Nick F

The trop PV looks too well-organised and strong to allow any amplification of ridges to build north to allow a downstream northerly of any potency or longevity. I guess we'll need to carry on kicking that can down the road for the next cold and wintry fix, let's hope it's not too long a wait.

I've always thought the GFS had a knack of picking up northerlies best at range that do come off in the 20 years+ of weather model watching, so certainly worth entertaining the idea in the run up to Xmas, despite the ups and downs last few days. How long lasting and potent it will be is too far off to contemplate though.

Every year we come back and get on the same roller coaster of emotions tugged by 4x GFS daily runs blowing cold or mild when there's hints of a pattern change on the horizon Not a bad effort by 12z GFS to get coldies on a high to start the evening ...

From the studies I've read, the N Atlantic tripole tends to have have a positive feedback later in the winter if it's only recently appeared. The tripole likely appeared due to the -NAO from mid-September through to late November, with low pressure systems on a southerly track over the N Atlantic cooling waters during autumn. It's feedback to the atmosphere is not an immediate impact, but can be linked to further episodes of -NAO in coming months. 2009-10 and 2010-11 winters featured the tripole. Will not be the only factor that may bring a -NAO though, SSW / -eQBO weakening the PV will help too.

Yes, but that would be dry cold for most of them, away from downwind areas of Great Lakes - which may get Lake Effect snow. NE USA normally needs a low hugging the eastern seaboard, of which there isn't around then, otherwise it's mostly dry and bitterly cold other than flurries. For us, could be a lot worse than the 06z GFS op, some cold outbreaks in there, but also some mild sectors toppling in from the NW. At least that troughing is digging deep to our east - which will help pull in arctic air from the north and maintain the deep cold to our east and northeast, should it come the time to tap in the coming weeks,

UK Severe Convective & Storm Forecast - Issued 2023-12-10 10:20:29 Valid: 10/12/2023 1000 - 11/12/2023 0600 SEVERE CONVECTIVE WATCH - SUN 10 DEC 2023 Click here for the full forecast

Quite an inversion going on, especially in the south. Clear skies at night lead to temperatures dropping like a stone near the longest night of the year if the air is dry, which it would be under a strong upper level ridge with dry air subsiding from high up - which also evaporates any cloud. Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4972905

Always the optimist! The trop PV is not one for splitting to allow height rises over Greenland on recent GFS runs, maybe a new trend that won't reverse and get worse just before Xmas, or it may revert back to decent splitting into separate vortices over N Canada and NE Europe like the more colder runs of previous days. More runs needed. 12z GFS does at least drag down some cold arctic air, but with the TPV not splitting to allow the Atlantic ridge to build north over Greenland, any cold incursion would be prone to being toppled from the NW by mild sectors.

Quite an inversion going on, especially in the south. Clear skies at night lead to temperatures dropping like a stone near the longest night of the year if the air is dry, which it would be under a strong upper level ridge with dry air subsiding from high up - which also evaporates any cloud.

I looked at the long draw SWly flow at 850 hPa, with T850s of 10C reaching the UK from the Azores around the 17th and all's not what it seems at the surface ... Even the highs in the afternoon of 17th aren't screaming overly mild - more average. All an educated guess that far off though ...

Morning. Nice to see 00z GFS op in a festive mood with a wintry look to start Christmas Eve. I suppose, ideally, we see the high building NE from the Azores gain high enough latitude to keep it calm and chilly, with night frosts and develop some surface cold, before the high migrates NW and an upper trough drops SE into Scandinavia and thus opens up the doors to the arctic in time for Xmas. However, 00z EC continues to show the high not gaining enough latitude so we end up with a mild and possibly cloudy flow off the Atlantic - especially further north, south maybe clearer and frosty.

A look back on the North Sea storm surge which brought flooding to eastern coastal communities, 60 years after the Great North Sea Flood of January 1953. View the full blog here

So, a week of changeable weather from the west off the Atlantic, potentially deep low on Sunday crossing the north needs watching, it looks like the weather will settle down again from Thursday week with a strong signal from 00z EPS/GEFS for a rise in pressure. High pressure building in from Azores looks favoured, but where it eventually ends up positioning as an anticyclone could determine if it will be mild & dry or chilly & dry with frost. It could end up being milder in the north with flow from the southwest nearer low pressure to the northwest and colder towards the south. But some differences between models and uncertainty in the shape and orientation of the strengthening tropospheric polar vortex will affect the position of the jet stream and thus determine where the anticyclone will position.

