Met4Cast

We've probably got a window of opportunity for cold weather interests 10th-20th February. Away from a few deterministic runs though we're not really seeing much of a signal for strong high latitude blocking, the cold being signalled within this period from NWP modelling is mostly Scandi trough driven with the Atlantic jet south shifted in response to the recent surge in momentum. Indeed, the ECM mean shows the above quite well. No real block but strong Scandi trough signal funnelling cold air southwards across the UK and more broadly NW Europe. AAM tendency is now falling following the passage of the MJO into the Pacific and where we go from there is rather uncertain, especially when you factor in the (for now) potential of yet another SSW. The lack of any real sustained blocking appearing on NWP modelling is a concern for me re: longevity of any potential colder patterns, we don't really want to be relying on nothing more than a Scandi trough. Certainly those in the north are far more certain to see something of interest vs those of us in the south based on current modelling. Still a long way off with quite a few different variables at play, in any case though - Certainly colder than we've seen recently.

The MJO has moved into the western Pacific and this eastward progression over the past couple of weeks has resulted in a strong rise in total AAM following the recent very strong +MT events. The impact of the +EAMT event in particular has led to another strong Pacific jet extension eastwards (warm USA signal and down stream propagating Rossby waves) Cyclonic wave breaking in the western Atlantic may help to amplify heights northwards towards Greenland but modelling this is extremely complex, some runs manage it but many don't. Quite a complex setup as per usual. This surge of momentum into the atmosphere should begin to reshuffle weather patterns somewhat into February. On balance for the UK - I'd expect the persistent Iberian heights to begin weakening into the 2nd week of February with the possibility of weak heights developing to the north/north west allowing for the risk of colder weather & increasing snow risks, particularly in the north, things are less clear cut further south but NWP modelling is signalling a cooling trend across the board in any case. I'm not currently seeing anything to suggest prolonged deep cold or widespread significant snowfall within NWP modelling or otherwise, but certainly an increasing risk of colder weather as we go through February (more primarily week 2 into 3) Original post: https://community.netweather.tv/topic/99814-model-output-discussion-22nd-jan-2024-onwards/?do=findComment&comment=5026437

The MJO has moved into the western Pacific and this eastward progression over the past couple of weeks has resulted in a strong rise in total AAM following the recent very strong +MT events. The impact of the +EAMT event in particular has led to another strong Pacific jet extension eastwards (warm USA signal and down stream propagating Rossby waves) Cyclonic wave breaking in the western Atlantic may help to amplify heights northwards towards Greenland but modelling this is extremely complex, some runs manage it but many don't. Quite a complex setup as per usual. This surge of momentum into the atmosphere should begin to reshuffle weather patterns somewhat into February. On balance for the UK - I'd expect the persistent Iberian heights to begin weakening into the 2nd week of February with the possibility of weak heights developing to the north/north west allowing for the risk of colder weather & increasing snow risks, particularly in the north, things are less clear cut further south but NWP modelling is signalling a cooling trend across the board in any case. I'm not currently seeing anything to suggest prolonged deep cold or widespread significant snowfall within NWP modelling or otherwise, but certainly an increasing risk of colder weather as we go through February (more primarily week 2 into 3)

My thinking is starting to shift from "not much chance of notable cold" to "a possibility of notable cold". I'm still not convinced that we're going to see sustained high latitude blocking despite the current momentum surge from the tropics in the form of a very strong +MT event. Whilst the MJO is not to be taken into isolation, phase 7 is more supportive of Atlantic ridging (indeed, NWP modelling has started to signal this more strongly in recent runs) rather than Greenland or Scandinavian blocking. A colder spell of weather, at least relative to what we have at the moment seems likely post 7/8th February but prolonged deep cold with widespread snowfall risks continues to be a lower likelihood to me. Another dry northerly before the high topples? Potentially. Saying that - We don't necessarily need mega blocking to produce snowfall at this time of year so even a relatively mediocre could bring about snowfall.

HUGE momentum surge coming out of the tropics at the moment with a large +EAMT event leading to a rather intense Pacific jet extension, the result of this is a very above average USA. In terms of the UK - Atlantic ridging seems favoured week 2 of Feb. High latitude blocking remains elusive however, still not convinced we're going to see prolonged deep cold on the back of this.

@Paul An improvement but still feels like a step backwards compared to how it was previously to me. There are still more steps involved.

