From                                           Subject
--------------------------------------------------------------------------------------
001 Phil Bagust [paisley at cobweb.com.au]            Adelaide 9.00am
002 "Andrew Miskelly" [amiskelly at ozemail.com.au]   Low NSW Minima
003 Paul_Mossman at agd.nsw.gov.au                    Low NSW Minima
004 "Andrew Miskelly" [amiskelly at ozemail.com.au]   Tornadoes - Myth/Fact
005 Phil Bagust [paisley at cobweb.com.au]            SA (was Low NSW Minima)
006 "Jane ONeill" [cadence at rubix.net.au]           T shirts
007 John Woodbridge [jrw at pixelcom.net]             Tornadoes - Myth/Fact
008 Michael Scollay [michael.scollay at telstra.com.  Tornadoes - Myth/Fact
009 Anthony Cornelius [cyclone at flatrate.net.au]    Tornadoes - Myth/Fact

--------------------------------------------------------------------------------------
001

X-Sender: paisley at mail.cobweb.com.au
Date: Thu, 8 Jul 1999 09:13:33 +0930
To: aussie-weather at world.std.com
From: Phil Bagust [paisley at cobweb.com.au]
Subject: Re: aus-wx: Adelaide 9.00am
Sender: aussie-weather-approval at world.std.com
Reply-To: aussie-weather at world.std.com

Radar shows the front crossing St Vincent's Gulf and lots of red.  Time to
grab the camera methinks.....

Phil 'Paisley' Bagust
paisley at cobweb.com.au
www.cobweb.com.au/~paisley


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002

From: "Andrew Miskelly" [amiskelly at ozemail.com.au]
To: [aussie-weather at world.std.com]
Subject: aus-wx: Low NSW Minima
Date: Thu, 8 Jul 1999 11:48:15 +1000
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Hi all,

Some NSW forecasts got it wrong last night where temps are concerned. It
seems they were expecting the high cloud associated with the low to hang
around, forecasting 01 for Goulburn for example where it actually got down
to -04. I guess that massive high just wanted to have the last laugh!

This mornings forcasts show that the low is comming over a little slower
than BoM expected with most of the patchy rain delayed until tomorrow.

What's happening in Adelaide Phil (and others)? Nice radar!

Andrew.
--
Andrew Miskelly
Illawarra/Southern Tablelands
amiskelly at ozemail.com.au


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003

From: Paul_Mossman at agd.nsw.gov.au
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To: aussie-weather at world.std.com
Date: Thu, 8 Jul 1999 12:35:14 +1000
Subject: Re: aus-wx: Low NSW Minima
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The high cloud stayed around here Andrew and was quite mild last night - I
washed the car in shorts at 10.30 at night!!

Beautiful mild day here again, with horse tail cirrus clouds sweeping across -
some high cloud to the North and South. Seems the cold air is gradually making
its way across with some moisture at high levels.

Paul at a magnificent Port Macquarie.


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004

From: "Andrew Miskelly" [amiskelly at ozemail.com.au]
To: "AusWx" [aussie-weather at world.std.com]
Subject: aus-wx: Tornadoes - Myth/Fact
Date: Thu, 8 Jul 1999 14:59:07 +1000
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Hi all,

Of all of the articles and books I have read about tornadoes I would have to
say that almost exactly half have gone either way in declaring fact or
fiction that 'alot of damage to buildings can be put down to the rapid drop
in air pressure near and inside most tornadoes'.

(For those who don't know, the rapid drop in air pressure near tornadoes has
some degree of explosive effect on closed structures when the relatively
high air pressure inside the structure cannot be equalised - this is why
windows blow out, and many believe should be open during the storm.)

I believe this to be true and think it's a good explanation as to why we
often see a phenomonum where a house can be demolished and the two adjacent
houses can seem untouched. If it were true it would also have interesting
implications on the measures that are used to determin the ferocity of
tornadoes.

Does anyone have any views as to why this may or may not be true?

