Model Output Discussion - Into Winter

[Big Gally]

Reminds me of 2018 when we developed streamers from the east. Central belt got 40cm+ a cheeky red warning ️

[clark3r]

This evenings runs will be interesting, I am also hoping now the low stays south to let snow showers come in and colder temps 

[Methuselah]

2 minutes ago, clark3r said:

This evenings runs will be interesting, I am also hoping now the low stays south to let snow showers come in and colder temps 

They'll be CRUCIAL! 

[Jason M]

8 minutes ago, Jacob said:

One question, how low do uppers have to be to get ice days? I'm quite new to this as you can see by my rank

Complex question unfortunately. It depends on the airmass and also differs according to sun strength. In late Nov / December and most of Jan -6c/-7 uppers would suffice if airmass is continental in nature (easterly) and hangs around for a couple of days. In a maritime north westerly you might struggle to get ice days with -8/-9c uppers. As we go into Feb the depth of cold needed becomes greater due to the sun gaining power. 

[northwestsnow]

Dew points from East versus Dew points from anything with west in it

= chalk and cheese.

[Cambrian]

0z EPS charts from yesterday and today at days 10 and 9 respectively -

 

Today’s 0z shows a better build of heights to the west of the UK and Ireland, extending south from the polar and Greenland heights. The contour lines show a more clearly defined ridge north through Iceland. The Atlantic low is modelled further southeast into the Azores. It does look like there is a better gap being made for the building of the ridge just to our west. 

It makes a massive difference down the line, yesterday’s day 15 compared with today’s day 14. Instead of being to the south of Iceland, the Atlantic trough is much further west to the south of Greenland, visible in both the low heights and the contours. It’s progression into Western Europe is much arrested.

 

There is a markedly diminished rise of heights into the Mediterranean and the build of heights into Scandinavia that the models were flirting with yesterday is removed, leaving room for the slack European trough to remain in place.

And if that isn’t stark enough, look at the difference in the T850s. 

 

It looks like this cold block could well prove very hard to shift.

[Mcconnor8]

Better blocking to Greenland on the ECM 06z control compared to the 0z, and colder 850s across the country on Sunday as well. Another upgrade.

Looks like we will get a slider coming through to the South a couple of days later and renewed blocking building behind it.

Edited November 27, 2023 by Mcconnor8

[PiscesStar]

Just now, Mcconnor8 said:

Better blocking to Greenland on the ECM 06z control compared to the 0z, and colder 850s across the country on Sunday as well. Another upgrade.

Does that mean the south will see snow 🌨? 

[Turnedoutniceagain]

25 minutes ago, Jacob said:

One possibility in the long term is that we could get proper cold in December but we get stuck under high pressure which leaves us with getting cold weather but no snow which would be a disappointment 

This is the best winter weather - high pressure, clear days, freezing nights. Perfect 

[mulzy]

22 minutes ago, Jacob said:

One question, how low do uppers have to be to get ice days? I'm quite new to this as you can see by my rank

It depends.  Uppers of +3 can give freezing temperatures via an inversion and uppers of -12, especially in early Spring may not result in sub-zero temperatures at the surface.  

[sheikhy]

8 minutes ago, northwestsnow said:

Dew points from East versus Dew points from anything with west in it

= chalk and cheese.

Oh yes cold continental dew points of -8=lovely powder snow a lot of the times!same dew points from the west yes it still snow but more the wet variety!!!

[danm]

38 minutes ago, NewEra21 said:

I think we’re seeing why it’s so vital to get that low to stay as far south as possible on Thursday now, it brings in deeper cold and then let’s see where we go from next weekend onwards.

I know some were hoping for snow from it, and I understand that as we’re all so snow starved in this country. But I feel that would have been sacrificing any potential longevity of this spell.

Things can still go very wrong of course, but this low going south and missing the UK gives us the best chance going forward imo.

Agree. The trouble with these battleground scenario set ups is that unless the block is strong enough, forcing the low to slide away E/SE then the snowfall tends to be temporary as milder air is introduced. Even if the low does slide away to the east, we'd need another injection of cold air as much of the initial cold will have been mixed out. It's fine margins and very high risk/high reward, but even the high reward can lead to a dumping that can melt away within 12 hours. 

The ideal set up here is the low staying south, deeper cold being advected west towards us, a convective E/NE'rly and then battleground/slider set ups to end it all after a week of cold. Is that too much to ask for?? 

Edited November 27, 2023 by danm

[Nick F]

00z and now 06z GEFS H500 mean by day 10 quite bullish to push Atlantic troughing east across NW Europe

00z EPS H500 mean at day 10 more blocked - with a ridge just to our west .

Be interesting to see if GFS backtracks on its keenness to bring back the default unsettled Atlantic zonal train or whether EC is wrong.

More closer in time, now Thursday's low looks off the menu, there looks to be a brief window for wintry showers, perhaps falling as snow inland, to affect eastern areas Thursday night / Friday morning in the strong NEly wind, before winds back northerly later on Friday and into the weekend, with most places becoming dry away from coasts. ARPEGE below Friday morning:

No widespread snow event on the horizon, far north and east likely the best place to be to catch a flake, drier and sunnier in the west.

