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John Hall · January 14th 08, 06:54 PM posted to uk.sci.weather

In article
,
writes:
I'm off to the Alps in a week and as such have been examining the GFS
Ensembles. I've noticed that the ensembles have been quite consistent
with high pressure expected to build to the north/west [of the Alps]
allowing cooler/colder conditions to prevail.

Yet the actual operational run seems to be quite keen to maintain the
high over Spain with, no ridge to the north, [and bring freezing
levels up to nearly 3000m, not good for skiing] On a number of
occasions is has been a clear outlier.

Is there any explanation for this? Does the operational run, over
time, hold greater weight over the other perturbations? Should I be
nervous about getting ‘milded out’

I believe the operational run uses a finer grid for its calculations and
so, other things being equal, should be given more weight that
individual ensemble members. But if 80% or 90% of ensemble members are
going for something different from the operational run, then they are
quite likely to be right. After all, a purpose of the ensemble is
presumably to indicate occasions when the operational run is likely to
be wrong.
--
John Hall
"Honest criticism is hard to take,
particularly from a relative, a friend,
an acquaintance, or a stranger." Franklin P Jones