Author Topic: Help with BSCH charts  (Read 5029 times)

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Offline Antonio (stormboy)

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Help with BSCH charts
« on: 18 March 2010, 02:02:37 PM »
Hello Australiasevereweather Members. I have been on this forum for a few years and slowly have been learning more and more except for one thing I am confused about. I noticed allot of chasers use BSCH for something called shear / cape / lifted index charts. In the picture below I ask the difference between say the 805mb shear chart and the 300mb because I have noticed they both show very different things. If you could please help me I am very thankful for some information. Thank you.

Antonio.

Offline Jason(pato)

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Re: Help with BSCH charts
« Reply #1 on: 19 March 2010, 10:46:39 AM »
Hi Antonio,

The shear charts are a representation of winds throughout certain levels of the atmosphere. 850mb shear values  are indicative of wind speed and direction at about 2600m above the surface whereas 300mb show whats happening around 9685m above the surface. The 300mb level can usually show the presence of the jet stream if there are very strong winds plotted ie 80kts plus etc. If you are a regular user of BSCH you would be aware that clicking on CAPE/LI chart you will get a forecast sounding for the area you click on. Here you can also see what wind speeds are happening at various levels of the atmosphere. I'll give you an example:



On the left hand side are the levels of the atmosphere ie 1000mb up to 200mb and its corresponding elevation from the surface and on the right you can see the wind direction and speeds represented by the barbs. I won't go into descriptions of the sounding as there is another thread dedicated to that subject here:

http://www.australiasevereweather.com/forum/general-weather-all-topics-that-are-not-current-severe-weather-should-be-posted-here/understanding-aerological-diagrams-soundings/

Hope this helps in some way,

Cheers Jason
South Lismore, Northern Rivers NSW.....Supercells are us!!

Offline Antonio (stormboy)

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Re: Help with BSCH charts
« Reply #2 on: 19 March 2010, 02:02:09 PM »
Thanks this helped allot will have plenty to read now thank you very much. Oh and what does cape do? I know when there’s allot of colour it is most likely going to storm?

Antonio.

Offline Jason(pato)

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Re: Help with BSCH charts
« Reply #3 on: 20 March 2010, 12:56:35 AM »
CAPE stands for Convective Available Potential Energy. Generally when the CAPE number is higher ie 1500-3000 j/kg the likelihood of convective development increases. However you must bear in mind that even if there is a high CAPE number it doesn't always guarantee there will be storms. For instance CAPE could be progged to be 3000 j/kg and you would be thinking that explosive storm development is going to occur, but if the atmosphere is lacking moisture or has a strong CAP the 3000 j/kg of CAPE could possibly go to waste. I can remember a week last year where CAPE was forecast to be above 2000 j/kg for several days, however there was a strong CAP in place and nothing occured. Surface temps would have to have been somewhere above the 40 deg mark for convection to initiate and just didn't happen. Heres a link to a guide to forecasting thunderstorms, I've found this very helpful and informative and it breaks down the art of forecasting a potential storm day in easy to read sections:

http://www.downunderchase.com/storminfo/stormguide/index.html

Always remember don't be afraid to ask questions no matter how silly you may think they sound.....thats the way I've learnt what I have so far.  Michael Bath can attest to my constant badgering of him for information in regard to forecasting storms  :P. Anyway have a read of the forecasting guide and you may just have a better understanding of the key indicators for storm development.

Cheers Jason
South Lismore, Northern Rivers NSW.....Supercells are us!!

Offline Antonio (stormboy)

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Re: Help with BSCH charts
« Reply #4 on: 20 March 2010, 03:10:02 AM »
Well think you for that Jason I am glad to hear that I’m not a goose for asking these questions. Ha-ha. Hey just some advice i purchased this today

http://cgi.ebay.com.au/ws/eBayISAPI.dll?ViewItem&item=260544630051&ssPageName=STRK:MEWNX:

does anyone think it is okay for forecasts and also is digital as accurate as mercury thermometers? Thank you all.

Antonio