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WhiteFox

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    Work (not really!), computers, weather, snow-chasing, travel.<br />Reading (not Reading!).

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  1. Don't think so. For what seems like ages we have been looking at around 21st January for the change to cold. Anything before that is a bonus, but after is now coming into the realms of the expected. All signals are now green, with the exception of a single amber light for NE US storm over the weekend, and even if that amber light is correct, it is a slowdown in the charge towards cold rather than a turnaround. The background signals have been signposting this for some time, and now we are on the cusp. I'm looking forward to @nick sussex musings on irritating shortwaves that may be the difference between heavy snow and slightly less snow rather than the more normal knife-edge situations we usually find ourselves in.
  2. Only if that signal for the Euro trough disappears. The ECM almost takes it too far south, but this is no ordinary setup which we've seen in that past.
  3. It's a cracker whichever way you look at it. We don't often get to see a cold slack flow over ground that may already have snow cover. Could be some very cold overnight minima if that did verify. The words "penetrating frost" spring to mind...
  4. Yes, it's one option and precarious at points, but it's such a complex setup that it seems unlikely. Having said that, the Low pressure is still diving towards the south, so other opportunities for snow and it seems that the Euro trough remains a strong signal! Any other time we'd love to have a chart like that. Only thing remaining now is to get more ensembles onside and it's looking good.
  5. There are no indisputable facts which is why statements like "downgrade" or "upgrade" in are meaningless in isolation. It's all probability on deterministic models, and although probability increases as you get closer to T0, it doesn't always increase at the same rate. That is why you cannot say that one run or another will definitely "nail a pattern".
  6. It's no more and no less important than the 0z run. It could easily show a GFS style evolution tonight and then revert back to the 0z tomorrow morning. We will not know for sure until the energy moving into the US on the STJ phases with the energy coming from the PFJ and even then there will still be small variance. Background signals consistently favour the Euro trough as highlighted by @Glacier Point, so it is meaningless to write off any cold solution at this stage especially as the signals for northern blocking actually increase as we go forward.
  7. Upstream is important of course. I think for the first attempt we are reliant on the upstream flow playing ball. However, with MJO forecast to go into phase 6 by around 23rd I think that we will be less reliant on tiny differences upstream. In short, probability of much colder air increases with each subsequent system dropping SE. At the moment we are totally reliant on SSW overriding MJO signal and the correct phasing of energy over the US. With MJO onside, we should start to see more outcomes favour better variations no matter what happens upstream (although of course there is still linkage).
  8. Don't get drawn in is the answer. People post a chart and proclaim downgrade as if that is the end of it. The truth is that the atmosphere is highly dynamic and no prediction by a deterministic numerical weather prediction model can be taken as the truth at any point ahead of T0. Model output is a function of the input data and the algorithms. Both are far from perfect so a slight error at a point in time increases exponentially as you progress through the run, hence the seemingly big differences. No amount of statements saying "the 12z runs are really important" changes the basic fact that we are feeding imperfect information into an imperfect model. That is why we should wait until we see the ensemble runs which give us a good idea of where the greatest uncertainty begins, and compare to previous runs; doing so enables us to pinpoint where models are struggling to handle particular permutations and where we should hold our patience for further information.. Comparing one point in time chart from one operational run to another is a route to madness but is, I freely admit, incredibly compelling in situations such as these.
  9. It's one solution amongst others. ECM and cluster, current GFS plus ensembles and UKMO (so far as we can see) largely back the colder solution. It may be that the GFSp has the correct outcome, but we can only go on probabilities dictated by the models we have and, at the moment, it favours the colder outcome.
  10. Based on those ensembles only, it's in a sizeable cluster right through to day 7, after which there is no clear signal. Scatter becomes too random after day 7 to be able to discern a favoured trend. But, the background pattern is unchanged. For now, ensembles give reasonable guidance to day 7, after which it is pointless trying to figure out what happens at the detailed level.
  11. Nope. Deep midwinter cold with very little solar energy. An easterly has the potential to be very potent at this time of year! @s4lancia called it just about right with his probabilities earlier on I think. About 65% in favour of an easterly right now, but details to be defined. If easterly sets up a shown by Wednesday/Thursday as shown in GFS 6z then you would expect to see disturbances travelling East to West towards the UK.
  12. Nothing is yet certain. For some time it's been looking like around 21st was the date for a real change and that doesn't seem to be too far out. Slight delay as MJO passes through unfavourable phases but think this is a signal being largely overriden by the SSW downwelling. As the MJO moves towards phase 6 we see the signal for northern blocking to increase. This is not the place to talk about Met Office forecasts, but given the uncertainty and their public duty, it is not surprising they do not ramp up prospects for cold, choosing instead to mention the possibility. Those who need to know will have been briefed of likelihoods and will plan accordingly. FWIW, if you are interested in seeing what goes through a forecaster's mind when looking at events, Google "nws discussion NY" and you can read their description of how they out together the forecast for the upcoming potential storm.
  13. It shows a building Scandinavian high with a negatively tilted trough approaching. That low to the West would slide SSE and the Scandinavian high ridge west. Would the high sink? Don't think so looking at the shape of the pattern.
  14. Classic battleground situation. The alignment of the low to the west suggests pushback to me. Far too distant to look at in detail of course, but good signs
  15. Yes, and indeed the ECM is trending towards that outcome towards the end of the 0z run.
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