Met4Cast

Here's the GEFS from the 1st January Not sure there's any archive just had this saved for some reason.

The most interesting aspect of the MetO update is the complete lack of the word "rain" across the entire forecast period, "snow and sleet" featuring a few times. This suggests to me that they are not making much of any 'milder' incursions. Either way, unsurprisingly they are not in camp GFS but very much favouring the EPS/UKM/MOGREPS blend & probably GloSea6.

FWITW the 00z ECM is highlighting where I broadly expect things to head as outlined in the quoted post from yesterday. Cold air across the UK vs incoming disruptive lows = high impact snowfall events. I do think the ECM is being a little too progressive with the lows though, I suspect the first couple will "miss" and pass to the south, again still looking towards the 20th - 20th as a timeframe, although a day or two before can't be discounted given current modelling. The GFS is absolutely horrible when it comes to handling split flows in the Atlantic & disrupting low pressure systems, it depends to blow them up and barrel them through before correcting ever south closer to the time so I'd not worry too much about what the GFS or GEFS is showing for that matter. UKMO, ECM and to some extent GEM will give better guidance going forward. All in all - No changes to the outlook. Original post: https://community.netweather.tv/topic/99706-model-output-discussion-into-2024/?do=findComment&comment=5003036

These lows tend to trend further south so I would expect models to occasionally barrel them through and bring in mild weather quickly but the reality will likely be a much slower transition. I.E more than 1 attempt to bring in milder weather with the potential for multiple snow events. Again though, where that boundary lies wont be known for a while. It's possible northern areas will remain in cold air throughout (mentioned this in the above quoted tweet) Indeed! Fully expecting that which is why I'm not entirely buying the modelling around the 17th at the moment bringing those lows in, suspect it'll be more delayed than that. (though, it doesn't ALWAYS trend south as you say, not something we can 100% rely on!)

It's far too early to look at that kind of detail, the polar boundary will still be shifting 100-200 miles across varying runs & modelling until we start getting to much shorter lead times. The risk is there but naturally the further south you are the more likely you are to see transient snow events vs all snow events, that's just the way it often goes. A decent channel/N France runner though could deliver even to the south coast so.. in short, potentially, but also potentially not.

FWITW the 00z ECM is highlighting where I broadly expect things to head as outlined in the quoted post from yesterday. Cold air across the UK vs incoming disruptive lows = high impact snowfall events. I do think the ECM is being a little too progressive with the lows though, I suspect the first couple will "miss" and pass to the south, again still looking towards the 20th - 20th as a timeframe, although a day or two before can't be discounted given current modelling. The GFS is absolutely horrible when it comes to handling split flows in the Atlantic & disrupting low pressure systems, it depends to blow them up and barrel them through before correcting ever south closer to the time so I'd not worry too much about what the GFS or GEFS is showing for that matter. UKMO, ECM and to some extent GEM will give better guidance going forward. All in all - No changes to the outlook.

46/51 of the 12z EPS had a technical SSW reversal. If we do see a reversal then I expect modelling to be even less reliable than it currently is in the med-extended. There is a lot going on at the moment so getting caught up in every individual deterministic run searching for precise desired outcomes makes even less sense than it usually does. EC46 comes frustratingly close too.. Original post: https://community.netweather.tv/topic/99706-model-output-discussion-into-2024/?do=findComment&comment=5002306

46/51 of the 12z EPS had a technical SSW reversal. If we do see a reversal then I expect modelling to be even less reliable than it currently is in the med-extended. There is a lot going on at the moment so getting caught up in every individual deterministic run searching for precise desired outcomes makes even less sense than it usually does. EC46 comes frustratingly close too..

In terms of where the polar boundary lies that is something that's going to shift north & south probably 100 times before we actually get to the period of interest, I wouldn't place too much focus on that. Returning momentum in the form of the jet stream edging back northwards seems a certain bet, it will happen at some point as the MJO continues it's progression eastwards and on the back of the recent (but brief) AAM tendency dip. How this looks synoptically will depend on how much blocking we retain to the north. It could be that the jet doesn't quite get into the UK and instead we remain cold for far longer (the 00z and 06z GFS det runs played with this scenario) or it could be, like the GEM we see a widespread, high impact snow event (perhaps multiple) as lows push up into the cold air across the UK. Current thinking is the 20th-25th for a potential Atlantic return (of sorts) and therefore increasing risk of high impact weather. Where? How? Who knows, that wont be resolved for a longgggg time. In any case, we've already seen a return to +AAM tendency and frictional torque will soon return to +ve followed by another likely +EAMT event driving AAM tendency upwards, total GLAAM & GWO remain coupled with the El Nino base state. MJO progression likely through the Maritimes and back into phases 6 >7 around the end of January/beginning of February (MJO timing always difficult). In essence, any waning of the block and Atlantic return will likely be temporary with renewed blocking likely into early February, perhaps Greenland/Scandinavia, more likely is we wont see the block to the north become completely eroded, cold air will never be far away. Very, very positive moving forward away from the chopping and changing of NWP outputs and attempting to nail down precise details 10+ days away. Original post: https://community.netweather.tv/topic/99706-model-output-discussion-into-2024/?do=findComment&comment=5002281

