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KLR1269

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    Yorkshire and E England regional discussion

    in Yorkshire & E.England Weather Discussion

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    2 hours ago, Kasim Awan said:

    It is possible to make a snow forecast, one has to just be aware of the uncertainties involved and communicate them. Failure to communicate and identify the risks involved imo carry more weight & potential responsibility afterwards. It's always worth giving a fair probabilistic view than remaining glued to the fence. With that in mind, the below is my post in the Mod thread I have had a request to post on here.

    Yes, you effectively covered my point about the uncertainty as all the unorganized precip will do is prevent the ground environment below 200 metres (which is where there is marginality) from being conducive.

    Given the projection of a well defined area of precipitation tomorrow, the outcome of some snow to lower levels producing a lowland area of snow maybe no greater than 5-25,000km^2 (up to 10% of the UK) with accumulations of 1-6cm in the favored stretch is fairly high in confidence. Of course, there are mechanisms which increase snow with altitude (orographic lift, lower temperatures, lower ground temperatures), and this means locally 20cm+ is possible for somewhere like Queensbury tomorrow. This is most favoured to occur across West Yorkshire, South Yorkshire, Notts, Derbs, into the North & East Midlands before moving towards the home counties. Even in this situation, there will be marginality on the north, south, west and eastern side of the snow area which will all result from slightly different thermodynamic mechanisms. North & east - lack of evap cooling. West -Fohen effect, lack of evap cooling. South - lack of cold air and low dew point injection from east. Defining which areas will see this is very uncertain and is down to nowcasting, however this does not take away or limit the main precip area evap cooling derived snow from verifying.

    A strong consensus (70%) of weather models show this area verifying, the uncertainty is more to do with placement further south. The outcome of snow to lower levels in the Northern areas is not a certainty infact far from it however, the probabilistic forecasting method is always the way to go with consensus whilst leaving room for other possibilities which is what I've done, and you have covered here. Other outcomes include a more northerly track (some of Harmonie runs) and a more unorganized precipitation regime. However, I feel at this moment it would be unrealistic to go with 50/50 or even say "too close to call" for the precip further north at least, given the data for the triple point system which I am looking at. This does not discount a more unorganized precip area from occurring, just gives it a chance of say 25% whilst remaining aware that the higher confidence of snow for some areas (S Yorkshire, North & East Midlands) means imo a warning is valid from both an impact and likelihood perspective. Further south there is a risk of some snow too which of course will be bounded by the same spatial marginality mentioned above. Uncertainty is always the case with snow it's about doing the best one can with the data provided and forecasting knowledge to warn the public beforehand.

     

    Brilliant post. I love that you have name dropped Queensbury mate. I live at Mountain which is Queensburys highest point. Hopefully we get a right pasting.  

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