Harald Richter

Group,

Victoria is an interesting place today.  After an extended period of very dry conditions (near the surface) a very deep and dry mixed layer has been built (see 12UTC 03/10 sounding).  The moisture came in aloft and some of it worked its way into the boundary layer adding low-level moisture into an unstable sounding.
This morning's MML trace rewarded us with an LI of -8.1C, which is one of the best values I have seen at MML.  CAPE is uncharacteristically "fat."

The near-suface cool moist air needed a bit of prodding to reach its LFC, and courtesy of the low in NW VIC combined with some insolation in N and NE VIC and a N flow impinging on the mountains, we now have an electrified convective fest in progress. Check out the following satellite image:

Harald
 

John McBride

Gedday,

 I had a look at the Melbourne sounding, as pointed out by Harald.  It is so beautiful, I dropped everything and have placed it on my web-page for all to look at.

I am not sure what is going on the lowest 100 Hpa; but have a look at the mixed layer structure for both last night's trace (blue on the sounding on my web-page) and for this morning's trace (red).  As you all know, a well mixed layer is represented by a vertical profile constant in mixing ratio and also constant in potential temperature or theta....  Have a look at these soundings... How well mixed can you get???  The process is interesting and possibly is something a young-old thunderstorm man like Harald understands,; but I don't...

Having been educated at the edge of  the great Plains in Colorado by people like Alan Betts and Bill Cotton, I had always thought of deep well-mixed layers as being a result of contintal summertime day-time heating.  Clearly something else is going on here.
 

Another interesting aspect of the current situation is there is a very nice convergence/confluence line extending east-west across Victoria, all within quite a light wind regime.  I have put that as well as links to a maptool link and some current radar images up on my webpage.

Over to you Harald

1.  Maptool loop

2.  Melbourne radar 0310  0320  0330  0340  0350  0400  0410

Current windmap, showing convergence line:

John McBride

Date: Fri, 4 Oct 2002 05:32:27 +0000 (GMT)
From: John McBride <jmb@bom.gov.au>
Subject: AND... Lightning too

Have a look at the current GPATS image:

         http://serva.vic.bom.gov.au/mcidas/data/IDV65060.gif

JMcB

Harald Richter
JMB typed:

> Having been educated at the edge of  the great Plains in Colorado by  people like Alan Betts and Bill Cotton, I had always thought of deep  well-mixed layers as being a result of continental  summertime day-time
> heating.  Clearly something else is going on here.

That's (nearly) what might have happened here - the deep mixed layer off
the surface came riding NW-SE trajectories.  The mixed layer source region
was probably NW VIC into SA.  It should be warm enough there to build
a deep surface-based ML given the air is as dry as my bank account
at the end of a pay period...
 
The latest VIS is even more impressive than the previous one - I've added
it to

   http://gale.ho.bom.gov.au/bm/internal/wefor/staff/hxr/hrichter.htm  (Copy here)

Harald

Mick Pope

what does the colour coding on the vis pics mean?

John McBride
On Sat, 5 Oct 2002, Mick Pope wrote:

> what does the colour coding on the vis pics mean?
>

White means "Struth!!!"

Blue means "Crikey!!!!"

        John McB

Gary Weymouth
re colour coding on vis pics:

These are normalised visible images -
brightness altered as if the illumination intensity (not angle)
was from overhead sun everywhere..
The colour scale is at the bottom of the image.
The furthest right is the brightest.
These effectively represent planetary albedos (strictly reflectance)
as seen by the satellite.

So purple-blue is highly reflective planet - principally deep cloud,
though high cloud tends to appear a little brighter than low cloud
of the same optical depth.

Regards,
Gary
Mick Pope
Thanks Gary,

just a tad more technical than struth & crikey!  :)

Rob Webb

Hi all

We tend to get some really deep well-mixed layers when we get a few days of
westerly across our hills. We tend to modify our traces west of the divide
for the coast by picking some of the temps along the top of the divide and
assuming that we have a mixed layer down to somewhere between that and the
coastal air, it gives you a better feel for strength of the cap.

The trouble is that often the dry air to the west is the stuff getting
lifted.

 All we need is a nice shallow change to track along the coast and in can do
wonders to the CAPE. Sometimes the change can get a little deep and
everything remains capped, other times in can used the elevated terrain to
get the initiation.

Starting to sound like I like these TS things. (They fill up the time
between fire outbreaks)

Rob
NSW Sev Wx