing the anomaly chart:

But which isn't a real Scandi High at all and doesn't bring coldies what they want.

Always look for low 500 hPa height anomalies to our South in addition to high anomalies to the North or Northeast, if it's a true Scandi High you're after.

Original post: https://community.netweather.tv/topic/100917-winter-approaching-forecast-and-model-discussion-commentary/?do=findComment&comment=5164820

[chionomaniac]

I’ve been keeping an eye on this one and great to see the snow reports tonight. In this kind of set up when we have cold air embedded for a few days then I wouldn’t be surprised to see a few unexpected snowfalls. We have a main depression to the east of the country, sub -5°c 850 temps over the whole country with small vortices being produced to the west on the periphery of the colder air. It doesn’t take much for one of these to produce unexpected snow ( especially at night) at short notice despite the probability being low. 
Following on I expect the Irish to name Storm Bert, but lots of uncertainty after….

In a Nina year we need to take this early scenario and any disruptive wave breaks into the Strat, before we get into winter and a super Strat vortex. But I Am kind of expecting a mid to late winter SSW too that will disrupt any winter pattern that has set in. ( probably mid messy mucky highs over the southern uk) 

 

Original post: https://community.netweather.tv/topic/100917-winter-approaching-forecast-and-model-discussion-commentary/?do=findComment&comment=5165739

[Allseasons-Si]

Don't know if this has been posted,haven't checked back on the thread yet but looks promising up top...

Original post: https://community.netweather.tv/topic/100917-winter-approaching-forecast-and-model-discussion-commentary/?do=findComment&comment=5165706

[Anthony Burden]

Morning all,Snowing and settled in Oxford 8 am probably back edge of front must say did not expect lovely to see in a low lying city.

[Coldie24]

 northwestsnow That’s what usually happens after an early cold snap in November.

Saw it in Nov 1988.

Original post: https://community.netweather.tv/topic/100917-winter-approaching-forecast-and-model-discussion-commentary/?do=findComment&comment=5166203

[tight isobar]

Not thee- most desirable sets@ exmwf/ gfs- ens.. however nor, definitive breaches.. milder preferred but enough scatter to look for scope.. across upcoming raws-‘ops’…

[Mcconnor8]

UKMO 6z is interested in Thursday.

Original post: https://community.netweather.tv/topic/100917-winter-approaching-forecast-and-model-discussion-commentary/?do=findComment&comment=5166686

[johnholmes]

I doubt that the cold will persist much after Friday that is using the 500 mb anomalies as a guide. They did pretty well in predicting the upper pattern for this cold snap/spell. For the last couple of outputs they have shown more of a westerly Atlantic flow along with a rise in contour heights around the UK

Climate Prediction Center - 6-10 Day 500mb Outlook

WWW.CPC.NCEP.NOAA.GOV

 

Original post: https://community.netweather.tv/topic/100917-winter-approaching-forecast-and-model-discussion-commentary/?do=findComment&comment=5166723

[Mike Poole]

ECM clusters this evening, looking at the medium term, T192-T240:

Cluster 1 (33) has a pretty decent stab at a Scandi high, clearest signal yet, that’s actually the control run that’s shown.  Cluster 2 (18) has a southwesterly, but is possibly building towards a Scandi high at day 10.  Promising in this timeframe.

T264+:

Cluster 1 (25) continues the Scandi heights theme, even with link up to Greenland.  Cluster 2 (17) is +NAO.  Cluster 3 (9) builds a ridge in the Atlantic.

Original post: https://community.netweather.tv/topic/100917-winter-approaching-forecast-and-model-discussion-commentary/?do=findComment&comment=5167249

[Kirkcaldy Weather]

 

[Met4Cast]

I think we're going to have to accept that a +NAO period is likely but there is hope going forward into December.

