Errrr - the 1200 chart shows that the Black area that extended South virtually to LGW up to 0600 this morning (
and was predicted to hang around until tomorrow at earliest) has now moved (VERY) rapidly North and shrunk a lot, so the southern boundary now runs through central Scotland.
This is crazy! Clearly the VA cloud could not really move at anything like that rate between 0600 and 1200 the same day, even in gale-force southerlies (which we ain't got anyway). Furthermore, the behaviour of VA clouds does not include ash suddenly falling to earth, which is the only other simple explanation for the change.
So what's going on? Reworking of the modelling software? Redefinition of the input data (which was perhaps overly pessimistic up until this morning) or duff / very fast-changing (??) weather / mass airflow data?
You tell me!
Until it's clear how this change suddenly occurred, it seems that VACC forecasting has a bit of a credibility gap to fill (and maybe plenty of spare ash to fill it with!).
