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Skullzrulerz

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    Model Output Discussion. 3/12/2022. How cold will it get?

    in Forecast Model Discussion

    Posted

    45 minutes ago, NewEra21 said:

    Hope these lows stay as far south as possible, even if it means the UK misses any meaningful snow. 

    Would rather we lock in the cold than get a few hours of snow before the mild pushes through. Just my opinion of course!

    It's usually the usual trend that these lows go south, knowing us it's bound to go North.

    I do agree with you though, we need to have the cold locked for any surprises regards snowfall.

     

    • Like 1

    Model Output Discussion. 3/12/2022. How cold will it get?

    in Forecast Model Discussion

    Posted

    37 minutes ago, Tamara said:

    And so the same prognosis moves into another day and starts to firm up the timetable for the first half of December. The short to medium term consolidating the cold theme for NW Europe (and very wet but equally at least very mild/quite warm down here)

    The interest beyond that remains how long the weakness at the tropopause/stratospheric boundary can sustain the -ve AO/NAO pattern. Most all of this has been driven through the remarkable longevity of tropical forcing during the second half of autumn and programme of poleward +ve AAM anomaly eddies propagating from the tropics into the extra tropics and creating the highly amplified tropospheric pattern to forge the weakness at the boundary to the lower stratosphere.

    As stated previously, tropical forcing is now heading into a periodicity timeline cyclical lull - which in simple terms means that the poleward forcing ammunition within the troposphere is being withdrawn and it is the built-up momentum unstable inertia lag at higher latitudes that is driving the -ve Annular Mode pattern into the medium term. 

    This, to stress again, is not sustainable indefinitely.

    While a trickling seeping away of angular momentum and consequential attempts to inject renewed polar jet energy downstream will initially interact with the upper tropospheric weakness and 'roadblock it - as time goes on in the absence of renewed poleward momentum c/o tropical>extra tropical forcing, then the upper tropospheric levels will stabilise, and more organised vortex layers higher up should descend and turn the Arctic Oscillation increasingly less negative.

    This implies the polar jet being less and less disrupted and 'roadblocked' and returning on a flatter downstream path and with the jet stream returning incrementally northwards - through the attritional processes discussed in many previous posts.

    It underpins my own scepticism expressed a few times about SSW potential. There is no top-down mechanism whatsoever here and, at present, there is no tangible sign or route to one. Falling angular momentum persisting well into December and towards New Year most probably wholly focussed on a slow but sure battleground focus heading from south to north over time.

    It all becomes highly speculative beyond that and with a lot of winter remaining and renewed westerly winds stirring in the Indian ocean perhaps attempting another poleward tropospheric lead on the atmospheric circulation.  Before that though, while finely balanced, it could be that the coming couple of week sees peaking coldest and potentially snowiest peak for NW Europe before the last third of the month and into the New Year sees a relaxation from the south and milder air making inroads from the SW. For my part of southwest Europe, a distinctly wet period looks to remove further the severe drought issues of over 12 months - before with luck a more settled period arrives as pressure rises with the jet stream heading northwards, bit by bit.

    So a very basic tldr is, cold to very cold before the final third of December, then it becomes warmer/milder and wet at times.

    What happens in the new year is most likely going to be mild.

    For of course Spain/Portugal hopefully there's a period of wet weather where hopefully there's some relief in the short to medium term.

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