 The MJO transitioning through the Indian Ocean phase 2-3 which supports a move away from the current blocked/colder pattern, high frequency waves will meet across the Indian Ocean in the coming days & this will amplify the MJO wave, this is well represented on the RMM plots with a sudden increase in amplitude;

As a result, we're going to see some fairly strong WWB events in the Indian Ocean, likely transferring into the Pacific as the MJO progresses eastwards.

This higher amplitude orbit transitioning eastwards into the Maritimes will kick start the +FT > +MT cycle helping to drive AAM tendency upwards, likely from a higher starting base than the previous cycle so I am expecting a more robust AAM response compared with the previous MJO cycle which ended up being rather muted. 

With this in mind, a +NAO phase seems very likely in the next couple of weeks once blocking wanes, exactly which shape this takes remains to be seen, I doubt it'll be a full on Atlantic onslaught with high pressure possibly close by, particularly to the south. 

Mid December into the second half of December is the next period of interest in terms of blocking potential. We just need to keep an eye on the sPV/tPV and hope we continue to see them in a de-coupled state.

Original post: https://community.netweather.tv/topic/100917-winter-approaching-forecast-and-model-discussion-commentary/?do=findComment&comment=5167671

[Blessed Weather]

41 minutes ago, Met4Cast said:

We just need to keep an eye on the sPV/tPV and hope we continue to see them in a de-coupled state.

Yep, a key point. The forecasts for 'up top' are a cause for concern atm, with the sPV potentially heading for record breaking strength as we head into Dec according to GEFS:

Source: http://weatheriscool.com/

Original post: https://community.netweather.tv/topic/100917-winter-approaching-forecast-and-model-discussion-commentary/?do=findComment&comment=5167722

[nick sussex]

The ECM spreads do show some uncertainty to the nw running se. Interestingly the ensembles for Iceland show a large spread in pressure with scope for higher pressure there .

In terms of the UKMO it should be noted that it has the flattest upstream pattern. 

Highlighted by the low there .

So the ECM at T120 hrs .

 

The UKMO for the same time .

This means the energy is spilling more east rather than se . It also effects that area of higher heights over ne Canada and into southern Greenland . 

Original post: https://community.netweather.tv/topic/100917-winter-approaching-forecast-and-model-discussion-commentary/?do=findComment&comment=5167739

[Jordan S]

The low moving into France tomorrow bringing an area of rain/sleet/snow into parts of the south/southwest tomorrow morning with falling sleet/snow inland, some snow accumulation is possible, a few cm's in a few places, rain in the far southwest.

Convergence along the northern/northeastern periphery of the precipitation could produce small spots of heavy sleet/snow amongst lighter precipitation, the areas of rain/sleet/snow tends to (but certainly not always) be slightly northeast than model output usually suggest for these exact scenarios, so in fact don't be surprised if the area of inland snow albeit perhaps lighter (apart from those possible small pockets of heavier precipitation) reaches mid/east Wales and then other southern counties of England upto south Midlands further east/southeast then to probably just west of London for a time, producing a possible covering of 1-3cm quite widely in some places even to relatively low levels, with a bit more (4-7cm) on high ground above 150-200m in a few spots, but this is more uncertain so certainly not to be taken as definitive but the potential is there.

(30%) Probability..

 

The below image more likely, (60-70%) northern/northeastern most point of the precipitation reaches far south Wales and areas just southwest of the Cotswolds, which could give similar totals to just described above for a few places, again rain/sleet for far southwest, largely sleet in other coastal spots and though unlikely, intermittent falling (not settling) snow not to be completely ruled out for a few in any heavy bursts.

Most of the precipitation heads into France regardless. Snow showers for Scotland, some significant accumulations likely in some inland areas.

Central/South republic of Ireland looking set to see significant and quite widespread snowfall tonight / early tomorrow with significant accumulations to some lower levels away from the far south, with upto 10-15cm possible in some places, on especially ground above 200m, locally more is possible.

Now with the deep low for the weekend and slightly beyond..

