So you can predict exactly what is going to happen re scandi if you can predict exactly how the lobe will develop - which just takes the forecasting problem back to a day earlier. Not a dramatic advance in weather prediction IMO.
I mean to be clear this is a very specific scenario. All I did was look at the forecasts with the cold spell, and those with out and tried to isolate the cause. It always came back to how that lobe was resolved, and there is a very easy to understand mechanism as to how the lobe effects the build too:
Strong GS lobe -> Low heights pushed over scandi -> HP builds further south -> Cold air shunted south
So what this means for this specific scenario is you don't have to worry about anything else, all the uncertainty is contained in how this lobe is resolved. So, for example, although ICON6Z doesn't look like a big upgrade, it really is because the Lobe is alot weaker. There almost seems to be a threashold where, if crossed, you get the cold weather. As things stand now we are '1 upgrade' away from a cold spell but the uncertainty is starting to reduce now, and I suspect the 12Z will be the last chance for the lobe to stay weak enough to get the cold scenario.
I should also point out that Z500 is one of the easiest things for models to predict. Upper level meterology is much easier than all the turbulant nonsense that goes on near the surface; so when you get big uncertainty in this upper level geopotential field; the consequences are pretty straight forward. Strong lobe = bad, weak lobe = good.
Edited by user
02 February 2023 14:12:39
| Reason: Not specified