Winter Approaching: Strictly Model Discussion (and highlights)

[Community Team]

As part of the new thread layout, this is the accompanying thread to the Forecast and model commentary discussion. This thread will also house the highlights from that thread, with those posts with enough 'insightful' reactions copied into here. 

This thread is strictly for discussing output from numerical weather prediction models including short and medium range and seasonal models. It will also include insightful posts auto-copied over from the Winter: Forecast and Model Commentary thread. Discussions in here can include charts and forecasts for surface, atmosphere and stratosphere conditions and as such may include forecasts and updates regarding QBO, ENSO, MJO, Polar Vortex and other teleconnections.

In short - if you prefer a slightly slower paced, more strictly on topic discussion around the models and teleconnections, this is the thread to use. There's no requirement for posts to be in depth or a level of knowledge required to post in here, so long as your posts are model/teleconnection related. 

[WYorksWeather]

Whilst it is of course exciting to look beyond day 5, towards the snow possibilities next week, I think it is useful to look at UKV. This limits us to the 5 day time horizon.

I'll start this at day 3, with the 850hPa, running to day 5. These actually look quite promising. The first push of cold air fails to get all the way south, but then the second push on Monday looks to be very cold. By Monday, -10C 850hPa into the far north, and even in the far south no higher than -5C. Where precipitation does fall, snow would be possible just about anywhere, and virtually certain further north.

Daytime maxima begin to fall away. By Monday, an ice day is possible for Scotland and high ground in England.

Overnight lows also fall away. Sunday morning is cold for Scotland with widespread air frost. By Monday morning, air frost spreads as far south as the Midlands, and ground frost as far south as London.

Moving back to afternoons, by Monday, dew points look widely below zero for Scotland, as well as northern and eastern England. Some marginality for Wales and the far south and south-west of England.

 

So, with all that said, now time to look at precip. UKV is showing some snow showers into Scotland on Saturday, but still rain further south. This continues on Sunday. By Monday, just hints of precip remaining as snow further south.

And finally, just for fun, the snow depth chart at day 5. No substantial accumulations away from Scotland by this stage, but perhaps as much as 20cm for the Highlands, and widely 5-10cm.

Summary

What is always interesting about these charts is that by definition they show us what is going on within the reliable, certainly in terms of broad pattern. By day 5, regardless of what happens afterwards, we have cold air sweeping down across the whole of the UK. We have dew points compatible with snowfall for a large swathe of England, and all of Scotland. In terms of actual snowfall, we have fairly widespread snow in Scotland.

Overall, not a bad place to be at day 5. I think for forecasting, this as about as far as I'd be prepared to go at the moment. Of course, charts further on will continue to be of interest, but I wouldn't be expecting them to verify.

Original post: https://community.netweather.tv/topic/100917-winter-approaching-forecast-and-model-discussion-commentary/?do=findComment&comment=5157808

[Allseasons-Si]

 northwestsnow  HarvSlugger

GEM ens

not a heart beat...and a flatlined mean...

 

 

Original post: https://community.netweather.tv/topic/100917-winter-approaching-forecast-and-model-discussion-commentary/?do=findComment&comment=5157645

[Jordan S]

GFS of course shows a period of sleet/snow for northern areas from this low for the 19th, there has been some consistency from this model so this track not to be discounted.

But my thoughts are that slower development of the low will take place after emerging to the west of the UK with a more southerly track.

Eventual track of the centre possibly moving southeast across south Ireland then over either south Wales or southwest England with some snow for a time inland over parts of these areas/rain and sleet to the south of the centre before slowly clearing to our south and moving east into western Europe, we'll see, wouldn't be surprised if some decent accumulation occured of a few cm's on higher ground with a cm or two to lower levels, depending on timing.

The below for the possible low pressure system on the 19th.

UKMO showing a slightly more northerly solution compared to the above, more complex low though too bringing wintry precipitation in similar areas to the GFS with heavy rain and very strong northerly winds in the southeast, the GEM not really interested with a more southerly solution missing the UK nearly entirely, but it seems likely a low will form and cross somewhere further south in this timeframe.

Winds from the north/northwest likely dominating through the majority of next week keeping it cold, this itself bringing some frequent showers especially along windward coasts those falling as sleet or snow just inland with some possibly merging to give longer spells of wintry precipitation, these may spread further inland and south at times even into England and Wales, particularly from any areas of lower pressure development that may push south-southeast along the flow.

Winds may turn more to the west by the end of next week along with further attempts to bring lengthier precipitation and milder air into the west or southwest for later in the week, raising snow risks further for some at least temporarily as well as the risk of heavier rain and windy weather into the southwest.

Original post: https://community.netweather.tv/topic/100917-winter-approaching-forecast-and-model-discussion-commentary/?do=findComment&comment=5157656

[Ciarán]

This is actually a good video.

 

Original post: https://community.netweather.tv/topic/100917-winter-approaching-forecast-and-model-discussion-commentary/?do=findComment&comment=5157584

[phil nw.]