I wouldn't be expecting much of a shake up from the zonal / unsettled outlook by mid-month. More like around Christmas time for the pattern to change to a more blocked one, *if* the MJO reaching P7 and 8 mid-month sufficiently amplifies the upper flow over the N Atlantic and Europe after around a 10 day lag. But no guarantees. No point getting too hung up over most model runs over the next week or two not showing cold scenarios. The current model outlook is bog standard default fare for December, what we normally see, until wave driving from an uptick in tropical forcing over the Pacific to high latitudes picks up mid-month to change the mid to high latitude upper flow patterns upstream. . Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4969697

I wouldn't be expecting much of a shake up from the zonal / unsettled outlook by mid-month. More like around Christmas time for the pattern to change to a more blocked one, *if* the MJO reaching P7 and 8 mid-month sufficiently amplifies the upper flow over the N Atlantic and Europe after around a 10 day lag. But no guarantees. No point getting too hung up over most model runs over the next week or two not showing cold scenarios. The current model outlook is bog standard default fare for December, what we normally see, until wave driving from an uptick in tropical forcing over the Pacific to high latitudes picks up mid-month to change the mid to high latitude upper flow patterns upstream. .

Areas of rain spreading in off the Atlantic will turn readily to snow as it bumps into cold air over the UK tonight and again on Sunday night and Monday, with a risk of travel disruption. View the full blog here

Better set the alarm for 4am then Looks dry on most models for that time. Afternoon may see some flurries.

Don't think we can totally discount the idea of a more southerly tracking jet taking lows under the UK and Ireland which stay in the cold air in the day 7-10 range, fair few GEFS postage stamps show this option, but its not the favourite evolution in the medium range for now.

Yes, since looking at the 00z EPS and clusters, it does look like the writing is on the wall, as per last post. It seems upstream forcing over N America and Pacific will start to overwhelm any blocking over the N Atlantic later next week. MJO RMM plot which combines the standard MJO with the current 120-day signal of the background base tropical forcing pattern suggest MJO getting into P7 on Dec 15, P8 on Dec 20, P1 on Dec 25. So perhaps for the festive period of late December we may see a return of more blocking. Scandi high? Phase 7 in Nino in Dec Phase 8 in Nino Dec

Does look like the writings on the wall for the demise of the cold spell from EPS mean and also clusters in 2 camps, the Atlantic trough taking charge having largest support by a big margin.

Looking a dry cold spell for most, any wintry showers limited to northern Scotland & eastern coastal areas in the main, perhaps a dangler down the Irish Sea into Pembrokeshire and Cornwall too. May feel like a waste of cold enough air for some snow, but it is what it is, and I guess it makes a change from mild, wet and windy weather that we've endured most October and November. The breakdown from the Atlantic keeps showing, but still too far out to be sure of its arrival for now.

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.

Looks like GFS has dropped the far N Atlantic / Griceland block idea, but still toys with a southerly tracking jet with wedges of high pressure to the north of the jet to delay any attempts of a milder breakdown from the Atlantic. Still no concrete signs of a return to mild zonal, ignore the mild SW'erlies in FI ... for now.

Morning. I see that low from the Azores, that I thought wouldn't be a player, returns on the scene & moves toward S England Thursday, bumping into cold air - to bring a potential snow event somewhere. Too far off to have confidence on this event, due to uncertain track of this low, could well end up missing us and tracking into France like previous runs. GFS doing its usual blowing the low up too much, so probably too far north in track. Still the chance of wintry showers in the NE flow that follows, especially for eastern areas.

Another EC det blocked and cold through to day 10. The T850s don't look particularly cold, as in will produce convective wintry showers, but imagine if the flow is slack the cold will build at the surface. Hard to pin down features that may bring some snow at the moment, but looks like the Azores low will not be a player, rather a low dropping south over Ireland before heading east close to the south mid-to-late week could bring some precipitation, perhaps wintry, to the west and south. Also low pressure over the North Sea could bring some wintry precip to more eastern areas later in week.