Andrew.
--
Andrew Miskelly
Illawarra/Southern Tablelands
amiskelly at ozemail.com.au

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--------------------------------------------------------------------------------------
005

X-Sender: paisley at mail.cobweb.com.au
Date: Thu, 8 Jul 1999 14:42:49 +0930
To: aussie-weather at world.std.com
From: Phil Bagust [paisley at cobweb.com.au]
Subject: Re: aus-wx: SA (was Low NSW Minima)
Sender: aussie-weather-approval at world.std.com
Reply-To: aussie-weather at world.std.com


>What's happening in Adelaide Phil (and others)? Nice radar!
>
>Andrew.

Well, the forcast is for rain easing to showers with the odd storm, but
what we have here at present is just middle level mush and steady, light
rain. :(

Phil 'Paisley' Bagust
paisley at cobweb.com.au
www.cobweb.com.au/~paisley


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006

From: "Jane ONeill" [cadence at rubix.net.au]
To: "Aussie Weather" [aussie-weather at world.std.com]
Subject: aus-wx: T shirts
Date: Thu, 8 Jul 1999 15:28:41 +1000
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T shirts have left the supplier today - will be to me in 3 working days -
and I will distribute post haste.  Sorry for the delay but I thought you'd
like to be kept informed of progress.

Jane ONeill
Bayswater, Victoria

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007

From: John Woodbridge [jrw at pixelcom.net]
To: "'aussie-weather at world.std.com'" [aussie-weather at world.std.com]
Subject: RE: aus-wx: Tornadoes - Myth/Fact
Date: Thu, 8 Jul 1999 16:32:30 +1000
Organization: Pixel Components
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Hi Andrew,

The modern hypopthesis is that the drop in air pressure is itself not 
anywhere near as much a factor as the wind speed over a roof structure, 
which acts similarly to an airfoil (Bernoulli effect), causing very great 
pressure drops particularly on the lee side of pitched roofs, resulting in 
the roof lifting off due to the pressure differential.  The orientation and 
pitch of the roof thus would be significant variables in determining the 
amount of lift generated on the structure.  Once a building has lost it's 
roof, internal walls are exposed to the full force of the wind plus have 
lost a fair degree of bracing - thus the house is then easily dismantled by 
the wind.

Analysis also suggests that leaving windows open is likely to cause at 
least as much damage, if not more, than when they are closed, because it 
assists in creating pressure differentials within the building itself. 
 Many large tornadoes hide an inner structure which may consist of a number 
of small very intense suction vortexes as small as 10m, which circulate 
around the tornado 'eye'.  It is thought that these are primarily 
responsible for the selective damage patterns often observed, having the 
ability to slice through a building destroying one half and leaving the 
other relatively unscathed.

Regards,
John.
>snip

Of all of the articles and books I have read about tornadoes I would have 
to
say that almost exactly half have gone either way in declaring fact or
fiction that 'alot of damage to buildings can be put down to the rapid drop
in air pressure near and inside most tornadoes'.

(For those who don't know, the rapid drop in air pressure near tornadoes 
has
some degree of explosive effect on closed structures when the relatively
high air pressure inside the structure cannot be equalised - this is why
windows blow out, and many believe should be open during the storm.)

I believe this to be true and think it's a good explanation as to why we
often see a phenomonum where a house can be demolished and the two adjacent
houses can seem untouched. If it were true it would also have interesting
implications on the measures that are used to determin the ferocity of
tornadoes.

Does anyone have any views as to why this may or may not be true?

Andrew.
--
Andrew Miskelly
Illawarra/Southern Tablelands
amiskelly at ozemail.com.au

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 -----------------------jacob at iinet.net.au------------------------------

--------------------------------------------------------------------------------------
008

Date: Thu, 08 Jul 1999 17:39:25 +1000
From: Michael Scollay [michael.scollay at telstra.com.au]
Organization: Telstra Strategy & Research
X-Mailer: Mozilla 4.5 [en] (X11; I; SunOS 5.5.1 sun4m)
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To: aussie-weather at world.std.com
Subject: Re: aus-wx: Tornadoes - Myth/Fact
Sender: aussie-weather-approval at world.std.com
Reply-To: aussie-weather at world.std.com

John Woodbridge wrote:
> 
> Hi Andrew,
> 
> The modern hypopthesis is that the drop in air pressure is itself not
> anywhere near as much a factor as the wind speed over a roof structure,
> which acts similarly to an airfoil (Bernoulli effect)...
[snip]

