Date: Fri, 06 Sep 2002 10:25:25 +1000
From: David Williams
To: laps_feedback@BoM.GOV.AU
Subject: RE: Well done to the modellers.

        I send this e-mail to compliment all those in the modelling game for
the guidance that they offerred over the past 24 hours. The ability of
the models to have predicted the middle level development as they did,
was somthing that I would certainly have struggled to have interpreted
myself. Whilst there may have been some subtle variations from one model
to another, I think it is fair to say that it was definitely a success
and worthy of acknowledgement.

        Well done,

        Dave.

John McBride

Dave,

Could you expand on this a bit, or grab (or point me to) the relevant gif
files.. so I could put a short discussion on my webpage?

John McB

Dave Williams
       John,

        I don't normally save GIF files, and have tended not to recently,
because it was ending up a waste of time and energy on my part. I could
capture a few products from the 12Z model run but the guts of the good
stuff by the models would have been best served by the 00Z run. I don't
know if there are any products available from NMOC etc that you could
grab.

        In short, we had quite a deal of castellanus around y'day and it is a
cloud I take great interest in, for the simple reason that the
instability associated with it is NOT surface based and is hence
trickier for forecasters to appreciate. It is unwise to be too specific
about the timing of any thunderstorm activity in these circumstances.

        The models were advecting over some warmer 850hPa air overnight and at
the same time an upper level jet was moving steadily across the middle
of the continent. This jet was able to induce some good middle level
uplift and resulted in a significant increase in the cloud cover
overnight. So if you were to include some of the 6 hourly satpix it
would show up nicely.

The 500hPa temperatures were predicted to cool off
quite significantly across NSW and this wasn't obvious from the
observations 12hrs earlier. It wasn't due to any advection it was from
the upmotion and was well captured. Hence there was a marked
destabilisation of the atmosphere overnight, overwhelmingly associated
with the approach of the jet stream, which coincided nicely with the low
level warming. I think it is fair to say that these are situations in
which forecasters have no choice but to follow the models, as it was
difficult for us to 'see' any obvious signs prior to the onset of the
development.

        I believe it would serve as a worthwhile case study for anybody
interested in highlighting the ability of the models to capture the
dynamics of such a situation. Sorry I don't have anything more to offer
and time is restrictive today, but those who can isolate some of the
guidance that was available y'day would do well to pass it onto you for
inclusion in whatever further discussion takes place. I believe such
discussion would be very informative for forecasters and modellers
alike.

        Again, well done.

        Dave.