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Old 17-02-2013, 01:13   #1
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CAPE

Not being a regular user of these forums, I may have put this question in the wrong place.

I would be interested to know if anyone have experience of using the Convective available potential energy parameter? It should be a guide to lightning risk.
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Old 17-02-2013, 04:50   #2
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Re: CAPE

Well the lightning risk in that both potential buoyant energy and the strength and vertical profile of the tropospheric wind fields are important in the process of storm development. Further, operational experience suggests that the combinations of wind parameters and instability parameters vary considerably from one lightning storm situation to another. Numerical models suggest that the type of storm that develops in a given situation (e.g., an isolated supercell) is related to both the vertical wind profile and the potential buoyant energy of the air in the updraft entrainment layer.

I hope this helps.
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Old 17-02-2013, 05:24   #3
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Re: CAPE

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Originally Posted by franksingleton View Post
....

I would be interested to know if anyone have experience of using the Convective available potential energy parameter? It should be a guide to lightning risk.
Frank

I have used CAPE from the GFS model, specifically when crossing the ITCZ. Zygrib includes a box to request the CAPE parameter, but does need internet access. While sailing, I use airmail2000 to get gribs and more. airmail2000 does not include a checkbox to request the CAPE parameter, but it can be tricked into doing just that: Create a grib request for a selected area, (screenshot 1) and add ",CAPE" to the outgoing email. or manually craft the request email to saildocs:
GFS:24N,24S,120W,022E|2,2|0,12..168|PRMSL,CAPE

The received grib-file does include values for CAPE, and viewfax can display CAPE, see screenshot 2 and 3.

Regarding it's usefulnesss: I can't really say it helped avoiding night-long lightning storms. Learning more about seasonal weather and (warm-) current patterns would have been more helpful.

Dirk
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Old 17-02-2013, 07:10   #4
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Re: CAPE

Thank you Mark.
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Old 17-02-2013, 11:20   #5
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Re: CAPE

Many thanks to both. I have been experimenting with getting and showing CAPE values. As you say, zyGrib gives a good display and can be used with GRIbs from Saildocs. The WeatherTrack App is also a good display, if you are ashore.

Do you find the values quoted here, re to be useful?


CAPE Index How Unstable

< 1000 Slightly
1000-2500 Moderate
2500-3500 V ery
3500+ Extremely


Mack, when you talk about wind profile, I assume that you mean vertical shear? Rather similar to tropical storm formation, I would be looking for little shear. Is that your experience? Do you look for troughs?
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Old 17-02-2013, 12:56   #6
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Re: CAPE

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Frank

I have used CAPE from the GFS model, specifically when crossing the ITCZ. Zygrib includes a box to request the CAPE parameter, but does need internet access.
ZyGrib has an email interface now, you have to register on their forum to get a username and password which lasts for 2 months, not quite long enough as it happens.

Chris
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Old 17-02-2013, 13:05   #7
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Re: CAPE

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ZyGrib has an email interface now, you have to register on their forum to get a username and password which lasts for 2 months, not quite long enough as it happens.

Chris
Thanks for the heads up. Is there any advantage over using Saildocs? The 2 months would seem a problem.
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Old 17-02-2013, 13:12   #8
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Re: CAPE

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Thanks for the heads up. Is there any advantage over using Saildocs? The 2 months would seem a problem.
Not especially but some people like to just use the one system for everything. I set it up and played with it but prefer the saildocs method from within Airmail , handcrafting as necessary to get nogaps or something like that.

One thing I have noticed is that ZyGrib doesn't display precipitation from the saildocs gribs; anybody know of a work-around for that?
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Old 17-02-2013, 13:35   #9
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Re: CAPE

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Thanks for the heads up. Is there any advantage over using Saildocs? The 2 months would seem a problem.
It looks like good old airmail+saildocs still has a couple advantages for the bandwidth-impaired: it estimates file size, allows for a moving forecast (higher detail grib, follows the predicted boat position)...

Quote:
One thing I have noticed is that ZyGrib doesn't display precipitation from the saildocs gribs; anybody know of a work-around for that?
I didn't know, thanks for the warning. I have no idea why...

Dirk
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