I saw a mention just recently of  polar lows.They usually pop up at short notice so wont be in current modelling.This could be something that crops up in a few days though.A look at the 500hPa temperatures just to the north in 5/6 days and the models are showing as low as-42c which is low enough for these PLs to form and drift south next week.

12z GFS as an example

They may well produce spells of snow as these minor disturbances drift south in the northerly flow producing a cluster snow showers or even a period of snow.

Just something to keep an eye for as well,of course,as the lows moving in from the northwest sliding south east.

 

Original post: https://community.netweather.tv/topic/100917-winter-approaching-forecast-and-model-discussion-commentary/?do=findComment&comment=5157470

[nick sussex]

Very nice UKMO .

Two chances of frontal snow  associated with those shortwaves for favoured areas .

And some decent cold uppers which have improved over recent runs.

The GFS looks a bit ropey with the second shortwave and the UKMO is far better in possible evolution post day 7 .

Pre ECM my cold potential rating edges up to 7/10.

 

Original post: https://community.netweather.tv/topic/100917-winter-approaching-forecast-and-model-discussion-commentary/?do=findComment&comment=5157527

[Allseasons-Si]

A calm for the nerve's,...still looks cold barring a couple of en's including the gfs that goes teet's up in the mid term.

mean dew point below zero of which will aid cold to the surface,again a blip on the gfs so nothing to worry about at this stage.

also notice the PPN spikes,there could be a good dumping of snow in the right places where the low/s track into the cold air and this won't be resolved yet.

 

Original post: https://community.netweather.tv/topic/100917-winter-approaching-forecast-and-model-discussion-commentary/?do=findComment&comment=5157569

[Eagle Eye]

The - VE EPO that sets in play the whole setup with the Greenland-Canada based high with a trapped US low pressure system (E. G. A reversal of the zonal setup which helps to create the - VE zonal mean zonal wind across the north Atlantic and holds the pattern in place for a few days which should heighten snow risk)  is well forecasted now. It looks very strong on ensemble members, it's looking good for cold and potential snow risks. Following for specific low pressure systems for snow risk. 

 

This will also help keep the Stratosphere for interfering for now and should send strong EHF into the Stratosphere to at least slow down the polar-night jet development. That's the good thing about this cold, it also allows for a heightened risk of further cold into Winter proper. Especially with the Ural high, often a good sign for cold potential in winter to last if it lasts for a while and holds up into winter in some shape or form but it can be a fairly transient signal however it's something to keep an eye on. 

 

I'm personally surprised at how well this late Autumn is going. Because there are some signals there that keep me hoping that we might have further and better cold spells in a winter where the background signals aren't looking like they're going to be that favourable. 

Original post: https://community.netweather.tv/topic/100917-winter-approaching-forecast-and-model-discussion-commentary/?do=findComment&comment=5157848

[bluearmy]

Over the past few days, the ec46 has been drifting cooler for December. It now shows n europe with pretty.much no above av surface temps to the 23rd dec when it ends. I cannot recall the last time this model would not have shown above av temps for the U.K. in any of the weeks in the whole 46 days 

the signal for high pressure and above av heights in the Atlantic is good. But we need to see a low anomoly develop to our east at some point. I think it will

Original post: https://community.netweather.tv/topic/100917-winter-approaching-forecast-and-model-discussion-commentary/?do=findComment&comment=5157841

[Mike Poole]

You can see why the ECM mean slightly deteriorates at day 10 from the clusters, T192-T240:

Clusters 1 (19 members) contains the op and looks similar, solid.

Cluster 2 (9 members) extends the trough further south and is excellent. 

So that’s well over half the probability, but the pattern deteriorates day 10 on clusters 3 and 5, on 3 Euro heights make an unwelcome appearance, and on 5 the Azores high gate crashes the party.  Cluster 4 would probably remain cold with cold air in place.  

Original post: https://community.netweather.tv/topic/100917-winter-approaching-forecast-and-model-discussion-commentary/?do=findComment&comment=5157811

[Allseasons-Si]

 SollyOlly I will refrase that

we coldies do get exited and we deserve it after a few winters past

The EC op was a slight mild outlier agains't the mean.

the EC cluster's then with the op in cluster 1 showing an ATR by day ten

and is reflected by the CPC 6-10 and 8-14 day height anomalies...

 

 

Original post: https://community.netweather.tv/topic/100917-winter-approaching-forecast-and-model-discussion-commentary/?do=findComment&comment=5157853

[Cold Winter Night]

 northwestsnow

Indeed, blocking regime dominant throughout December on today's output. I won't complain.

Original post: https://community.netweather.tv/topic/100917-winter-approaching-forecast-and-model-discussion-commentary/?do=findComment&comment=5157810

[nick sussex]

Would be good if the ECM could weaken that low to the east . We don't have the depth of cold that can survive that much mixing.

Better to have a slacker flow . The NH set up is quite rare later on with the PV in Siberia and decent heights over Greenland .

I'm slightly disappointed in the ECM. It's like someone turned up with some 5 star ingredients and the chef delivered a 3 star meal !

