Understanding 'shear' with Storms ?
 

Have I got this correct with regards the effect of wind shear with
thunder storms?

Yesterday (24th), most of the south of the uk was under the influence of
some very warm air, with some notably high dew points. Cooler air was
closing in from the west which at higher altitudes was moving basically
from west to east, where as the general flow at the surface was between
the SE to SW. The cooler air aloft spread across from the west before
the warm air below had moved on, creating very unstable conditions, some
would use CAP and Li values. But basically the "Envionmentl Lapse Rate"
(ELR) was such that a parcel of hot air rising would be super cooled to
give the effect of the storm we saw yesterday. I think the values are
normally 4°c per 1000ft, or was it metres?

I also suspect the here in the SE, we had a little bit of a home grown
scenario, given the higher temperature and dew point values compared to
the rest of the southern half of the country. Subsequently, between 12
noon and 14:30 the whole thing went "Bang".

So have I got my facts right when I say that the wind shear is the
cooler air aloft moving over a the warmer yet from a different
direction? Also, I would imagine it is this type of shear that can get
the atmosphere spinning and spawn tornado's.

Many thanks
--
Keith (Southend)

'Weather Home & Abroad'
http://www.southendweather.net

Understanding 'shear' with Storms ?
 

There are two kinds of shear: directional shear and speed shear. In
directional shear the wind direction changes as you ascend. This has the
effect of twisting the updraughts and downdraughts as they ascend /
descend.
Speed shear is when the wind speed changes with height (either higher or
lower) and also twists the updraught and downdraught motion.

(Perhaps too) simply put - doubtless i'll be corrected:
no or little shear: single cell (low CAPE)/ pulse (moderate CAPE) /
severe pulse thunderstorms (high CAPE) - downdraught swamps updraught
after 30 minutes or so and the cloud collapses. Showers in wintertime in
the UK are generally of the first type. Darwin (Australia) thunderstorms
are of the last type.

The UKMO mini-tornado (registered trade mark from Birmingham office) is
caused by the updraught spinning up in low shear conditions as it
tightens. Not that a T7 is a mini-tornado. But I digress (:

optimum shear(!): misocyclone, mesocyclone (supercell - high CAPE),
(mini-supercell - low CAPE) - rotation is set off within the cloud and
updraughts and downdraughts are out of each other's way and in
equilibrium. Tornadoes form in the boundary between updraught and
downdraught in these storm types. Misocyclones form in the UK in
wintertime and for mesocyclones think USA, Australia, China.....

high shear: multicell - updraughts and downdraughts are skewed and
daughter cell forms next to parent cell which eventually collapses.
Multicells form in all values of CAPE but the higher the better.

very high shear: nothing happens (clouds are shredded)

Keith (Southend) wrote:
Have I got this correct with regards the effect of wind shear with
thunder storms?


--
Les Crossan,
Wallsend, Tyne & Wear
54.95N 1.5W
Home of the Wallsend StormCam and the Backup USW FAQ -
www.uksevereweather.org.uk

Understanding 'shear' with Storms ?
 

Hello Keith,

I hope that you don't mind me top posting.

There are a number of sites you can look at:
http://homepage.ntlworld.com/booty.w...E_SHEAR_TS.htm

Two very good sites, if you can get used to the American accents.
http://meted.ucar.edu/mesoprim/cape/
http://meted.ucar.edu/mesoprim/shear/

The full list of online met modules at:
http://meted.ucar.edu/resource_modlist.php

HTH
Joe
Wolverhampton
175m asl


Keith (Southend) wrote:
Have I got this correct with regards the effect of wind shear with
thunder storms?