In terms of where the polar boundary lies that is something that's going to shift north & south probably 100 times before we actually get to the period of interest, I wouldn't place too much focus on that. Returning momentum in the form of the jet stream edging back northwards seems a certain bet, it will happen at some point as the MJO continues it's progression eastwards and on the back of the recent (but brief) AAM tendency dip. How this looks synoptically will depend on how much blocking we retain to the north. It could be that the jet doesn't quite get into the UK and instead we remain cold for far longer (the 00z and 06z GFS det runs played with this scenario) or it could be, like the GEM we see a widespread, high impact snow event (perhaps multiple) as lows push up into the cold air across the UK. Current thinking is the 20th-25th for a potential Atlantic return (of sorts) and therefore increasing risk of high impact weather. Where? How? Who knows, that wont be resolved for a longgggg time. In any case, we've already seen a return to +AAM tendency and frictional torque will soon return to +ve followed by another likely +EAMT event driving AAM tendency upwards, total GLAAM & GWO remain coupled with the El Nino base state. MJO progression likely through the Maritimes and back into phases 6 >7 around the end of January/beginning of February (MJO timing always difficult). In essence, any waning of the block and Atlantic return will likely be temporary with renewed blocking likely into early February, perhaps Greenland/Scandinavia, more likely is we wont see the block to the north become completely eroded, cold air will never be far away. Very, very positive moving forward away from the chopping and changing of NWP outputs and attempting to nail down precise details 10+ days away.

I'll take a messy evolution if we end up here..

I might have to take a break from this thread, far too many getting emotional over weather charts, nothing has changed. GEFS mean is nice. Broad direction of travel remains exactly the same.

MOGREPS give a high (90%+) probability of >1CM across Sussex, NW Kent, Surrey and higher ground of S London today. A much smaller <10% probability of >5CM. We should see surface convergence begin to focus showers into N Kent/SE london > Sussex this afternoon.

Absolutely nothing falling under the blues as I suspected. Going to need to be under the more scattered brighter green echos to see much I think.

Strange, I'm right on the river Medway and the snow a short while ago settled immediately. No marginality whatsoever!

The vast majority of the lighter stuff probably doesn't actually exist, ideally need the darker blues/greens to see falling snow, anaprop is a fairly large issue in these situations.

Nope, had a 2 minute moderate snow shower about an hour ago and it began to settle immediately.

It's a real shame convection is so shallow today, lower heights and we'd be looking at a proper event! Having said that despite shallow convection the lower levels are rather saturated with much drier air above the cloud layer so the usual issues with evaporation etc shouldn't apply today in theory. A few CM in the lucky spots by the end of the day possibly.

Hmm.. it doesn't show countrywide blizzards and 20 foot snow drifts so this run is rubbish /s Much better from the GEFS and once again signs of the colder weather being extended, our Greenland high pressure is fighting to stick around! Interestingly the EPS 00z were much more tightly clustered and also prolonged the cold compared to previous runs. We are well and truly back within the upgrade cycle.

Forecasts and modelling evolves, the pattern has adjusted slightly, we're continuing to see improvements run to run with cold air across the whole of the UK, a growing risk of disturbances within a very unstable flow moving southwards along with the potential for disruptive frontal snow moving in from the SW. I really don't think you're paying attention to what's actually being shown here, you just want to moan about, with respect, absolutely nothing.

The GEM is absolutely a model I take more seriously these days, it used to be relegated to the cannon fodder folder alongside NAVGEM and JMA but it's come along way in recent years, absolutely a key player up there with the GFS, ECM and UKMO imo.

The multi-model ensemble continues to highlight the broad evolution re mid month cold. A fair amount of spread but broadly cold air remains in place up to or after the 20th. The NAEFS (GEFS & GEPS) continue to highlight the broader expected synoptic pattern well, been keeping an eye on this and it has generally been very consistent. Returning momentum in the form of the jet stream will likely begin to nudge northwards in the 20th-25th period and this is the period where we could see some high impact snowfall events, indeed the GEM highlights this scenario well with weather systems moving into some very cold & stagnant air across the UK, albeit perhaps a few days earlier than suggested above (probably too progressive in removing forcing from the high)

Some won’t be happy until we see a return to snowball earth and even then I’m sure they’d find a reason to complain. Great modelling across the board this morning, the GEFS extend the cold (using -5C isotherm as the guide) another day or two with a tighter clustering of cold members. Details chop and change but the broad direction of travel remains the same. The GEM & UKMO are pick of the bunch for me.

The dendritic growth layer (DGL) is a zone where snowflakes are efficiently made & can be an indication of heavy snowfall. The layer sits above the convective layer today across the SE within much drier air so most snow across the SE will tend to be light as a result. It’s a shame heights aren’t a little lower, subsidence aloft really is limiting the convective depth.

Slightly improved GEFS mean in terms of blocking strength. 12z 18z