Gedday,

I realise that, with all the RD's and Supermets holidaying up in the Dandenongs, no one is actually reading this discussion.  However, in the hypothetical situation  there is actually someone out there, I thought I would talk about something other than n = 1 Rossby waves, just for a change.

Today we have a north-south rainband oriented across central-eastern Victoria.  The synoptics consist of relatively weak upper level forcing (western side of an upper trough) but superimposed above a moist easterly flow at low levels.  The reason it is interesting is that it was a forecast failure in that no rain was mentioned for central Vic, and the model forecasts gave the rainband further east (along the coast) and generally further north.

satpic:rainfall to 9am,500_anal, LAPS rainfall prog,  Meso-LAPS rainfall prog
 

At first I thought the error must have been due to the models moving the upper trough east of where it actually was.  Looking back at the progs, however, that isn't the case; so the reason for the failure has to be related to some subtlety in the divergence fields associated with the upper trough.  Have any of you operational people or mid-latitude synoptitians any insight on this?

Another reason it is interesting is that, with the rain, one would not expect a Melbourne/Spillane eddy.  However, looking at this morning's 23UTC maptool display there was a very clear Eddy located over the Bay.  There is a low-level inversion, and there is weak easterly flow at the surface; so it probably is the eddy; though it could be a weak surface vortex developing out of the rain situation.

cheers

John McB

Harvey Stern
Hello John et al,
   This seems to be an excellent example of "differential vorticity advection".
   Should we write a paper presenting a case study?
   What do other people think?
Harvey.

Phil Davill

> Hi Harvey,
>  Would it be worth myself writing a simple module inside "kenny" (the
> model display program used by many operational forecasters) to calculate
> and display differential vorticity advection as a way of helping
> forecasters to understand why the excellent computer models (produced both
> here and overseas) are going for development of systems.
> Phil Davill

Harvey Stern

Hello Phil,
   Yes, I think that would be really good for you to write a
"differential vorticity advection" module inside "Kenny". This
would be a wonderful diagnostic aid for identifying vertical
motion.
    Another parameter that is difficult to diagnose subjectively, and is
important for development of systems, is "differential thermal
advection".
    Would it be possible to also develop a module for "differential
thermal advection"?
     Regards,
Harvey.