Original post: https://community.netweather.tv/topic/100917-winter-approaching-forecast-and-model-discussion-commentary/?do=findComment&comment=5157749

[Geordiesnow]

 nick sussex Very good analogy Nick! You can have your split PVs and sexy charts all you like but if you got a chilly NW'ly wind and 850s are only around -4 then for the vast majority it will be rain falling. 

It really crucial for the initial northerly to be as east as possible and ideally not have too much of a NW'ly element to it to allow the coldest air to hit the UK right away and any less cold sectors to be well out in the North Sea. I always find the ECM tends to have marginally less cold 850s in colder set ups than the GFS but I do suspect that is more correct as more often than not the UKMO can be similar. I don't think there is anyway of knowing for absolute certain exactly what the current 850 temperature are but it something to bear in mind and whilst we are talking about a degree or two in difference, it could be the difference between wet and white.

Original post: https://community.netweather.tv/topic/100917-winter-approaching-forecast-and-model-discussion-commentary/?do=findComment&comment=5157768

[Allseasons-Si]

Remember when i posted this the other week,...well look at the models now...

it does bear a resemblance to that synoptically looking at the latest models

and whilst i was browsing my post history i came to look at the ECM mean from 3 day's ago for day ten to now at day 7 and the height's have gained strenth in the Atlantic and over Greenland and a further dig south of the trough

today's mean at 168 on the left.

 

 

Original post: https://community.netweather.tv/topic/100917-winter-approaching-forecast-and-model-discussion-commentary/?do=findComment&comment=5157912

[LRD]

The much-maligned EC46 predicted both the insipid 'cold' week back in January and the subsequent return to mild or very mild weather for February. It was solid on that for days quite well in advance despite other signals hinting at the cool (couldn't really call it cold away from the far north) regime continuing

The gradual encroachment ever further north of the high anomalies near us and to our West on the EC46 is an interesting trend. Coupled with the trend to not push high anomalies into Europe means there is interest. No more than that at this range, of course. But better to show that then European high anomalies

Precip anomalies also show drier than normal conditions to our north, north-west and west for much of the run. Even moving to Scandi by the end. Weak signals that far out, obviously, but they are there. There are no significant wetter anomalies to our south or south-east yet. Something to look out for on future runs perhaps. It might all end up being wrong but it's currently there

Original post: https://community.netweather.tv/topic/100917-winter-approaching-forecast-and-model-discussion-commentary/?do=findComment&comment=5157911

[Turnedoutniceagain]

Widespread disruption next week - plan accordingly

 

[Allseasons-Si]

Gefs mean at 144,...a lot better

Original post: https://community.netweather.tv/topic/100917-winter-approaching-forecast-and-model-discussion-commentary/?do=findComment&comment=5158012

[Daniel*]

Cold air mass upgrading on GEFS 18z on Monday at 850hPa -6.9C London and -8.7C Glasgow. Good trends.

 

Original post: https://community.netweather.tv/topic/100917-winter-approaching-forecast-and-model-discussion-commentary/?do=findComment&comment=5158040

[Mcconnor8]

 

GEFS snow probability for Tuesday, will be interesting to monitor how this trends over the next few days

Original post: https://community.netweather.tv/topic/100917-winter-approaching-forecast-and-model-discussion-commentary/?do=findComment&comment=5158067

[Ali1977]

I like this, as it’ll likely move slightly south over the next day or too

UKMO slightly further south and importantly lols amazing at 144

Original post: https://community.netweather.tv/topic/100917-winter-approaching-forecast-and-model-discussion-commentary/?do=findComment&comment=5158101

[Dennis]

forecast 850Hpa next tuesday

the low track will be the case that day 

Original post: https://community.netweather.tv/topic/100917-winter-approaching-forecast-and-model-discussion-commentary/?do=findComment&comment=5158130

[nick sussex]

Disagreements from early in with that shortwave energy to the nw .

The Euros now develop that early which cuts off the southwards push of colder air .

The GFS gets the cold air further south before the shortwave runs se.

The UKMO takes the second shortwave much further south , the ECM takes this further north and deepens it .

So Euros have two developed shortwaves the GFS just one .

It's all a bit of a mess .

Sorry to say more runs needed ! 

You'd prefer the cold south before the shortwave otherwise you rely on the cold air being pulled into the northern flank to get that snow as it tracks across the UK .

 

Original post: https://community.netweather.tv/topic/100917-winter-approaching-forecast-and-model-discussion-commentary/?do=findComment&comment=5158219

[bluearmy]

The fifty ways that the eps see Tuesdays low 

    
 

Yesterday’s 12z run had around a third of the members with this feature (yesterday’s 00z run around a quarter) and it was generally further south and slacker. It’s tough to find any members now that don’t have it. Purely on the basis of trend you’d assume there will be a system. Pinning down its path is now the question because that will also likely dictate how much it deepens and that feeds into whether it trundles across or swings more ne. 
 

remaining v tough to forecast next week

Original post: https://community.netweather.tv/topic/100917-winter-approaching-forecast-and-model-discussion-commentary/?do=findComment&comment=5158239