Great post! This part is particularly worthy note & sums up my current thinking too. Given current strat forecasts & continued MJO uncertainty and how this will factor into the broader windflow framework I'm not confident we'll end up in a situation with sustained HLB this time around. The strong +MT event is certainly of note though and like you, I wasn't expecting the event to be quite this extensive but I suspect an amplified MJO has helped this, combined with probably a little bit of luck. The Pacific Jet extension will once again begin to feed anomalous warmth across the USA perhaps helping to take some of the sting out of the current strong +NAO jet raging across the Atlantic. It does seem the current +NAO will run out of steam but I'm yet to be convinced that this will then translate to a strong -NAO or robust blocking in places capable of feeding properly cold air south (or west) into the UK.

@bluearmy I’m having flashbacks to the previous cycle when many of us thought models were overplaying the signal decline but modelling ended up being right with that, albeit the atmospheric state is very different now compared with then. A case of waiting & watching, again!

I’m certainly not ruling out another cold spell, just not entirely buying it just yet. Especially given the uncertainty wrt the MJO at the moment. Sustained HLB seems a lower likelihood outcome but another boring northerly is a possibility.

@northwestsnow If that’s the best synoptic we’re seeing within NWP modelling currently then it’s a concern. We know how blocks are often “watered down” and that’s barely a block to begin with Really want to see NWP modelling throw out some more extreme blocking scenarios at that range. Can’t say i’m overly excited by the prospects of another dry northerly..

Not overly optimistic. We might get some amplification but i’m not personally seeing a route to sustained high latitude blocking/prolonged cold. @MATTWOLVES 3 “A couple of weeks ago” things looked far more favourable for a strong bout of HLB, things have unfortunately changed since then. Forecasts/thoughts evolve based on new evidence.

I like the new "quote select" feature, that's definitely something that'll come in handy when trying to quote a specific part of someones post but absolutely hate the removal of the quote feature in general, it seems like a step backwards to me. I don't think it 'cleans" things up, it just confuses things. Replies to hours old posts will have less context to them and without the context of the quote, posts will make absolutely no sense. The "quote select" feature is too hidden. I don't think this solves anything, it simply adds to problems imo. A definite step backwards. EDIT: The mod thread is already a sea of username @'s with no context provided.

Given the huge amount of spread at just day 4/5 on the ensembles i’m not sure why we’re placing much hope in the extended which has a huge amount of spread both mild and to a lesser extent, cold. The MJO forecast remains rather uncertain, the stratosphere is gaining momentum & will soon be above average (albeit not so much lower down) and momentum budgets aren’t overly favourable either (as described by Tamara a few days ago re: equatorward rather than poleward fluxxing). If we’re hanging out hats on a few extended range ensembles, we really are in trouble!

This must be the most boring the outlook has looked all winter, at least we had something to talk about with the storms etc during the first half & indeed this week. Going forward though? Nothing but “bleughh” across all modelling & ensemble suites. Perhaps we’ll get a bit of amplification at some point in February but I can’t see it at the moment.

What did previous look like a good chance of sustained high latitude blocking during February is rapidly fading. Despite an increasingly favourable MJO signal into the western Pacific, we’re missing a vital ingredient & that’ poleward propagating +AAM (westerly momentum). The arrow shows the previous “starting pistol” of +AAM anomalies propagating poleward through December & indeed into early January, this along with the MJO helped to support & sustain the recent blocking we’ve seen around the UK/over Greenland. Unfortunately, this time +AAM is increasingly glued to the equator & we’re not seeing this fluxing towards the pole, this helps (despite the MJO) to inflate the European ridge & indeed, a very strong signal for this within NWP through the remainder of January. A flat, mostly mild end to the month with low pressure systems deflected northwards, potentially stormy at times for Scotland. The reflective wave from the SSW hasn’t helped things either. So.. my hopes for something sustained in terms of cold/snow are rapidly fading. Original post: https://community.netweather.tv/topic/99793-model-output-discussion-cold-spell-ending-what-next/?do=findComment&comment=5022187

Your last sentence absolutely nailed it. By nature this thread is very "outcome" focused, i.e wanting cold and many trying to find evidence to fit with that desired outcome. Rather, that's the wrong way around. You should form conclusions based on the evidence at hand. But, many of us in here want to see cold/snow so naturally the thread skews the way that it does. Unfortunately the issue with that is when things do "go wrong" many throw the toys out of the pram and target those that attempt to distance themselves from chasing "desired outcomes" and instead, like yourself, try to forecast based on the most likely outcomes based on the evidence at hand. The GSDM isn't perfect, teleconnections aren't perfect, modelling isn't perfect. When forecasting, particularly at range you do have to make some assumptions & educated guesses on how things may evolve & what that could lead to in terms of broadscale patterns & indeed more local, regional detail. My point is, just because things are skewed/favour blocked & subsequently cold outcomes it doesn't mean something wont change or the forecast wont evolve. Some things simply cannot be forecasted at long-range, you can have all the favourable teleconnections in the world pointing towards blocked/cold outcomes but if something in the shorter timescale (i.e in this case a SSW) occurs, the entire forecast can shift. That doesn't mean the "teleconnections" are rubbish, it doesn't mean they've "failed", it just means something else has occurred which has shifted the pattern and sometimes that shift can be substantial. In terms of the cold spell just gone - It was clear the Atlantic would attempt to return, this was well sign posted and HLB was expected to relax, I posted this on January 11th: This return to Atlantic weather wasn't a sudden shock. Granted, the snowy breakdown didn't happen but the evolution has gone mostly as expected. There had been some musings/hope that ridges of high pressure would hold up to the north of the UK keeping the UK within the colder air but a strong Canadian vortex shifting east into the Atlantic put that to bed. So, when people say "the forecast has gone wrong" etc I'm really not sure what they're talking about.

