Kevin Parkyn:

Date: Mon, 21 Jan 2002 15:59:40 +1100
From: Kevin Parkyn <k.parkyn@BoM.GOV.AU>
To: LAPS Feedback <laps_feedback@bom.gov.au>
Subject: Sunday change across Victoria

Hi all and Graham,

Another wind change across Victoria last Sunday, which had similar
characteristics to a number of changes we have had this summer. This
particular event was associated with an inland low pressure trough
extending into Victoria and moving gradually eastwards. To complicate
matters slightly there was also a cold front approaching Victoria from
the southwest. Frontogenesis had taken place on the far southwest coast
late on the Saturday and its presence became less discernible overnight,
however by Sunday morning there was evidence of a trough near the coast
that gathered momentum during the day. The combination of these two
features made for an interesting wind change.

LAPS did not handle the timing of the wind change very well, perhaps due
to the complexity of the situation. Consequently MesoLaps and the 5km
model also performed badly. The midnight run (give or take an hour!) was
a obviously slow and this was compensated for when preparing and issuing
forecasts and warnings. In the mean-time, anticipation in the RFC over
the 00Z model run was mounting to see if the local model had caught up
with the change in line with NCEP. Too our suprise the MesoLaps slowed
the change down further, which was a bit disconcerting. Although it did
pick up the strengthening of the winds a couple of hours after the
change quite nicely.

Similar characteristics associated directly with wind changes of late
over Victoria have been:
- initially very shallow with only a marginal drop in temperature inland

- little if any convection or rain
- only a very gradual increase in surface moisture
- usually an increase in the southwesterly wind a couple of hours after
the change
- followed by a more noticeable drop in temperature as the layer of
cooler air increases

Just a few thoughts following on from Geoff Feren's comments last week
and Graham's comment that LAPS_feedback had been a bit quite lately.
Perhaps we've all been digesting John's essays on the
synoptic_discussion thread.

Regards,

Kevin Parkyn
Meteorologist
Severe Weather Section
Victorian Regional Office
Bureau of Meteorology