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Trom

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  1. I agree the low heights to the SW stop the high above us sinking but surely the strat warming in 4 days won’t be quick enough to effect the trop in the timeframe needed to impact this cold snap. That would be an extremely quick response. Interested if you think it could be that quick.
  2. Yes odd - clearly that chart isn't -4 to +4 standard deviations. +/- 2 captures 95% of all observations. So >4 standard deviations would be so infrequent that this can't be what he means. Am I missing something here? Googled +/- 4 sigma and it's 99.993% of observations.
  3. Clearly convective snow can’t be forecast much in advance this spell has underlined. I kind of new that but still have been surprised about the frequency of snow showers over a number of days. Today was leaving South Croydon at 6am to catch a flight to Amsterdam. Amazing windchill here. I also got a picture of a frozen canal but can’t seem to upload it. Back to Gatwick midday tomorrow. Flight currently saying no delays expected. We shall see.
  4. The slower retrogression of the high pressure is having the impact of keeping that low further South.
  5. Movement in the ICON and GFS to keep the low further South on Friday. Got to hope that movement is sustained on future runs as it would keep our area in much colder uppers.
  6. The operating run has greater resolution. The control uses the same initial data as the op but is run in low resolution. The ensembles are run in low definition but have tweeks to the starting data. Purpose of the ensembles is to add support to the results of the operating and control runs. The ensembles can also be used to identify clusters which give us an idea of future trends. What they can't really be used for is analysis of individual perbs with some kind of hope that they will materialise.
  7. 2 standard deviations captures 95% of all observations around a mean. Does, of course, depend on the mean being accurate in the first place.
  8. Well GFS 18Z showing a couple of days of South Easterlies which keeps the snow risk this weekend. Then the Atlantic breaks through and giving us a westerly regime. By T72 high pressure is edging in leaving us in a southwesterly regime and hence mild but dry especially to the south of the country. Temperatures up to low/mid-teens for most of England by T90. By T117 were again in a more westerly regime as the high pressure ebbs east. We then seem to alternate between westerlies and south westerlies. Scotland flirts with a short-lived North Westerly by T138 bringing temperatures there down and the rest of the UK is in a North Westerly by T156 which will, therefore, bring a dip in temperatures to lower single digits but nothing that will bring snow away from mountainous areas in the north-west. By T183 it's back to south westerlies. Doesn't look inspiring.
  9. I've got to agree. Looking at it the surface temperatures look too high on Monday for most areas (seems to be around 5c). At the moment to me, it really looks like elevation is needed, even in the North. Snow chances do look to increase as the week progresses but with the flows direction, it all still remains highly marginal away from high ground. As for the south I really can't see anything other than sleet next week. I do hope I'm wrong and those 850's dip a little further to get the right side of marginal for more widespread areas.
  10. Whilst it's relatively quiet on here it's interesting that from a behavioural aspect that the December of 2010 has certainly skewed perceptions that late November can be cold and early December are particularly snowy months but March 2013 has not skewed perceptions that March is particularly wintery. Of course January and February are the historically most wintery for the UK. I wonder if psychologically it's because November and December are the start of winter whilst March is the end (obviously not meteorological seasons before some one calls me out). Anyway letting past events impact on future unconditional probabilities aka the gamblers fallacy is a repeating feature of the models thread come winter time and has been for many a year. So it looks Atlantic driven for the next week, albeit a relatively benign Westerly pattern. Unsettled would be the definition especially the further West you are. Then it's wait and see wether the SSW can shake things up in terms of a last cold shot.
  11. This is exactly the conclusion I formed some time ago. There's no doubt that they have an effect but the correlations between all these measures or at least current understanding of them seems to be limited. I very much admire Tamara et al who are willing to share there knowledge as our understanding of the interplays between them develops. They are often the target of some posters when things don't go to plan but I think we need to accept that our understanding and hence usefulness of these measures In terms of forecasting rather than hind-casting will improve over time. pioneering is how I see this area right now and I have great respect to those who are willing to share their musings publicly.
  12. With regards to verification stats are they for the global output or more geo specific. The only reason I ask is that if they are for the model output as a whole I'd imagine the UK with its complicated global position would have lower correlations. Is this a fair comment to make? Edit: Sorry ignore I see this has been answered later in the thread.
  13. Is the GFS the most progressive post it's update? It was the first to hold the Atlantic back.
  14. Poor old GFS getting a bashing. Don't forget it was the first model that attempted to hold back the Atlantic when Meto and ECM were being far more progressive. Noticeable as the GFS has the reputation (deserved or not) for being the most likely to default to zonal. Does it still have this post upgrade? It certainly has a tendency to sniff something out then underplay it relative to ECM before moving towards the Euro output. I read somewhere that it's slightly inferior stats were due to the initialisation data and that it had some years ago been run with ECM initialisation data which improved it's verification stats. Also thank you to those that have championed more volatility information being posted with mean charts. I notice quite a few posts of means along with ensemble charts which personally I've found to improve my ability to interpret those mean charts without having to delve around to find volatility. I'm guessing if the trends continue this place will be a lot busier and all the behavioural dissonances will rear their heads. Anyway so much more positive than a few days back.
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