On 18/11/2024 at 15:30, Jordan S said:

The low pressure system for Saturday certainly might cause a few issues, been highlighted for a good few days from model output, possible 45-55mph wind gusts in some inland areas of England and Wales, upto 65mph possible on exposed coasts, risk of brief snow on the leading edge, more significant snow for central/northern Scotland a possibility throughout as this seems to be the area that may be to the north of the low centre which in fact looks to stagnate for a time to our west during Saturday before moving through Sunday into Monday, introducing colder air at least temporarily with high briefly out west, but the next weather system potentially approaching from the west by midweek next week.

Nothing really different expected compared to my thoughts from a couple of days ago on Saturday's deep low, but can add some more detail, the centre of the deep low pressure system for Saturday remaining to our west for a time as mentioned, heavy rain spreads northeast through the day, heavy snow preceding it in some northern/northeastern areas, with some temporary significant accumulation to high ground most likely, small risk of freezing rain in one or two spots in the north of England/northern Ireland..

Saturday morning..

Wind gusts of a very strong with 50-65mph along west and south coasts of England/Wales, maybe even 75mph in one or two very exposed coastal spots here (this much more likely later Saturday night and possibly Sunday.

Strong Inland gusts of 35-50mph are likely in many central, and eastern areas of England, 45-55mph over some southern and western counties of England, Wales/northwest England/parts of Scotland and northern Ireland, locally slightly more in exposure, especially round the coasts with some gusts upto 65-70mph possible in one or two coastal spots elsewhere further northwest exposed to the southwest wind.

Wind speed/not gusts are in knots below (knot conversion 1 knot= 1.15mph, the ECM (though not the only model, with the exception for the UKv) tends to often exaggerate wind speeds particularly for inland areas but nevertheless it shows the extent and locations of strong winds well, wind predictions from models most closely correlate to actual observed gusts when dealing with a strengthening low pressure system crossing the country or from frontal waves/wave depressions.

Any snowfall in the north/northeast turning back to rain for the majority, but may remain as snow for a while longer for parts of high ground of Scotland before possibly turning back to rain, turning much milder for central, southern England and Wales later Saturday and on Sunday with a slow moving front lingering and keeping intensity over southwest England stretching northeast through Wales and into central/ northern England, a wave is likely to develop along the front, delaying it's clearance until later on Sunday from eastern parts, could be 75-100mm in the wettest spots of Wales on high ground, with 25-50mm more generally here and indeed locally some other parts of the west and far south of England. 10-20mm everywhere else, locally a bit more, plenty of showers further north west, longer spells of rain in few places here.

Winds are likely to also strengthen within and just ahead of the rain once again later Saturday night and possibly through much of Sunday over much of Wales at first then more central/southern and eastern England with frequent gusts inland likely of 45-55mph more widely than earlier Saturday, locally 60mph possible in exposure, for west and more especially south/southwest coasts of England/Wales gusts could more frequently reach 55-65mph, locally a bit higher.

Further northwest winds ease later Saturday/Sunday then strengthen as the low centre moves across during Monday, but steadily weakening by then, snow risk possibly returns for high ground of Scotland.

As previously mentioned, high pressure to our west behind the low pressure system, with another low pressure system likely moving in later in the week next week bringing more rain and strong winds, though less so.

Higher pressure may linger for southern/southeastern England keeping things drier for longer before unsettled conditions probably return here Thursday or Friday next week.

Original post: https://community.netweather.tv/topic/100917-winter-approaching-forecast-and-model-discussion-commentary/?do=findComment&comment=5168024

[Yarmy]

Maybe we should all be using the FuXi ML model. 

The charts are on the ECM open charts site, but I just get spinning wheels for 500hpa geopot so I don't know if they are available generally.

Original post: https://community.netweather.tv/topic/100917-winter-approaching-forecast-and-model-discussion-commentary/?do=findComment&comment=5167962