[northwestsnow]

Exeter going with a delayed breakdown so probs siding with EC ..

[Mcconnor8]

1 minute ago, northwestsnow said:

Exeter going with a delayed breakdown so probs siding with EC ..

UKMO model is much closer to EC than GFS in the reliable so not a suprise.

[BalderstoneNick]

27 minutes ago, Jason M said:

Complex question unfortunately. It depends on the airmass and also differs according to sun strength. In late Nov / December and most of Jan -6c/-7 uppers would suffice if airmass is continental in nature (easterly) and hangs around for a couple of days. In a maritime north westerly you might struggle to get ice days with -8/-9c uppers. As we go into Feb the depth of cold needed becomes greater due to the sun gaining power. 

Yeah to this Jason, so many variables, including inversions where the temps are 'flipped' so 850's can be relatively high but temps and ground level can be around freezing at below all day.

It's a bit like the 'will it snow' question we have in the uk isn't it! For this I generally just look at the 850-1000 charts to get an idea of the layer from clouds to ground. Normally not far off. Need the dam to be at least 130 (blue) on the attached I've found..for my locality anyway. Prob different in other areas

[BLAST FROM THE PAST]

 Notable temp drop down here in last hour.  11c at midday,  now 7c….and cooling.  Breeze picking up from north as the LP slides into the continent.  Love it

 

BFTP

[GokouD]

24 minutes ago, Turnedoutniceagain said:

This is the best winter weather - high pressure, clear days, freezing nights. Perfect 

Unless you work from home in a badly insulated house! I'd rather a good dumping of snow for a few days and then a nice warm-up 

[Mcconnor8]

Going to be a good round of 12z runs for extending the cold into next week and lower 850s this week I think based on the 6z trends, soon focus will start to turn to snow as we get into the high res models range.

[andy989]

Temperature has dropped like a stone here and there’s the odd flake falling. I think the summits around here will be white if we get overnight showers 

[Kirkcaldy Weather]

Starting with my post here

 

'Should see the shot of a snowstorm into the Northeast of America currently looks like 2 weeks from now as the +PNA really comes through'

With this I provided in the above post 

So moving + 2 weeks here's how we look

Super pleased how development has panned out with the parts I highlighted pretty much on point too

Now taking this chart also in the above post 

 372hrs

Syncing to where we go by Thursday ie 30th November 

Truly awesome and it highlights something I'd been looking to address for a long time, all too frequent we have opinions of charts equivalent in that time range being tarnished as 'fantasy island' which is unnecessary it just means seeking which 500hpa evolution fits most suitable given teleconnections feeding into said timeframe.

Shifting back to my post on 7th November which contains these from the CFS which are between 600 and 700hrs timeframes

 

Again link to the evolution we are witnessing 

 

Special and astonishing conditions present at both surface and UPPER atmospheric levels and yes i have noticed a negative mindset reference in the previous thread to using that terminology which is ludicrous.

Once the cyclonic developments during Thursday Friday and part of Saturday transfers eastward we will have further developments taking a track quite similar which have possibility of further wintry conditions particularly for Northern parts of the UK which keep supportive upper level ingredients and can benefit from north sea convection given suitable orientation of these lows

Into the late stages of Dec week one this transition will take us into a perfect representation of MJO phase 1 into December pairing into supportive teleconnections feeding into this timeframe which I have discussed prior in extensive detail  

 

 

Start of the trend to phase 2 evolution showing great too  

Given we still await the move to phase 3 probably within roughly 3-5 days I maintain my views here

 

'Given its just emerging there certainly isn't a rush for such evolutions but great the path being discovered already 🌨'

 

[Kasim Awan]

Hard to believe that most of the UK only has a slight chance of barely scrape a dusting by the weekend from these synoptics but that looks to be the case as it stands.

[Lord Grogon]

Dumb question from an ignorant fool.

Why do models trend low pressure systems south? 

Is it simply some sort of empirical bias? i.e. they don't always all trend south, some go the other way. But it tends to pop up in the higher profile situations where more people are watching.

Other point is that is if they do go south, why don't the people who program the models adjust for it over time? Afer all a model is just a big computer program that should use ever increasing levels of historical data to improve it's accuracy. 

 

[Howie]

1 minute ago, Lord Grogon said:

Dumb question from an ignorant fool.

Why do models trend low pressure systems south? 

Is it simply some sort of empirical bias? i.e. they don't always all trend south, some go the other way. But it tends to pop up in the higher profile situations where more people are watching.

Other point is that is if they do go south, why don't the people who program the models adjust for it over time? Afer all a model is just a big computer program that should use ever increasing levels of historical data to improve it's accuracy. 

 

I think it's because the often model them to strong further out. A stronger low will try to move north east while a weaker low will move on a more southerly track

[Kasim Awan]

1 hour ago, Big Gally said:

Reminds me of 2018 when we developed streamers from the east. Central belt got 40cm+ a cheeky red warning ️

As it stands there has been a significant reduction in the modelled strength of the convective flow which now looks fairly weak. I'd say snow showers mostly restricted to coastal counties with 1-4cm here, with the odd feature bringing a dusting inland locally.