Yesterday (24th), most of the south of the uk was under the influence of
some very warm air, with some notably high dew points. Cooler air was
closing in from the west which at higher altitudes was moving basically
from west to east, where as the general flow at the surface was between
the SE to SW. The cooler air aloft spread across from the west before
the warm air below had moved on, creating very unstable conditions, some
would use CAP and Li values. But basically the "Envionmentl Lapse Rate"
(ELR) was such that a parcel of hot air rising would be super cooled to
give the effect of the storm we saw yesterday. I think the values are
normally 4°c per 1000ft, or was it metres?

I also suspect the here in the SE, we had a little bit of a home grown
scenario, given the higher temperature and dew point values compared to
the rest of the southern half of the country. Subsequently, between 12
noon and 14:30 the whole thing went "Bang".

So have I got my facts right when I say that the wind shear is the
cooler air aloft moving over a the warmer yet from a different
direction? Also, I would imagine it is this type of shear that can get
the atmosphere spinning and spawn tornado's.

Many thanks

Understanding 'shear' with Storms ?
 

Joe Egginton wrote:
Hello Keith,

I hope that you don't mind me top posting.

There are a number of sites you can look at:
http://homepage.ntlworld.com/booty.w...E_SHEAR_TS.htm

Two very good sites, if you can get used to the American accents.
http://meted.ucar.edu/mesoprim/cape/
http://meted.ucar.edu/mesoprim/shear/

The full list of online met modules at:
http://meted.ucar.edu/resource_modlist.php

HTH
Joe
Wolverhampton
175m asl

Excellent stuff Joe.

Thanks

--
Keith (Southend)

'Weather Home & Abroad'
http://www.southendweather.net

Understanding 'shear' with Storms ?
 

Besides the one in the USW FAQ there's this one from the University of
Illinois, forgot to add it in this morning and I've been busy ):

http://ww2010.atmos.uiuc.edu/(Gh)/gu...wind/home.rxml

(copy and paste it in)

Les

Keith (Southend) wrote:
Joe Egginton wrote:

Hello Keith,

I hope that you don't mind me top posting.

There are a number of sites you can look at:
http://homepage.ntlworld.com/booty.w...E_SHEAR_TS.htm

Two very good sites, if you can get used to the American accents.
http://meted.ucar.edu/mesoprim/cape/
http://meted.ucar.edu/mesoprim/shear/

The full list of online met modules at:
http://meted.ucar.edu/resource_modlist.php

HTH
Joe
Wolverhampton
175m asl


Excellent stuff Joe.

Thanks


--
Les Crossan,
Wallsend, Tyne & Wear
54.95N 1.5W
Home of the Wallsend StormCam and the Backup USW FAQ -
www.uksevereweather.org.uk

Understanding 'shear' with Storms ?
 

Les Crossan wrote:
Besides the one in the USW FAQ there's this one from the University of
Illinois, forgot to add it in this morning and I've been busy ):

http://ww2010.atmos.uiuc.edu/(Gh)/gu...wind/home.rxml

(copy and paste it in)

Les

Keith (Southend) wrote:

Joe Egginton wrote:

Hello Keith,

I hope that you don't mind me top posting.

There are a number of sites you can look at:
http://homepage.ntlworld.com/booty.w...E_SHEAR_TS.htm

Two very good sites, if you can get used to the American accents.
http://meted.ucar.edu/mesoprim/cape/
http://meted.ucar.edu/mesoprim/shear/

The full list of online met modules at:
http://meted.ucar.edu/resource_modlist.php

HTH
Joe
Wolverhampton
175m asl



Excellent stuff Joe.

Thanks



Thanks Les, plenty of reading to be getting on with :-)

--
Keith (Southend)

'Weather Home & Abroad'
http://www.southendweather.net

Understanding 'shear' with Storms ?
 

Les Crossan wrote:
Besides the one in the USW FAQ there's this one from the University of
Illinois, forgot to add it in this morning and I've been busy ):

http://ww2010.atmos.uiuc.edu/(Gh)/gu...wind/home.rxml

(copy and paste it in)

Les

Thanks


That's a great site, I've their CD version.

Joe
Wolverhampton
175m asl