Evidently you've not been reading the forum very much, then. Highlighting potential based on the evidence available isn't "ramping". Things didn't evolve as expected and it's important to know why & what changed. Simply saying "well that didn't happen ah well lets move on" doesn't teach you anything, it doesn't provide any context as to why. The teleconnections produced the Greenland blocking & two week colder spell we've just seen across the UK, this was well advertised weeks in advance, indeed, talks really started to pick up on this in early December! Goings on in the troposphere & changes have meant that the February period (still 2 weeks away, by the way) has evolved to show different weather patterns. What has "failed" there, precisely?

"Background signals" haven't failed, though. They only take you so far and micro details are important, shorter range changes are important. There have been several rounds of strat warming and it seems the most recent one "reflected" if you like, this helped to draw the Canadian PV eastwards towards Siberia which flattened out what previously should have been a more promising pattern for cold. Things change, forecasts evolve. Anyone expecting snow outside their front door or cold in a small area such as the UK purely based on teleconnections doesn't understand them, or is placing far too much emphasis on their ability to predict the micro pattern. Broadscale pattern they've done incredibly well this winter. Unfortunately, short-term prospects that simply cannot be forecasted at range (such as the SSW) can disrupt and change expectations. That doesn't make the teleconnections/background drivers useless. The background drivers (GSDM, MJO etc) should be used as diagnostics of possible broadscale patterns and to provide context to NWP modelling, they cannot be used to say "London will see snow in 2 weeks". Forecasts constantly evolve and unfortunately on this occasion, unforecastable consequences have disrupted expectations. It's not about being right or wrong, it's about analysing the situation based on the evidence you have available and forming a conclusion, when the evidence changes or shifts so must too the formed conclusion, that's just the nature of this game.

We've just had a 2 week period of below average temperatures across the UK with many areas last week recording the coldest nights for a good number of years, that's pretty sustained in my book. We might not have seen widespread heavy snowfall but it was still a notable cold spell & period of blocking.

Ha, quite.. We really do have such rotten luck in this country. To have the cold spell just gone cut short (in part) by a SSW really is the peak of UK weather irony

Given a lag of 20ish days in terms of momentum driving pattern changes, at least the first half but probably longer, by which time the MJO will likely have become unfavourable again. So.. eeek. That’s not to say colder spells/snaps won’t happen but i’m really struggling to see anything supporting sustained high latitude blocking, the type that had been favoured previously through February.

What did previous look like a good chance of sustained high latitude blocking during February is rapidly fading. Despite an increasingly favourable MJO signal into the western Pacific, we’re missing a vital ingredient & that’ poleward propagating +AAM (westerly momentum). The arrow shows the previous “starting pistol” of +AAM anomalies propagating poleward through December & indeed into early January, this along with the MJO helped to support & sustain the recent blocking we’ve seen around the UK/over Greenland. Unfortunately, this time +AAM is increasingly glued to the equator & we’re not seeing this fluxing towards the pole, this helps (despite the MJO) to inflate the European ridge & indeed, a very strong signal for this within NWP through the remainder of January. A flat, mostly mild end to the month with low pressure systems deflected northwards, potentially stormy at times for Scotland. The reflective wave from the SSW hasn’t helped things either. So.. my hopes for something sustained in terms of cold/snow are rapidly fading.

It's completely pointless worrying about what the output is showing when the ensembles look like this. What a complete and utter mess.

Not sure I have the energy for another round of this nonsense Good to see the first hints of something appearing in the extended outlooks though. Keeping an eye on the ensembles, would like to see more dipping into cold/deep cold territory..

Oh GEM you are a cheeky sausage. This is a great example on how following the GSDM/MJO & broader teleconnective drivers can give context to NWP modelling. We’d throw this out & ignore it, but given this is the exact pattern being advertised it gives it a little more credence. EDIT: As outlined by @Mike Pooleabove!