My cousin did the structural engineering design on our recently
(within the last 2 years) completed renovations. Standards called
for the capability of withstanding a 1.5kpa lifting pressure on 
the flat roof during a 120kph SSW gale. Lift the wind speed to
F3 velocities and you could be looking at nearly 3kpa. Given a
roof area of 50sq.m, that's a total lift force (as opposite to
weight caused by G of 150 metric tonnes (3 tonnes / sq.m). I
think the maths is right:-) Anyhow, that roof is tied-down with
6x12mm brooker rods cast into reinforced concrete columns
which break at about 22 tonnes each. Somehow, I don't think
our roof would stay on in F3 sort of winds:-(

Michael Scollay       mailto:michael.scollay at telstra.com.au
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009

Date: Thu, 08 Jul 1999 22:50:55 +1000
From: Anthony Cornelius [cyclone at flatrate.net.au]
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Subject: Re: aus-wx: Tornadoes - Myth/Fact
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Reply-To: aussie-weather at world.std.com

Hi all,

I agree with John totally on the Bernoullin effect + multiple suction
vorticities...however, in regards to the windows open, I personally
believe (in my limited knowledge of this) that it would make no
difference.  Nearly any tornado that goes over a house is likely to
smash windows, either from the force of winds or debris, you'd expect
this to occur almost instantaneously as a torando/suction vorticy moves
over your house.  My thoughts on why it was considered that leaving
windows open was bad advice was that you would waste valuable seconds
just opening a few windows in the house, when (crudely) quite often a
few seconds can mean the difference between being speared to death by a
debris, or gaining suitable shelter.

It would also be dangerous to be anywhere near a window during a tornado
- for example, the Nov 4, Brisbane 1973 tornado went over my mum's
house.  Thank God, no one was in the house at the time, as they had huge
glass doors that opened up onto a balcony.  There were glass spinters
that had pearced through the couch.  Clearly, if anyone was running to
open the windows/glass doors - if the tornado went over at the same
time, you'd have no chance...

Anthony Cornelius

John Woodbridge wrote:
> 
> Hi Andrew,
> 
> The modern hypopthesis is that the drop in air pressure is itself not
> anywhere near as much a factor as the wind speed over a roof structure,
> which acts similarly to an airfoil (Bernoulli effect), causing very great
> pressure drops particularly on the lee side of pitched roofs, resulting in
> the roof lifting off due to the pressure differential.  The orientation and
> pitch of the roof thus would be significant variables in determining the
> amount of lift generated on the structure.  Once a building has lost it's
> roof, internal walls are exposed to the full force of the wind plus have
> lost a fair degree of bracing - thus the house is then easily dismantled by
> the wind.
> 
> Analysis also suggests that leaving windows open is likely to cause at
> least as much damage, if not more, than when they are closed, because it
> assists in creating pressure differentials within the building itself.
>  Many large tornadoes hide an inner structure which may consist of a number
> of small very intense suction vortexes as small as 10m, which circulate
> around the tornado 'eye'.  It is thought that these are primarily
> responsible for the selective damage patterns often observed, having the
> ability to slice through a building destroying one half and leaving the
> other relatively unscathed.
> 
> Regards,
> John.
> >snip
> 
> Of all of the articles and books I have read about tornadoes I would have
> to
> say that almost exactly half have gone either way in declaring fact or
> fiction that 'alot of damage to buildings can be put down to the rapid drop
> in air pressure near and inside most tornadoes'.
> 
> (For those who don't know, the rapid drop in air pressure near tornadoes
> has
> some degree of explosive effect on closed structures when the relatively
> high air pressure inside the structure cannot be equalised - this is why
> windows blow out, and many believe should be open during the storm.)
> 
> I believe this to be true and think it's a good explanation as to why we
> often see a phenomonum where a house can be demolished and the two adjacent
> houses can seem untouched. If it were true it would also have interesting
> implications on the measures that are used to determin the ferocity of
> tornadoes.
> 
> Does anyone have any views as to why this may or may not be true?
> 
> Andrew.
> --
> Andrew Miskelly
> Illawarra/Southern Tablelands
> amiskelly at ozemail.com.au
> 
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